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Messages - phatt

#2236
Tubes and Hybrids / Re: First Hybrid
October 10, 2009, 05:27:40 AM
Quote from: awdman on October 09, 2009, 10:46:17 PM
is this the schematic? http://schematicheaven.com/boogieamps/boogie_vtwin.pdf

Hi awdman,
          Yes! that is the schematic I based my ideas on.
It is a most intelligent way to intergrate Valves with opamps.

Here is a rough circuit drawn from memory of how I built mine,,, bare in mind this was many years ago but might help you to come to a better understanding of how to go about such things.

Note the mistake on Vtwin drawing; *R24-270k* around U1b is *Wrong* 27k will make it much more civilised.
I did not use all the addon bits just the clean section thru the tone and onto the pwramp output.
I've moved on from this stuff as I've found that it is better to throw money and time at the business end of an amp,, ie, A Tube Poweramp is more useful as that is the one thing SS can't do to well.

Having said that, a Valve preamp circuit like this will certainly improve a SSAmp.

I can't stress enough that any *One off* ciruit like this you really need to spend a lot of time breadboarding it all *RD FIRST*,,,Then build,, Otherwise there is a good chance you are just adding to the land fill.
Have fun, Phil.
#2237
Tubes and Hybrids / Re: First Hybrid
October 09, 2009, 06:38:46 AM
Hi folks,,, if you are trying to get your head around tubes into SS,, then download the Messa V Twin circuit and just build it less all the cab sim add ons,,and that will make your life a heck of a lot easier than trying to work out the maths.

Note; as long as the plate cap decouples the HV tube then the signal voltage is the only concern.
Generally the biggest signal AC voltage is only 100VAC max so as long as the *First* cap is 400volt rated then the rest can be 100 volt caps.  This is obviously how the Vtwin circuit gets around it all.

PS, I've built the Vtwin circuit into a SS Amp so I know it works just fine.
Cheers, Phil.
#2238
Hi raypist,
              It's effectively a master volume that is left alone once set.
Ideally this would be a *Fixed* Voltage divider *inside the Amp* but that's
going to make a lot of work for you.

When an Amp is designed there is a limiting value before the main power Amp which has nothing to do with the master volume on the front.

IF a master volume was the only limiting R across the signal path before the main power stage then the guitar player would not know how much volume was safe.
Much like a popoff valve on a turbo engine,,, without it the driver has no way of knowing when to back off the throttle (master volume) and the engine would certainly self distruct.

In your case my guess is the Amp is not designed well enough to cope with 4 ohm loads.   A fan won't fix it,,, nor a bigger heat sink.
Output transistors with a bigger *Current Capacity* would likely fix it but then you would have to rebuild the whole output section.  :duh
Makers want to make their gear as loud as they possibly can as the competition is fierce,, so in the end they push things to far and this is the result.

I'm just showing you the simplest way round the issue if you are prepaired to loose some of that extra power.
You may find that 8Ohms is all round a better solution.
IMExperience 8 Ohms is giving the power amp a better chance of coping with hot enviroments and gives a better margin of error,,,, keeps it away from the danger zone of * to much current dissapation *
Phil.
#2239
Hi,,
If you have a volume pedal handy that will save time.
Just back off the volume a tad and see if the problem goes away,,,, if so then consider a small jiffy box with a 100k Volume pot hard wired inside and 2 short length guitar plugs. Not that hard to wire up.
Cheers Phil.
#2240
Quote from: raypist on September 25, 2009, 03:18:02 PM
well im hoping you half-assed electricians aren't chalking this one up as a win.

Ha Ha With comments like that you won't recieve many chip points. :-*
I don't know your gear but as a general rule 4 Ohms load on a SS power stage will dramatically up the *Current* the output devices have to deliver. (the lower the load the higher the current)

Hence you are triping the safety relay circuit.

Although a lot of gear quotes 4 Ohms as safe, some don't cope to well.
If the Amp has an EFX loop you could insert a simple volume control at that point which would enable you to just dial back the big signal that would be going to the power stage.
I had a similar problem with a DJ setup years back which was solved by lowering the final preamp output signal just enough to stop the silly thing triping out.

