Author Topic: Little angel chorus issues  (Read 1083 times)

Unclereaper

Re: Little angel chorus issues
« Reply #20 on: September 07, 2020, 06:57:43 PM »
Its was in when I tested it all

Unclereaper

Re: Little angel chorus issues
« Reply #21 on: September 07, 2020, 06:58:14 PM »
It was in when I tested it all

anotherjim

Re: Little angel chorus issues
« Reply #22 on: September 08, 2020, 04:54:18 AM »
I would test without the PT2399. There is a path for clean audio through 1C1 so you should prove you can get it and prove the 5v regulator is giving 5v to IC1 via its pin3 as explained earlier.
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ElectricDruid

Re: Little angel chorus issues
« Reply #23 on: September 08, 2020, 07:54:14 AM »
Ic1 4.8.  2.9  3.5  0.02  2.1. 2.4.   2.2.  6.7. Ic1 pin 3-4 pass continuity

If 3+4 have continuity, something weird is going on, because you've got different voltage readings for two pins which are supposed to be connected together. Can you check to see what's happening?
I think IC1 is the dual opamp Tom.

Gah, I'm going to stay out of this from now on! I seem to keep getting the stick by the sticky end. ;)

Carry on, everyone. Good luck!

rankot

Re: Little angel chorus issues
« Reply #24 on: January 30, 2021, 03:55:24 PM »
I have the very same problem - sound is passing, but no chorus.

Measured everything, but voltages on PT2399 pins 5&6 are suspicious:
1 5.0
2 2.5
3 0.0
4 0.0
5 2.1
6 0.46
7 1.03
8 1.03
all the rest sit at 2.5V

Schematic is here:


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anotherjim

Re: Little angel chorus issues
« Reply #25 on: January 30, 2021, 04:52:58 PM »
Standard advice.
Don't attempt to start testing with the go-faster low resistor (your R23). If it won't run without that, suspect a latch-up of the PT2399. With power off, short all its pins out with some metal foil for 10 seconds or so - this to discharge any static build-up in the chip.
Test again in your vibe mode, starting with the minimum LFO depth. If hear signal, increase LFO until you hear pitch warble.

In my experience, the chip doesn't much like running above 21Mhz or so. Can you measure the frequency on pin 5?
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rankot

Re: Little angel chorus issues
« Reply #26 on: January 31, 2021, 11:09:27 AM »
Standard advice.
Don't attempt to start testing with the go-faster low resistor (your R23). If it won't run without that, suspect a latch-up of the PT2399. With power off, short all its pins out with some metal foil for 10 seconds or so - this to discharge any static build-up in the chip.
Test again in your vibe mode, starting with the minimum LFO depth. If hear signal, increase LFO until you hear pitch warble.

In my experience, the chip doesn't much like running above 21Mhz or so. Can you measure the frequency on pin 5?

I have removed R23 and tried to sweep LFO depth in "Vibrato" mode (so no original signal), but it's doing nothing. It just seems that the attack of the note is lost, but no delay at all. This is what I have at pin 5 of PT2399 - don't mind that reflection from my lamp, it's almost good square signal. Div size is .1us, so I have nine periods at 8 divs. It is 11.25MHz, right? It seems that LFO's not working. I don't see any voltage variation on pin 2.

This is what I have at pin 5:


Also, without R23, pin voltages are like this:
1 5.0
2 2.5
3 0.0
4 0.0
5 2.87
6 2.47
7 0.66
8 0.66

So there's a difference at pins 5, 7 and 8.

Also tried to use another op amp (TL 072 instead of RC 4558), but no difference at all.
« Last Edit: January 31, 2021, 11:37:34 AM by rankot »
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anotherjim

Re: Little angel chorus issues
« Reply #27 on: January 31, 2021, 02:53:26 PM »
I'd say the clock VCO is now working. However, the audio needs investigating. The attack only sound suggests heavy gating. This could be because it getting through via leakage/capacitive coupling.
Input audio heard at pin15 suggests the input opamp is good. Audio out at pin12 suggests the delay line is working.

I have damaged some PT2399's. Its opamps and clock worked. I put it down to excessive voltage swing applied to pin 2.
Others have fixed them by the discharge with foil trick.
Croeso i Diystompboxes.