# DIYstompboxes.com

## DIY Stompboxes => Building your own stompbox => Topic started by: lars-musik on July 01, 2020, 05:52:14 AM

Title: Help to calculate/identify this bass control
Post by: lars-musik on July 01, 2020, 05:52:14 AM
Dear Forum,

I found that I can built a Benson Preamp on my old PCB I created for a Wampler Plexidrive in a 1590a. However, the bass control calls for a 2M pot and I can't find any in a small 9mm version that would accomodate the mini enclosure.
Now I'd like to change the pot (orange) to a more reasonable value but can't identify what is what in that tone-shaping fraction of the cicruit in order to calaculate the surrounding r and c values to, say a 100K or 500K pot and still have a comparable range.

(https://i.postimg.cc/vTTqKh1M/Bass-Benson-q.jpg)

Lars
(https://i.postimg.cc/JHw5Dbcd/Bass-Benson-q.jpg) (https://postimg.cc/JHw5Dbcd)
Title: Re: Help to calculate/identify this bass control
Post by: merlinb on July 01, 2020, 06:05:34 AM
VR5 is just a variable resistor in parallel with C3. You could just use 1Meg for VR5 and leave the rest alone, it will get you close enough to the stock circuit (slightly less cut available).

But if you want to be anal about it, use a 1Meg pot for VR5, then halve all the other resistances R4/R5/VR1, and double all the capacitances C12/C3/C4.
Title: Re: Help to calculate/identify this bass control
Post by: lars-musik on July 01, 2020, 06:12:23 AM
VR5 is just a variable resistor in parallel with C3. You could just use 1Meg for VR5 and leave the rest alone, it will get you close enough to the stock circuit (slightly less cut available).

But if you want to be anal about it, use a 1Meg pot for VR5, then halve all the other resistances R4/R5/VR1, and double all the capacitances C12/C3/C4.
No absolutely not. Close enough is good enough.

Thanks!