Dirtbaby - Thin Board

[MAO]

I was getting distortion on the repeats, but not where expected.

With my audio probe, PT2399 pins 15 and 14 sounded fine. Pin 3 on IC4 was good, but pin 1 had some distortion, then pin 7 on IC4 had even more, or was at least louder.  I swapped ICs, no change.

R23 and R24 were correct values and soldered well.   

I removed the gain through IC4a by pulling R24 and replacing R23 with a jumper. Seems like the distortion issue is resolved.  T1 still allowed enough volume compensation for the repeats given the reduced gain through IC4a. (Thanks Madbean!)

Question is, what effect does reducing the gain of IC4a and the removal of C23 have on the sound?  It may have sounded a bit darker, but I couldn't really be sure without having a side by side comparison.

Maybe a better question is what is the function of C23?

As I'm writing this, I'm also wondering if C23 was the culprit all along. I don't want to risk buggering up the board by pulling any more resistors or capacitors, I'll wait for some feedback before continuing.

Since I removed the gain, maybe I need to tinker with the value of C22 too?   

Thanks,
Mike

[Boba7]

Cant help you but I just bought a thin board, so I'm interested in any explanations!

Glad you got it working tough.

[MAO]

So by removing the gain through IC4a, I'm not getting any noise now, but the repeats seem too weak.

I plan to replace C23 and R24 then try different values with R23 to see how much gain I can add back in before the noise returns.

I forgot to mention I did increase the values of C8,C9 and C10 per te build doc to 4n7, 2n2 and 2n2. I also increased C13 to 47n to get rid of the hiss. Maybe those changes are somehow to much for the stock gain through IC4a?   

The funny thing is, I think the gain is only 2.35 through IC4a, seems strange that small amount of gain would cause the distortion. Plus I would think others would have posted the same issue.

Any suggestions?



 

[darrenw6000]

Have you soldered the led(D2) because not doing that will make it distort

[MAO]

Yes, thank you. In fact, I now use the same LED trick on every PT2399 build :0)

Thanks Jon Patton!

[Boba7]

Hey,

Any news regarding your issue? Hope you enjoy your build. I'm probably gonna start mine soon.

[jimilee]

There's a thread around here addressing just this issue. A little search voodoo should do the trick.


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[Boba7]

I think the thread you're thinking of is about white noise more than distortion. But it is definitely helpful.

[jimilee]

Oh, right.


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[MAO]

Sorry for my late reply...

After replacing R23, R24, and C23, no change with the distortion. I then reduced R23 to 16k and that seemed to take care of it, I may have increased it to 18k, not sure which of the two values I settled on, but if you get distortion as I described in the original post, I would suggest socketing R23.

I also settled on 15n for C13, this added a bit more hiss back in than I would have liked, but it was to dark with 47n.

It still seems strange I'm the only one who mentioned the noise at IC4a, makes me wonder if lowering R23 just masked the true cause, maybe somewhere earlier in the circuit.

I sent it to a buddy to checkout, I'll report back if something else comes up.

[Boba7]

Hey Maoriente,

I just built a thinboard Dirtbaby, and I happen to have distortion on the repeats too. But then I tried running it a 18v, and the distortion's gone. And I much prefer the higher headroom offered by doubling the voltage. I will definitely put a charge pump in the pedal with the dirtbaby.

Hope it helps.

I also changed C10 (1,5nf), C12 (150nf) and R4 (30k) and the pedal sounds just amazing to my ears!

Edit: c13 back to original value, slightly changed c10

[MAO]

Cool, I will try the same. Thank you for sharing!

I was able to eliminate the distortion as I had described above, but wasn't thrilled with the final sound.  Will definitely try your suggestions.

Curious, was R4 adjusted to 30k before or after you had powered with 18v?  Did this change help with the distortion or just reduce the oscillation?

[Boba7]

I adjusted R4 cause raising c12 to 150nf also raises the delayed signal volume. It affects the feedback only, not the distortion.
Now I can get almost infinite delay around 3 o'clock and then its oscillation madness!
By the way i put 2 back to back 1n4148 from lug2 to lug1 of the feedback pot to get a more usable oscillation volume.

And I finally put C13 back to its original value, and raised C10 to 1,5nf. I think its the final change.

So we have:
- 18v
- C12: 150nf
- C10: 1,5nf
- R4: 33k

Its just amazing to my ears!

[Boba7]

So I just found out that my green leds voltage drop are all over the place.
You may want to select one with a voltage drop superior to 2v. In my experience below that I got distortion on the repeats.