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Author Topic: 60W Power amplifier  (Read 36443 times)

R.G.

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Re: 60W Power amplifier
« Reply #15 on: August 07, 2007, 01:07:16 AM »
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R.G. - Have you always this paranoid about SS amps?

I might reply "LJ - Have you always been this paranoid about protection circuits and tube amp?" with just as much basis as you ask that. But the short answer is no. It took fixing several that had been smoked to make me appreciate an amp that not only works when things are good, but works when things are bad, too.
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Obviously your logic has a strong bias towards tube amps.
I don't think that follows at all. But your logic certainly has a strong bias towards SS amps. So maybe we're both dirty, eh?

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Why pretend that a "no plug in jack" resistor is the same as "open circuit protection".
Well, for one thing, that's what it is, so I guess I feel justified in my "pretense".

I don't know anyone who puts a "no plug in jack" resistor in because they like the colors. It's there for open circuit protection, no other reason. Or can you propose another reason for it to be there?

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For example, isn't it just as likely to have your tube amp speaker cord run over by a guy with a metal wheeled cart? And wouldn't that accident have roughly the same if not higher chance of producing an open as a short?
Actually, it will most likely produce first a short, then sometimes an open as well. But that's neither here nor there.

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Why would you accept the odd sound of protection circuits? Because when they start operating it means I'm abusing the amp? Sorry, but that definition of abuse rests with the designer that didn't know his subject - Amps of any type are routinely "abused" by overdriving them since the sixtys.
Let's rephrase that just slightly.

Because (a) you have been routinely abusing SS amps and/or seen others do so since the 60s and (b) some of the amps you abused didn't have protection circuits and lived through it and also (c) you also don't like the sound when a protection circuit activates, you conclude that (d) all amps would work fine and not go up in smoke when abused even if they did not have the protection circuits you don't like the sound of. It doesn't take much formal logic training to see that D is not implied by A and B and C.

Why would you accept an amp that just might go into meltdown if the output is shorted and live with paying for that if the amp can be economically repaired? Do you really mean that when an amp self protects and you only heard an ugliness, you think it would both not have sounded ugly and also not have died if only the protection circuits were not there?

How do you know that the only reason that amp you didn't like the sound of didn't suffer a meltdown is because the protection activated and made an ugly "squark" instead of a puff of doped silicon?

If your definition of the designer not knowing his subject is that the sound made when the protection activates is unpleasant, then yes, I guess that you might say that. But then, how do you know that he didn't know his subject and saved you a trip to the techs? (Yes, be patient, we'll get to techs in a minute.)

And then while we're working on not knowing the subject, there's that small matter of SS amps not caring if a speaker is connected or not and tube amps often not living through it. So maybe we oughta not toss around "knowing the subject" so much, eh? After all we're both "professional grade" people, right, not those beknighted, naive, bumpkins who pass as comsumers, right?

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Since tube amps don't have protection circuits that corrupt the sound, does that imply that tube amps are not abused when overdriven?
No it doesn't. What it does imply is that SS amps are both (a) less able to withstand prolonged overloads and (b) cheap enough to make it reasonable to put in protection. There's a long history in the technical literature extolling just how few milliseconds it takes to melt holes in a silicon die if you get the right combination of wrong circumstances.

Once again, you're missing that logic thing.

Tube amps don't have protection circuits, sound corrupting or not, because (a) it was too expensive to design them in back when design with tubes was current and (b) tubes take larger overloads to melt down than transistors do. There's a long trail of technical literature on that one.

The long lag on overload and the cost of protection meant that no one could economically produce tube amps that way. But tubes do melt down when abused enough. Somewhere in my boxes of memorabilia I have a 6L6 with a conical indentation in the glass over part of the plate and a tiny, tiny circular hole at the bottom of the cone. The guy got it hot enough to melt the glass and let the air in. It just took a while.

The most common comment that tube amp techs hear when people bring in blow amps is "It sounded really great just before it blew out. Can you make it sound that way all the time?"

But it was a good try at backwards logic again. Does that work for you a lot?
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If a blown tube can be accepted in persuit of tone, no reason that a blown transistor can't be equally accepted.
Of course it can. But you know, when I was fixing amps between semesters, and through a long association with repair guys over the decades, not one of them has told me that customer said that a SS amp sounded really great just before it blew out. Guys go to SS amps because they want them to be more reliable than tube amps. You see, I heard this story...
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My favorite "tube tone that's not" story is Frank Morino of Mahogany Rush. An interview came out sometime during the early 1970s and one of the questions was "What amps do you use". His response was two Acoustic 260's. The next question from the obviously clueless interviewer was "Do you use any special tubes to help you get your sound?" I remember exactly how the response was written: "<pause> Uh... no. The 260's are solid state amps. Tubes are too unpredictable for me."

And while we're on that, I've seen guys retube between sets after losing one. Did you ever see someone replace his output transistors between sets?

I didn't think so.   ;)

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What's a tech? Oh, you mean those delusional self appointed guru's of tone that won't even look at an SS amp.
Had a bad time getting service, have we?   :)

teemuk

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Re: 60W Power amplifier
« Reply #16 on: August 08, 2007, 03:03:47 AM »
Could you supply pointers to the debunking and corrections, please?

I never collected a list of them but, for example, Pritchard Amps website had some technical info about "Audio Myths & Truths"

http://www.pritchardamps.com/audio_myths.cfm

I think that one is the best of the ones I could provide if I thought it for a while...

R.G.

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Re: 60W Power amplifier
« Reply #17 on: August 09, 2007, 12:16:44 AM »
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I never collected a list of them but, for example, Pritchard Amps website had some technical info about "Audio Myths & Truths"
http://www.pritchardamps.com/audio_myths.cfm
I think that one is the best of the ones I could provide if I thought it for a while...
I went and read it. Actually, I don't see any debunking or corrections there. Pritchard points out where Hamm was misinterpreted and where Hamm was talking about microphone amplifiers and may have missed some things like output stages, but I didn't see where he said Hamm was wrong.

