Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Topic started by: coca on January 09, 2012, 10:45:18 AM

Title: FOREPLAY 2 VOLUME CONTROL
Post by: coca on January 09, 2012, 10:45:18 AM

 I have lost the right channel in my audio system, and I have traced it to the right side sweet whispers switch attenuator. I plan to go back to a potentiometer, with  the original value of 100K. My question is,If I connect the pot up the way the sweet whispers is in the foreplay 3, will I have to change the value of the P.E.C. to something of smaller value? The preamp I am refering to is the FOREPLAY2

Thanks in advance.

Bernie.

Title: Re: FOREPLAY 2 VOLUME CONTROL
Post by: Paul Joppa on January 09, 2012, 11:17:25 AM

The Foreplay III us a shunt-mode control, and that connection does not work without a large-value series resistor (like twice the potentiometer resistance). In addition, if the potentiometer resistance is large there is some risk of loss of treble due to its interaction with the 12AU7 Miller capacitance. While you are theoretically good to go with up to 50K, I am not confident at values greater than 20K - sometimes we perceive things that are "too subtle to hear" (theoretically).

Title: Re: FOREPLAY 2 VOLUME CONTROL
Post by: coca on January 09, 2012, 03:30:03 PM

Thanks paul, I can get a 10K pot, although it will not be audio taper. I will have to gamble that I can get away with a linear taper pot.

Bernie.