Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Foreplay III => Topic started by: Ritchie on September 06, 2010, 12:02:29 PM

Title: Replacing mono pots with stereo 100k in Foreplay III
Post by: Ritchie on September 06, 2010, 12:02:29 PM

I would like to remove the mono stepped attenuators and replace them with a 100k stereo stepped att.
I will be wiring the volume control in the normal position not the shunt configuration.
Is the 100K value pot ok in this circuit?

Thanks.

Title: Re: Replacing mono pots with stereo 100k in Foreplay III
Post by: Paul Joppa on September 06, 2010, 12:16:58 PM

The 100K value is just fine. We use that value in the Quickie, SEX amp, Stereomour, and Crack.

Be aware that the maximum gain will increase by 10dB.

Title: Re: Replacing mono pots with stereo 100k in Foreplay III
Post by: Ritchie on September 06, 2010, 01:18:23 PM

Paul,

I am assuming the extra 10 db is without the 33k resistors and if I left them in, it would be approx. 5db
increase at max. gain? Is this correct?

thanks.

Title: Re: Replacing mono pots with stereo 100k in Foreplay III
Post by: Paul Joppa on September 07, 2010, 02:02:09 PM

Yes, that's correct. But if you are going to use a series resistor, even with a "normal" pot topology, I'd stay to a lower resistance, 50K or less. Otherwise you can get a high resistance before the tube at intermediate volume settings, and the Miller capacitance of the tube's grid will affect the treble.

Title: Re: Replacing mono pots with stereo 100k in Foreplay III
Post by: Ritchie on September 08, 2010, 01:00:53 PM

Thanks Paul.

Title: Re: Replacing mono pots with stereo 100k in Foreplay III
Post by: Paul Birkeland on September 10, 2010, 06:05:52 AM

Hello Ritchie,

I might also recommend installing some series resistance between the input selector and the input of the 100k pot.  In my personal preamps, I will often have a selectable resistance switched in here to get the best range out of the attenuator.

Title: Re: Replacing mono pots with stereo 100k in Foreplay III
Post by: Ritchie on September 10, 2010, 12:17:48 PM

Yes, I was thinking of starting with the 33K series resistors that are already in the circuit.
I believe this should get me deeper into the 100K stepped attenuator I'm using.

Thanks,
Ritchie