Then too, Pritchard is in a frenzy to sell his own patented circuits and Pritchard Amps, so there's some marketing going on there as well.

So could you provide more pointers? I don't see any debunking there. In fact, I don't even see that any bunk was uncovered to de- .

teemuk

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Re: 60W Power amplifier
« Reply #18 on: August 09, 2007, 04:47:18 AM »
Well, if you think it that way you're right.

However, consider this: Hamm's paper created (or at least greatly assisted in creating) the myth about tubes creating even harmonics and transistors the odds. Basically, I see Hamm's paper just as a collection of results that he got when he measured only four widely different microphone preamplifiers ("...four different commercially available preamplifiers, using two or more stages of amplification. All the circuits use feedback, a couple are push-pull"). The paper does not present any universal differences between tube and solid-state, like the title falsely indicates it would. Unfortunately, too many people treat that paper as a gospel.

Since Hamm shows no schematics of the tested circuits we never know exactly what happened inside those either. Did some of them limit the bandwidth more drastically than the others? How much feedback was used? Even the test setups are highly controversial: For example, one plot shows clearly that one of the transistor amplifiers either oscillates or "settles" on the verge of clipping, thus exhibiting some "ringing". No wonder it shows more higher harmonic content during clipping. Is this fair comparison? How about the setup where all measured tube preamps were SE and solid-state ones PP? Will that tell anything fair about harmonic content of solid-state versus tube or will it tell more about harmonic content of SE versus PP?

Hamm is of course right in his measurements and conclusions that were based on to them, no question of that. How universal his conclusions are is a whole different matter. The way I see it, he only made some generalizations that are accurate only in some specific cases - and that has been pointed out by Pritchard and many others.

LJ King

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Re: 60W Power amplifier
« Reply #19 on: August 09, 2007, 12:58:37 PM »
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If your definition of the designer not knowing his subject is that the sound made when the protection activates is unpleasant, then yes, I guess that you might say that. But then, how do you know that he didn't know his subject and saved you a trip to the techs? (Yes, be patient, we'll get to techs in a minute.)

Yes, that is my definition - ignorant or not caring about the tone his customer is after.

More than likely he is probably an expert in the subjects of protecting his company's warranty, doing what he is told, and praising complexity as a virtue - since simple and elegant design is beyond his abilities.

Then again, I can see that by designing an amp without tone, that I won't use could save me mega bucks on repairs.

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But it was a good try at backwards logic again. Does that work for you a lot?

There is no backwards to my logic - I just don't have any myths to protect.

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Of course it can. But you know, when I was fixing amps between semesters, and through a long association with repair guys over the decades, not one of them has told me that customer said that a SS amp sounded really great just before it blew out.

Obviously since you didn't hear the truth through hearsay it must be false. And you think my logic is backwards?  :lmao:

You might check out this post on another forum by Terry Manning:

http://recforums.prosoundweb.com/index.php/m/184338/0/#msg_184350

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Guys go to SS amps because they want them to be more reliable than tube amps.

Sounds like what a corporate engineer wants to believe of his company's customers.

An SS amp can be more reliable than a tube amp. But with a complex design, built with marginal components augmented with protection circuits in hopes that it might survive the warranty period, it will have lousy tone. With a good simple design, adequate components, and no protection circuits - it will have great tone.

And yes teemuk, before you say it - probably lousy specs.  :) Tone isn't about specs, but it is 100% personal preference.

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Had a bad time getting service, have we?   :)

Good service, yes - bad service, nope, plenty of that to go around. After the third incident, when my amp was "shelf fixed" (claimed to be repaired but it was never even touched - just sat on a shelf for a week), I decided to stop wasting my money.

teemuk

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Re: 60W Power amplifier
« Reply #20 on: August 09, 2007, 02:21:35 PM »
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But with a complex design, built with marginal components augmented with protection circuits in hopes that it might survive the warranty period, it will have lousy tone. With a good simple design, adequate components, and no protection circuits - it will have great tone.

I can't quite agree with you... Perhaps you can name names. How about these?

Lab series L5/L7/L9/L11 - Fairly complex, include a protection circuitry
Acoustic Control 260 - Fairly complex, has protection circuitry
Roland JC-120 - Fairly complex, older versions had protection circuitry
Vox Valvetronix series - Ones I've seen have a chip amp power section (extremely complex), thus protection circuitry as well
Fender MH-500 - Very complex, has protection circuitry
Fender Steel King - Quite complex, has protection circuitry
Peavey Renown 400 - Fairly complex, has protection circuitry
Peavey Bandit - Many models, some quite simple some quite complex, include a protection circuitry
Sunn Beta series - Fairly complex, include a protection circuitry
Sunn 1200B - very complex, has protection circuitry
Sunn Coliseum series - Fairly complex, include a protection circuitry
Randall Warhead X2, Very complex, has protection circuitry
Randall Warhead, RG75, RG80 & RG100 - I haven't seen schematics of these. However, judging by their age I'm 99,9% sure they are fairly complex and have a protection circuitry
Old Marshall SS amps - Fairly simple, include a protection circuitry
Standel amps from seventies - fairly simple, include a protection circuitry
Polytone Amps - Fairly simple, include a crude protection circuit
Hagström GA-85 - Totem pole output, fairly complex, I assume the regulated supply was current limited (this was very rare)

Of course the term "complex" is quite subjective. Most of the aforementioned amps follow the 3-stage Lin topology, most have a differential input. If you break that kind of circuit to pieces it - in most cases - does not actually seem that complex; however, if you should build the concerned circuit from scratch you might change your opinion. That is how I defined what is complex and what is not in this case. In every example the preamplifier is usually extremely complex when compared to the power amp circuit.