I would be annoying Randall if you want better answers.
Cheers Phil.
#2241
Quote from: armstrom on September 23, 2009, 03:16:25 PM
Way off topic here, but just to respond to R.G.'s last post:

This is why I plan to build a nice, low wattage tube amp that has exactly the sound I want (Maybe a Fender Champ design, AX84 P1, or even a 1W firefly) then get the best dummy load you possibly can and feed it into something like a LM3886 power amp.
The trick is finding a good dummy load and voicing the power amp/speaker combination correctly. My end goal is to have an amp that I can switch between having the tube amp drive the speaker directly or have it drive a dummy load and let the SS power amp drive the speaker. The only noticeable difference should be the maximum volume available (at least that's the goal!). We'll see if I ever really get there :)

It all boils down to how do you want to achieve the "tube tone" in a louder, lighter and more reliable amplifier package. I see two possibilities, you can either get the tone in the same way people have been doing it for decades, then just make it louder with a high quality SS power amp. Or do you invest lots of time and effort trying to "emulate" the sound of a tube amp without using tubes?  Depends on what you're after really. It's almost a guarantee that the cost of building a hybrid amp will be significantly higher than an emulating/modeling amp just because of the "iron" required by the tube section.

It seems to me that the "tube sound" has almost been relegated to only a few genres of music (dirty blues, for example) and a set of purists who must have it for what ever reason. If you look a areas that used to be dominated by tube amps (hard rock, heavy metal, etc...) you have to admit the trend seems to be moving toward using extensive effects systems (pedals, rack-mount modelers, whatever) feeding into a super clean solid state amp like a JC-120 or something similar. The wall-o-marshalls just doesn't seem to popular any more :)

It's just my $0.02 though. I've likely completely missed the mark on this.

Hi armstrom ,
No I don't think it's too far off,,, in fact you are closer to tone heaven than you think. 0:)

You are not missing anything, It's by far the most useful Amp configuration I have used, EVER!!
If you wish I will post some drawings of my *PhAbb ReAmp* setup to show how easy it is to impliment such a system.

My tube Amp section is just a 2 knob simple affiar built from old radio parts.
All the other tweaking is done via simple SS gear.
Compared to the cost of big name gear (SS or Valve) my setup is dirt cheap.

Cheers Phil.

#2242
Hi Teemu, Thanks for your input, Obviously you have far more knowledge than I will ever attain and I seriously respect your ability and taking time for us less knowledgeable folk.
Judging by Neosho's last comment you are not far off the topic :)

My main point was The **PowerAmp Frequency Response curves** surley most of what you refer to is *Preamp tone shaping*.

Unless I'm seriously misguided the Response Plot of a modern DC coupled *PowerAmp* is almost always flat, I do understand that some tweaking of this is possible but probably not to the extreme that is achivable with Old Valve circuits.
Yes, I'm fully aware that in the *PREAMP* Stages of modern SS gear their is a lot of tone tweaking going on.

No one seems to give any thought to the SS powerstages cept for some defined impeadence (or current FB) which in my experience does almost nothing to the tonality of the output.

With Guitar Valve PowerAmps, Transformers can be (Are) wound to different specs to alter these curves. then there are interstage coupling tweaks and other places in the power stage that alter the Freq curve/line.
In some classic Valve circuits it seems there maybe a 40Db or more drop from 100Hz down to 10Hz. I've not found a SS DC PowerAmp where this kind of cut is possible.

To say the least; "Big tone shaping curves" is not an inherint trait of DC power stages and although I obviously have limited knowledge on Exact details I have fiddled around long enough to pick up on some of the basics.

I assume you get to play with more toys than I ever will so point me to a SS circuit that can reproduce an Early Marshall powerstage Comp and tonal Honk.
I won't live long enough to build every theroy that comes along and most times you have to take a half educated guess at what is worth wasting time and money on.

I've not stumbled across anything cept for the Valvetronic concept (looks slick, sounds average) that comes remotly close to the sound I'm wanting.
Thanks Phil.
#2243
Neosho,
       Before you part with your money on new gear just get a simple sequence of events like this;
A Parametric EQ>> dist pedal or box>>> A Graphic EQ >> into a SS Amp.  It might help you grasp just how important *ToneShaping* is.

Even with such a basic setup EQ before and after Dist will sound far more convincing than just relying on overated promises of advertising blab. insert fancy brandname Amp.

FWIW I've just recently been inside both a Tech21 Trademark 60 and a Fender Performer 1000.
Both these amps seem to be using CFB among other tricks and Seriously niether Amp comes remotely close to the Control over dynamics I have available via my Setup.
The P1000 was dated 92 and trademark is about the same era.

