Zero Point SDX fuzzy delays and other problems

[TylerPerson]

Hey, all,

   So, I recently acquired all the parts for the Zero Point SDX, got it soldered, actually rocked it before I boxed it for once (and will from now on), but sadly, it was no bueno. The mix, rate, depth, and delay pots all sound like they're working properly, as well as the ghost and mod switches, but here's what's wrong.
   The most obvious thing is that the delays sound distorted and a little low in volume. They're not a sharp, piercing distortion like when I had an incorrect feedback resistor value for a previous build of mine, but ugly fuzz. In general, they're weak and sound like crap, and it remain like this no matter how I tweak the knobs and switches (and on that note, the slam switch doesn't sound like it does anything too). The next problem is that when I turn the feedback knob, it'll usually go from one repeat, to at most 4-5 over the course of the whole turn. It's typically only 3 repeats max, though. And here's the final problem: the path and rotary switch don't really do anything. All the path does is sometimes make the delays a bit louder, depending on which position the 3p4t switch is at. Also, all 12(?. I thought it was only supposed to be four) positions on the 3p4t either kill the delays, or will do absolutely nothing at all besides popping to certain positions.
   All in all, it's a mess. But, hey, at least the modulation portion of the circuit works. Anyway, here's what I've done to try and fix it...
   First, I double checked that all the resistors, caps, diodes, etc were correct. I also checked the orientation for the caps and such. Everything was exact, which isn't too much of a surprise seeing as I triple checked each component before soldering it on the board in the first place. The only component I wasn't able to verify was C34, because the value is hidden behind C35. Anyway, once that all passed, I took the voltages of the ICs (see below), and after all that, I checked for solder bridges, both with and without shinning a bright LED light above and below the board. Of course, there's nothing wrong I can see. Now I'm getting frustrated. The next idea was to change out all the ICs and socketed resistors. Still, nothing changed.
   And now, here I am, plagued with a phantom of a problem, broken and seeking advice to my conundrum. Does anyone have any idea what's wrong, or what I can try next? I hate to have such an awesome sounding pedal not work, so I'm determined to fix it.

Ic volages:
IC 1- TL072:
1: 4.66V
2: 4.66V
3: 4.66V
4: 0V
5: 4.66V
6: 4.66V
7: 4.66V
8: 9.3V

IC 2 - PT2399:
1: 4.95V
2: 2.48V
3: 0V
4: 0V
5: 2.94V
6: 2.47V
7: 0.53V
8: 0.61V
9: 2.47V
10: 2.47V
11: 2.48V
12: 2.48V
13: 2.48V
14: 2.47V
15: 2.47V
16: 2.47V


IC 3 - PT2399:
1: 4.96V
2: 2.47V
3: 0V
4: 0V
5: 2.95V
6: 2.47V
7: 0.64V
8: 0.67V
9: 2.47V
10: 2.47V
11:  2.47V
12: 2.47V
13: 2.47V
14: 2.46V
15: 2.47V
16: 2.47V


IC 4 - TL074:
1: 4.66V
2: 4.67V
3: 4.23V
4: 9.33V
5: 4.66V
6: 4.67V
7: 4.67V
8: 4.67V
9: 4.66V
10: 4.66V
11: 0V
12: 4.67V
13: 4.67V
14: 4.68V
 

[madbean]

Your voltages look fine.

You need to set the correct position count on the rotary switch. It has a removable washer with a little tab. The tab goes in the "4" notch. Make sure you turn the shaft fully counter-clockwise first. Then set the tab. You should now have four positions of rotation.

As far as the fuzzy repeats, you are going to need to audio probe to find out where that is introduced. Probe pin 14 on both PT2399s to listen to the output. Does the fuzzy delay happen at the first or second? If the delays sound fairly clean in both places, we need to look further down the audio path, such as pins A, 5,6,7,8 of the rotary switch. I don't know yet if the fuzzy delay and reduced repeat volume are related or not. Audio probing should help tell us that.

[TylerPerson]

OK, I'll put together an audio probe in a day or so and post the results. Thanks for the quick response, Brian!

[TylerPerson]

OK, so, pin 14 of both PT2399's output the same weird, fuzzy delays.
I also checked IC1, the TL072, and pin 1 outputs a clean, no delay signal, but pin 7 outputs fuzzy delays as well. I should also just note I changed R3's value to 470k ohms as stated in the revisions.

[TylerPerson]

Update:
So, the fuzzy delay disappeared, and pedal finally sounded normal. I didn't know why, but I didn't question it. I then played around with R48 and R31 to see how I liked the delays with and without those resistors, as told in the build page for the effect. Turns out there was no difference in delay times, only going to around 500-600ms either way. Perplexed, I went back to audio probing today, and wouldn't cha know, the fuzzy delays are back. So I started following the signal through the circuit, and I found that pin 14 of IC3 delays around 600ms, but pin 14 of IC2 puts out a delay of only around 200ms. I also checked the output at pin 9, and IC3, gives out another fuzzy delay of around 100ms or so, but on IC2, a distorted, feedback like oscillating noise that's sometimes high pitched and sometimes lower. I'm not sure if that's wrong or not, but it sure doesn't sound right. Just in case, I've also checked around, and nothing appears to be causing shorts. I'm stumped once more. This thing has a mind of it's own lol.

[jimilee]

Battery or dc adapter?

[TylerPerson]

DC adapter.