Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: isaac_teller on December 20, 2020, 03:29:13 pm

Title: post phase inverter master volume
Post by: isaac_teller on December 20, 2020, 03:29:13 pm

Hello. Is it possible to use a single-gang 1 Meg pot as a crossline master volume on a fixed-biased amp or does it screw up the bias? Thank you.

Title: Re: post phase inverter master volume
Post by: sluckey on December 20, 2020, 03:32:49 pm

Quote from: isaac_teller on December 20, 2020, 03:29:13 pm

Hello. Is it possible to use a single-gang 1 Meg pot as a crossline master volume on a fixed-biased amp or does it screw up the bias? Thank you.

You can safely do that. I bet you wont like it.

Title: Re: post phase inverter master volume
Post by: d95err on December 21, 2020, 12:13:19 pm

I agree with Slucke; it’s simply a bad circuit (fixed or cathode bias).

In my experience, it has a really bad taper, like an on/off switch, even with a log pot. By the time you start to notice any significant volume reduction, it’s also cutting so much bass and introducing other unwanted artefacts that the tone is unusable.

Find a demo of a modern AC30 where they’re running with the crossline master way down and you’ll see what I mean.

Other people may have better experiences though.