madbeanpedals::forum

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

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

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

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

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

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

Thanks,
-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?

Quote from: Teddy on July 27, 2013, 08:55:34 AM
The delay repeats distort, when strumming guitar loud.

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

Quote from: Teddy on July 27, 2013, 09:06:06 AM
And also, i think the distortion is mostly heard on the first repeat of delay.

Quote from: Teddy on July 27, 2013, 09:12:24 AM
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?

Yes, distortion in every filtering mode.

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

Quote from: Teddy on July 27, 2013, 11:27:57 AM
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.

Quote from: Teddy on July 27, 2013, 11:27:57 AM
Yes, distortion in every filtering mode.

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

Guitar volume turned down = less/zero distortion

Feedback level doesn't change amount of distortion

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.

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

Quote from: Teddy on July 27, 2013, 12:03:23 PM
And the delay sound quality is lower, the longer the delay is.

To a certain degree this is expected...

I checked resistor values R8-R20, they are correct

what's next?

And thanks for replies, it's great to have support.

Thanks,
- Teddy

I checked resistor values R8-R20

they are correct

what's next?

Thanks for your replies, i really am thankful to get tech support.
- Teddy

1) You are sure your guitar signal is not simply too hot?

2) Take a magnifying glass and closely inspect your soldering. There may be unwanted bridges or cold joints. Take a continuity meter and check suspect points.

3) Try to listen to the delayed signal at different points (between C16/R14, after C31/before the mode switch for a start) to find where the signal starts to degenerate.

I will do the following, thank you.

I'll let you know, when i'm done :)

Thanks,
- Teddy

Quote from: kothoma on July 27, 2013, 11:30:40 AM

Quote from: Teddy on July 27, 2013, 11:27:57 AM
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.

Just to make sure, this louder first repeat is the most distorted one?

One more idea. This distortion can be heard at all mix levels where you still hear delays?
(If not: check R40).

Yes, the first repeat is the most distorted one.

Also, i think, the feedback pot is way too sensitive.
It oscillates before 12 o clock

-Teddy

Quote from: Teddy on July 27, 2013, 12:28:49 PM
I will do the following, thank you.

I'll let you know, when i'm done :)

Glad to be of help. Good luck!

Hello....

Just asking, how sensitive the feedback pot is supposed to be?

I think it's oscillating before 12'o clock

Thanks,
-Teddy

Quote from: Teddy on July 27, 2013, 12:43:01 PM
Yes, the first repeat is the most distorted one.

Also, i think, the feedback pot is way too sensitive.
It oscillates before 12 o clock

Everything looks like your delayed signal level is way too high. Continue as proposed.

It's distorting either because of the diode clamp across the feedback pot or simply because PT2399s will distort with a signal larger than 2.5v. It's more likely to be from the feedback diodes since it doesn't distort as much when you flip the path switch (which redirects the first and thus loudest signal) and even the bare signal from a guitar is large enough to clip them(never mind one that's amplified by U1).

Ok... i tried the ZP SDX with a drum machine, output level @ max
i hear no distortion ! crazy...

Then with a guitar, distorts badly.

I really don't know what to do..

I built myself a simple audio probe, to listen to the signal.

But i don't know really, what to do.

Thanks,
-Teddy

Hello!

Thanks for giving me info on how to fix the SDX pedal.

I'm just thinking, that should i post a sound sample?

Off topic:

How to attach a sound file to the forum?

Thanks,
-Teddy

fast_delay.zip

Here's a second sample,

a slower delay setting

-Teddy

anyone? bumping...

=)

-Teddy

Quote from: midwayfair on July 27, 2013, 02:00:48 PM
It's distorting either because of the diode clamp across the feedback pot

But the diode clamp is after the pot and he said it distorts at any feedback level.
I understand that already the first (not feedbacked) repeat is distorted.
So I would exclude this.

Quote from: midwayfair on July 27, 2013, 02:00:48 PM
or simply because PT2399s will distort with a signal larger than 2.5v.

Either this or one of the feedback loops around the internal op amps is wrong, causing too much gain.
So either the input level of the delay line is too large or the output level gets too large somehow.
That's my best guess.

Quote from: Teddy on July 27, 2013, 02:16:32 PM
Ok... i tried the ZP SDX with a drum machine, output level @ max
i hear no distortion ! crazy...

Then with a guitar, distorts badly.

Are the two input levels comparable? Can you measure them?

Quote from: Teddy on July 27, 2013, 02:16:32 PM
I built myself a simple audio probe, to listen to the signal.

OK, what do you hear after the first PT2399?

hey, did you check the .zip files containing mp3's?

they were posted an hour ago

please, comment on them
is there anything wrong, or am i just dreaming...

