Pitch Witch trouble

[MaWi]

Hi everyone,
this is my first post here; I just finished a Pitch Witch, and it works somehow, but not as it should.
Bypass works.
The on/bypass LED works, though I´m not sure it it supposed to blink when on.
The delay part works, although all the delays come with a very ugly buzzing/distorted sound .
The modulation part works, if I use a flashlight on the LDR; the yellow LED blinks, but very very dim, even in a dark room barely noticeable. It also blinks as dim in bypass mode, maybe it is supposed to do so?
I appreciate all your help, be patient, my understanding of all electronic things is sub-basic on a good day

 

[Nostradoomus]

Post some clear pictures so we can see what we’re working with!

 

[MaWi]

Yes, here you go,
Front:


The stuff on the 3PDT-board is just flux, there is no short.
And back:

There is no short between any of the pots and the pcb.
I hope the pictures can help.

 

[p_wats]

Built one of these recently too. The bypass LED intentionally blinks with the LFO.

How are you voltages looking?

Have you adjusted the trumpet to avoid distortion?

Where did you get the PT2399 chip?

Oh, and most common with this build us the dual pot shorting against the circuit. Do you have anything between the pots and the circuit board?

 

[MaWi]

Thanks for Your reply,

I have played with the trim, but everything louder than "nothing" gives me this buzzing on the delays.
I bought this as a kit here: https://www.musikding.de/Pitch-Witch-Bausatz , the PT2399 was included.
I have definitely no shorting between any of the pots and the pcb.
I don´t know what to look at with voltage, as I said, my knowledge of all things electronic is nearly nonexistent; I have a DMM, though I need instructions where to measure what...

 

[p_wats]

Sorry to belabour this point, but how are you sure there is no shorting between the board and the pots? I don't see anything separating them---many pots come with plastic covers on the back, or they can be bought separately to ensure no shorting. On my build I had to use a layer of foam between the dual blend pot and the board, otherwise it would have touched and caused issues.

If the back of the pots touches the connections on the board you could be in trouble (which is a very common error with this build).

Probably not the problem, but the photo makes it look like the + connection (red wire) could use some more solder.

Is there a lot of flux on the board? Looks very shiny/slick. Might not be an issue, but some folks would recommend cleaning the board with isopropyl alcohol.

Hard to tell from the photo, but which opamp are you using using (bottom right IC)? Can't tell from the photo, but make sure pin 1 is in the top left of that socket.

For measuring, if you connect the black wire of your DMM to a ground point (one of the jacks or a "-" pad on the board, for example, you can then use the red wire to take voltage readings (you could try the outer legs of your regulator, to ensure 9v on one side and 5v on the other, then you could measure all the 2399 pins).

Have you ever used or heard of an audio probe? That would be really helpful too.

 

[MaWi]

Thanks for your reply,

I put stripes of thick plastic sheet between pots and pcb, I just removed them for the pictures.

The "+" connection is good, the photo makes it look like it has not enough solder.

I will try to remove the flux, I thought this was not necessary, as the solder was of the "no clean"-variant.

The opamp is RC4558, I´ll check the orientation, but I am pretty sure that is is ok.

I will measure the chips.

Not sure about the audio probe; my DMM has a mode where it gives an acoustic signal to test for continuity, is this the same?

 

[MaWi]

So, I measured the PT2399 and the result is
1: 4.98
2: 2.49
3: 0
4: 0
5: 2.8
6: 2.49
7: 0.85
8: 0.85
9-16: 2.49

seems weird, that on the 9-16 side all pins have the same value?

 

[MaWi]

More numbers:

LM386 (IC1)
1: 1.34
2: 0
3: 0
4: 0
5: 4.29
6: 8.78
7: 4.43
8: 1.34

RC4558 (IC4)
1: oscillating, 3.4-5.1
2: 4.4
3: 4.4
4: 0
5: oscillating, 2.8-5.7
6: 4.4
7: oscillating, 1.9-7.3
8: 8.78

78L05 (IC2)
output: 4.98
input: 8.78
common: 0

I hope this helps you guys to help me

 

[zgrav]

looks like your pcb and the footswitch would benefit from cleaning with a toothbrush and isopropyl alcohol. even when the solder says "no residue" it still is a good practice to clean the board. the connections on your footswitch have a lot of solder on them -- much more than you needed to get a good connection. heat can damage the connections and reliability inside the footswitch, so that is one reason it is better practice to get a good connection with less solder.

putting together an audio probe will let you trace your audio going through the pedal to see where your distortion is coming from.