I have found out that most of the amps, which reputedly have nice tones, do indeed include a protection circuit - unless they are old enough to have a totem pole output - in which case building a protection circuit was often considered too complex. Also, back in the days when amps with totem pole outputs were manufactured not that many people knew how a protection circuit should be built anyway. Most SS amps were considered reliable just because they ran "cooler" than tube amps. There are few examples of good simple amps that did not include a protection circuit (like Acoustic Control Model 150) but when compared to reliable and respected guitar amps following the "modern" Lin topology these belong to minority.

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And yes teemuk, before you say it - probably lousy specs.  :) Tone isn't about specs, but it is 100% personal preference.

Well... I wasn't going to say that since I agree with your statement. However, I have found out that usually the amps with good specs also tend to have a tone that I like. Anyway, that is - of course - only my perception of the matter.
« Last Edit: August 09, 2007, 02:35:23 PM by teemuk »

LJ King

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Re: 60W Power amplifier
« Reply #21 on: August 09, 2007, 04:23:44 PM »

Hmm... yeah, maybe I'm lumping too much under the general term "protection circuit". It's the short circuit protection I primarily don't find very toneful.

The Acoustic 260 doesn't have it, the 361 did.

The Sunn Beta (or Alpha, same power amp) does sound ugly once the power amp is overdriven. Never played a Coliseum. I'd include the Concerts in the simple-without classification.

Not really familiar with the other amps you mentioned. I did have a late 60's Standel that I wish I never gotten rid of, but I just couldn't move it as well as other things.

Ok, answer me this: What is it about the transformer driven totem pole topology that makes it unreliable? Fine, it usually doesn't have protection circuitry, but does that make the topology "inherently" unreliable? Is it the transformer?

Maybe unreliable in the case of a direct short to the outputs, but if you don't do that - I haven't seen them fail under "abusive playing situations" with the exception of some with underrated output transistors - but that would be a misapplication of component, not the fault of the topology.

Everybody tells me they are unreliable, so I just want to know what makes them that way - other than "they are old design, not modern technology".

Tube circuits are even older... but what were those tube amps that used a transformer drive by Fender? PS somethings? I saw a schematic once and almost died laughing.


teemuk

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Re: 60W Power amplifier
« Reply #22 on: August 09, 2007, 06:23:06 PM »
You got it wrong: It's not the transformer that makes them unreliable. But let' see...

- The oldest amplifiers used germanium output devices - need I say more?
- The old transistor datasheets were poor, this caused that many circuits following the datasheet information were poor as well
- At the time when older amps were designed thermal effects were pretty much unknown. Usually the heatsinking was very much lacking because of that.
- The totem pole circuits generally lack a short circuit protection so they are more vulnerable to faults of that type (mentioned already)
- The older amps generally did not have a stabilizing Zobel network in the output

Basically, the answer to your question is the one you eagerly try to deny: "They are old design". In modern designs these shortcomings were acknowleged and corrected. Other stuff that is generally bothering those old totem pole circuits is:

- The older amps used poor thermal tracking schemes (i.e. tempco resistors, simple diode strings etc), which usually did not cause thermal runaway but prevented creation of precice bias circuits. In BJT designs a precice bias setting is pretty significant if you want to get rid of crossover distortion
- The interstage transformer caused a lot of phase shifts so only little feedback could be used to eliminate distortion - otherwise a risk of instability was introduced
- The interstage transformer is expensive and heavy. It must be custom made and on top of that is moderately difficult to drive. I can't think of many reasons why to bother using one. (There are some though).

I know that inherent non-linearity does not bother all the people BUT it does bother people who want to create linear amps. Old tube amps ARE NOT linear amps and that is often too easy to hear. If someone likes them, fine - and I know that many people prefer the unlinearity but... ...I prefer linear amps because they provide a CLEAN output and one can always convert them unlinear with a suitable external circuit. This has been done many times with excellent results. It doesn't work backwards, though: You can't turn an unlinear amp linear with an external circuit - you need to redesign it. This is all I have to say about the issue.

The protection circuit I mentioned belonging to all those listed amps (except the Hagström) WAS a short circuit protection.

The Acoustic Control Model 260 DID have a crude short circuit protection as well. See:
http://acoustic360.homeunix.net/images/schematics/260_160.jpg
Note the diodes D5, D6, D7, D8 and D9. Now, if I'm correct these limit the driver's base voltage to a certain level and protect the devices if current through emitter resistors is high enough to create a large enough voltage drop (U=IR). It's definitely not a very good protection, likely quite audible as well. Nevertheless, it's a short circuit protection. Similar crude circuit was used in few other amps as well - sometimes only at one "side".

Personally, I prefer a multislope VI-limiter that both tracks SOA more accurately and can be made inaudible because it can be set to trip outside typical operating conditions. As a side note, usually most amplifiers would also require something to prevent VAS saturation as well (i.e. Baker Clamp). For simplicity it is often omitted although the added complexity might make the protection to operate more "transparently" and "softer".

I say it again: If the short circuit protection causes some noises it is either designed poorly (most of them are) or it just saved your amp from blowing.

R.G.

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Re: 60W Power amplifier
« Reply #23 on: August 11, 2007, 10:03:45 PM »
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If your definition of the designer not knowing his subject is that the sound made when the protection activates is unpleasant, then yes, I guess that you might say that. But then, how do you know that he didn't know his subject and saved you a trip to the techs? (Yes, be patient, we'll get to techs in a minute.)
Yes, that is my definition - ignorant or not caring about the tone his customer is after.
It amazes me that you can ignore the obvious - if the amp dies, there is no tone for the customer to care about. I think you must work in some elected office. You're fairly nimble at ducking an issue while making it seem like you answered. Most people like that have lots of practice.

I can tell you with some certainty that an audio design engineer that chose letting the amp destruct versus making an unpleasant sound for a moment would not be employed for long. You seem to think that designers with grudges against "real people" customers get all the work. It doesn't work that way.

But you don't want to talk about the technical issue that the unpleasant sound and not melting down are related do you? You'd like to think that any protection circuits whatsoever are useless, would you not?