Thanks
-Teddy

Quote from: Teddy on July 27, 2013, 04:58:20 PM
hey, did you check the .zip files containing mp3's?

they were posted an hour ago

please, comment on them
is there anything wrong, or am i just dreaming...

As I don't have one to compare (yet), I don't really qualify to comment on them.
Through notebook speakers it doesn't sound too bad to me ;)
Need to listen again through my nearfield monitors.

What settings did you use?

Hey, im not sure of the settings, as i haven't put knobs on it =) =) =)

I think there's too much noise when using the long delay time

Oh, and to your suggestion on debugging the circuit:



When you say, probe after the first PT2399:

do you mean to sound probe after R14?
Where it connects to R21,R15, and R16?

Yes, or before R14 directly after C16.

Okay, i probed after c16

probe result: i hear a delay, that has a slightly noisy artifact.

-Teddy

Noisy or distorted?
Next queck at C31.

noisy, not distorted...

ps. i did reflow some solder joints that seemed bad, and i think the distortion vanished.

but now i'm struggling with the noise/hiss issue

Quote from: Teddy on July 27, 2013, 05:35:00 PM
ps. i did reflow some solder joints that seemed bad, and i think the distortion vanished.

Bingo! Congratulation!

I presume this is the same point as point A on the rotary selector.

I hear a delay, its ok sounding. A bit of hiss.

But the problem with hiss is, that when i play while the delay is sounding,
the noise somehow amplifies. it's hard to say how it is, but that's
why i posted those sound files. =)

Thanks,
-Teddy

Quote from: Teddy on July 27, 2013, 05:35:00 PM
but now i'm struggling with the noise/hiss issue

Perhaps you should try a few different PT2399 more?
They seem to vary much in quality.

will do!

i'll report after changing PT2399's.

- Teddy

Okay, i changed the PT2399. Last fresh pair i have.... =)

Tone changed a bit, but the hiss problem is still there.

I'll post a new sound sample soon.


Thanks,
- Teddy

Here i go again =)

attachment long_delay_2.zip
contains long_delay_2.mp3

Is it just me, but do i hear a lot of sizzling noise on the repeats?

Thanks,
-Teddy

OK, I can hear the hiss. Don't know how much is normal.

Is it the same in every filtering mode?
It shouldn't. Depending on the selected filter more or less hiss should go away.

Yes, the hiss is the same on every filtering mode.

Hiss goes away a little, when delay is shorter.

I'll try probing to find out when the hiss starts.

- Teddy

Well, the odd thing is, that the hiss is louder when guitar signal is present while the delay sounds.
Like, playing a chord and holding it, instead of quickly strumming and muting strings.

Any ideas?

Also, when delay is turned down, the hiss is less audible.

Thanks,
-Teddy

There's no hiss on the dry signal with mix all the way down?

The hiss is on the wet signal (the delays) only?
It is stronger while there's also a dry signal?

Dry signal is good, with mix down. No hiss, when mix is all the way down.

The hiss is on the wet signal only (delays).

The hiss is stronger when there's also a dry signal.

Thanks,
-Teddy

Quote from: Teddy on July 28, 2013, 10:56:30 AM
The hiss is stronger when there's also a dry signal.

But the hiss is already in the dry signal (after the mode switch or at the mix pot)?

No hiss in the dry signal.

-Teddy

Oops, sorry, wanted to ask:

But the hiss is already in the wet signal (before or after the mode switch or at the mix pot)?
So we can rule out the dry path and the mix stage.
The hiss comes from somewhere in the wet path.

Does this his go away with lower guitar levels?
The dry signal always also goes into the first delay line.
So the hiss could come directy from within the first PT.

I'm not sure, if the hiss is present before or after the mode switch or mix pot.
(i will probe it today)

Hiss doesn't go away with lower levels.

Thanks,
-Teddy

I don't see voltages anywhere in this thread.  Posting voltages of the IC's may possibly help.

Josh

Hello!

What voltages do you need, specifically?

Thanks,
-Teddy

Hello!

One more audio clip.
long_delay_noise_3.zip

Delay = MAX
MIX = MAX

This clearly shows the issue.

When delay is backed down, to almost minimum, then there is almost no noise.

Oh by the way, the distortion exists before the filtering section, probed it.

Thanks,
-Teddy

Voltages of IC3 measured against GND

1 VCC = 5.02V
2 REF = 2.436V
3 AGND = 5.5mV
4 DGND = 5.5mV
5 CLK O = 2.997V
6 VCO = 2.436V
7 CC1 = 0.690V
8 CC0 =0.690V

9 OP1-OUT = 2.437
10 OP1-IN = 2.434
11 OP2-IN = 2.433
12 OP2-OUT = 2.433
13 LPF2-IN = 2.436
14 LPF2-OUT = 2.442
15 LPF1-OUT = 2.436
16 LPF1-IN = 2.436

Voltages of IC 2 measured against GND (they are essentially the same as IC3...)

