Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Norwatt on January 19, 2011, 12:52:06 pm

Title: Touchy volume pot in vibroverb build
Post by: Norwatt on January 19, 2011, 12:52:06 pm

I recently finished building a Vibroverb 64 clone (AA763) and it works fine (and sounds good too, I must say :smiley:). The only thing that really puzzles me is the volume control on the vibrato channel, which gets really loud really fast. The Normal channel has a more even response. I compared it to a non-MV silverface Super reverb, and both channels has the same response curve on that one.

Both pots in the vibroverb are the same (Alpha 1MA).

Does anyone know what might be the cause ( and the cure) ?

All help would be much appreciated!

Title: Re: Touchy volume pot in vibroverb build
Post by: Geezer on January 19, 2011, 01:44:01 pm

Have you tried swapping out the pot?

Maybe a linear taper disc got mixed in with the audio tapers(?) & your "audio" pot is actually a linear.

Or, the pot may just be faulty.

G

Title: Re: Touchy volume pot in vibroverb build
Post by: Norwatt on January 20, 2011, 03:32:18 am

Thanks for the input on this one Geezer , I will try swapping it for another one.

Kjell

Title: Re: Touchy volume pot in vibroverb build
Post by: Norwatt on January 20, 2011, 04:32:35 am

I swapped the pot , but it was still the same.... But then, after comparing my amp to the schem/layout for the nth time I noticed a missing 220K restistor that connects  the 10pF / 4,7M / pin 7 of V4 to ground. Problem solved.......

Title: Re: Touchy volume pot in vibroverb build
Post by: Geezer on January 20, 2011, 07:12:11 am

Quote from: Norwatt on January 20, 2011, 04:32:35 am

I swapped the pot , but it was still the same.... But then, after comparing my amp to the schem/layout for the nth time I noticed a missing 220K restistor that connects  the 10pF / 4,7M / pin 7 of V4 to ground. Problem solved.......

Ha! Glad you got it figured out!

G