So let's get this clearly
1. LJ, do you understand that a protection circuit activating can save your amp from being destroyed?
Please do your best to answer with yes or no. I realize you will not, but it'll be fun seeing you try not to.

If you answer yes, why not just own up to you'd rather pay repair bills?

If you answer no, can you give some *technical* justification for not believing it? It can be demonstrated, you know. When I say "technical" I mean "repeatably measurable or observable facts which can be verified by someone other than you". So far, your technical justification seems to be "well, I used to abuse SS amps all the time and they didn't die very often." That's not a technical justification. 

If it's just what you'd like to believe, that's OK too. But believing doesn't make it fact.

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I say it again: If the short circuit protection causes some noises it is either designed poorly (most of them are) or it just saved your amp from blowing.
You're dead correct, teemuk. But I think you're wasting your time. I suspect that LJ will not turn up any backup info to support his opinion. He's long on opinion and short on fact. He'll never give you that last "or...".

LJ King

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Re: 60W Power amplifier
« Reply #24 on: August 12, 2007, 12:35:26 PM »

I have no problems understanding how short circuit protection works and have no doubt that it will prevent excessive current flow during a short of the output.

But you're missing my point - obviously blinded by the delusion that more complexity makes you a better engineer. I'm sure you can recommend much simpler alternatives to solve the "problem" of the user shorting the output of an SS amp - without affecting the sound while providing protection. And I'm just as sure you have a "technically superior" reason why they won't work as well as those that do affect the sound.

Just like the only real reason to call a transformer driven totem pole design "unreliable" is to claim that it is an old design and not technically superior to modern designs. A reason that could equally apply to any tube design if there wasn't a bias for simpler tube designs (pun intended) to provide better sound.

Kind of like claiming a model T Ford is unreliable because it wouldn't survive a crash into a brick wall as well as a modern vehicle. The obvious solution is "don't do that!!"

Suppose you came up with a novel circuit for a tube amp. It offered all sorts of technical benefits - longer tube life, better linearity, faster slew rate, and even open output secondary protection. The trade off is of course that as the user started pushing for power tube distortion, the sound would get glitchy and if they insisted on pushing it harder, the amp would shut itself off.

Would it sell? Of course not. Despite all of the technically superior reasons, no one would buy one, or if they did they would return it pretty quickly once the problem with the sound was discovered. Fender's technically superior improvements to eliminate that "awful distortion" during the silverface era is a good example.

Maybe a corporate engineer would lose his job by designing an SS amp for tone instead of short circuit protection "just in case". After all, the corporate machine couldn't save money by using cheaper devices, couldn't downgrade the construction, and the amp might not make it through the warranty period before failing. The engineer also wouldn't be living up to his job description by failing to be "able to design and implement complex circuits that meet or exceed all specified cost constraints". Definite reasons for being fired - no doubt.

Herd members in "good standing" just simply don't like mavericks - mavericks interfere with their erroneous and delusional perceptions about themselves.

But despite your well justified reasons to help protect my amp from me (and all I have to do is give up on good sound making another myth true); there are plenty of vintage SS amps out there, without short circuit protection, still providing great sound despite any opinion of unreliability by you.

That sir is a FACT - but one you will deny cause I can't give you an all inclusive list of all the well satisfied users? Even if I could, you would just chalk it up to a collection of opinions and not a "technical justification" - only because it doesn't match your opinion. You only accept hearsay as fact when it matches your opinion.

I picked up one this weekend - for only $25 bucks. An EH dirt road special (now I don't have to build my own). I couldn't believe it and it was all an accident. It was in a pawn shop, in great cosmetic condition and the only problem was it didn't work. Only a faint hum sound when it was turned on. The guy at the store claimed his electronics tech estimated a $200 repair bill minimum and he just wanted to get rid of it.

About 5 minutes of debugging found the problem. No, it wasn't the output transistors or anything in the power amp section. Since I'll have to remove the board to replace the defective component, I'll post a picture of the output transistors and the heat sink - you'll just love it. Yes, despite no short circuit protection of any kind (I posted a schematic in another thread), AND it still has the original 1979 vintage output transistors.

The problem is the 4558 opamp in the preamplifier. The second side (pins 5,6,7) is hosed. It's run off a single polarity +15 supply with the non-inverting input biased at half. I get 7 1/2 volts at that input, but only 2 volts at the output and inverting input.

Don't these things have protection circuitry? Oh well, I guess it DID survive roughly 28 years with it.

R.G.

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Re: 60W Power amplifier
« Reply #25 on: August 12, 2007, 03:57:06 PM »
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I have no problems understanding how short circuit protection works and have no doubt that it will prevent excessive current flow during a short of the output.
Kewl. OK, we have one point. You will accept that there are situations where protection circuitry works and can save an amp.

But you say you understand how it works. Tell us.  :)

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But you're missing my point - obviously blinded by the delusion that more complexity makes you a better engineer. I'm sure you can recommend much simpler alternatives to solve the "problem" of the user shorting the output of an SS amp - without affecting the sound while providing protection. And I'm just as sure you have a "technically superior" reason why they won't work as well as those that do affect the sound.
But I think you have a problem there. First, you don't know me, and so making the leap that I'm blinded by anything, even delusion, into a love of complexity shows that you're babbling again. Fact is, the simple overcurrent clamp is very, very difficult to improve on for short circuit protection. I don't have a solution to protecting from shorts that is simpler. And I don't have a solution to protecting from short circuits while not affecting the sound.

I think, in fact, that we can logically prove that's impossible. If an output is shorted, there is no sound, by definition. The short has seen to that. So once the short starts, sound ceases. What short circuit protection does is keep the amp from dying during the duration of the silence.

And this points up another issue with your argument. You do not realize that short circuit protection and safe area protection are not the same thing. I deliberately didn't correct that gap in your background for a few posts now.

