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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.

QuoteHad 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.

Quote from: Blacklabel on August 09, 2007, 03:21:53 AM
and it still wont work..i am now going to replace the 2, 220k 1 watt resistors that are linked to them also and see if that works...any suggestions please post..thanks

Replacing a 220 ohm 1 watt resistor with a 220K 1 watt resistor isn't going to help much. I hope it was just a typo.

Quote from: Blacklabel on August 07, 2007, 06:11:12 AM
Hi, I Replaced the 2 Main Elec Capacitiors..and the Diodes that ground straight after them....and it still wont turn on..anyone got any ideas on what might be wrong...thanks

Remote debugging is difficult at best - even with pictures (hint).

Hopefully you used the proper zeners and not regular diodes, and installed them with proper polarity.

What voltage readings are you getting at the replaced caps?

R.G. - Have you always this paranoid about SS amps? Obviously your logic has a strong bias towards tube amps.

Why pretend that a "no plug in jack" resistor is the same as "open circuit protection". 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?

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.

Since tube amps don't have protection circuits that corrupt the sound, does that imply that tube amps are not abused when overdriven?

If a blown tube can be accepted in persuit of tone, no reason that a blown transistor can't be equally accepted.

What's a tech? Oh, you mean those delusional self appointed guru's of tone that won't even look at an SS amp.

Teemuk - thanks for mentioning Peavey. I didn't know they had been around that long. I've read through some of the articles on the site. I especially enjoyed the transtube article by Hartley. I really loved the part about the double blind "guess which amp is SS" test!!

Nah, musicians friend was just trying to make a sale.

Joe, low frequency abuse to an amp doesn't make any sense to me. Perhaps you could explain your reasoning - especially an example of what you would look at for rebuilding. Meanwhile, I'll explain mine.

There is no component in the special 130 (or any amp for that matter) that is going to be adversely affected by the octave lower (or lower for 5/6 string) bass frequencies. Resistors don't care, transistors in the op amps don't care, and capacitors - being frequency "affected" will respond based on the frequency - either they will pass it or attenuate it if it is too low, so they really don't care either.

Now I admit this may be due to my limited design work, but I can't even begin to think of a way or design that would "on purpose" self destruct when it receives a low enough frequency. I am not a peavey expert by any means, but it would not make good business sense to design a power amp specifically for guitar usage. Taking Sunn as an example, within each series such as the Concert, Coliseum Alpha/Beta, the same power amp is used regardless if the unit is Guitar, Bass, PA or Slave.

Besides, for a bass amp, extended low frequency response is not always necessary nor is it even desired. Many bass amps attenuate the response of the lower octave (+) to reduce problems caused by excessive bass response - muddy sounding bass and wasting acoustic energy rattling the drums and the rest of the band stand being a couple.

Heck, the ampeg SVT speaker cab drops in output pretty drastically at frequencies below 100-110hz and yet is known for its tight bass sound.

Cool... I'll use a socket. Thanks!

Ok, I'm an op-amp novice, so be gentle.

The Mike Matthews Dirt Road Special's preamplifier is built around the 4558. Two pretty simple non-inverting stages with two feedback paths each - one being a resistor only and the other being "frequency selective" for implementation of the tone and bite control.

I'm thinking I want to replace the 4558 with a TL072. For no other real reason than I have an amp that uses TL072 and it sounds pretty good, and as I understand it, the 4558 is considered a "low quality" device for audio.

I have done some homework. The pin-outs for the 8-DIP package are the same. The critical supply voltage and common mode signals and a whole bunch of other things I don't have a clue about are the same if not better with the TL072.

I can't see any reason why I couldn't just swap a TL072 for a 4558.

Anyone see anything I can't?

Thanks!

I was getting together a parts list to build this amp when I noticed something that got me to thinking.

The collectors of the output transistors are tied together.

The thought was - is it really necessary to ground the heat sink? If the heat sink is ungrounded, then the output transistors could be mounted directly to it without a mica insulator.

So... if I mount the transistors directly to the ungrounded heat sink, would it still be advisable to use a heat sink compound between the transistors and the heat sink?

No link? 

Oh well, no hope for us myspace limited folks. 

No, don't have any idea what was used on Afterburner. For what it's worth, a Legend was used on Eliminator - I'm not familiar with them, but it's supposed to be a hybrid, tube preamp and 50w SS power amp.

The ZZTop CD's are unfortunately remixed versions - not copies of the master tapes used to produce the vinyl recordings copied to CD. That's a shame because they really screwed it up. Supposedly the "six pack" CD collection were all remixed in only three days - "specifically for CD" which is a crock. Some are way too bright and others are very dull sounding.

