I built the dirtbaby delay pedal, and the delay effect is really great. All of the controls work as expected and it sounds very cool. My only problem is that I'm getting some distortion with the effect engaged. If I'm playing with a clean sound through the amp and then setup the pedal to produce the same relative volume when engaged, I get some fuzz/distortion effect. I'd really like the pedal to be clean. Anyone seen this problem in the past or have any ideas where to look?
I had the same problem with a 2015 Dirtbaby. Tried running it at 18v and it worked like a charm.
You could also just try different IC's, it did make a difference in my 2016 board.
And also one thing to consider is the internal delay level trimpot. Try boosting the delay level. This way when it hits the blend pot it's quite loud and you won't have to turn up the volume too much to get unity gain. I'm not being very clear but just try, maybe it'll work.
Thanks for the reply! You mean substituting different ICs (like a 5532 for a 4558 type situation) or just a different IC of the same type to see if there's some subtle gain difference from chip to chip or whatever?
yeah a different IC. I think I put a 5532 in IC4 and it made a big difference compared to a OP275 I had in the first place.
Also try a higher voltage if your capacitors allow it. :)
have you got the green led installed, not having that in can make it distort
There is a thread here addressing this issue. It involves changing a few caps. Sorry, I don't have the link.
Sent from my iPhone using Tapatalk
Quote from: jimilee on March 13, 2017, 01:03:53 PM
There is a thread here addressing this issue. It involves changing a few caps. Sorry, I don't have the link.
Sent from my iPhone using Tapatalk
I think the caps change is more about the inherent PT2399 noise (psscht on the repeats) than the distortion.
I do have the led in there. However, I double checked and I used a 3mm green diffused as opposed to the listed 5mm. Think that could make enough of a difference?
Quote from: taeagan on March 13, 2017, 04:54:37 PM
I do have the led in there. However, I double checked and I used a 3mm green diffused as opposed to the listed 5mm. Think that could make enough of a difference?
Nope, it shouldn't.
Maybe I have it in there backwards? I'll check tonight. Can I "hot swap" this led without frying the board?
So I fiddled around with the LED and also swapped out IC4 with a 5532. No appreciable difference.
The distortion is in the delay part of the circuit. If I set Level to the same volume as the bypassed signal and turn Blend all the way down (to get only the dry signal), I don't get the distortion. The distortion is in the repeated delay signal when I blend it back in. Any thoughts on how to reduce distortion in that part of the circuit?
Quote from: taeagan on March 14, 2017, 08:54:57 PM
So I fiddled around with the LED and also swapped out IC4 with a 5532. No appreciable difference.
The distortion is in the delay part of the circuit. If I set Level to the same volume as the bypassed signal and turn Blend all the way down (to get only the dry signal), I don't get the distortion. The distortion is in the repeated delay signal when I blend it back in. Any thoughts on how to reduce distortion in that part of the circuit?
Do you have another working PT based delay you can test the PT chips in?
I made a unboxed Cavedweller with a 16pin ZIF socket just to test PT2399's in for this very reason.
I have had PT2399's give me distortion & swish sounds on repeats before and it all pointed to the chips. I am not saying this is your exact problem but it will at least rule it out.
Cody
Quote from: selfdestroyer on March 14, 2017, 09:27:02 PM
Do you have another working PT based delay you can test the PT chips in?
I made a unboxed Cavedweller with a 16pin ZIF socket just to test PT2399's in for this very reason.
I have had PT2399's give me distortion & swish sounds on repeats before and it all pointed to the chips. I am not saying this is your exact problem but it will at least rule it out.
Cody
Yep, pt2399 can vary a lot!
Also you should really try it at 18v. It worked for one of mine. Cant explain why since my 2nd was fine at 9v, but it worked
There's some info regarding distortion here:
http://www.madbeanpedals.com/forum/index.php?topic=23559.0
My situation in that thread:
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.
Thanks for the link to the other post. Just to note, I tried swapping out PT2399 chips (I had a couple others) and this made no difference. Also, I ran it on 18v and got no improvement in the distortion on the repeats. If anything, the higher voltage seemed to make the repeats more warbly if that makes any sense. Like they had more of a vibrato effect on them.
I'm going to try socketing C12, C10, and R4 as described in the other post and mess with the values. Of course this requires taking the whole thing apart again :)
If you can peek at the board when you're testing it, do you notice the Green LED hugging the 2399 lighting up? Strike a really hard, high volume chord and see if it glows. If not you may have it in backwards (or a really low output instrument I suppose, but its worth a look anyway)
Yes, I checked and the led glows. It got me thinking about the post in the other thread talking about the forward voltage of the led. All of my green diffused checked out in the 1.8v area. I don't have any leds with a voltage drop greater than 2v as the other poster had suggested (at least not according to my meter).
Quote from: taeagan on March 22, 2017, 02:18:24 AM
Yes, I checked and the led glows. It got me thinking about the post in the other thread talking about the forward voltage of the led. All of my green diffused checked out in the 1.8v area. I don't have any leds with a voltage drop greater than 2v as the other poster had suggested (at least not according to my meter).
Oh yeah I remember it made a big difference in the last Dirtbaby I built.
Ok. So I socketed c12, C10, and r4 as per the other thread. No difference at either 9v or 18v.
Is there another LED or diode combination that I can try? I'm not sure that I completely understand how the "green led trick" works. If it's limiting the signal to the forward voltage of the led, should I try something with a lower forward voltage? My green LEDs all measure 1.8v on the meter. Should I try a red one? Or am I washed up here and I want something greater than 1.8v?
I did find an older thread where midwayfair stated:
"Keep in mind that ALL PT2399 delays have harmonic distortion problems. That sounds like a soft, static-y, trashy distortion on the repeats."
http://www.madbeanpedals.com/forum/index.php?topic=17796.0
Maybe that's what I'm hearing? Maybe I'm trying to run down something that can't be fixed?