"Little Angel" - Super Simple PT2399 Mini Chorus

[jfrabat]

OK, I resoldered the spots that seemed that had no contact on the top layer, changed the PT for one on the Deep Blue Delay BB (so I could be 100% sure it worked) and tried the pedal.  No change.  This is REALLY frustrating!  Any ideas on what to check?

[EBK]

 What's your supply voltage measuring?
Could you double check the color bands on R8? They look off....
Did you end up socketing a replacement transistor?

Also, could you take a picture of the markings on your transistor?

[jfrabat]

What's your supply voltage measuring?
Could you double check the color bands on R8? They look off....

I checked the bands and its OK.  You probably noticed on a different pic the same, right?

You probably saw this one too...  But just in case.  Values are:

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

Did you end up socketing a replacement transistor?

Yes



(perspective makes it look like a super tall transistor, don't it?)

Also, could you take a picture of the markings on your transistor?

Here:

[anotherjim]

With power off. The transistor and the PT2399 taken out. Measure the resistance between the PT2399 socket pin 6 and pin 4.

[jfrabat]

With power off. The transistor and the PT2399 taken out. Measure the resistance between the PT2399 socket pin 6 and pin 4.

2.2K. 

Looking at the diagram, it should be 2.2K, right?  Because the other grounds get disconnected as I take out the the transistor, right?

[anotherjim]

Correct, it should be 2.2k. I was asking to prove that there couldn't be a short circuit there, since removing the transistor made no difference. The PT2399 should run with 2.2k to ground from pin6, but yours doesn't seem to want to. There could still be other reasons for the fault, but I feel this should be checked out...
...so, the next thing I would do is to remove one end of that 2k2 from the board so you can temporarily solder a higher value resistor in its place - anything from 4.7k to 47k will do, just to see if you can get some delayed sound out of it. Keep the transistor removed for this test.

The Deep Blue, has a fixed resistor of 2.7k to pin6 (it's only the 2.7k when the delay pot is set to minimum resistance). I would be surprised if the difference between 2.2k and 2.7k is enough to make it work or not work, but I'd want to prove it.

[jfrabat]

At this point, Im willing to try anything, so thanks for the pointer.  How can I check if the signal (dry signal) is actually making it to the PT?

[anotherjim]

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.

[jfrabat]

I will test it tonight

[jfrabat]

Took a little hiatus...  Already finished an Engineers Thumb Compressor, and close to finishing a Deep Blue Delay (humidity permiting my painting it!).  Once that's all done, it's back to this one (the only one I have not gotten to work!).

Sent from my SM-G935F using Tapatalk

[jfrabat]

OK, guys, I still need help on this one.  I took some time off (well, not really "off", just changed projects and made some more pedals; I actually made the Engineer's Thumb Compressor, and a Deep Blue Delay clone, both of which are working wonderfully), but considering I have 2 of these boards built, and that neither one has worked, I wanted to get back to them and finally get one of these suckers to actually work.  Plus, I could really use a Chorus on this pedal board:


Got 5 pedals working (technically, 6, but I do not like the sound of the 6th); one that is not.  Not a terrible record, but lets make it better!

By the way, both the Screechy Cat and the Vulcan Rat overdrives are getting a make over and will be done in 1590B size; I have a board for a Phaser that I will build soon, and between that one and this pedal, I will need the space!  I also ordered a kit to make custom length cables to neaten everything up a bit.  I will not, however, use the old enclosure I made for the Little Angel because (1) I already used the same color for the Deep Blue Delay, and (2) I rather go smaller into the 1590B enclosure, but I will keep the same graphic style as the other one.  I'll just probably go with a metallic violet color or something along those lines...


Old enclosure

Anyway, where do I begin to check this darned pedal? As for the PT's, I tested them all in the Deep Blue Delay (when it was in BB form; I took that apart and actually built the pedal now), and they all worked.  The issue is still that the dry signal goes through, but not the wet signal (I get no chorus effect).

Here are my voltages:

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

[EBK]

Glad you still haven't given up on this! 

It's been a while, so we may end up rehashing stuff from before.
As for that transistor, I'm assuming the emitter is at 0V, not the collector, as you've listed it.

[jfrabat]

Yeah, that was a typo...

Sent from my SM-G935F using Tapatalk

[EBK]

Ok.  Looks like you have the same voltage on either side of R12 (the 100R resistor).  That suggests your transistor is not conducting.  This is consistent with the base voltage being so low.  Now, why isn't that base voltage getting any higher?

A test:
With the transistor out, measure the voltage at the middle pin of that socket (where the base would go).  That node should reach about 0.7V 5V.  if it does, then I would say you have a bad transistor.
If that voltage doesn't reach 0.7V 5V, then it could be a bad cap or diode.

There may be an error on your board.  I'm going back to find the schematic....

[jfrabat]

OK, Thanks!  I will test tonight.

Sent from my SM-G935F using Tapatalk

[EBK]

Hmm...  In the build docs for your board (http://jmkpcbs.com/wp-content/uploads/2014/10/Little-Angel.pdf), the schematic shows the diode on the base of Q1 going to ground, but other schematics show it going to +5V instead....

I've edited my test.

[jfrabat]

You know, I never actually checked the schematics of the JMK board, but you are right.  It is different from what I have found online for the Little Angel.  This is the one I was using when I did my own board:



And this is what the build docs show:



The diode is certainly going to GND (vs 5V).  Could that be the issue?

[EBK]

You basically had the same exact problem with each build, whether it was your own or theirs, right?
(Their board might be correct despite their schematic error.)

[jfrabat]

You basically had the same exact problem with each build, whether it was your own or theirs, right?
(Their board might be correct despite their schematic error.)

Yeah, but my first board was crap, and the second one, although better, I do not feel confident that the issue was not the board.

[jfrabat]

Ok.  Looks like you have the same voltage on either side of R12 (the 100R resistor).  That suggests your transistor is not conducting.  This is consistent with the base voltage being so low.  Now, why isn't that base voltage getting any higher?

A test:
With the transistor out, measure the voltage at the middle pin of that socket (where the base would go).  That node should reach about 0.7V 5V.  if it does, then I would say you have a bad transistor.
If that voltage doesn't reach 0.7V 5V, then it could be a bad cap or diode.

There may be an error on your board.  I'm going back to find the schematic....

Ok, new readings of Q1 at the socket:

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

This is with the 2N2222 out...

Battery measured 9V



Sent from my SGPT12 using Tapatalk