Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: fossilshark on March 31, 2025, 07:14:54 pm

Title: AC30C2 volume/gain pots do nothing.
Post by: fossilshark on March 31, 2025, 07:14:54 pm

Hi all! I got this Vox AC30C2 on the bench with a strange issue. On both the normal and top boost channel the master volume and individual channel volumes do not turn down the volume. The amp is at max (or at least very high) volume at all times. The top boost tone controls, tremolo, and tone cut knobs seem to function perfectly. The reverb does not seem to function at all but I am going to deal with that later.

I am thinking this is a bad ground somewhere, any advice on where to start?

Also this amp gives serious chinesium vibes, anything else I should double check just in case?

Title: Re: AC30C2 volume/gain pots do nothing.
Post by: fossilshark on March 31, 2025, 07:40:25 pm

The pots in question seem to be grounded per schematic, could they just be bad pots?

I forgot to mention, this unit is suspected to have water damage, although I cant find any obvious signs of corrosion on the PCB.

Title: Re: AC30C2 volume/gain pots do nothing.
Post by: Merlin on April 01, 2025, 03:18:30 am

Sounds like bad pots, like the ground terminals have corroded or broken away from the carbon track

Title: Re: AC30C2 volume/gain pots do nothing.
Post by: Latole on April 01, 2025, 04:48:13 am

Bad solders at the pot or in the circuit close to the pot.
Defective pot

Title: Re: AC30C2 volume/gain pots do nothing.
Post by: fossilshark on April 01, 2025, 06:22:08 am

Awesome thank you guys, I will order and install new pots and see where we are at.

Title: Re: AC30C2 volume/gain pots do nothing.
Post by: fossilshark on April 11, 2025, 10:43:08 pm

Hi guys, I could use some help. I replaced all the pots and while some of the issues are fixed, the master volume pot still does nothing to affect the volume of the amplifier.

The normal/top boost gain pots are working BUT no matter what channel I have it plugged into both gain pots control the volume.

Any idea what I should look into next?

Title: Re: AC30C2 volume/gain pots do nothing.
Post by: tubeswell on April 13, 2025, 04:06:53 am

Quote from: fossilshark on April 11, 2025, 10:43:08 pm

Hi guys, I could use some help. I replaced all the pots and while some of the issues are fixed, the master volume pot still does nothing to affect the volume of the amplifier.

The normal/top boost gain pots are working BUT no matter what channel I have it plugged into both gain pots control the volume.

Any idea what I should look into next?

Cracked PCB traces
Cracked jumper wires