Safe area protection is what keeps your amp from melting down under conditions where there is not a short, just too high a current-voltage product on an output device. The more reactive a speaker load, the more that output current and voltage diverge from being in-phase, and the more transient power which can be seen by the output device. For bipolar transistors - but not MOSFETs, that's another story - there is an are of voltage-current operation where the V*I product causes breakdowns at lower powers than any of the power rating, voltage rating, or current rating. This is the "second breakdown" region, and it's a fundamental limit on bipolar transistor longevity.

Safe area protection is what trips your amp's protection when it's not shorted. Notice that just like short circuit protection, your amp is already operating in a condition which will lead it to break if this goes on for a few microseconds too long. This, by the way, is as much fact as short circuit protection.

So let's go with question #2: Do you believe that there are situations where safe-area protection can prevent your amp from dying? Again, please try to limit yourself to yes or no. I noticed you were unsuccessful last time, just as I predicted. I'm guessing you'll do a LOT of dancing to avoid saying yes or no to this one.

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Just like the only real reason to call a transformer driven totem pole design "unreliable" is to claim that it is an old design and not technically superior to modern designs.
There's that lack of a technical background thing again.

If we're going to discuss reliability on some basis other than "Wull, I used 'em atta way for thutty yars an' they nevah failed me yet!" we need to get to some basis for discussing reliability. I did power supply design for five years, field failure analysis for a year, and design-for-reliabilty reviews for power electronics for another year. What is your training and experience in analyzing power electronics for reliabilty? Is it just using them until they break or don't break yet?
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Kind of like claiming a model T Ford is unreliable because it wouldn't survive a crash into a brick wall as well as a modern vehicle. The obvious solution is "don't do that!!"
The obvious answer is that very few people do that out of choice. "Just say no." went out with Nancy Reagan. It never worked with auto crashes. So given that you will INVOLUNTARILY be forced to crash into a brick wall, which one do you want, the model T or the modern vehicle. I know which choice I'd make. Your choice is what we used to call an "IQ test decision".

Besides, what you SEEM to be arguing for is your right to keep driving Model T's around in a large open field in which are a couple of brick walls while blindfolded, insisting that they will survive just fine because you haven't hit a brick wall yet.

I have to tell you - it's kinda fun to watch.   :)
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Maybe a corporate engineer would lose his job by designing an SS amp for tone instead of short circuit protection "just in case".
I just have to go review my list of logical fallacies. The cleverness in that kind of statement is that if you get the answer without the person pointing out that NONE of the previous discussions talked about the hypothetical engineer designing an amp with or without protection circuits (note my correct use of protection circuits, not "short circuit") choosing to design NOT for tone. The point of shaping comments like that is to goad the other side into accepting the premise that if an engineer is designing for longevity under abusive conditions, he is designing tone out. It's one of the sneaky ways that politicians tar the opposition, and a standard trick.

There is no designing FOR tone and NOT FOR protection (again noting that "short circuit" has nothing to do with it, see above again). The two are not antagonistic concepts.

It may be possible that you see them as antagonistic because to you "tone" only happens on the edge of circuit failure. If that's the unstated condition in your mind, you need to do some more thinking.

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After all, the corporate machine couldn't save money by using cheaper devices, couldn't downgrade the construction, and the amp might not make it through the warranty period before failing. The engineer also wouldn't be living up to his job description by failing to be "able to design and implement complex circuits that meet or exceed all specified cost constraints". Definite reasons for being fired - no doubt.
That's correct. How do you define doing your job? Do you want to damn the engineer for wanting the job, the company for wanting to make a profit (which, if you'll think it through, is the only reason you can have any amplifier at all), or both of them for not asking you first? At which of these stops do you get off?

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Herd members in "good standing" just simply don't like mavericks - mavericks interfere with their erroneous and delusional perceptions about themselves.
So you're a member of the maverick herd, who pride themselves on not being in a herd, and all uniformly going their uniformly separate ways, right?  ;D

I love it - rebel without a clue.

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But despite your well justified reasons to help protect my amp from me (and all I have to do is give up on good sound making another myth true); there are plenty of vintage SS amps out there, without short circuit protection, still providing great sound despite any opinion of unreliability by you.That sir is a FACT - but one you will deny cause I can't give you an all inclusive list of all the well satisfied users?
Nobody ever said that all amps without protection died instantly. I certainly didn't.

There are even a few of your model T Fords around that haven't been driven into brick walls. However, I would wager a considerable sum that if you drove one of the remaining Model Ts into a brick wall, either it would be scrapped, cannibalized, or there would be a hefty repair bill, which is what you're trying to deny. Sometimes people can walk across minefields and not get killed. It depends on the density of mines and what for lack of another word we'll call luck.

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Even if I could, you would just chalk it up to a collection of opinions and not a "technical justification" - only because it doesn't match your opinion. You only accept hearsay as fact when it matches your opinion.
Actually, my "hearsay" comes from people who practice the art, write textbooks, teach, make a living by getting things to work - over and over and over. I guess that yes, you could call that a better grade of hearsay. Call it informed hearsay. Who you gonna bet on - the guys who do it all the time or the uninformed?

The race is not always to the swift nor the contest to the strong - but that's the way to bet.

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I picked up one this weekend - for only $25 bucks. An EH dirt road special (now I don't have to build my own). I couldn't believe it and it was all an accident. It was in a pawn shop, in great cosmetic condition and the only problem was it didn't work. Only a faint hum sound when it was turned on. The guy at the store claimed his electronics tech estimated a $200 repair bill minimum and he just wanted to get rid of it.

About 5 minutes of debugging found the problem. No, it wasn't the output transistors or anything in the power amp section. Since I'll have to remove the board to replace the defective component, I'll post a picture of the output transistors and the heat sink - you'll just love it. Yes, despite no short circuit protection of any kind (I posted a schematic in another thread), AND it still has the original 1979 vintage output transistors.

