Master volume on a SE amp?

[PRNDL]

I'm designing a single-ended amp with reverb and tremolo - it's based on the princeton reverb with a cathode follower before the tone stack.

At present, there is a master volume before the output tube. I'm wondering if this is a good idea.

The basic idea is to allow preamp distortion at any volume, but it's a low-watt amp, so that might not be necessary.

There's also the stigma against master volumes, which were added to Fender amps in the CBS era.

Plus, the master volume adds a coupling cap to a fairly simple circuit.
It's not the same as a push-pull amp, where it seems to make sense.

Any opinions are greatly appreciated!

[Chuck H]

Sure it's a good idea. If it'll give you what you want. The idea behind a small amp is that it won't be too loud. In that respect being able to turn it down seems like a good idea and a master volume control is the easiest way to do it.

OTH there are other ways to turn down an amp. Unless your building the preamp with a distortion circuit I don't think you'll get much satisfaction from a tweed Princeton style preamp with a master volume. Power scaling is still enjoying some popularity and attenuators are another option. A built in attenuator for a small amp could be done very easily. Power scaling is a little more complex and probably inappropriate for a simple PTP amp. Gary Moore (one of our members) uses a screen voltage reduction circuit that is said to work very well and could be incorporated into a PTP amp. I don't know the details of that circuit though.

Chuck

[mooreamps]

The power brake that I use does work in conjunction with a master volume. The power brake regulates the plate current, and thus the bias, of the power tube(s). When the power brake is dialed down, it's both a drop in plate current and bias. As such, then the master volume can be adjusted to control the amount of power tube saturation by the player.

I've not installed my power brake into a fixed bias P/P amplifier as yet, but I am seeing no reason why it would not work. I've read other threads where others report some non-linear tracking issues using other power scaling circuits, so I am going to look at addressing this problem in the near future. Well, using my circuit, not the the plate rail circuit that seems to be more popular with the other builders.




-g