 

[MaWi]

Thanks for your tips,
I looked into the audio probe, it seems easy enough, I´ll build one later this evening, I hope it gives me a hint about the buzz/distortion; I find it weird, that this buzz/distortion is only on the delays, the original guitar sound is fine.
And that still leaves me with the too dim yellow LED.

 

[p_wats]

Thanks for your tips,
I looked into the audio probe, it seems easy enough, I´ll build one later this evening, I hope it gives me a hint about the buzz/distortion; I find it weird, that this buzz/distortion is only on the delays, the original guitar sound is fine.
And that still leaves me with the too dim yellow LED.

Just to clarify, the delay signal in this circuit is pretty lo-fi. As you get longer with the delay times the result will be noisy/dirty repeats---that's just the nature of this circuit.

If you turn the delay time to more of a slap-back setting and lower the blend a bit, do you still get distortion?

 

[MaWi]

Yes, even with slap-back and low blend this noise is there.
though It is not like the delay itself is distorted, it is like this: I hit a string, and as soon as the first delay sound comes (no matter short or long delay time), a layer of buzz is added on top of the delay and the original sound.

 

[p_wats]

For what it's worth, in my build I went with a TL062, instead of the 4558, as I found that to increase ticking/noise.

 

[MaWi]

Maybe using a TL062 is something I look into in the future, first I need to get the modulation working and get rid of that ugly buzzzzz...

 

[MaWi]

Ok, I build an audio probe last night, but honestly I have no Idea how to go on now. I learned that I have to follow the audio path in the schematic of the circuit, but I don´t know enough to read the schematic. If someone of you guys could mark the path in the schematic or make a list of the components I have to check, would be very helpful.

 

[MaWi]

Quick update:
I swapped the yellow LED for an ultrabright green one (didn´t have any more yellow ones), wich I bended so that the light shines directly on the LDR, and now the modulation works.
So far success.
The ugly buzz is still there; I re-soldered every single connection and made sure the hammond is groundet properly, but to no avail.
I found out, that the depth pot (top left in second picture) influences the bzzzz; if depth is turned all the way clockwise, noise is gone, when turning counterclockwise, buzz gets more.
Any ideas?
Damaged Pot?
One of the chips not good?

 

[markseo]

Hey! Did you find a solution? I am more or less having similar problems... I have changed the LDRs position and now I have much better modulation (also at first I was doing my tests either outside the enclosure or with the case open, so there was a lot of luminc contamination for the LDR to work properly). But I am getting a very buzzy and noisy sound altogether and I seem to only get an effect when the delay is on (even at almost 0). Any inside would be great

 

[matito33]

Yes, here you go,
Front:

View attachment 9616
The stuff on the 3PDT-board is just flux, there is no short.
And back:
View attachment 9618
There is no short between any of the pots and the pcb.
I hope the pictures can help.

Hello! How did you connect the double potentiometer, the B50k on the right side? I cannot find the information online and cant see the connections on your picture properly... Thanks!

 

[UnAnimus]

Hi - Similar problem here.
I bought a kit from Musikding. The modulation works just fine, but the delay signal has a crackling/static sound when connected to the amp. I aslo tried it on a Nux Mighty Air (a mini modelling amp with wireless plug). In this case, the audio defect didn't come as a crackling noise, but rather as a high pitched whine.

If the noise was constant it could be rather cool (a sort of added lofi component), but since it comes with the delayed signal it gets really percussive and really annoyingly in your face.

I've tried it in the metal box and outside of it. Same problem. Tried resoldering all the joints. Same problem. The pots have isolating stickers on the backs.

Wit all knobs set around noon, I get similar voltages as MaWi:
IC1
1: 1.30
2: 0
3: 0
4: 0
5: 4.35
6: 8.70
7: 4.35
8: 1.31

IC2
output: 5.02
input: 8.72
common: 0

IC3
1: 5.01
2: 2.51
3: 0
4: 0
5: 2.78
6: 2.51
7: 0.14 (differs from MaWi's reading; sensitive to knob settings)
8: 0.74 (differs from MaWi's reading; sensitive to knob settings)
9-16: 2.51

IC4
1: oscillating, 3-5ish, i have an old & poor dmm
2: 4.37
3: 4.37
4: 0
5: oscillating, 3-5ish, i have an old & poor dmm
6: 4.35
7: oscillating, 2-7ish, i have an old & poor dmm
8: 8.71

Finally, a pic of the "upside" of the PCB mounted in the box.

Any help is appreciated!