The problem is the 4558 opamp in the preamplifier. The second side (pins 5,6,7) is hosed. It's run off a single polarity +15 supply with the non-inverting input biased at half. I get 7 1/2 volts at that input, but only 2 volts at the output and inverting input.

Don't these things have protection circuitry? Oh well, I guess it DID survive roughly 28 years with it.
So - how many others of those you got? They're kinda rare, aren't they? Not a whole lot of them survived?   :)
« Last Edit: August 12, 2007, 10:57:44 PM by R.G. »

LJ King

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Re: 60W Power amplifier
« Reply #26 on: August 13, 2007, 07:34:56 PM »
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But I think you have a problem there. First, you don't know me, and so making the leap that I'm blinded by anything, even delusion, into a love of complexity shows that you're babbling again. Fact is, the simple overcurrent clamp is very, very difficult to improve on for short circuit protection.

You have the problem R.G. You even point it out:

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I don't have a solution to protecting from shorts that is simpler. And I don't have a solution to protecting from short circuits while not affecting the sound.

I think, in fact, that we can logically prove that's impossible. If an output is shorted, there is no sound, by definition. The short has seen to that. So once the short starts, sound ceases. What short circuit protection does is keep the amp from dying during the duration of the silence.

Your love of complexity as a virtue is so great you are so obviously blinded to anything that threatens to take that beloved complexity away from you.

Of course there is no sound during a short, but I seriously don't get how that proves there is no simpler solution. All you proved is you can't see one.

Maybe one day someone will give you one with permission to use it.

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And this points up another issue with your argument. You do not realize that short circuit protection and safe area protection are not the same thing. I deliberately didn't correct that gap in your background for a few posts now.


Sorry, but you rattle on about nothing too long to waste space reproducing it for you. But - ok, assume I don't.

A glichy sound by any name is still a glichy sound.

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So let's go with question #2: Do you believe that there are situations where safe-area protection can prevent your amp from dying? Again, please try to limit yourself to yes or no. I noticed you were unsuccessful last time, just as I predicted. I'm guessing you'll do a LOT of dancing to avoid saying yes or no to this one.

"Yes", there are some situations where what you are calling "safe-area protection" can prevent an amp from dying.

But that does not imply that what you are calling "safe-area protection" is necessary or desirable in all cases.

What you are calling "safe-area protection" isn't because it only monitors one of the variables. Current limiting would be more accurate.

And you can say I was unsuccessful again, but the problem is with the hidden assumptions of your question. Qualify those assumptions and I have no problem with a yes or no answer.

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What is your training and experience in analyzing power electronics for reliabilty? Is it just using them until they break or don't break yet?

Yes. Reality is fact - theory isn't. If it doesn't break in use, then it is reliable. Bridges built only on theory do fall down, and in doing so, theory changes.

I doubt it, but you may have heard the saying: "when reality conflicts with theory, develop another theory".

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So given that you will INVOLUNTARILY be forced to crash into a brick wall, which one do you want, the model T or the modern vehicle.

I will never be INVOLUNTARILY forced to short the output of my amp. That is just one of your hidden assumptions.

The rule about plugging in the speaker before turning the amp on pertains equally to solid state - you won't short the output by plugging in the cable. Deny that one.

And common sense tells me not to use a long speaker cable, so it's physically impossible for it to be run over.

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There is no designing FOR tone and NOT FOR protection (again noting that "short circuit" has nothing to do with it, see above again). The two are not antagonistic concepts.

It may be possible that you see them as antagonistic because to you "tone" only happens on the edge of circuit failure. If that's the unstated condition in your mind, you need to do some more thinking.

I don't have a clue what tangent this is. No, tone doesn't happen only on the edge of failure. But with your mandatory protections, tone doesn't happen.

Again, since you keep avoiding the question, why don't you recommend these things for tube amps? Wouldn't having them produce a nice glichy sound be equally "great amplifier design?"

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That's correct. How do you define doing your job? Do you want to damn the engineer for wanting the job, the company for wanting to make a profit (which, if you'll think it through, is the only reason you can have any amplifier at all), or both of them for not asking you first? At which of these stops do you get off?

Thank you... I had a feeling you only do as you are told.

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So you're a member of the maverick herd, who pride themselves on not being in a herd, and all uniformly going their uniformly separate ways, right?  ;D

I love it - rebel without a clue.

Actually rebels are quite different. Herd members don't mind them as much as mavericks as rebels are just as easily controlled. But of course I wouldn't expect a herd member like yourself to understand the difference.

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Nobody ever said that all amps without protection died instantly. I certainly didn't.

No, you just call them "unreliable" with nothing to back up the claim other than intentional destruction or some unlikely accident.

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So - how many others of those you got? They're kinda rare, aren't they? Not a whole lot of them survived?   :)

Only the one. I don't think they are that rare. Most people like them too much to give them up. Ever played one?

R.G.

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Re: 60W Power amplifier
« Reply #27 on: August 14, 2007, 02:02:34 AM »
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Your love of complexity as a virtue is so great you are so obviously blinded to anything that threatens to take that beloved complexity away from you.
Like I say, LJ, you don't know me. To someone who does, this is more proof that you don't.

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Of course there is no sound during a short,

But you were moaning about tone loss when short circuit protection is activated. Did you not see the problem? Short circuit protection activates... when... there... is... a... short.

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but I seriously don't get how that proves there is no simpler solution. All you proved is you can't see one.
The politician is back. If you read what I said, I said that I didn't see a simpler solution. You're the one who's trying to make that be me saying that it proves there is no simpler solution. That came out of your keyboard, not mine. Me not seeing a simpler solution is not proof of anything - other than I'm honest about it when I don't know.

By the way - I do have the professional background, experience and training to make it significant when I say I don't know of a simpler way. I know a lot of ways, just no simpler ones. I've designed a lot of power electronics. What have you designed?

