I replaced the pots in my AC30

[paologregorio]

I have a `73 Vox AC 30 that I had rewired to 1960s Top Boost specs awhile back, complete with tube rectifier, et cetera, and had a new baltic birch ply cabinet made for. The amp sounded incredible after all the work was done, and has continued to be my main guitar amp. It had these cheap 70s plastic shaft pots that I did not replace at the time, but did have replaced after one started to go bad on me at rehearsal a few weeks back. I was amazed to find that my amp is LOUDER with the quality, solid, metal shaft pots that my local amp tech replaced the cheap pots with. Has anyone else experienced anything like this? It's nuts, I barely turn my amp past three now. I use distortion, but really have to back the level off what it was at before to keep from blowing everyone out. It's amazing that those cheap pots were sucking so much volume out of my amp.

[doctorwho]

I no electrical expert, but that almost sounds like the difference between audio (exponential/logarithmic) taper and liner taper potentiometers ...

[johnallg]

I no electrical expert, but that almost sounds like the difference between audio (exponential/logarithmic) taper and liner taper potentiometers ...

Agreed. Did he also use the same value pots to replace the old ones?

[jingle_jangle]

Linear (non-audio) taper pots in an audio circuit will have alll their effect on the circuit in about the first 5% of their rotation.

So, if you are experiencing all your action in one small area of the rotation, go for audio tapers of the same value.

[paologregorio]

I'm pretty sure the amp tech put the correct type of posts in. The range does not seem different from the pots that were in the amp before with respect to action, it just seems LOUDER. He's quite familiar with the AC 30 circuit, among others. Additionally, when I brought the amp to him and explained the problem he specifically told me to leave the amp with him so he could read the values off all of the caps so as to be sure and order pots with the same values. He knew the brand of pots that were in the amp. They were very cheap, having plastic shafts, and they were not fully enclosed. They had a cover that went over the interior components that was held on by four tabs rather than being a full enclosed flat cylinder with a metal shaft. I think they were just old and cheap, maybe they had more resisance in them? He's quite the professional; he converts PC board amps to hand wired amps, as well as constructs his own hw amps and builds hw amps to order for customers. He does great work. I have no complaints about the results, just pleasant surprise. The amp has always sounded really good to my ears, it just sounds even better now. It is a fantastic amplifier. I'll bring it to the confluence this year so attendees can play through it. I was thinking of bringing that amp, my CC2x, and a Fender Black Face Twin reissue, that I will probably have hand wired before the confluence by this same amp tech. All of these amps seemed to be asked about recurringly by forum members, so it might be nice for inquiring folks to have a chance to play through these amps, at least at the "jam session", and in the confluence area itself, so long as no one cranks the volume and blows everyone else's ears out.

[wolfgang]

There are different audio taper characteristics. The old U.S. made characteristic is -12 dB on half way (perfect for the tonestack circuit), european characteristic is -20 or even -26 dB on half way.

Wolfgang

[paologregorio]

There are different audio taper characteristics. The old U.S. made characteristic is -12 dB on half way (perfect for the tonestack circuit), european characteristic is -20 or even -26 dB on half way.

Wolfgang

Interesting!

Thanks for all of the input everyone. Fascinating stuff.

The pot that was giving me trouble, and which lead me to replace all the pots was the volume pot on the brilliant channel. It might have been going bad for awhile, and I only noticed the problem when the shaft on the pot developed vertical "slop", as well as a hum, which was when I took a goo look at all of the pots and decided to replace all of the pots on the amp.

[pieholden]

speaking of replacing volume pots on AC 30's, what are the values ( ohms/taper, etc.) of the volume pots in original early 60's AC 30's? and what is a reliable resource to find said parts?...along those same lines, does anybody know where to find the trem/vib selector as well ( not the speed switch), thanks, not having much luck finding a VOX parts website.

[paologregorio]

speaking of replacing volume pots on AC 30's, what are the values ( ohms/taper, etc.) of the volume pots in original early 60's AC 30's? and what is a reliable resource to find said parts?...along those same lines, does anybody know where to find the trem/vib selector as well ( not the speed switch), thanks, not having much luck finding a VOX parts website.

This is exactly what my amp tech did. Unfortunately, I do not have an email contact for him. He replaced all of the tone/volume pots using original value pots, as well as the vib/trem selector switch.

[pieholden]

thanks,.... yeah, my amp will be sounding amazing, and then one of those volume pots will get jiggled into a dirty spot, or dead spot, even, and there goes the whole take. I've tried to clean them, but I seem to be causing more of a mess than anything else ( we've all heard the warnings about cleaning amp. pots ) The cleaner does make the pots more loose feeling, but they still have glitches etc. that are permanent, I assume. I've looked up many ( typically very hard to read ) AC30 schematics online, and as close as I can make them out, they appear to be 500K pots, and I assume that an "audio taper" would be appropriate, but I'm still guessing...as for the trem/vib switch , don't know anything ( other than mine is shot ). I would think this stuff would be a little more "common knowledge" out there in the geeky tube world ( a party of which I have to admit to being a member )....somebody must have the answer. I'm not marching out to Radio Shack for answers any time soon, that's for sure.