Yes, I agree - all those companies I mentioned are defunct - but I seriously doubt that more complex circuits, hi-fi designs and additional protections would have had any bearing on their demise - other than possibly make it happen sooner.

Seems to me that there is a life-cycle that eventually affects most corporations. A company starts up, produces innovative products... then stagnates into bureaucracy, starts using "market research" and focus groups to tell it what to do, drives out all of the geniuses (aka mavericks) that gave the world those innovative products and settles into "business as usual" waiting for the coffin to close. Sad in a way. The only companies that survive this cycle are the ones that are "reborn" and get a chance to start the cycle over again at the beginning - Fender is a good example, although they are now back in stagnant mode.

Acoustic started out with some "state of the art" designs. The 361 does have differential inputs and short circuit protection. Fortunately they left that stuff out of the 260. I don't know about it's 270 successor. I lost interest in Acoustic around 74-75 - if that's when they went hi-fi, maybe that is the reason. I didn't like the sound although I can't put my finger on a reason, although I still love the sound of a 260. I'm surprised you didn't say they "de-evolved"... IIRC, they used a transformer driven totem pole design in the 150s?

I don't disagree that the Thomas/Vox Beatles were unreliable. But I don't believe that is just a natural consequence of the transformer driven totem pole design - there are too many reliable examples using this design out there. However, ANY DESIGN, if overextended, will transition into unreliability. I consider the Beatle power amp way overextended - the Royal Guardsman is probably on the edge.

I don't consider the Buckingham to be overextended. 35 watts, 8 ohm minimum load, three transistor transformer driven totem pole power amp. I don't believe they were ever converted to silicon outputs. I've had one for almost 20 years, overdrive it constantly (within the range of the preamp limiter which I have cranked up for as little limiting as possible - but I believe it only has a 6db range of adjustment, if I estimated correctly). I'd never do that to a Beatle, but this little amp just loves it. I do expect the outputs to give up eventually - probably due to age and thermal cycling more than anything else.

The Orion. I hated when Sunn discontinued it - and it's brother Aquarius which I have never seen outside of the 68 catalog - it was probably never released. Power amp overheating problems as I recall. I've never seen the power amp - there are rumors that it had germanium outputs and/or it was too enclosed without a chance of cooling air circulation.

How about the Sunn Concert? The earlier ones used a transformer driven "dual" totem pole in a "grounded bridge" configuration with a floating power supply for the outputs. Used with a minimum 4 ohm load, these amps have proven their reliability. What usually happens is that someone sees that the 1975 and later version is rated for 200 watts into 2 ohms and thinks they can run the earlier Concert into 2 ohms. The later design - trying to get 200 watts out of four 2N3055s into 2 ohms, even though the bridge configuration was dropped in favor of parallel output transistors, is what I would consider the edge of overextension. These later versions are just not as reliable as the early ones.

The Baldwin power amp has proven reliable. In the C1 Custom, 45 watts into 2 ohms (the 2 12" speakers are 4 ohm units connected in parallel - the extension speaker jack is in series). Also a transformer driven totem pole. A voltage amp (NPN silicon) to mix and boost the two channels, directly coupled to the Class A (PNP germanium) transformer driver. The secondary side uses six PNP germaniums, same type as the driver, paralleled three per side. Feedback is from the output (after the coupling cap - it's single supply) to the emitter of the transformer driver, and through a 2.2K resistor to the base of the "grounded" side of the output string only. Unlike the Thomas/Vox, there is no limiting - with the possible exception of the eventual clipping of the class A transformer driver. The emitter resistors of the outputs are .47 ohm fusible links however.

The Kustom K200B power amp is dual supply +/-39.5 volts, no output cap. It has differential inputs, typical class A VAS. One unsual aspect is each output transistor has a separate driver transistor. The short circuit protection doesn't seem to affect the sound even when driven to clipping, unlike other more hi-fi power amps. A single transistor on each side is used to shunt the drive signal at the base of the driver transistors through a diode. The control signal is derived across a 1 ohm emitter resistor to ground on both of the output transistors on that side, and is summed to the base of the shunt transistor through separate 1K resistors.

The earlier Kustom K200A series didn't have short circuit protection and are in general regarded as the better sounding of the two. The K200A is can have overheating problems which were solved in the K200B by an increase in chassis size, better mounting and more airflow over the output transistors. John Fogerty stuck with his K200A-4 - probably more for the additional advantage of having all effects available on one channel and not split between two channels like the K200B-4 design - but you will notice, he always had a backup ready to go if necessary!!

