# Boogie Monster trimpot adjusting?



## Kroars (Mar 15, 2020)

I’m about to start populating the Boogie Monster and just realized I’m not sure what to do with the four 100k trimpots.  If there was just one, I figured I could simply adjust by ear -with 4 I’m a little skeptical.

I don’t suppose someone could give me a quick rundown on how to adjust them? Do I use a multimeter? If yes, what am i shooting for?

Thanks for your time.


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## Nostradoomus (Mar 15, 2020)

It’s for adjusting the JFETs, check this video out


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## temol (Mar 15, 2020)

You can start with biasing each transistor @ 4.5V (measure voltage on a drain of the transistor). Then experiment  . Make slight adjustments - for example  go up and down 1V wiht 0.2V steps and find the best setting for you.


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## Edenspace (Jul 26, 2022)

temol said:


> You can start with biasing each transistor @ 4.5V (measure voltage on a drain of the transistor). Then experiment  . Make slight adjustments - for example  go up and down 1V wiht 0.2V steps and find the best setting for you.


Reviving this in 2022. I’m biasing the transistor that controls the 2 bottom transistors but they are wildly different values? Do I just need to match these jfets?


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## temol (Jul 27, 2022)

Edenspace said:


> Reviving this in 2022. I’m biasing the transistor that controls the 2 bottom transistors but they are wildly different values? Do I just need to match these jfets?



You have to be more specific. Use component names from the pcb/schematic. What do you mean by wildly different values?


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## Kroars (Jul 27, 2022)

If I remember correctly, you’re only biasing four out of the six(?) 201’s. I think the circuits pretty forgiving with somewhere between 4.5v-5.5v on the drain leg of each of the four -personal preference difference anyway.


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## Edenspace (Jul 28, 2022)

temol said:


> You have to be more specific. Use component names from the pcb/schematic. What do you mean by wildly different values?


Q4 and Q5 are what I am trying to bias in between 4.5-5.5v but when I get Q4 close to 4.5v, Q5 is at 0v or damn near close. When I get Q5 to 4.5v, Q4 is up to around 8v. Can't even find a happy middle ground between the two. Just wondering if I need to match the 201s gain to get these to match.


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## Edenspace (Jul 28, 2022)

Kroars said:


> If I remember correctly, you’re only biasing four out of the six(?) 201’s. I think the circuits pretty forgiving with somewhere between 4.5v-5.5v on the drain leg of each of the four -personal preference difference anyway.


So there are four 100k trimpots. Trim 1, 2, 3 all individually bias Q1, 2, and 3 while Trim 4 biases both Q4 and 5. Q4 and 5 are just wildly different values and the pedal does not sound good at all.


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## temol (Jul 28, 2022)

Look at the schematic and compare Q4 and Q5. You can change drain voltage of the Q4 with a trimmer, but Q5 has fixed drain voltage (should be equal to the VDD). Measure Drain voltage of the Q4 and Source voltage of the Q5. With Q4 set to 4.5V you sould have similar voltage on Q5 Source. 
You do not have to bias Q5.


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## Kroars (Jul 28, 2022)

Edenspace said:


> So there are four 100k trimpots. Trim 1, 2, 3 all individually bias Q1, 2, and 3 while Trim 4 biases both Q4 and 5. Q4 and 5 are just wildly different values and the pedal does not sound good at all.


Where did you get your 201’s?


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