Dirtbaby 2015 white noise on repeats - 03/28 sound sample added(zero point mini)

[MAO]

Can't catch a break, I've been struggling getting the Aquaboy deluxe to sound clean, so I put it aside and built the Dirtbaby. Everything seems to be working but I get a white noise on the repeats.

Audio probe on PT2399 pin 15 signal is clean, but white noise on the delayed signal on pin 14.

Reflowed solder, tried different ICs before I used the audio probe and found the noise is coming out on pin 14.

I must have had beginners luck with delays when I built the Zero Point SDX a few months back, fired right up with no issues. It's been a frustrating week with these other two...

[MAO]

Sorry, forgot to post the voltages

VD 7.8v
VC 8.14
VB 3.87

PT2399
1 - 4.96
2,6,9 thru16 - 2.48
3,4 0.0
5 - 2.97
7 - 0.57
8 - 0.61

FWIW, the PT2399 sounds better in the moodring, has some white noise on pin 14, but less noticable

[madbean]

Is the noise present in all settings of the delay pot or just toward the max delay?

[MAO]

Thanks for the help!

It's there, but less noticeable on short delay, worst sounding with delay knob all the way down, then cleans up quite a bit the 1st 1/8 turn, then progressively gets louder as the pot is turned up.

I'm using the 50k Lin for the delay pot, in fact all values are per the build doc except the 2u2 NP caps, I'm using 2-1u NPs in parrallel for each.

[MAO]

Best thing I've tried so far was 25k Lin for delay pot and 68k for R35. Kinda minimizes the white noise but max delay is much shorter. I tried lower and higher values for R37, stayed with 220k.

Hope there is something else to try.

Mike

[MAO]

Well, the white noise/hiss is still to much even with the 25k delay pot.

Is there something else I could try?

[madbean]

There's going to be some noise, but you really should not have any with the delay pot all the way down and very little with it in the first half. So, possibly something is awry in the filtering. Have you double checked to make sure all your resistors and caps are the correct values?

If so, here is something else you can do: Increase C9 and C10 to 2n2 and C19 to 47n. Socket these while you are at it. This should clamp down that noise quite a bit. If it goes too far, back off C19 to 22n. Let me know what you think of the results.

Also, have you put in the correct LED on D2? I found this made a huge difference in my build.

[selfdestroyer]

Also, have you put in the correct LED on D2? I found this made a huge difference in my build.

Found the same here.

Cody

[MAO]

I do have a 5mm green diffused LED and all the cap values have all been verified. I also checked all the resistors around the PT2399.  I have a few more LEDs, I could swap it out just to be sure. 

I have noticed something with the delay pot today. When turned all the way down, there is a wierd noise coming through when not playing. When I turn the knob to about 8 o'clock the noise disappears, and as long as I'm not playing it stays quiet when maxed out. When playing, the repeats have the hiss. The noise with the delay turned down almost sounds like RF noise.

I've got to assume something is out of place or not soldered well.

Once I re-flow solder again, and double check everything around the delay pot, if no change I will then try the value you noted above.

Would the delay pot noise be related to just that part of the circuit? i.e. C3, R37, R38, PT2399 pin 6 and ground?  The depth pot didn't have any affect on the noise I was getting when the delay pot was turned all the way down.

How critical is C3 value? I have 2 1u NP in parallel measuring just under 2u.  Can a regular 2u2 electro be used, if for nothing else but troubleshooting?

[madbean]

C3 can be 1uF, no problem. I made it 2u2 since there was already one for C33. In fact, the LFO will work even with C3 jumpered but it's there for potential noise isolation between the delay and modulation.

What you are describing with the delay pot is definitely not kosher. You might have a jinxed pot. Some contact cleaner would be my first step before replacing it (if you have it). So, my guess is that the noise and pot issue are somehow related. Having just boxed my own DB build up today I can tell you for sure that noise should not be much of an issue in this build except for the unavoidable artifacts you get when running the PT2399 over 400ms.

Your voltages looked pretty good and I assume that they are stable on the PT. Your VC/VD/VB are a bit on the low side, though. You might want to just jumper out R42 while you are at it. And last but not least, try a different power supply when noise is a problem (goes for any build).

[jighead81]

I have the same problem, sounds amazing but I can't get past the "hiss", and I don't even use very long delay settings. I haven't done the cap changes yet but I will soon. Will things improve once it's boxed up maybe?

*UPDATE*

Did the cap changes, (socketed all the listed caps), and I stuck with just putting 2n2 into C10.  Got all the hiss down to where I barely even hear it, like hardly at all, and it's totally acceptable.  This is definitely going into a box now.

[MAO]

I haven't been so fortunate, even with 2n2s and 47n for C19 still to much hiss to my liking. (when letting the notes ring out)

I'm having the same issue with a Zero Point Mini I just built today, tried 4 new PT2399s, all sounding the same. Powered with 9v, 15v and a 9V battery. Same results.   

Maybe it's supposed to sound this way with PT2399s?

To be clear, with delay 1/2 way up, mix 1/2 up, feedback minimum, no modulation, if I play a chord and hold it, there is a hiss that appears and lingers as the notes decay. It happens on single notes too when I let the notes ring out. If I cut the notes or chords short, you can't really tell, but the hiss is there. The hiss reaches "unacceptable" levels with the resistance on the Delay knob above 16k. Gets worse as the knob is turned up further. 

I doubt it supposed to work/sound like this. I don't recall the Zero Point SDX sounding this way.

[slimtriggers]

I get this, too.  But I would describe it as distortion as the notes decay.  I wasn't sure if that was supposed to be that way or not.  I tried the cap swaps, but it sounds the same. 

[madbean]

Where are you guys getting your PT2399 chips from?

[jighead81]

I got mine from Tayda and Paul's store. The one I got from Paul was cleaner sounding than any of the tayda ones.  I've still got noise though, just not as bad after the cap changes.  Running it at 18v also.
Is there a store that sells these tested and with low noise?