"Little Angel" - Super Simple PT2399 Mini Chorus

[jfrabat]

By the way, the 1N4148 is in fact going to ground, in case that's important...  all other readings are sa,e as above.

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[EBK]

Hmm..  so something else (cap or diode, likely) is pulling that voltage down... We can set aside the possibility of bad transistor for now.... Edit: Hmm....

[jfrabat]

Audio probe. You should hear the input on the PT2399 pin 15. That is the point at which the input goes into the delay.

You should hear delayed signal out of its pin 12. This is where it comes out of the delay. If there is signal out of pin 12 then it is working with "some" delay.

I got signal in pins 9, 12, 14 and 15 (only checked that side) on the PT.  On the TL, only on pin 1... that does not sound right, though, right?

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[jfrabat]

Swaped TL082 for TL072.  still only pin 1 has signal..

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[anotherjim]

An inverting op-amp:-
The +input (Pin3) has the DC reference voltage. No signal.
The output (Pin1) is the signal output. We expect signal.
The -input (Pin2) is a "virtual ground" if it's working properly. Would you expect signal on a ground? No signal is correct.
The input signal will be present at the input end of any resistor feeding the -input, not at the pin.

The same will be true of all the internal op-amps in the PT2399, which are all fixed as inverting. So you find signal on pin15 (output) but not on pin16 (-input).

That 1N4148 should indeed have it's cathode tied to Vb (5v). As it is, it's a coin-toss as to whether the diode or the transistor base-emitter will have the lowest forward voltage drop. If the diode's drop is higher (they often are but NOT always), it is having no effect on the transistor and not really doing anything at all. If the diode drop is lower then it will steal current from the transistor base-emitter and prevent the transistor turning on fully or never.

Please read back for the earlier trouble shooting hints. If you remember, those earlier attempts were sabotaged by faulty PT2399's.

[jfrabat]

An inverting op-amp:-
The +input (Pin3) has the DC reference voltage. No signal.
The output (Pin1) is the signal output. We expect signal.
The -input (Pin2) is a "virtual ground" if it's working properly. Would you expect signal on a ground? No signal is correct.
The input signal will be present at the input end of any resistor feeding the -input, not at the pin.

The same will be true of all the internal op-amps in the PT2399, which are all fixed as inverting. So you find signal on pin15 (output) but not on pin16 (-input).

That part I get; but isn't Pin 7 also an output?  Should there not be any signal at Pin 7?  Or am I missing something?

That 1N4148 should indeed have it's cathode tied to Vb (5v). As it is, it's a coin-toss as to whether the diode or the transistor base-emitter will have the lowest forward voltage drop. If the diode's drop is higher (they often are but NOT always), it is having no effect on the transistor and not really doing anything at all. If the diode drop is lower then it will steal current from the transistor base-emitter and prevent the transistor turning on fully or never.

So, how do I test this?  Do I remove the diode and jump it to 5V?

Please read back for the earlier trouble shooting hints. If you remember, those earlier attempts were sabotaged by faulty PT2399's.

The PT's were actually all working; we thought they were faulty, but they all proved to be working when I tested them one by one in the Deep Blue Delay...

[anotherjim]

TL072 pin 7 is indeed an output. However, there is no audio signal feeding any of its inputs. This op-amp is part of the LFO sweep oscillator, without which, there cannot be a chorus effect.

You can remove that diode for now. It is not essential.

[jfrabat]

TL072 pin 7 is indeed an output. However, there is no audio signal feeding any of its inputs. This op-amp is part of the LFO sweep oscillator, without which, there cannot be a chorus effect.

You can remove that diode for now. It is not essential.

OK, now it makes sense.  I will remove the diode and give it a go tonight.

[jfrabat]

UPDATE: I was looking over everything, and I noticed for some reason or another, I had swapped one of the pot's pins.  I decided to just wire the pots directly to the board instead of using wires (since I am making a new enclosure anyway, it's not really worth the trouble of using wires).  Tried the board.  Same thing.

So I figured the diode could be the cause.  Un-soldered one pin and tried it.  No change.

When I went to pick up the board, I got singed by something hot.  Turns out the 78L05 was hot enough to burn.   I thought maybe it was damaged, so I replaced it.  Same result (and new one still gets as hot as the old one).

Somehow I think the 78L05 should get hot, but not THAT hot, right?  What else could be the problem here?

[EBK]

Hmm.... Something is drawing too much current.  This is without the transistor and without the diode?

[jfrabat]

Hmm.... Something is drawing too much current.  This is without the transistor and without the diode?

With transistor.  With and without diode is the same.

[EBK]

I find myself wondering if you have bad transistors.  Does the regulator get hot without the transistor in the circuit?

Luckily, those regulators have a thermal shutdown circuit, so they should still work after burning your fingers.

If you still get a lot of heat off that regulator without the transistor, replace the electrolytic cap that connects to that diode.

Could you take a look at R8? In two of your pics, it has this hideous, pale look, but in another, it looks fine.  It's bugging me.   

[EBK]

Ok, new readings of Q1 at the socket:

C: 2,43V
B: 0.455V
E: 0

This is with the 2N2222 out...

This is so odd.  Was this without the diode too?  If so, the only thing left is that electrolytic cap, acting like a 6k7 resistor.  Or, your 68k resistor is WAY out of spec.
Either way, they don't explain the regulator heating up.

