Chunk Chunk problems (solved)

[Doctorjello]

Hey everyone- long time/first time.

I built a Chunk and went to test it tonight. I get bypass but no effect. I'll do the pictures and voltage dance tomorrow, as once it looked failed I went to bed! I was wondering if anyone had a layout of the audio path for this circuit so I could probe it after I double check values and reflow joints. Thanks in advance!

[jimilee]

The audio path should be in the BOM. That's a pretty straight forward circuit, make sure you calibrate it, that will stop you from getting sound.


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[Doctorjello]

Thank you. I see it now, I think. I printed the doc in black and white. Is the audio path the blue or red line?

My calibration went pretty smoothly with one exception: Q1-3 all dialed in easily. But Q4 would jump from 2.xx to 7.xx with imperceptible movements. I finally got it close to 5 in the end, but my Spidey senses are telling me perhaps my issues could be there.

[jimilee]

Blue, here is a cool tutorial Brian put together, I had the same question. There are others linked from the projects page.
http://www.madbeanpedals.com/tutorials/downloads/MBP_Understanding_Layouts.pdf

[Doctorjello]

Ok I have some new Intel. I've probed it and found some anomalies. First off, I found I had a whole pack of 100Mresistors labeled 100r, so R19 and 20 were way wrong! But all the same, after changing them out I still lose signal right around there.
I get signal from S to R1, R2,3,C1, R4,C3, Q1, TP1 and TP2, but neither of the other two legs of either trimmer. I have signal at Gain and C6, but around C10 and Q2 the volume drops. I have nothing at Mid or Bass or anywhere further on, so it must be on this side of the board.

I also have voltages.
Supply- 8.98v (wall)
Q1:
D 5.23
S .26-.36
G 0

Q2:
D 5.3
S .22
G 0

Q3:
D 5.29
S .1
G 0

Q4:
D 4.78
S .18
G 0

Q5:
D 4.79
S 6.5
G 8.05

I recognize that those are different from the desired readings, but I'm not savvy enough to know what they mean.
This build will also firmly represent the very last one I make with board mounted pots.

Never. Again.

Thanks for any assistance here. I'll work on pics, though I'm not sure what help they'll be.

[Doctorjello]

Does the middle leg variance on Q1 mean anything? All of my other readings were pretty solid. That one fluctuated.

[Doctorjello]

Good evening once again. I took some time off and came back to this build tonight. I removed all of the board mounted pots and wired them up so that I could regain access to the components buried beneath. I reflowed every joint on the board while I was at it. I'm sure I'm not the first to apologize for the photos. I'm a sound guy, not a photographer!

When I rebuilt it, I rebiased and took readings, as shown below:
Q1: 4.74 .23 0
Q2: 4.43 .09 0
Q3: 5.32 .21 0
Q4: 4.81 .22 0

For entertainment value I also checked Q5: 8.04 6.5 4.81

My problem is still the same: bypass works, nothing when engaged. The buzz I hear changes when I sweep the gain. Anything obvious that I'm missing here? Next step is to remove the 3PDT and rewire it. Thanks all!

[m-Kresol]

your gate voltage on Q2 looks low. this would also result in the volume drop you described for the audioprobing. How was your gain pot setting when you measured it? how does turning it affect your voltage on gate of Q2 and the sound at the test point of Q2?

I think you have an 180R (brown-grey-black-black-brown) for R8 instead of 1k8 (brown-grey-black-BROWN-brown). hard to be sure from the pics. that could very well be the culprit. Please check that (and all your other resistors for that matter). I think it's the same for R14 and R4! while at it, check R16. it should be yellow-purple-black-brown-brown.
I suggest measuring your resistors prior to soldering them in. makes mistakes like this far less frequent. At least check the resistor code.
hope that helps. good luck

[Doctorjello]

Oh man do I hope that's it. Would certainly explain why it's exactly the same after reseating everyone. I'll check it tonight when I get home. I have already had an issue on this build where a 100 and 100k were reversed in my containers. Much appreciated. Will report back!!

[Doctorjello]

Unfortunately all four of those were actually correct. Must just be the lighting throwing off the colors. I'll still sit down this week and see about verifying every one of them again. 

[Doctorjello]

Figured I'd let this one sit in the Bin of Shame for about a year and what a difference a year makes! I've been revisiting my bin lately with sharper, more experienced eyes and as of tonight two failed projects have been resurrected. I rebiased everything tonight, tightened up all grounds and gave it a whirl and it fired up! What an amazing pedal this is.

I've never found myself to be the kind of person capable of having "too much gain" but this comes close. Am I right in understanding that the EQ section is supposed to sit about 12 o'clock and be used as a boost or a cut? If I push them all, it goes to oscillation and squealing. But at 12 I can dial in good sounds.

Thank you to everyone who helped me out last year. And to anyone considering the Chunk, go for it. Get some reliable transistors and dive in. Cheers!!