I kinda have this history of saying when I don't know something. I always did want to know not only what I know but what things I didn't know, too. It helps. You ought to try it some time. Practice saying to yourself in the mirror "I don't know [whatever]." It'll make a much bigger person out of you. Did you want me to provide some historical quotes about people who won't admit when they don't know something.

I didn't think you did.

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Maybe one day someone will give you one with permission to use it.
Actually I got that permission a long, long time ago. But thanks for thinking of me.
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Sorry, but you rattle on about nothing too long to waste space reproducing it for you. But - ok, assume I don't.
I already assumed you didn't. In fact your posts showed it pretty plainly. The issue is whether you would admit it.
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"Yes", there are some situations where what you are calling "safe-area protection" can prevent an amp from dying.
ALL RIGHT!! LET'S HEAR IT FOR THE MAN!!  He's growing up!

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But that does not imply that what you are calling "safe-area protection" is necessary or desirable in all cases.
OK. That's fine. My contention was that sooner or later, depending on how you used the amp and how the loading was done, you would run into a situation which would damage the amp, requiring repair or junking the amp. You've fought that contention tooth and nail, only to finally admit that
(a) short circuit limiting does not damage amp tone
(b) there are situations where safe area protection protects an amp.

Only a fool does the same thing in all possible cases. You're trying to press the issue that there must exist at least some cases where safe area protection is not (a) necessary or (b) desireable. Well, duh. At least you've backed off the claim that no protection of any kind is ever necessary or desireable. But we did have to drag you there kicking and screaming.

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What you are calling "safe-area protection" isn't because it only monitors one of the variables. Current limiting would be more accurate.
Like you finally admitted, you don't understand it. So how is it that you are qualified to act as a critic? If you don't understand it, how do you know what it monitors, what it doesn't, and how accurate it is, both in an absolute sense and a relative sense against other protection forms?

Safe area protection, if well designed, monitors many of the variables that happen to the output devices and start shutting down the output devices when they start getting to dangerous conditions. Well designed safe are protection watches absolute current, current-voltage product, time variance of CV product, and load impedance.

I could give you the lesson about why safe area protection is more accurate than current limiting, but as you said
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you rattle on about nothing too long
so if you ever want to know how it works, ask.

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And you can say I was unsuccessful again, but the problem is with the hidden assumptions of your question. Qualify those assumptions and I have no problem with a yes or no answer.
No, you did OK. You admitted you didn't understand it. Bravo. You're getting better. Keep practicing.

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RG said: What is your training and experience in analyzing power electronics for reliabilty? Is it just using them until they break or don't break yet?
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LJ said:Yes.
OK. So you don't have any training or experience in analyzing power electronics for reliability. Well, no big surprise, but once again, I was just seeing if you were honest enough to admit it.

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Reality is fact - theory isn't. If it doesn't break in use, then it is reliable. Bridges built only on theory do fall down, and in doing so, theory changes.
And mothers kiss babies and bake their kids apple pies. Who said anything about theory? I've spent more than a few days peering at the burned-out guts of a power supply or amp that let the magic smoke out and designing something that replaced the hulk and didn't die. 

People with theory-envy want really badly to tar anyone with formal training with the brush that they have no real world experience. You misjudge it badly if you think that's the case here. I've known engineers who were useless. But I've also known guys with degrees that are the right ones to have on your side in crunch. It's another logical fallacy to assume that theory is always wrong, or that an engineer worth his salt will hold onto a useless theory.

Let me reproduce something that you seem to have missed from my last post:
Actually, my "hearsay" comes from people who practice the art, write textbooks, teach, make a living by getting things to work - over and over and over. I guess that yes, you could call that a better grade of hearsay. Call it informed hearsay. Who you gonna bet on - the guys who do it all the time or the uninformed?

The race is not always to the swift nor the contest to the strong - but that's the way to bet.


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I doubt it, but you may have heard the saying: "when reality conflicts with theory, develop another theory".
Yeah, I've heard it. We had a few other sayings back in engineer-land that you probably haven't heard.
"You can't bullshit electrons."
"Put whatever you like in your design drawings, but Mother Nature waits for you at the end of the assembly line."

Your anti-tech bigotry is pretty dated (and herd-following, as I know that's near and dear to your heart) but it's not very accurate. Did you think it's original? Did you think it's clever? If you get right down to it, it's a form of pride in being ignorance; the idea that people who have training and experience in a technical field must be wrong. Save yourself a lot of money - don't get into a lot of wagering on technical issues.

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I will never be INVOLUNTARILY forced to short the output of my amp. That is just one of your hidden assumptions.
OK, lessee here. You're never going to plug the wrong cord in. You're never going to get a whisker of wire or metalized foil in the wrong place in less-than-ideal conditions and time pressure. You will never, ever, no-how, no-where, no-time ever make a mistake.

If that's your contention, you are either not human or a liar. And yes, I guess it is fair to say that humans will make mistakes to be one of my assumptions. So tell me, and again, try to answer yes or no - are you trying to tell me that you will never make a mistake?

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The rule about plugging in the speaker before turning the amp on pertains equally to solid state - you won't short the output by plugging in the cable. Deny that one.
Why should I? If you are silly enough to use plugs that will short the output and also silly enough to demand that there be no protection of any kind in your amp, OF COURSE you have to make up rules to try to never make a mistake.

...uh-oh... there's that mistake word again.  :)

What I can tell you is that none of my amps, with the exception of my old Thomas Vox amps, care a whit whether you plug the speakers in first or not. You can plug the speakers in and short the output with a crowbar with the amps being driven to full power and there may be a momentary hiccup, but there's no smoke, no flames, hardly even a burp. More importantly, you can plug any speaker load you happen to find into them, and no combination of loads or lack thereof will have me muttering as I solder in new output devices. Or replace tubes. My tube amps are stable under no-load. I ...um... have that protection resistor in there that I told you about.

The TV amps are special. I keep them in a kind of sheltered workshop for sentimental reasons.

