Boogie Monster Debug

duffy_lane

Member
Hey y'all. Having trouble with my Boogie Monster build.
Not getting any sound thru the Auditorium test platform but the LED lights up. (I don't think the auditorium is the issue.)

Here was the test setup (is the wiring correct?):

@peccary suggested I clean the flux. So I did with isp alcohol, toothbrush and kim wipes.
Here's where I'm currently at (Trimpots are all over the place from me trying every single position lol):

Quirks about the build:
- Used MPF102 transistors instead of J201
- Used 2.21M instead of 2M2 for R5

Boogie Monster Build docs: https://docs.pedalpcb.com/project/BoogieMonster.pdf

Please let me know if I can provide any extra pics and info. Thanks!
 
Set the drain voltage of Q1 to Q4 to half the supply voltage. Q5 - Drain sould be around supply voltage (slightly lower), source - probably around 5-6V. Then inject some signal and start checking with the audio probe from the input.
This is the signal path
1612724553669.png
 
SICK!!! @Nostradoomus I have not biased them. Got em from pedal hacker electronics.
I'm new to this and my multimeter is a pos (looks like this should be my next investment) Which mode did you use on the meter to test the transistors?

@temol This diagram is helpful (I think I understand your outline and recommended drains). I might have some questions on this though.

Excited to try this, will report back after a quick errand. Appreciate y'all!
 
So I've been trying to bias the MPF102's using this multimeter set to the 200K option at the bottom left. (this is the only setting that's giving me a reading)
Touching the ground meter lead to the GND wire at the bottom of the auditorium board
And the positive meter lead to the Drain of the JFET's based on the docs here

I can adjust the values of:
Q5 = 5.4
Q3 = 3.7

However, the rest of the transistors won't read anything other than 1.8
I've tried adjusting all the trimpots but the only JFET's that change value are Q5 and Q3.

After reading this post: https://forum.pedalpcb.com/threads/boogie-monster.2300/
it looks like its time to try swapping out the JFET's that are reading 1.8

I'm confused to the point where I'm not sure if any of my leftover MPF102's are working.
I've read this smallbear blog post and watched some videos on testing & biasing transistors but the values my meter shows are just weird.
Does anyone have a better explanation or other resources I could look into?

Is this why people socket transistors? Are there any performance drawbacks of socketing a transistor?
Regardless, I'd rather learn how to test and bias them correctly bc it's obviously possible.
 
No.. and no.. start all over again but this time set the multimeter to DC voltage readings not resistance readings.. :)
So not 200k but 20V range (set the dial to approx 11 o'clock).
 
hmm, that entire range including 20V reports 0.00 or -0.00
Even tried it on brand new J201s from Mouser.

Sanity check: The pedal is not supposed to be plugged into power correct?
I just have an instrument cable plugged into the input jack as mentioned in the video @Nostradoomus linked above.
 
1. connect power supply to the pedal/pcb.
2. Make sure it's on, then measure the voltages.

You are going to measure the voltage. No power = no voltage.
 
Not sure why I thought that video said to only have an input jack plugged in LOL
Thank you so much for your patience @temol finally got it working!! A little quiet but I know how to adjust that now!

One thing I noticed while adjusting the trimpots: the jump in voltage was high between 3-7V, like the meter reported ~3.5, and the voltage would jump to like 7 or 8 when I tried to adjust it barely past 3.5

Why would that happen?
Could I have worn out the trimpot a bit from turning it so much?
 
Back
Top