Volume controls on gain stages

[Mick Bailey]

I've never really come to a conclusion on which is the best way to control the gain of an amplifier that has three gain stages followed by a cathode follower. I've tried the following approaches with an old DIY amp I built many years ago and revisited it over the holidays;

1. Single gain control after the first stage. Everything else hard-wired. Simple and works fine with good graduation over the range from clean to overdriven.
2. Twin-pot (dual) volume control, one after the first stage, one after the second. Slight reduction in background noise, but the point at which the amp breaks up is later on in rotation - most of the overdrive is in the last third of rotation.
3. As per 2, but individual control for each stage. Seems to give a broader range of sounds, especially with mild overdriven, crunchy sounds with my Tele. There's a different feel with gain 1 at max, and using gain 2 as the control, compared to gain 2 at max and using gain 1 as the control. Plus different sounds with both controls set at various points throughout their range (compared with configurations 1& 2). The downside if that it's more fiddly to use - constantly playing around with two controls.

One issue is by the time the amp is rewired it's difficult to recall exactly how things sound - no direct A-B comparison.

The preamp is the same as the High-Octane circuit. Different power amp and higher voltages;

[catalin gramada]

I vote for classical: "Gain" after first stage and "Master" before power stage . It works all the time and cut floor noise down for "bedroom level". Happy New Year 2023 !

[Chuck H]

I've experimented a bit with the dual gang gain control. My ideal is to have a hot rodded amp capable of higher gain tones that still stays clean on the volume adjustment to the same approximate setting as a typical vintage amp. On top of that you want that lower adjustment to be idealized for clean tones and the higher adjustment idealized for overdrive. These two criteria usually need different early stage EQ characteristics. Typically more scooped for cleans and more mids/less bass for overdrive. There are only a couple of ways to manipulate this with the volume control circuit.

One way is the bright cap. This one is obvious. It's easy to get too bright quickly and it seems there are always compromises. The other way is to add a load to the wiper on the volume control so that circuit impedance increases with adjustment. Then use a coupling cap value small enough to limit bass when the volume control is at higher settings (with a lower circuit impedance) but big enough that at lower settings (and a higher circuit impedance) the knee frequency moves lower and allows more bass for a fuller clean tone. This also suffers compromises. But these are fun things to experiment with and some day I hope to design an amp that behaves like a classic model up to about five on the volume control but morphs into a hot rod at all settings above that.

For just noodling around at home I like the two volume controls. I enjoy the infinite permutations, fiddling and the extra flexibility in tonal options. But there's more probability for discordant setting with this arrangement. So for a "working" amp, being used for gigs and such, I like the one volume control for efficiency and to KEEP me from fiddling.

[Mick Bailey]

I've now settled my preference is to have two volume controls, though to commit this to my amp I'd need to reconfigure the FMV tone stack to a 2 knob design. I had a Judge Roy Bean stack in for a few years and this gave by far the best range of sounds, but trying to get back to a particular sound was frustrating due to the interaction and unpredictable relationship between the controls. For a good while I've intended to build an amp with a replaceable panel to swap in different tone stacks and get back to a bit more experimentation.

[Zozobra]

There is also the Jose/Friedman/diode clipper preference of having the gain control after the 2nd stage too.