Neither of these amps have any ability to develop a sweet spot between clean and compressed.
Yet I have the original marketing phamphlets for the Trademark60 and it's just so OVERHYPED and overrated.
I doubt if the other makers are any more or less *Honest* in their appraisial of their own equipment.
Phil.
#2244
Hello again dsmnoisemaker ,,
Sorry if I'm missing something but just re read *United States Patent US5467400*

You said;  "It is not a cabsim..its a replica of what a high impedance amplifier output does to speakers..a cabsim may be added after that to simulate an actual speaker response."

So I'm scratching my head because from where I'm standing It's the same thing just coming at it from a different perspective.
effectivly achiving the same thing ,,except I assume you are trying to do it with the 4096 to add the distortion thing. But I might be missing something.

Best of luck with all. Cheers Phil.
#2245
Quote from: Neosho on September 17, 2009, 10:59:54 PM
Hi phatt:

You asked, "why not use an output transformer?"  Good question...

I am not sure if it would help or hurt.  It seems like it would be very good at preventing DC offsets from getting to the speaker and damaging it.  Instead, the amp's transformer would become damaged.  At least you wouldn't be frying speaker coils due to a transistor getting shorted to the power rail, so that's some progress.

I know that old amps like Acoustic used transformers, but maybe it was because they were limited on the availability of transistors (only NPN? was available for awhile).

The hi-fi amp books I have read argue against output transformers.  I have Doug Self's book and Slone's book.  But their interest is sound reproduction.  The cons are: transformers add cost, aren't really needed, cause phase shift, make the amp more narrow band, add weight and mechanical complexity.  Certainly you never see output transformers in newer SS amps built by Fender and Tech21, etc.

I have seen the theory that transformers have some ability to saturate non-linearly, and that is part of vacuum tube tone.  I think there is even some patent where the author introduces DC offset on purpose to try to imitate tube tone.  I don't know if these things are provable or just wishful thinking.  I know the some of the tube people think that it's helpful to use a high class transformer to get the best sound, and there are differences in the construction that are important.  Mercury Magnetics sells an upgrade transformer kit for the Valve Junior for asking price of $299... seems like a lot of money for an amp that can be seen on craigslist for $100.

Do you have a theory about output transformers?


Hello Neosho,
                  I think *Brymus* found some good ones to study,,
Thanks Brymus Very good stuff there. :tu:
*Neosho* asks,,  Do I have a Theory?  Oh Yuk I hate those things.
For me it's called Trial and Error,, (mostly ending in Error though)  :o
I'm just a hobby geek,, I'm useless at maths and many other things in life but music and the workings of Audio systems have always facinated me.
So ever so slowly I just absorb stuff.

To cut to the chase, most muso's covert the sonic result of output stage compression/distortion found in *some* tube amps. (not all I should add)
It would seem that no matter how many preamp stages and or distortion gizmos are used it just can't quite deliver the same sonic result.

I can only assume this is what you are chasing.  Join the  :duh club
If I could do this trick with SS I would but no one has ever been able to reproduce *THAT Sound* via a SS system.

First lets establish what we are shooting for.
I'll roughly quote the words of *Kevin O'Conner*,
"If you wish to Maximise Tubyness,, a Small PP Common Cathode bias,, no FB,, and moderate HT."
The one big advantage of valve power stages is there very large range of dynamic compression.  The Above just maxes that effect.
So a super clean 100 Twin is a mugs game if you are looking for all the inbetween dynamics. I built a tube Amp on that advice and indeed I got exactly what I wanted.
So if you want to achieve it with SS then that might be a good refference point.

If I was to have any theroy it would be THUS:
Transformer coupling (ie, the classic PP output stage) is unique in that it *Floats* the AC signal on a HIGH DC Volatage potential.
In my limited ability to explain such things all I can think of is a concertina effect or spring where the AC signal can rise and fall and (via some quirks in transformers) can at times rise momenterily *Well above* the DC inside a transformer primary winding.

Surely this Just can't happen in the modern DC coupled SS Amp where the signal (at the output) is basically at Ground.
There is also a Very Rigid PSU in SS and hence the signal litteraly *Slams into a brick wall* of rigid DC,,, Limiting the ability of ANY large signal swing. The result is a hard clip along with a whole lot of other things.
I'm probably talking to a lot of experts so no need to rehash the obvious.

There are some points that don't get much attention one being the *Response Curve Difference* between SS an Tube output stages.
A SS power stage is almost always *Dead Flat* often from very low (ie, 10 Hz or lower) whereas Tube power stages of calssic valve Amps can have quite dramatic curves. You can tweak DC powerAmps a bit but all the major tone tweaking has to be done in the pre stages. Interesting to note that Valve amps of a past era often had masses of bass in the preamp section and often very steep rolloffs below 100Hz in the power stage.
I'm far from the expert but my guess is it's gonna sound a lot different.
I'll leave the better qualified folks to debate whether that be good or bad.