1 VCC = 5.02V
2 REF = 2.439V
3 AGND = 5.7mV
4 DGND = 5.7mV
5 CLK O = 3.043V
6 VCO = 2.436V
7 CC1 = 0.685V
8 CC0 =0.690V

9 OP1-OUT = approximately 2.45volts, every pin from 9 - 16
10 OP1-IN =
11 OP2-IN =
12 OP2-OUT =
13 LPF2-IN =
14 LPF2-OUT =
15 LPF1-OUT =
16 LPF1-IN =

Well, if there's anything more that comes to mind, that would help with my build of ZPSDX,
i'd really appreciate it.

Thanks,
-Teddy

Quote from: Teddy on July 28, 2013, 04:06:29 PM
Voltages of IC3 measured against GND

3 AGND = 5.5mV
4 DGND = 5.5mV

Voltages of IC 2 measured against GND (they are essentially the same as IC3...)

3 AGND = 5.7mV
4 DGND = 5.7mV

Shouldn't those be at 0.0V?

I put the GND of multimeter to 9V wall wart power supply -

when checking with continuity meter, i get 0.6ohms resistance, measured
from AGND/DGND to GND.

I quess, that explains why i see 5.7mV.

What do you get if you check against the G pad on the board?

When measuring against board GND, i get 0.00V

So that's fine.

The other voltages look reasonable to me.
Perhaps someone can compare them to an actual build.

Ok, what's next?

Quote from: Teddy on July 28, 2013, 02:56:06 PM
One more audio clip.
long_delay_noise_3.zip

Delay = MAX
MIX = MAX

This clearly shows the issue.

When delay is backed down, to almost minimum, then there is almost no noise.

So the dry signal is clean as long as there are no delays mixed in.
The delays are OK as long as there is no dry signal.
While the dry signal sustains and delays are mixed in there is hiss.

As this also happens at lower levels I don't suspect the mix stage (IC1B).
So the hiss probably is generated within IC2/IC3 or around them.
The ghost switch is off? (Have you checked R21/R22? They are on a path where dry signal could bleed into the delays if they are too low.)

R21 checked = 220k
R22 checked = 150k

This hiss. You not only hear it at the output but also in the wet path after the first delay line?

yes, it's in the wet path as well.

but i have to sound probe again, to be sure about first delay line.

But when probed from after C31, i'ts hissy and dirty. (selector point A)

And, when i turn delay time to shorter, the dirtiness vanishes.
When delay time is minimum, sound is ok.

Quote from: Teddy on July 28, 2013, 05:54:30 PM
when i turn delay time to shorter, the dirtiness vanishes.
When delay time is minimum, sound is ok.

As already mentioned this is to be expected, to a certain degree.
PT2399s are far from being HiFi.
But these are really hissy. And I suspect it's them.
All from the same batch?

yes, all are from the same batch
from the same vendor

I will go tomorrow to shop more PT2399
From a different vendor.

But hell, i went through 6!! of the PT2399, and none work.

damn... if it's the PT2399's.

=)

-Teddy

If you're positive that the component values and the soldering are right then perhaps you should try to get different PTs.

You don't happen to have a Rebote Delay or Cave Dweller nearby to test them?

Sorry, I have no more ideas, at least for today.

No, i don't have other delay pedals to try PT2399 with.

Your sound samples sound right. I'm not sure what you're expecting out of the PT2399 delay chips, but I don't hear anything abnormal there, and they're always going to have some noise at longer delay settings, and it's going to sound cruddy in some filter settings because the bandwidth is larger than the chips are made to handle.

Also, I mentioned that you can measure the voltage at pin 7 on the PT2399s while playing. If you're seeing anything around 2v or higher, your pickups are probably just overdriving the chips. I don't see that you did this. If you're using humbuckers or even higher output single coils (like ceramic pickups in some Fenders), you can easily overdrive the PT2399, and no amount of debugging or swapping chips is going to do anything about the fact that your signal is exceeding the power rails that the chip runs on.

Finally, just a note about some netiquette: you're waiting less than an hour sometimes before bumping your thread, sometimes adding more information and double and triple posting. This has made it very hard to follow your debugging and has cluttered things up. It would also help if you followed the template in the Tech Help Rules thread and very clearly laid out all the information in one place for everyone. We don't have the circuit in hand and you're spoonfeeding us vital information only when pressed for it. The Rules Thread specifies what is needed to help debug for a reason.

Hello!

I've been too enthusiastic about this build,
sorry for posting too much.