Amplifier design ????

C Dixon · From: Duluth, GA USA

In a thread in the "Bar Chatter" forum, some of us wrestled with the differences between tube vs SS amps.

It got me to thinking. And over my many years with the engineering staff at the now defunct RCA corporation, it became an object of discussion many times concerning musical instrument amplification.

The consensus was, "I would NOT want to be a musical instrument amplifier design engineer!"

Why is this? Well, I know of nothing as subjective as perceived sound! NOTHING!

Here is an example: IF I gave a brand new and brilliant young engineer the task of designing the perfect steel guitar amplifier, in all likelyhood he would design it so it reproduded the sound coming out of a steel exactly as it was. That is; "100% true fidelity". And then I would have to fire him!

Reason is, we steelers do NOT want it to sound like it came out of our steel. Because it sounds awful! Yes it really does!

So, at this point what would a more experienced design engineer do?

He would turn in his badge!

Not really! In all likelyhood, he would realize the delima and design in wide equalization (tone) circuits to permit the player to vastly change the sound of his beloved instrument to satisfy his tastes.

And thinking back over the years, I must conclude that the "shift"/"mid-band" circuit has to win first prize in this scenario. Here is why. The natural sound of a PSG is not pleasant if amplified perfectly. And the frequencies around 800 Hz is the problem.

That is why the Peavey amps has, IMHO, become sooooo very popular amongst steelers. Those two controls permits a player to instantly correct (from a sound perception point of view), + or -, the "unsatisfactory", albeit natural sound coming out of the steel.

Or at least this is my observation.

Many will no doubt vehemently dissagree.

God bless them and you,

carl

Jack Stoner · From: Kansas City, MO

Carl, you are absolutely correct.

I've built some "homebrew" amps and they never sounded right, because they were "high fidelity" or reproduced everything exactly.

The Paramid circuitry that Peavey has in their amps really does wonders for the EQ. I notice that some other amp manufacturers are starting to add that to their amps.

The "Hi Fi" of the original transistor amplifiers were crap and for many years tube was the only way to go for musical instrument amplification. Tube amps do not have the inherent fidelity that a transistor amp does and tube amps are responsible for the "natural sound" which in reality is a non-linear amplification curve. Newer solid state designs have overcome the sterile or "hi fi" sound that they were stereotyped as and in reality are probably better than tubes. If a tube amp, such as a Fender Twin (I use this as many consider this THE tube amp) and a newer design solid state amp were really analyzed with instrumentation (spectrum analyzers, scopes, etc) I suspect the solid state would open a lot of eyes.

Everyone tells me my MosValve 500 power amp has a "Fenderish" tube sound, and it's 100% solid state.

Bob Hoffnar · From: Austin, Tx

Jack,
SS amps can mimic a tube amp one particular sound at a time. But I have yet to play a SS amp that has the responsivness of a good tube amp. An example would be blues guitar players. They could get a sound that sounded good with a POD but they would lose a level of expression within there tone. Its a tactile response issue. I am not talking about distortion ! This is a very real thing even with super clean tone.

Tube amp technology has made huge advances along with SS.

Have you guys checked out the good stuff ?

Soldano
Riveira
VHT
Matchless
Kendrick
Aguilar

There are lots of small amp companies that are working wonders with instrument amplification.

If I found a SS amp that sounded good I would buy it and use it.

Bob

Ricky Davis · From: Bertram, Texas USA

I'm gunna have to agree with Carl in that your guitar will sound awful if you heard what it really sounds like. Main reason is guitars built these days are out of light weight cheap materials to keep expenses down. I know how much it cost to build one because I'm building one. I can't believe how many corners are cut with crappy sounding materials; just to make the guitar lighter and cheaper. What ever happened to build a guitar for Sound? Well it's no wonder everyone needs a big powerful SS amp that has no character of tone whatsoever in it; to hide with volume, the already crappy sounding guitar.>go figure.
Ricky

Mike Tatro · From: Oregon, USA

Guys, check out this white paper...
http://www.decware.com/debate2.htm

Jack Stoner · From: Kansas City, MO

Mike, that article was written in 1972. The amps of today bear no resemblence to the 1972 vintage amps.

