Vibroclone hiss (channel 2)

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arnod
Junior tube assistant
Posts: 2
(4/4/04 9:00 am)
 Vibroclone hiss (channel 2)
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 hi everyone,

I've used a Bandmaster Reverb for my Vibroclone project.
First, I blackfaced the circuitry. The amp sounded wonderful and way better. Really quiet.
Next I removed the mid pot in channel 2, installed a new reverb transformer and a twin OT. This is somewhere during this process that channel 2 became really hissy.
I tried every usual recommendations (swap tubes, clean and change tube sockets) but nothing improved.
I then installed an Ab763 Hoffman kit. I tought my problem would disappear with new pots and the new board but the constant hiss is still there.
Channel 1 is really quiet compared to channel 2. Without reverb tank plugged, turning up reverb pot increases hiss.
I also removed a few tubes to locate the problem on the board and with tubes only in V4 and V6 I have this constant hiss. Removing V4 tubes in any other configuration stops the problem.
would someone have an idea where to look for ? I feel like I've tried everything.

thank you very much
Arnaud
 
EL34  
I got your parts right here.
Posts: 2268
(4/6/04 4:06 pm)

  Re: Vibroclone hiss (channel 2)
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 Channel two has way more gain than channel 1 and so it is noisier.

You had to change something else somewhere. Hard to say what, only you can find it.

Different pre amp tubes, installed silver mica caps, etc.

Put the mid pot back to stock and see what happens.

Only do one mod at a time, turn on the amp and then do the next mod.
 
 
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