Passive volume control question.

[bernieclub]

I'm preparing to do some experiments with passive volume on my paramours.  If I can place the amps so that the inputs are very close to each other, and mount a pot within say six inches of the rca jacks, can I eliminate the input resistors all together and let the pot become the input resistor as if it's mounted on the chassis?
Thanks!
Bernie

 

[bernieclub]

maybe a better way to ask this...what is a reasonable maximum distance from the pot or input resistor to the tube grid?  Any one have an idea?

Bernie

 

[Paul Birkeland]

Hello Bernie,

On the Paramours, there should be a 249K resistor from grid to ground.  If you use a passive volume control with very short cables to the amp, the highest value I could see being sensible would be a 50K control. 

If you remove the 249K resistors and plug in your volume pot, you'll now have a situation where if the RCA cable slips out of the amp, the grid of the 12AT7 is now floating, and you risk tube damage.  I wouldn't do this, and having the 249K resistor in there isn't going to load your passive control unreasonably. 

There's also the grid stopper, which is a little 220 Ohm resistor between the RCA jack center pin and the grid of the 12AT7, and that also has to stay.

The Stereomour has the passive volume/balance controls acting as a grid leak resistor, but they will stay in the circuit regardless of whether anything is plugged in.

-PB

 

[bernieclub]

Thanks Paul!    Exactly the info. I needed.
Bernie