As far as sound, and we're getting away from the original question about amplifier design,
This really should be part of the original Tube/Solid State thread on the Bar Chatter forum, but tell me that Buddy Emmons or Hal Rugg or Doug Jernigan, etc., have bad sound.

[This message was edited by Jack Stoner on 28 February 2000 at 12:35 PM.]

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Well, I for one think they have a LONG way to go designing amplifiers. We're still in the stone-age in this department. The "bass-middle-treble" of the '50s became the "Peavey type" with a "shift" and "contour" control in the '60s. Big whoopie! Not much new has happened since then in one-piece amps.

Yeah, yeah, I know, you got a rack with 6 different things in it, and two extension cabinets...to do one job! Call that progress? Well, I don't! I want something to sound like any amp I care to choose, Fender, Peavey, Marshall, Vox, ect.. And while we're at it, make my Gibson Multi Harp sound like a '66 Emmons. Don't tell me it can't be done either! I can go down to the local discount store, and for $199, get a keyboard that will sound (exactly!) like anything from a Steinway Grand to a Jews' Harp!

What we need is something the size and weight of an old Twin, with 200 watts RMS, and a digital AND analog effects package, and a 24-band graphic E/Q with 20 db of boost and cut, with 2 EFFICIENT 12" speakers to handle the power. Now put it in a strong cabinet with tilt, and adjustable height legs, and make it easy to operate!

If you build it...we will buy!

Chris Lang · Posted 28 Feb 2000 3:08 pm

That is right for the most part. An amplifiers best performance is to be "TRANSPARENT", meaning that the signal going in comes out exactly the same..Where the "TONE" comes in is when we use the preamp tone controls..........Theorectically if your tone pots.are set at "0",then your steel would simply be amplified.....Not colored with tone controls or reverb.....Steel players seem to always want a different sound than what they can get straight from their steel.....Way to much emphasis is put on the lastest "effects unit", or the lastest this or that....Don't get me wrong, I happen to have the lastest processor(BOSS VF-1)....That is just what it is too, a PROCESSOR....something to alter the original or TRUE sound of the steel.....IMHO, most of that "good tone" we all seek is usually found in a good clean amp, with a touch of reverb and GOOD HAND AND FOOT COORDINATION...Once again,......IMHO

Bob Hoffnar · From: Austin, Tx

One way I look at it is that the amp is the resonator of the steel. It completes the instrument in a way. The body of a string bass is the amplifier. The body of a Martin guitar is the amp. I start out with the best acoustic sounding steel I can find then I complete it with amplification. Therefore there is no "perfect" amp and there never will be. The amp is an extention of the player and hopefully we are all a bit different.

I will add that you guys should really try out the high end tube stuff before you form judgements. But if you do get your checkbook ready. Its like the difference between those perfectly engeneered Ovation acoustic guitars and an old Martin.

Bob

Dan Tyack · From: Olympia, WA USA

Donny says:

Mike Tatro · From: Oregon, USA

Jack, I respectfully disagree. I think the article's basic premise is still valid today.

As I see it, the article does an admirable job of explaining why tubes inherently sound warmer, more transparent and are more tolerant of various input levels than *any* solid state design. It's physics and objective data, pure and simple (if you know what to measure).

Now, I'll be the first to admit that crafty engineering can mitigate the inherent nature of solid state circuits and God knows digital modeling amps sure get *close* to tube sounds. However, in the final analysis, you can't get a leopard to change it's spots.

I guess you can tell I prefer tubes ;-)

My .02, your mileage may vary.

