Problem with my PT-80

[balthazar40]

Sorry, dass ich auf English schreibe. Sagen Sie mir Bescheid, ob dass ein Problem ist. Danke !

I am currently building a PT80, and it doesn't work as expected. (or at all)
It doesn't really sound like a delay. I did ear something that sounded like a delay once though (wonder if it's a bad contact)...

Most of the time, the simply pitch gets higher and louder, until it emits a high frequency at maximum volume.
Imagine a 1000Hz frequency, multiplied by a xHz frequency, where x would be a time based on the Time knob. PRiRiRiRi !

In a nutshell, as soon as you start it with an input, it acts much more as an oscillator / frequency generator !

I looked at all the solderings, they seem okay. Also looked at the connections, seem okay too. I compared to the measurements I could find on GGG, they were quite similar, and I would expect that the slight differences would be caused by using different component values than GGG.

I am really not sure where to go from there, any help would be appreciated !

Here are my measurements:
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TL072 IC

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IC Pin 1    6.16
IC Pin 2    6.16
IC Pin 3    6.16
IC Pin 4    .0012
IC Pin 5    5.37
IC Pin 6    6.16
IC Pin 7    6.16
IC Pin 8    12.3

PT2399 IC

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IC Pin 1    5.08
IC Pin 2    2.54
IC Pin 3    0.0028
IC Pin 4    0.0028
IC Pin 5    2.75
IC Pin 6    2.53
IC Pin 7    0.9
IC Pin 8    0.9
IC Pin 9    2.54
IC Pin 10   2.54
IC Pin 11   2.54
IC Pin 12   2.54
IC Pin 13   2.54
IC Pin 14   2.54
IC Pin 15   2.54
IC Pin 16   2.54

SA571 IC (NE571, etc)

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IC Pin 1    0.89
IC Pin 2    1.79
IC Pin 3    1.79
IC Pin 4    .0018
IC Pin 5    1.79
IC Pin 6    7.28
IC Pin 7    7.27
IC Pin 8    1.79
IC Pin 9    1.79
IC Pin 10   5.33
IC Pin 11   1.79
IC Pin 12   1.79
IC Pin 13   12.3
IC Pin 14   1.79
IC Pin 15   1.79
IC Pin 16   1.26

TC1044S

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IC Pin 1    9.36
IC Pin 2    4.79
IC Pin 3    .00026
IC Pin 4    -.0005
IC Pin 5    .0025
IC Pin 6    4.51
IC Pin 7    5.89
IC Pin 8    9.37

Vielen Dank für die Hilfe !

[Uwe K.]

HI,
Difficult to evaluate with a remote diagnosis. The tensions agree in all cases. You should first take the PT2399 from the socket and make as amended a bridge of 14:16, as amended. Thus the signal path of the PT is bridged. Level control to the right and the clean signal must be heard.
If this works, only the PT2399 may be defective, but this has never happened with proper handling. And a few hundred are already through.

sorry for bad english

regards Uwe

[balthazar40]

Hallo Uwe,

vielen Dank für die Antwort ! Das ist sehr interessant.

Muss der Untershied groß sein, wenn ich den Level knopf benutze ? (mit einer direkten verbindung zwischen pin 14 &16)
Ich höre nur einen kleinen Untershied, zwischen Min und Max. Es existiert, aber für mich, dass ist circa 10% des Kompleten Signals.

---
clarifications in english: I connected the pins 14-16, played a bit, and it took me a second to actually notice the effect of the level knob. So I do hear the clean signal very well, plus a little 10% difference when playing with the knob. Is that how it's supposed to be ?

This is my 4th build, but 1st experience at really trying to debug a circuit.
I am unable to find any obvious mistake...
Thanks for the help, I really appreciate this !

Richard

[balthazar40]

N.B. Ich hatte eine andere PT-2399 zu hause, und habe damit das gleiche Problem.

[balthazar40]

After half a day of debugging the thing, I found that I simply cannot use the Repeat knob above 12 Oclock.
Anything between 12' and Max will end up with an oscillation... (and my ears hurting)
Otherwise, the delay seem to "work".
I'll keep investigating, and post on other forums, where someone might have an idea.

Edit: this is my problem. I'll try the trimpot solution.
http://www.diystompboxes.com/smfforum/i ... ic=34862.0

[Uwe K.]

Hi,
The repeat resistor in the layout is a 27K and greater then in the normal layout from the PT2399 (22k). The repeat funktion Is also dependent on the level at the Poti level (Dry/wet). If the the level knob in the max. (right postition) the full level goes to the repeat pot. Then is normal that the delay oszillated.

regards Uwe