Amplification

[Dave Stagner <dstagner@icarus.leepfrog.com>]

On Tue, 24 Sep 1996, Tom Attix* wrote:

> > also, are there any amp designers/builders among us?
> > I'd spoken with matthias about this before.
> 
> I've been poking the idea around. A nice all tube stereo amp (for my 
> Stick). I suspect I'm going end up building something more like a PA 
>than 
> a guitar amp. Do you know of any good sources for schematics?
> 
> -Tom Attix

I'd say your choice of amps and speakers is highly dependent on the
manner in which you intend to present the music.  Is this for a home
studio, or live playing?  Since you're playing Stick, you're going to
need to hit some REALLY low bass notes.  There are two ways to
approach this.  One is to use a heavy-duty biamped system with big
subwoofers to capture those low fundamentals (a Stick tuned down to
low A produces a 27.5hz fundamental!) where typical speakers (especially
guitar speakers) crap out.  Another is to just roll off that
fundamental octave and concentrate on a tight sound (this is why the
old Ampeg SVT bass amps with the 8 10" speakers sounded so great.
They rolled the fundamental right off, and just reproduced the first
order harmonic of the low notes.  The amp and speakers weren't
overstressed and sounded much tighter).  

Here's where you'll have problems with tubes.  The power requirements
for those low notes are enormous.  The odds are you'll see power
supply sag and its attendant distortion, which may or may not be a
Good Thing, depending on your POV.  Personally, I want as little
coloration as possible after my effects chain and looping devices, and
I think most would agree with me here.  So unless you're willing to
buy or build tube amps big enough to handle the bottom end of the
Stick without distortion (well over 100 watts), you'll have to limit
your volume, deal with distortion, etc.  

Solid state amps won't have the power problem.  Yeah, they don't sound
as transparent and nice as tubes, but you can get big 400w monsters
for reasonable money that will drive a 15" vented subwoofer to
deafening volumes without excessively coloring the sound.  

Getting to the point, I'd say the best approach by far for a Stick
player would be bi-amping, especially for playing live.  The Stick has
a ridiculously wide range compared to most instruments.  You need
something that can handle the deep low notes without compromising the
low-midrange fundamentals that make the higher registers punchy.  Use
an active crossover to split the signal before amplification.  Use a
high-powered solid-state amp and the best subwoofers you can afford to
get the bass.  Then use good studio monitors to handle everything over
120hz or so (you'll definitely want to play with the crossover here
for best balance).  

Tubes might help the higher stuff, but there are other problems.
Again, I'm presuming you're looking for a clean, transparent sound,
not guitar-like distortion.  This means an audiophile tube amp, not a
guitarist tube amp.  If you want a roadworthy system for live
performance, you'll have a problem.  Audiophile isn't meant to be
lugged around all over, and isn't mechanically robust like PA
equipment.  Older tube PA stuff distorts as bad (good!) as guitar
amps.  And you'll still want high power, even though tubes sound 
best at lower power ratings.  High-powered guitar-oriented pentode
amps might give you clean power at moderate volume.  But MOSFET power
amps have much of the smoothness of clean tubes without the hassle.  

Do NOT believe vendor specifications when looking for an amplifier!
Let your ears be the judge.  Amp specs are made in a pseudo-scientific
vacuum by treating the speaker load as a simple 8 ohm RC circuit with
negligible capacitance (this is electronics geek stuff.  Skip it if
you don't understand).  Speakers are NOT simple RC circuits, they are
complex, reactive devices that generate electrical distortion as well
as sonic distortion, and interact in unpredictable (and probably
unmeasurable) ways with the amplifier negative feedback loop.  The
upshot of this is that the speaker/amplifier combination is a single
system, not two separate systems, and it should be judged as such.

(as an aside in this already excessively long post, I think the
problems with the electrical behavior of speakers in the negative
feedback loop of the amplifier are the reason tubes sound "better"
than transistors, despites theoretically inferior specs.  This has to
do with the relatively low gain and high impedance of tube output
stages compared to transistors reduces the effects of
speaker-generated electrical distortion.  The Tubeworks MosValve power
amps emulate tube gain and impedance structures with MOSFETs, and
sound VERY good, at least for simulating the distortion of tube guitar
amp power stages.  But I digress severely)

Still with me?  Wow!  Again, look into bi-amping, using a big
solid-state amp to drive subwoofers to get the low end of your Stick,
and use good monitors to get the highs.  Whether tubes will improve
the sound of the monitors is a subjective call... let your ears guide
you.  Think about performance conditions... playing volume, touring
needs, etc, and balance your needs for clarity/low distortion,
mechanical robustness, and volume.  Even a simplistic bi-amped
solution should buy you better sound than tubes will.  But tubes might
sweeten it even more.

By "beauty," I mean that which seems complete.
Obversely, that the incomplete, or the mutilated, is the ugly. 
Venus De Milo.
To a child she is ugly.       /* dstagner@icarus.leepfrog.com      */ 
   -Charles Fort              /* http://www.leepfrog.com/~dstagner */