Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: steveo7868 on July 03, 2021, 07:58:30 am

Title: AC30 top boost extra knob function idea 10k resistor as pot
Post by: steveo7868 on July 03, 2021, 07:58:30 am
I have a weird idea to add a knob to the typical vox ac30 top boost tone stack, because I have a chassis
that has a faceplate for a mid knob, and I dont really want to change the tonestack that much
to make it a true TMB, what effect would there be if that extra 10k resistor from the  wiper of the bass pot
was made into a 10k pot? I did try this on the bench and it seemed to do something... possibly affecting the mids..
to be honest I would rather build it stock without this knob but, I just wondered about this idea..
Title: Re: AC30 top boost extra knob function idea 10k resistor as pot
Post by: jordan86 on July 03, 2021, 09:08:17 am
Your answer, and a world of experimenting possibilities, lies here:

https://www.guitarscience.net/tsc/vox.htm#

You’re asking about changing the value of R2 in this scheme.
Title: Re: AC30 top boost extra knob function idea 10k resistor as pot
Post by: pdf64 on July 03, 2021, 09:25:12 am
I’d use it for a switch to alter the coupling cap value from the input stage’s anode. That will bring in more mids, so it’s appropriate!
Title: Re: AC30 top boost extra knob function idea 10k resistor as pot
Post by: steveo7868 on July 03, 2021, 09:42:35 am
Awesome answer and sure enough it is a mid pot and all the way up its stock, or if you want more mids it looks like a 25k pot would be the ticket