SOLVED Jump Drive - Bass pot has no effect

[MattG]

I recently built the Jump Drive, (build report). I think it works as it should (and sounds pretty darn good), except for the bass pot seems to have no effect (or the tiniest effect when moved from one end of the sweep to the other; an effect so minimal as to possibly be just my imagination).

This is a fairly new project, and there is no schematic. So I'm not really sure where to start debugging. The marketing copy for the LPD Sixty8 says, "the Bass control is pre-clipping", which to me implies it's a Tommy/Timmy-style bass control, basically the pot acting as a variable resistor to form an RC filter to ground (or virtual ground). In other words, if my assumption is correct, there should be a very small number of components involved in this bass control, and if I knew what those were, I could focus my attention on them.

Anyway, open open to any ideas or suggestions!

 

[swyse]

This might help a bit or not at all, but if the pcb photo is correct then it has the bass control being connected to caps c2 and c3, which also shows c2 either going into or out of IC2 which is wired as a buffer. These designations are based on the build doc pcb photo. I think this makes it more likely to be a capacitor blending scheme where the 1uf is in parallel with the 100n and you're adjusting the resistance going into the larger cap to determine the amount of bass for the filter, which I assume is going to be the vref for the op amp doing double duty, assuming the pcb photo is accurate to the actual pcb.

 

[MattG]

but if the pcb photo is correct

I assume you're referring to the photo on the Jump Drive product listing page, right? That photo appears to be quite different from the PCB. My PCB is consistent with the actual PDF build doc. I know this because I had a moment of panic when I first sat down to check component values, as I initially thought I screwed up a lot of components (until I realized that photo is inaccurate). If you look at the gut shot of my build, you can even see some of the traces are different compared to that photo, e.g. there is a trace running from one leg of the bass pot to that resistor just north of it, and on to one of the drive pot's legs; that trace isn't shown in the photo.

This might help a bit or not at all, then it has the bass control being connected to caps c2 and c3, which also shows c2 either going into or out of IC2 which is wired as a buffer. These designations are based on the build doc pcb photo. I think this makes it more likely to be a capacitor blending scheme where the 1uf is in parallel with the 100n and you're adjusting the resistance going into the larger cap to determine the amount of bass for the filter, which I assume is going to be the vref for the op amp doing double duty, assuming the pcb photo is accurate to the actual pcb.

Despite the photo inaccuracies, you could certainly be right about how the bass pot works. (Another example of this cap blending scheme is the Dung Beetle's "fat" control, which is also a pre-clipping bass control.) With your idea in mind, I'll probe around those caps and see if that gives any more hints.

Thanks!

 

[MichaelW]

Hey @MattG I should had said something about this much sooner, but as you know , my Jump Drive only recently got off the "No love" list hahaha...

The Bass control on mine does the exact same thing as yours. Which is not much of anything. I didn't really notice it is as I rarely touch the bass controls on my pedals. I usually set it at noon and control the tone changes from the treble. But I think this is not an issue isolated to your build.

 

[MichaelW]

@MattG Try this.
Toggle switch in the "high" setting (up)
Max the gain knob.
Set the treble control to noon.
No rotate the bass from full CCW to full CW.
Can you hear it working?
(I'm using headphones at 7am...hahaha)

It's working on mine. Just real subtle.

 

[MattG]

@MattG Try this.
Toggle switch in the "high" setting (up)
Max the gain knob.
Set the treble control to noon.
No rotate the bass from full CCW to full CW.
Can you hear it working?
(I'm using headphones at 7am...hahaha)

It's working on mine. Just real subtle.

Yup, exactly as you described: noticeable, albeit very subtle with the gain at max. Kinda strange IMO, but I’ll assume no build mistake.

I was thinking about trying to mod it, but I realized I never really gave it an earnest try - I was too distracted by the presumably-faulty bass pot.

 

[Robert]

Sorry for not catching this thread earlier.

The bass control is subtle, this is normal.

It's not your typical lowpass filter or active EQ control, it introduces a larger 1uF capacitor in parallel with a smaller 100nF coupling capacitor.