Jack Stoner · From: Kansas City, MO

My take is the article was written in 72. The transistor devices that were the "state of the art" back then (e.g. germanium transistors) are no longer made. They have went on to different composition descrete devices and to IC Op amps. Back then RCA tubes were the best on the market. The US no longer produces tubes and all tubes are now made in Russia, but not to the standards the US produced tubes were.

If were going to take an article to compare, it needs to be one that has been researched and documented using the current technologies.

Everyone to their own about tube or transistor. However, the current thread subject is about amp design, not what technology we like or dislike. What type you prefer should be discussed on the Bar Chatter Forum.

Mike Tatro · From: Oregon, USA

Jack since you'e the moderator, I guess you can make whatever distinctions you please. For the record, I don't play PSG, so I believe my input on amp design might be off topic on bar chatter.

I think the white paper I posted has a lot to do with amp design. For the record, read my orig post... all I did was throw it out for consideration. I see nothing in any of these posts that is "off topic."

Do some soul-searching Jack... I think you're over stepping the bounds of even-handed, unbiased and fair moderation. I humbly suggest that you follow Brad Bechtel's example (of forum moderation)... less is more! (as long as folks are being civil to one another and *reasonably* on point).

[This message was edited by Mike Tatro on 29 February 2000 at 12:25 PM.]

Jack Stoner · From: Kansas City, MO

Mike, your input, as is everyone's, is welcome. However, the job of the moderator is to "loosely" keep it on the subject otherwise there wouldn't be a need for moderators. I have to fault myself too as sometimes I wonder off of the subject.

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Dan, modern synthesizers can fool a lot pianists...I don't think they would have much of a problem fooling a steelplayer!

Anyway, the point I was trying to make is that we want to change the sound of the steel with our amplifier. Most everyone (even you, I think) would agree that "Flat Response Amplification" doesn't work on steel. Now, if we agree that we want to change the sound, isn't it a pretty limited approach if we still want it to sound like the same (brand) steel guitar?

My point is (and I HOPE I'm still not talking over your head)...if a keyboard can sound like 200 different instruments...why can't we have an amp that makes a steel guitar sound like 25 "different" steel guitars?

Tubes could never do this, but solid state electronics could!

Bill Llewellyn · From: San Jose, CA

Carl,

There's so much to be said about amplifiers..... For a player, I actually see them as a part of or an extension of one's instrument, be it steel, 6-string, synthesizer, bass, or whathaveyou. So the choice of instrument usually greatly effects the "proper" choice of amplifier. Bass, keyboards, and PA systems usually call for very clean, straight sound with minimal coloration, and thus solid state amps have been popular for these for years. Guitarists, including steelers, often prefer tube amplifiers because they are less transparent (transparent meaning very flat frequency and phase response with minimal THD) and do effect the tone - call it warmth, presence, etc.

Tube amplifiers can have a different sound than transistor amplifiers for a few reasons. One is the overdrive characteristics of tubes is softer than transistors, generally, so when you push a tube amp it gives a warm growl instead of a crackle or screech. Transistor amplifiers can be designed to have a softer clipping characteristic, but I think generally they don't, partly because the manufacturer expects the user to stay within the amplifier's (usually generous) bounds. On the other hand they expect tube amps to get pushed. Another contributor to the tube sound is the power supply in the amplifier. These will sag a little as the amp's output gets louder, and that will color the sound a touch. And there's a seldom mentioned but very significant component in tube amps which effects their sound - the output transformer. Transistor amplifiers just don't have (or need) these. Transformers add a touch of non-linearity, plus band-limiting (both at very high and very low frequencies). I also think the feedback loop in tube amplifiers is of a bit lower gain, allowing the feed-forward colorations to remail slightly less corrected than in class-AB transistor amplifiers, which usually have a very high open loop gain and therefore greater degree of correction via feedback. (blah, blah.... what a nerd.) Now all of these tubish things vary from one amplifier to the next. In some tube amps they play a big part, in others they're insignificant. But the fact is that they can be very pleasing to the ear, and can really give an amplifier personality. (We haven't spoken of the speakers or their cabinets, which also play into the picture. That's a whole 'nother thread.)

