Zero Point SDX, help needed: Why the delay distorts when strumming loud?

[Teddy]

Hello!

I've built the Zero Point SDX.

Beautiful tone. everything works...

But, one issue:
The delay repeats distort, when strumming guitar loud.
Signal chain is guitar--->ZP SDX---->amp

Thanks,
- Teddy

[Teddy]

Hey, i forgot to mention that i used a 1uF film capacitor as C49, instead of MLCC.
Could this be the cause?

And also, i think the distortion is mostly heard on the first repeat of delay.

Thanks,
- Teddy

[Teddy]

hey one more thing...

i think it has something to do with the Path switch

switch turned off = delays nicely, without that much distortion

but anyway, it seems like the Zero Point SDX has little headroom.
Can this be improved?

Thanks,
-Teddy

[Teddy]

and still a question:

Is it normal to hear "digital hiss" ?
When the delay is heard, there's a definite hissing noise underneath.

the strange part about the hiss is:
-when playing, while the delay is heard = hiss (like playing a chord and holding it)
-when not playing, while the delay is heard = no hiss (like strumming quickly and then muting strings)

-the hiss is worse with longer delay times

Thanks,
- Teddy

[DutchMF]

I don't think using film for C49 will cause your problem, as it is in the modulation section and you didn't mention anything else about that. The first thing that comes to mind is the PT2399's. Not all of them are created equal, try some other ones (preferably from another supplier) and see if that helps. Also, since you mentioned the Path switch, check all component values and orientation in the filtering section of the circuit (and the rest too...). Good luck!

Paul

[Teddy]

Thanks for your advice... i'll try change the PT2399's

Thanks,
-Teddy

[Teddy]

Hello!

I tried changing the PT2399, still the same problem...
altough tone changed to a bit brighter.

I'll try to check the components in the filter section

Thanks,
-Teddy

Oh, could you be a bit more specific, where to look for a problem next?

[kothoma]

The delay repeats distort, when strumming guitar loud.

Distortion in every filtering mode?
At all or only high feedback levels?

And also, i think the distortion is mostly heard on the first repeat of delay.

i think it has something to do with the Path switch
switch turned off = delays nicely, without that much distortion

Path switch turned off - thats no filtering on the first repeat, right?

[Teddy]

Yes, distortion in every filtering mode.

Path switch on / off... works a bit akward. It makes the first repeat louder.

[kothoma]

Path switch on / off... works a bit akward. It makes the first repeat louder.

Yes, at least it could appear like that, because then the first repeat is unfiltered and has more highs.

[kothoma]

Yes, distortion in every filtering mode.

What about feedback level and guitar level?
Distortion disappears with lower levels?

[Teddy]

Guitar volume turned down = less/zero distortion

Feedback level doesn't change amount of distortion

[kothoma]

This is strange.
Just looking at Deep Mode there's not much (R39/C46) that could contribute distortion.
That would rule out the whole filtering section as culprit.
So maybe the signal is already distorted before the mode switch and filtering reduces this distortion somewhat so it is no longer noticeable?

How would you describe the sound of this distortion. Is it in the upper frequency range?

Anyway, I would start checking values of R8,...,R19.
Then looking for solderbridges, bad soldering, etc., the whole program.

[Teddy]

Hello!

Thanks for your quick replies!

I have an other issue.... that might have something to do with the distortion.

When delay is increased, hissing noise from delay repeats is loud.
And the delay sound quality is lower, the longer the delay is.

I will check R8-R20

[kothoma]

And the delay sound quality is lower, the longer the delay is.

To a certain degree this is expected...