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." Priceless!!

When did Mesa get credit for channel switching? I hadn't heard that one. I know Mesa had a patent on "mode switching" which isn't the same thing, and the primary cause of their suit against Acoustic.

I have some rather basic questions... and I guess my answers. I guess the umbrella question here is "why am I wrong in thinking what I think"?

o Why are specification related aspects like linearity, slew rate and bandwidth even being considered for a guitar amp?

Sure, if I were building a hi-fi amp, these specs would become more important. The purpose of guitar amps is to produce a sound - not to reproduce an existing sound accurately. I've never heard of these specs being advertised for tube amps, so I think they can safely be discarded for solid state amps.

o Protection circuits are necessary for the ignorant consumer and manufacturers that cater to them. Professional level equipment do not need them.

I guess this is more of a statement than a question. But as an example, take short circuit protection. When is it really necessary? When the output is shorted. Ok, what kind of idiot would short the output? An ignorant consumer.

Most professionals follow a simple rule that makes short circuit protection totally unnecessary: "Never power on an amp without a speaker load attached." Catering to people that ignore this rule (that pertains equally to solid state and tube amplifiers) isn't necessary for yet another reason: output transistors are cheap. Tubes on the other hand are at least an order of magnitude more expensive, not to mention the output transformer - but I've yet to see a tube amp with "open circuit protection" which is more damaging to a tube amp than a short circuit (other than low wattage plate and screen resistors acting as fuses).

So maybe the real question is: why use circuits designed to protect a device that is cheap to replace? Especially when they can adversely affect the sound.

o SS amps do not have a bad rep due to amps produced between 1965-1975. At least not the professional level SS amps produced during this time frame.

This is part of the myth of better sound coming from tubes. Look at what manufacturers were producing professional SS equipment during this timeframe: Standel, Thomas/Vox, Baldwin, Kustom, Acoustic, Sunn - probably more, but these were the larger players. Fender tried but failed due to manufacturing problems, not related to the design of the amp's circuits.

Pick one that contributed to the bad SS rep.

All of their power amp designs were simple, used very little feedback, were probably non-linear as heck, and all but Kustom (at least up to the introduction of the K200B in 1968) didn't use any short circuit protection.

What I think contributed to a bad SS rep - the sheer expense of purchasing an SS amp during this timeframe!!

Go to your record collection, and pull out ZZTop's Tejas. The guitar on the entire album was recorded through a Thomas/Vox Super Beatle. FACT! I remember a review in some magazine when the album came out - proclaiming the great tube sound of ZZTop does it again.

Quote from: R.G. on July 23, 2007, 06:31:49 PM
Just curious - why didn't you just use an LM3886 for the power amp? That's what I've done when running current feedback setups. It works fine. In this iteration of the current feedback where you're using the current feedback to in effect predistort the signal into the power amp you should have even less problems than normal with it.

It is very hard to come up with good reasons for making amps under 60W out of other than the LM3876 or 3886.

Other than "why the heck would anyone use a chip power amp?" - probably no reason at all.

I don't know if you would consider it a good reason to not use a chip power amp for under 60watts, but my reason is very simple - no short circuit protection, no current limiting.

I know engineers will tell me I need these things, but heck, I have been overdriving SS poweramps without them for over 35 years with great results - so nothing is going to convince me I need their tone defeating qualities this late in the game.

Teemuk's design is way too complicated for a 60 watt amp. I can build one with only 5 transistors and get great sound. Personally this design may be way too - lean towards tube emulation - for me.

No, it's not a case of me wanting to do it.

I got a note from a friend of mine. His amp is mainly tube but there are some op amps for the reverb. There is a separate supply for the op amps and it is supposed to have zeners across both sides of the dual polarity supply.

But instead, it has some kludge type wiring (i.e. "handwired" above the circuit board), no zeners, but hexfreds where the zeners are supposed to be.

I'm not sure if hexfreds could serve the same purpose, but then again I don't have a clue what the purpose could be. It's just some weird mod that doesn't match the schematic.

Sounds like two good names for a RPG.

Anyways, is it possible to wire up a hexfred so it behaves like a zener - like for voltage regulation?

Not having a circuit diagram posted, not knowing what a noisy cricket might even be, I can only ask one question:

Did you use carbon comp resistors anywhere in the circuit?

And this may seem sarcastic, but it really is out of my ignorance - does the Beavis audio site have any relationship to the butthole site?