Some here have said that the sound that comes out of the PSG is not so great and needs proper molding by an amp, perhaps with a good EQ. In my practice setup, I run my MSA Classic with a Super Sustain pickup through a Steel Driver II and a nice clean Lexicon MPX 100, and almost straight into my hifi (transistor) amplifier, into some nice speakers. There is some coloration, but that's almost all due to the Steel Driver and the speakers. And I like the sound! But then, I've never heard a Nashville 400 (except maybe on country CDs)....

(I've worked in or with audio electronics and recording for a few decades. I presently work at a company which makes hifi audio amplifiers. What does that make me? An opinionated nerd.)

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Bill * MSA Classic U12 7/4/wrist * www.rahul.net/thinker

Mike Bagwell · From: Greenville, SC, USA

Bill,

Have you checked out the McIntosh line of solid state power amps? They incorporate output transformers.
I used a Mac 275 tube amp for my steel rig many years ago. The 275 is a KT 88 powered unit designed for Hi Fi with a beautiful sound, although it weights about a 80lbs. I saw one for sale the other day for $5000 ouch!! Mine was a 60,s model that I bought and sold for much less.

Mike

Bill Llewellyn · From: San Jose, CA

Mike,

I'm not familiar with the McIntosh amp you mention. I do know thay have a very good reputation as an amplifier manufacturer. It does make sense to me there would be some transistor amp designs out there using transformers (though very few - transformers are as a rule not needed and always add cost), at least because of whatever particular coloration the transformer may add, if not for other reasons. Kinda like digital-to-analog converters which employ tubes. Hard to say what their effect is on the perceived sound, but if the effect is pleasing, there's value to it!

Referring back to Carl's original point, "I know of nothing as subjective as perceived sound! NOTHING!" Tons of truth to this. At our company, we have a demo room where listeners can sit and switch back and forth between our amplifier and a couple expensive competitors. Everything else in the system remains the same. Some of the comments on the perceived sound of the amplifiers can be likened to wine tasting. Lots of very interesting (and subjective sounding) adjectives which are very hard to translate into technical terms. The big audio companies even have "golden ears" folks who they have listen to all their amplifier products to ferret out the good and the bad, completely apart from bench measurements.

For players, I see the amplifier (and its speaker and cabinet) as part of the overall instrument. Tubes, transistors, transformers, effects, EQ, and so on, it's all part of one's musical expression!

Chris Lang · Posted 1 Mar 2000 9:45 am

Very good, Bill L, it is all a matter of taste, and perceived sound..........Like wine tasting, one may say "dry, yet subtle"......Oh, whatever.....If it sounds good to you, then it is good!!!...BTW,.. McIntosh amps are truly world reknown. Known for powerful clean,"TRANSPARANT" amplification of the signal.

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C Dixon · From: Duluth, GA USA

Thanks to all the respondents here. "Preciate it!

Some observations:

1. Whether one likes the sound of a SS or tube amp, in just about every case, the sound coming out of that amp is quite different from what the guitar is putting out!

2. And this is caused by the fact that most players (I think) have a sound in their head they are looking for. As such, they will buy, replace, borrow, and adjust and adjust until they get "that" sound they are seeking.

3. An amplifier that is flat from input to output reproducing exactly what comes out of the PU, is NOT satisfactory to most players.

Thus:

4. Tone controls, equalization circuits, paramid shifters, etc. are a necessity in the design of musical instrument amplifiers.

Again, thanks for responding. Lots of good points made here.

Finally, like I said in the opening, I would NOT want to be a musical instrument amplifier design engineer.

Why? Same reason I used to hate to service amplifiers for musicians!

Just what is meant by the following terms?

1. "Muddy"

2. "Glassy"

3. "Shaded"

4. "It doesn't sing!"

5. "No bottom"

6. "It just doesn't have it!

7. "No power"

8. "It doesn't cut through!"