The other point that gets missed is pentodes have a *Screen Grid* !!!
Try and find a SS device with one of them??
*Brymus* might be interested that although the *Turner* stuff looks very slick (the big PP 50 watter, which is likely a good SS HiFi amp) It probably whould not deliver the goods for guitar amps.
Just take a squizzy at some *Early fender deluxe* or similar tube Amps and *Take note* of the BIG Screen drop resistors in some of those schematics.

By far the fastest cheapest way to make a Tube Power stage *Compress* (early breakup) is to Drop the screen voltage. This has a huge impact on how the power stage responds to the incoming signal.
Modern valve Amps tend to run insanely high HT ,,have very little screen drop (ie, the screen is only a couple of volts below the plate). It becomes darn near  impossible for the output to compress unless it's fully dimmed so they *Have To* add many fancy tweaked up preamp gain stages and master volume knobs just to get some kind of distortion.
Hence it all becomes needlessly complex and a never ending battle to extract a good dynamic range to work in.
(some refer to this as,*the sweet spot*)


Back to OT's;
Whether you wish to design SS or Valves there is one *Transfomer Fact* I've discovered in my neverending journey.

Obsolete Electronics web pages (now gone I believe) had a very good little article about the Primaries of OT's and how they relate to *Guitar amp Tone*.
It seems that the *Lower primary windings* tend to **Accentuate the Second Harmonic content**
And it is widely accepted that these are the harmonics we like to hear.
The artical had refference to the original artical which was written in the 1940's so it was well known way back then.

Now add another *Known Fact*,,Some Early Marshall Amps had primary windings as low as 1700 Ohms pp (plate to plate)  (That's for a quad 100watter). A world away from HiFi Specs,, LOL.
Todays Marshall's it's more like 3000 Ohms pp. (I think?) and they sound nothing like the old ones.
Some early Marshall's are now revered for there magic tonal qualities.
To me it's obvious you don't want an OT that is capable of 300kHz bandwidth for great guitar sound.
So paying big money for a top end OT complete with all the fancy interleaving and exotic mu metals is likely a conterproductive waste of money. Tube or SS!!

I have built a 6V6 Amp firstly using a 6k6 OT and not happy I searched for a long time to understand my problem.
Long story short;
Without altering anything in the 6V6 circuit,,, I swapped for a 2K6 OT,,, BINGO!!! Insant tone heaven was the result.
So from my humble experience there is no *Theory* anymore it's more like concrete evidence that the Transformer plays a BIG BIG role.

Even without a *Screen grid* I tend to think a SS Amp would benifit greatly from a transformer coupled output,, much like the idea of the Turner Amp.
The b*t** for me is I will never possess the knowledge/skill needed to design a Tranz Coupled SS poweramp from scratch.
I've released my fair share of magic smoke from perfecty good Semiconductors, LOL! Even tried some back to back zeners across the feedback in dc poweramps and although it does compress it's nowhere near good enough.
*Joe's* come up with his neat little diode trick but looking at the wave forms produced I doubt it will be a serious contenter as it lacks the ability to saturate and square wave that is seen inside the OT of
a Valve Power Stage.

FWIW, I have opted for a Hybrid, that being a Modular Reamping setup where I soak a small Valve Amp,,, re eq and reamplifiy it via a big SS powerAmp.

For any short comings this system may have,,For $Cost outlay$ and importantly absolute control and flexability this is darn hard to beat.

Being able to Re EQ *After* the power tubes makes for a setup that delivers closer to *any toneshape, dist, any wattage level I wish to play at*. I can play in the sweet zone all night long.

Oh well that's bout it,, I wish you luck in your goals and hope you get it to happen.
Don't forget to have fun and play music also, Phil.
#2246
Quote from: Neosho on September 13, 2009, 09:30:01 PM
I want to try to design an SS amp that has some reasonable limiting on the preamp stages, but it is very hard to "softly" clip due to the crest factor problem.  The amplitude of the guitar signal's peaks are very large compared to the average signal.  So I haven't figured out any good approach that seems worth building.  I have tried the easy circuits (like diode limiters) that you see in the old schematics but they always sound very bad compared to a good tube amp or the digital processed modelers.  Anyway, I keep looking.  Thanks.

