(12-10-2014, 03:40 PM)bax Wrote: As you know, in a bass amp, a larger first node capacitance will provide more headroom and the amp can better cope with the lower notes which draw more from the power supply. With a guitar amp, if you are looking for an early onset of distortion, having less capacitance helps. Designing an amp for both bass and guitar often involves some compromises.
All useful info. But here, I think it depends...
As for the amount of filtering in the power supply (the combination of rectifier, C, L, and R all work together)--less filtering doesn't really make distortion's onset happen sooner. In fact, one can argue that more filtering lowers the effective DC voltage, lower voltage means sooner to distort, but with the voltages most amps are using, say 500v, +/- 5% rule is +/- 25v, which puts that in the generally negligible range. If anything, with all else being the same, more power supply filtering (yielding lower DC voltage) would mean earlier onset of clipping, rather than less filtering.
Volume (amp power) is also at play in conjunction with frequency here. The power filter caps are smoothing over the DC ripple and acting as a small current/voltage/power reservoir. With a given power supply and power amp arrangement that might not have any problem accurately delivering a tight, fast, accurate note at a specific volume (power) with a certain guitar at a fundamental *frequency* of 440hz, using a bass to play a note at the same fundamental frequency but a more dense harmonic content, it might start to struggle more than the other scenario. With either instrument playing a note at 220hz it may struggle more, at 110hz even more, and so on-- particularly in conjunction with a specific speaker configuration's response characteristics, as it likely drops off and needs increasingly more power to produce increasing lower frequencies at the same measurable (let alone apparent) volume/power.
Likewise, at 440hz but 10db louder than one started at, they may struggle more as well--same frequency. All depends on usual suspects for amp components, including the filtering, transformers, etc.
So filtering can't be totally isolated, even with the power supply--at what frequency, and at what volume/power output? Unless you design for the full audio spectrum and full possible output that can be delivered, volume and frequency affect response even more than they already do naturally, and sometimes to a very noticeable degree in a specific amp.
One thing is for sure--if you want more accurate reproduction of notes with a given design, with a "tight" transient and low frequency response, all else being equal, you want more filtering rather than less--"amp sounds better with a stiffer power supply," at least up to that design point where more filtering makes no appreciable difference.
Heavy metal guitarists are often looking for a "tighter" amp as much as a bassist is from their amp, so it's not always bass vs. guitar or clean vs. distorted in broad terms. As a guitarist running my Ampegs clean, the tight but massively powerful bass is one of the major reasons I play these amps instead of others. I don't play metal, but primarily play blues based music in some way...though many "blues" guitarists are first to seek an old tweed era Fender Bassman with less than the cleanest power filtering just as well.
Guitarists are known for *utilizing* amps with a sound partly affected by an amps sagging, swampy filtering when cranked (etc.) as a kind of 'effect' and growing fond of the quirks, the tone, etc. While people might try and duplicate such an amp including what happens with such an amp cranked up with the power supply/filtering struggling to keep up intentionally, NOW, for it's audio characteristics, that was rarely (if ever?) an original/early instrument amp design goal--the audio "effect" of things like how it clipped, power filtering, etc.
While designing a "quirky" amp (including just having a particular preamp overdrive tone) that is ideal for multiple things/sounds/instruments can be hard to impossible depending on how wide a scope the design targets, designing a amp for high quality audio instrument amplification first and foremost with some degree of flexibility (EQ, etc.)--which is what I think some Ampeg amps approached in some of their designs--probably works well. To my knowledge, the Ampeg V series guitar amps came out, and when they made the "bass version" in the V4b, and we see it's basically the same core amp with some slight tweaks in gain/EQ switches and reverb between the two, which suggest the original CORE design was for audio instruments, not so much "designed for guitar."
So while an instrument amp primarily designed for audio can't do exactly what all the one-trick pony (quirky) amps can do necessarily, I think it spans more flexibility and a broader audience when you design for accurate audio reproduction and can tweak from there, rather than one specific tone. If it is not even possible for an amp to produce audio cleanly and accurately, it's an amplifier AND an effect. It may sound cool, but you can't turn off that effect...which limits it significantly.
Personally, if the world ran out of tubes, and I had to play a solid state amp from what is available today, I'd probably play any basic, solidly designed bass amp with good EQ range, over almost every comparable solid state guitar amp "designed for guitar," and add reverb/echo and overdrive pedals like I always do...