9. "It doesn't bark"

10. "It lacks uhhhmmph!

Really??!!

Since I was never able to get into the head of the particular musician who used one or more of these terms, I had absolutey NO way of knowing what he was talking about!

So, I did what most technicians do and that is: run it through its "tests" and if and when it passed, I said, "Sounds fine to me!

Always attached a legitimate fee to the invoice and said pay me! Just like his Doctor and/or attorney would!

Be surprised how many, many, many times I could not find one single thing wrong, and they never brought it back.

So moral of story goes back to the opening:

I know of NOTHING as subjective as "perceived sound". Absolutely NOTHING.

God bless you all,

carl

Charles Brumm · From: Cupertino, California

Carl, there is one thing that I don't recall any mention of in this thread; that is the fact that a magnetic pickup has a very nonlinear response curve and requires considerable amount of equalization in the pre-amp to attempt an approximation of a flat response. The same is true of magnetic pickups in tape recorders and phonographs. Therefore if you plug your steel into a flat system, it won't sound very good.

As for the equalization that is used in guitar amplifiers for the magnetic pickup (instrument input); I don't know if there is a standard in use, but even if one exist there will be deviations for various reasons. If we include the variations in pickup response curves, I would say that your chance of hearing exactly what your guitar sounds like would be that of winning the Supper Lotto. And so, the above is one reason for the subtle differences in tone or overall sound when changing pickups or amplifiers (pre-amp equalization).

Ideally, an engineer would design a pre-amp for a specific pickup. But for most, it's a game of mix and match.

Keep on twidding those tone controls--Charles.

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Carl,

Just a closing thought...I know some steelplayers that can identify a brand of steel by listening to it. But I know of no one with such a talent for amps. Maybe that's because amps are a lot more alike (sound wise) than we're led to believe!

Ricky Davis · From: Bertram, Texas USA

If you tell me what guitar someone is playing; I can tell you exactly what amp he is playing through>

Ricky

Bobby Lee · From: Cloverdale, California, USA

I worked for Mesa/Boogie for 5 years (1980-85), and to this day I can spot a Boogie on the radio when I hear it. It's a very distinctive sound.

The amp designers at Mesa basically ignored the math when I was there. Amp design was by instinct and ear. New designs were tested by having an excellent guitarist (on staff) play a variety of instruments and styles. The ear was the test instrument against which everything was judged.

The underlying theme at Mesa was that the amplifier is piece of a musical instrument. It's not just something to make your guitar louder - it's a part of your guitar. We considered ourselves to be instrument builders.

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Sierra Session S-12 (E9), Speedy West D-10 (E9, D6),
Sierra S-8 Laptop (D13), Fender Stringmaster D-8 (D13, A6)

Bill Llewellyn · From: San Jose, CA

If you tell me which amplifier a player is using, I can tell you exactly which amplifier the player is using.

Charles has a good point. Magnetic pickups are by nature inductors, and when coupled with the amplifier's input resistance, input decoupling cap, and stray capacitances of the wiring going into the amplifier, you've got yourself a resonant low-pass filter. And since input characteristics vary from amp to amp, you'll get a different sound from amp to amp. Stick a variable-resistance volume pedal in between, and it really schmears things up. If you put a buffering box like a Steel Driver between PSG and amplifier, that variation concern should pretty much go away, i.e., the inductive pickup is isolated from the amp and sees an unvarying load, and what comes out of the buffer box shouldn't vary anymore as a function of the amplifier input. Your steel still looks into the imperfect input of the buffer box, though, so flat response is still elusive (it just won't change any more if you stick with the same buffer box).

Like b0b said, treat you amplifier (cabinet and speaker included) as part of the overall instrument. Buffer, pedal, and effects, too. And like Charles said, turn the knobs to your heart's content. It's all part of achieving your own tonality, musical expression, and creativity.

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Bill * MSA Classic U12 7/4/wrist * www.rahul.net/thinker

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