Forgive my somewhat ignorant observations here,,,,,
but why not use an Output Transformer? 0:)
Phil.
#2247
Hello dsmnoisemaker,
                             Very teck and a lot of this is over my head but Have built similar stuff using 4049 and it's ok but maybe just use the 4049 for dist and use the cabsim circuit. Marshall sim Will work far better, IMExperience.

Also maybe Take a look at small Laney Amps for ways to impliment the 4049.

Here is a screen shot at the Cabsim circuit,, I've built about 4 of these and only have one left. This is just a slightly different circuit to the one found inside the Marshall JTM 30/60 Amplifiers.
The circuit you post is no where enough for what you will need to make it sound convincing.

The trick to most of this stuff is about *Maximising Loss* not Max boost
. Once you get the *Tone Shape* Then apply some gain If you get my drift ;)

This circuit works well for Recording,, works well after guitar processors.
I don't like it as much for Live Use though. I use another setup for that.
Have fun, Phil.
#2248
Hi RG,
        Arrh!! Beautifully explained in plain english.
Easy to see why you have so many chip points 8)

Interesting to note that some of my first attempts at SS pwramp builds sounded quite good when driven hard. They do start to rattle and roll when cranked up but still not as good as a valve output section.

Just 7 BJT's and no saftey circuit cept for a PTC (Poly sw)

I guess it's a case of ;; if you want a good guitar amp build a cheap badly designed one which usually sounds better and far cheaper to make.

Which is not that much different to the old valve days and *Now* folks are trying to get old Tweed amps because they are starting to realise the basic amp designs of a past era distort in a much more user friendly way.

Even with their dismal power ratings they sounded so sweet.
you just can't get *the low power basic design magic* from a quad of 6550's running at some stupid voltage and probably running as tight as most modern SS poweramps. (great for Bass though)
My 2 cents worth. Phil
#2249
Hi,
If anyone is interested here is a pic of the board on a ten year old Performer 1000.
The two 5 Watt Zener's run at a stupid temp (burn finger in less than a second).

This amp had switching issues about 5 years ago,,, and this is *As I found it inside*.
My guess is the zener's solder pad had let go. As you can see it has been re touched with solder at some stage.

I also found R172/173 have been changed from 100 ohms (as per schematic) up to 120 ohms. Obviously not good enough as the Zeners where still overheating.

I've uped that value to 240 ohms and now the Zeners are only warm.
The voltage readings are now stable at -15.9VDC and +16.1VDC and the switching circuits are working normally.

The 3 x 470R 5Watt for the AX7 heater circuit are rather hot so I've raised them off the board as the tracks are starting to discolour.

I'll see how this runs for a few days before I'll claim success.
Cheers Phil.
#2250
Amplifier Discussion / Re: Class A solid state
September 07, 2009, 10:15:29 AM
Quote from: J M Fahey on September 05, 2009, 01:03:03 PM
Hi Phil. Those old transformers *did* have a built-in gap, even if apparently it was not there.
To begin with, the EI lamination was *not* interlaced, as in "regular" transformers, but had all "E"s facing the same side, and all "I"s together closing the magnetic circuit. This already provides a usable gap, simply because of die cutting defects and irregularities. To this some added a single sheet of paper (regular printer paper will do) which becomes invisible after varnish impregnation.
For *mechanical* mounting reasons, the first and last E/I laminations were interlaced, simply to act as clamps enclosing the others.
Thus, on visual inspection the transformer looks exactly as an ungapped one, it can be only seen by dismounting it.

Hi JMF,
          Looks like I owe you a chip point or two :-[
Yes I pulled some OTr's apart today and just as you say the *Lams* are arranged to make the gap.
Though no paper shim in the two OT's I've pulled apart?
Never the less there must be some low power point where this *Gap* is not an issue?

I'm sure you can understand my reason for persuing such an idea.
*If* almost any small Mains Tr can be used as an OT (Cheap and easy to source) and powered from the likes of a computer style SMPS (a lot deliver ~about~ 20VDC).
Then the cost is dramaticaly reduced to the point where anyone could build a small 1/2 watt Amp for very little outlay.
Hey this is a SS forum and a lot of *Chipamps* so I'm just trying to add something a little different.
At the moment it's only a novilty but with the right minds working on it I feel it may have merit.
Thanks for the help :tu:
Joe mentioned Dalington but I've had little success with those.
The circuit I've tried seems to have the highest output due (I think?) to the bootstraping effect but the distortion is huge. sounds Kinda nice going through the transformer but I'd like to have some clean headroom before I post a working unit. Phil