Mosfet Driver problem

[ELQ]

I just got PedalPCB Mosfet Driver (BK Butler Tube Driver variant) soldered and I'm facing issues. Bypass signal works fine. Also led is working. When I turn the pedal on, I hear a lot of noise and a very weak distorted signal. Pots are working fine. I tried adjusting the internal trimmers and found out that the "best" way is to turn the left one full counterclockwise and the right one full clockwise. In this case I get tiny bit more volume (still much weaker than the bypasses signal). Here are attached a couple of pictures. What might be the issue?

Thank you all in advance

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[eh là bas ma]

Hi, welcome !

For some reason, I can't zoom in on your first pic (soldering side), so it'll be quite difficult to spot something suspicious.

From what I can see, looks like you could try reflowing most of your soldering joints.


This link will surely be useful to you, in order to save some time :

DEBUGGING - What to do when it doesn't work

DEBUGGING - What to do when it doesn't work

www.diystompboxes.com

...and here is the best debugging tool :

Misc > Audio Probe : DIY Fever – Building my own guitars, amps and pedals

[DIY Fever] Audio Probe - very simple contraption that helps with debugging audio circuits

diy-fever.com

Audio probing the signal path all the way from In to Out, following schematics, will tell you where the signal is having an issue.

 

[Robert]

I believe you need to swap these two resistors. Their locations were changed in the new revision and the build doc hasn't been updated yet.

Generally when the PCB doesn't match the build documentation you should follow the silkscreen printed on your PCB.

 

[Shlendle]

I just got PedalPCB Mosfet Driver (BK Butler Tube Driver variant) soldered and I'm facing issues. Bypass signal works fine. Also led is working. When I turn the pedal on, I hear a lot of noise and a very weak distorted signal. Pots are working fine. I tried adjusting the internal trimmers and found out that the "best" way is to turn the left one full counterclockwise and the right one full clockwise. In this case I get tiny bit more volume (still much weaker than the bypasses signal). Here are attached a couple of pictures. What might be the issue?

Thank you all in advance

.View attachment 43031View attachment 43032

Hi, I have exactly the same issue, having completed my build today. The effect lacks volume compared to the bypassed signal and sounds very thin and raspy. My pcb is populated exactly the same as yours, the resistors/caps are in their correct places according to the silkscreen on the pcb.

Did you manage to get your pedal working correctly by switching those 2 resistors on the bottom left, as kindly suggested by Robert?

First post here!

Cheers

 

[allanshookphoto]

I have been searching for a solution to the same problem, This may be the answer! I think I have mixed up the 1M and 10K resistors. With mine, the sound is fairly good on it's own, but after a buffer or another "on" pedal. the sound is very thin and crispy with no bass. So, from the bottom up on the left side resistors, it "should" be 10k, 10k, 1M, 10k? Or do I have it correct?

 

[mybud]

I have been searching for a solution to the same problem, This may be the answer! I think I have mixed up the 1M and 10K resistors. With mine, the sound is fairly good on it's own, but after a buffer or another "on" pedal. the sound is very thin and crispy with no bass. So, from the bottom up on the lift side resistors, it "should" be 10k, 10k, 1M, 10k? Or do I have it correct?


View attachment 52207

Looks like that’s what has happened. Try desoldering and swapping them, with the best of luck for the exercise.

 

[allanshookphoto]

Well, I think you can see that I have a 1M in R2 where the silkscreen says it is supposed to be, and 10K in the other three. So I don't know what is going on. It's correct according to the plans and the silkscreen. The image that Robert posted above is different from mine.

 

[MichaelW]

Well, I think you can see that I have a 1M in R2 where the silkscreen says it is supposed to be, and 10K in the other three. So I don't know what is going on. It's correct according to the plans and the silkscreen. The image that Robert posted above is different from mine.
View attachment 52233
View attachment 52238

I'll try to remember to pull mine out and try it, but all of my pedals come after a buffer, my tuner I don't recall it sounding thin and trebly.

 

[jesuscrisp]

As discussed in another thread on the matter, the schematic has an issue with the input stage bias resistor. R3 should be 1M, R2 has to go.

EDIT: I see it was you who was asking in said thread. How about just trying what I said for now and see if that works for you? Doubt you get any better advice asking around in another 5 threads.

 

[allanshookphoto]

As discussed in another thread on the matter, the schematic has an issue with the input stage bias resistor. R3 should be 1M, R2 has to go.

EDIT: I see it was you who was asking in said thread. How about just trying what I said for now and see if that works for you? Doubt you get any better advice asking around in another 5 threads.

UPDATE: I replaced the R3 10k with a 1M. (I'm doing one component at a time). Now there is no discernable sound difference between direct from guitar, or through a buffer, or through an "on" pedal. As far as I can tell the pedal is behaving exactly as it should.
I would like to do more research to find out why that did what it did, what the correct terminology and description is for what that resistor does and how it changes the input impedance and behavior of the first op-amp gain stage. (We don't have to go in to that here, everyone has done more than enough already)
I've traded it in and out of my pedal board with the Muroidiea Distortion, and the levels and tonal qualities are within the same general ballpark, but I actually like the Rat better. The MOSFET definitely has a unique sound and would be useful in many ways, and it's nice to have that option now that it's working "properly".
Thanks for everyone's help.

​

 

[lrgaraujo]

UPDATE: I replaced the R3 10k with a 1M. (I'm doing one component at a time). Now there is no discernable sound difference between direct from guitar, or through a buffer, or through an "on" pedal. As far as I can tell the pedal is behaving exactly as it should.
I would like to do more research to find out why that did what it did, what the correct terminology and description is for what that resistor does and how it changes the input impedance and behavior of the first op-amp gain stage. (We don't have to go in to that here, everyone has done more than enough already)
I've traded it in and out of my pedal board with the Muroidiea Distortion, and the levels and tonal qualities are within the same general ballpark, but I actually like the Rat better. The MOSFET definitely has a unique sound and would be useful in many ways, and it's nice to have that option now that it's working "properly".
Thanks for everyone's help.

​

Good news that you got it to work!
Hint: you're looking for a non-inverting operational amplifier stage

 

[jesuscrisp]

So the bias resistor basically sets the input impedance together with the pulldown resistor (to some degree) and the inherent input impedance of the op amp (which is ridiculously high for most ones). For the exact calculation, you can check out the electrosmash articles on the Rat, Distortion+ and Guvnor for example. 1M is a common value with JFET input op amps such as the TL072.

As a general rule of thumb you want high input impedance (at least around 500K) to avoid exactly what you experienced, which is common in pedals like fuzz faces and the reason those usually go first in the chain. If its high, the pedal doesn't care so much about whether pickups, buffers or pedals with low or high output impedance go into it and it will therefore act more consistently.