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And common sense tells me not to use a long speaker cable, so it's physically impossible for it to be run over.
Kewl.
This "common sense"  you speak of - is that what you'd call "unstated assumptions" if I used it? Yeah, I thought so.

But back on topic, you're going to use nice, tidy, short speaker cables that will just ...barely... reach from amp to speaker, no trailing wire to roll over or step over here, uh-uh! That's great, until someone trips and knocks the amp off where it's sitting, or knocks the speakers over and breaks the plug in the jack, ...involuntarily... shorting your speakers.

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I don't have a clue what tangent this is.
Yeah, not having a clue does seem to be a problem. Let me help.
You said:
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Maybe a corporate engineer would lose his job by designing an SS amp for tone instead of short circuit protection "just in case".
The operant words being "for tone instead of short circuit protection". By that juxtaposition, you were trying to draw the picture that designing for tone was leaving short circuit protection out, and vice versa. You were attempting to present them as antagonists. So I said:
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There is no designing FOR tone and NOT FOR protection (again noting that "short circuit" has nothing to do with it, see above again). The two are not antagonistic concepts.

It may be possible that you see them as antagonistic because to you "tone" only happens on the edge of circuit failure. If that's the unstated condition in your mind, you need to do some more thinking.
Caught up yet, are we?
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No, tone doesn't happen only on the edge of failure.
OK, that's a step forward. I hear you saying "I can get tone without running my amp on the edge of failure." We'll come back to that.

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But with your mandatory protections, tone doesn't happen.
First of all, I never said they were mandatory. Smart to have, useful. Something I'd put in, yes. But mandatory? Gracious me, I'd never tell you what you could and could not have in an amp. I might snicker at the choices, but I'd try to do it in private to be polite.

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Again, since you keep avoiding the question, why don't you recommend these things for tube amps? Wouldn't having them produce a nice glichy sound be equally "great amplifier design?"
Avoiding the question? Not at all. I don't recommend them for tube amps because tube amps are not prone to the same kind of failures as SS amps. They are prone to a different class of failures, and didn't I already explain that one a few posts back?

But what you're trying to get me to admit is that I lump making glitches with protection circuits, and further that I think all amps should have glitches. Right? It won't work, because (a) I never said that, and if you misread it what way, go read again; (b) I have the opinion that well-designed protection circuits do not necessarily produce glitches in situations that are otherwise not damaging to the amp.

We have from you the following collection of statements:
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Hmm... yeah, maybe I'm lumping too much under the general term "protection circuit". It's the short circuit protection I primarily don't find very toneful.
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Of course there is no sound during a short,

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... But - ok, assume I don't(know how safe area protection circuits work).
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"Yes", there are some situations where what you are calling "safe-area protection" can prevent an amp from dying.

Let me synopsize some things you've written:
You've used SS amps for a long time.
You are OK with the failure rate you get with them.
You have heard some SS amps with protection circuits in them that you don't like the sound of.
You generalize from that last statement that all protection circuits are bad and should be avoided.
You do not understand short circuit protection circuits or safe area protection circuits.
You admit there are situations where short circuit protection and safe area protection can save your amp from being damaged.

I think the rest of this is not liking being called on it. You'd sure like to paint me as a guy who has no real practical knowledge, is a follow-the-leader automaton, and is technically trained and therefore must be wrong. As you yourself said, reality is fact - theory isn't. The reality is that your theories don't match amplifiers or me.

When you can design a heatsink so the power devices don't burn up, when you can design a multi-slope safe area protection circuit so a set of speakers won't activate it, when you can design and build a transformer driven totem pole output stage will be stable over initial component variance, thermal drift and aging, when you can count off some of the problems with believing a circuit simulator is telling the truth, when... oh, never mind. When you get to any of these and want to know more, drop me an email. I'd be glad to help you with some of the fine points.

joecool85

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Re: 60W Power amplifier
« Reply #28 on: August 14, 2007, 07:02:50 AM »
I don't have a clue what tangent this is. No, tone doesn't happen only on the edge of failure. But with your mandatory protections, tone doesn't happen.

Ok...I'm no amp tech or engineer, but I do know a bit about electronics and I play guitar.  Plus I'm the founder of this here establishment  :tu:  Anyway, how is it that you say tone doesn't happen with protection circuits?  The LM3886 has one of the nastiest protection circuits available (as far as gross noise if you ever hit it), but as hard as I've pushed my home built LM3886 poweramp, I've never hit the protection, and it sounds GREAT!  I get all kinds of compliments on that amp.  The tone in SS amps is all in the preamp really anyway, the poweramp should produce a non-colored, amplified version of what came out of the preamp.  The second most important tone quality for an amp is the speaker.  I'm all for protection circuits so long as you can make some good sounding music come out of the amp, and with an LM3886 it is totally possible.
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Re: 60W Power amplifier
« Reply #29 on: August 14, 2007, 07:24:18 AM »
Oh, I also want to add that I'm really loving this conversation.  Despite a bit of sarcasm this whole thread has been pretty respectful, extremely interesting and also informational. 

I just wanted to let you guys know it's not just you here, I've been reading this whole thing the whole time.

And before anyone makes assumptions about me, I'm 22 years old, a 5th year New Media student at UMaine (I'll be done my degree as I finish my 5th year here).  I'm working on designing a LM386 based preamp, even though it is technically a "power amp" it works well as a preamp, and more importantly to me, a line level box.  I've built several SS amps including two LM386 amps, a stereo LM1875 amp and a mono LM3886 amp.  I am the original founder of this website, however I am a co-admin with Chris, I am also the admin of my own website (thatraymond.com) and a moderator on offtopicforums.net  I am a computer enthusiast and own two Mac OS X machines and a PC box I use for running Ubuntu 7.04, when I need Win XP Pro SP2 for something I use my fiance's laptop.  I am 5'10" and have hazel eyes, I hate single coil pickups and I am blatenty biased to Les Pauls.
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