[jfrabat]

Ok, new readings of Q1 at the socket:

C: 2,43V
B: 0.455V
E: 0

This is with the 2N2222 out...

This is so odd.  Was this without the diode too?  If so, the only thing left is that electrolytic cap, acting like a 6k7 resistor.  Or, your 68k resistor is WAY out of spec.
Either way, they don't explain the regulator heating up.

Those readings I took with the Diode in place. 

I find myself wondering if you have bad transistors.  Does the regulator get hot without the transistor in the circuit?

Luckily, those regulators have a thermal shutdown circuit, so they should still work after burning your fingers.

If you still get a lot of heat off that regulator without the transistor, replace the electrolytic cap that connects to that diode.

Could you take a look at R8? In two of your pics, it has this hideous, pale look, but in another, it looks fine.  It's bugging me.   

OK, this weekend I will try it without the transistor and see if it still gets hot.  I will also replace R8 (68K) and the cap (you are talking about C13, right?)



Tonight, though, I plan to enjoy the football (as in the sport you play with your feet, not the other football that's played with your hands!) game between Costa Rica (where I live) and Panama (where I am from) for the World Cup elimination round.  GO PANAMA!

[EBK]

(you are talking about C13, right?)

Yes

Tonight, though, I plan to enjoy the football (as in the sport you play with your feet, not the other football that's played with your hands!) game between Costa Rica (where I live) and Panama (where I am from) for the World Cup elimination round.  GO PANAMA!

Enjoy!

[jfrabat]

Hi, guys.  I have been messing with a bunch of other pedals, but this one is still on my to do list.  So after 4 unsuccessful builds, I did the only reasonable thing; I ordered ANOTHER board (different supplier this time) and gave it a shot.  Unfortunately, I am getting the SAME results.  I get the dry signal coming through, but not the wet signal.

This is the board from JMKPCBs (the one I made some time back; actually, I made 2 of these, but this is the second one):



This is the newer board (from DELYKPCB):



I will continue troubleshooting the first one simply because I have the schematics for that one and not the new one (on these build docs).  Here's the schematic:



Here is what the pedal is doing (and yes, I tried it with the guitar; there is only dry signal):

Now, last time I took voltage readings, this is what I got:

Battery: 9.20V

TL082:
1: 4.68V
2: 4.68
3: 4.53V
4: 0V
5: 2.80 to 3.70V
6: 2.88 to 3.65V
7: 0 to 1.4V
8: 9.20V

78L05:
IN: 9.2V
GND: 0V
OUT: 5.01V

2N2222:
C: 0V
B: 0.449V
E: 2.43V

PT2399:
1: 5.01V
2: 2.5V
3: 0V
4: 0V
5: 3.40V (should be around 2.65V)
6: 2.43V (should be 0.61V)
7: 0.875V
8: 0.995V
9 to 16: around 2.5V with movements

As I mentioned on the video, the 78L05 is still getting hot as well.  Also, all my PT's checked out in the Deep Blue Delay, so I know they work (at least all the chips work on the delay pedal).  Any ideas what I should look at?

[Slowpoke101]

Just quickly.

The first picture (the one with the two pots mounted directly to the board) has a LM13700N OTA where the PT2399 is supposed to go. What happens when a PT2399 is installed?

Any chance of some pictures of the solder sides as well?

[jfrabat]

Just quickly.

The first picture (the one with the two pots mounted directly to the board) has a LM13700N OTA where the PT2399 is supposed to go. What happens when a PT2399 is installed?

Any chance of some pictures of the solder sides as well?

Oh, whao... I missed that one!  Let me put the right chip in and get back to you...

[jfrabat]

I think I know what is going on here...

Thanks to my previous error, I unplugged the pedal, and changed chips.  Put the new chip in, but forgot to plug the battery.  Since everything was running, as soon as I plugged the battery, I put the probe on the OUT pad, and VOILA!  MODULATION!  So I ran over to my guitar, but NOTHING!  Hmmmm...  Went back to the bench, and tested the signal; no modulation.  Now, the only explanation I have is that my PT's are going into lock up.  The thing is that I have 16 of them, and they all act the same way!  Is there a way to prevent lock up?

The odd thing is that the pots do not affect the modulation I am hearing.  In all the videos I have seen when you turn the pots, the PT will make an ATARI like sound while they are moving....  But not here.  I tried to make a video, but it is difficult to note the modulation sound on the video, but there IS modulation.  That is a step forward!

I will post the video tomorrow (it is loading).  Maybe it helps (but as I said, it is hard to hear the modulation in the video).

[Slowpoke101]

Just had a quick look at the smaller board. Noted the following;

R1 appears to be 68R (or is it 6R8) not 68K. D1 and Q2 may be toast.
R7 appears to be 10K not 330K
R12 is obscured and not readable. Supposed to be 4k7.
Q1 (78L05) regulator appears to be in backwards. Remove PT2399 and measure the voltage on pin1 of the socket. 5V is expected but will be much higher if in backwards.

All these observations were taken from the doco on the deluk website.

PT2399s can and do lock-up. Usually this happens when too much current is taken from pin6 before the chip has stabilized after power on. That is the reason for the delay circuit (Q2, etc) on pin6, it gives the chip a chance to stabilize.
Sometimes a locked-up chip stays that way after power down (weird but it happens). Take the chip out and short out its legs on a conductive metal plate (copper clad board is good) wait a minute and try the chip again.

Haven't checked out the first board yet (other than the LM13700 oops). I'll get there or someone else will.