"Little Angel" - Super Simple PT2399 Mini Chorus

[anotherjim]

I don't think 68k would stop it and will be surprised if it turns out to be the main fault, although it would be nice if that was all there was to it.

[jfrabat]

Keep unused PT2399 to one side for now. If a fault is damaging them, you don't want to kill them all.
Apart from a typo just then, 1M is brown/black/green, you're reading the resistors correctly.

Sorry for the typo; you are right.  And you make a good point about the PT2399's...

As you have spare PT2399, you might consider something like the Deep Blue delay next, which also requires one, but doesn't press the chip to its highest speed range. Then you can check if all the PT2399's you have are basically functional before throwing them out.

Actually, I was considering building an Equinox II Reverb (it uses 2 PT2399), but the delay is not a bad option...  I think a reverb is a bit more useful than a delay, so I's going that way.  But theoretically (assuming the PT2399's are still good to go and not toasted!), I should have 3 of them left over, which makes the delay a very good possibility for the next build (even if the 2 used PT's are bad, I still have enough)!  Still, before either, I have to get my Vulcan Rat off the breadboard and into a box!

68k instead of 33k for R13 means the chorus effect won't go as deep or obvious as it should be. If you don't have 33k, solder another 68k across the existing one.

I will switch all 3 resistors (I just got some 33K's, so no problem there) tonight and test.  If it does not work, I will take R22 out and try.  If THAT does not work, then I will take the transistor out.  If it STILL does not work, then I will replace R21 with a 47K as suggested.  I will report back tonight...

Nice one Jim, I was just wondering how low the effect would be with that change to R13. The depth pots 470k so I wouldn't have thought it would remove the effect completely

You know, now that you mention it, I think I am actually using a 500K pot, not a 470K...  Just because I could not find any 470K locally.  I will double check when I get back home tonight!  But it should not make that much of a difference, right?

I don't think 68k would stop it and will be surprised if it turns out to be the main fault, although it would be nice if that was all there was to it.

So what's your gut telling you?  If you had to give your best guess, what would you say it's happening?

Thanks!

Felipe

[anotherjim]

My gut say's the PT2399's are locking up because they don't like the 100R timing resistor.
A little backstory.
A chorus effect needs a variable delay, but it can't be such a long delay that it sounds like echo. Ideally, that's not much longer than 20ms. To get delay that in that range, the PT2399 needs to be run with a very fast clock speed. That clock is controlled by pin6 with a resistor connected to ground. The smaller that resistor is, the shorter the delay is.

It's beginning to look like recent (maybe in the last 3 years) chips run faster in the sub 1k delay resistor range than originally and cannot work with them as small as 100R as it makes them try to run faster than they can.
In the LA design, Q2 together with a 68k and 47uF  have been added. The gives a time delay after power-on which allows the chip to start with the larger 2k2 resistor. Then when the cap has charged enough to switch Q2 on, it gets full speed with the 100R. This is because the PT2399 data sheet states that the pin6 resistor should not be less than 1k when power is applied.

Pots have a wide value tolerance. Measure some for fun. It's easily possible to have a 470k that is higher value than one marked as 500k. Generally, most electronics works fine if components are within +/-10% and once upon a time production circuits had to make do with 20% components. If a circuit needs a very close tolerance part, such as 1% resistors, the drawing/BOM will ask for it.

[jfrabat]

Resistors have been replaced.  Nothing.  Disconnected R22.  Still nothing.  Replaced PT back to the original.  Nothing.  Voltage readings with R22 unplugged:

Pin 1: 4.97V
Pin 2: 2.48V
Pin 3: 0V
Pin 4 : 0V
Pin 5: 2.73V (IMPROVEMENT!)
Pin 6: 2.4V (PROBLEM!)
Pin 7: 0.461V
Pin 8: 0.520V
Pins 9 to 16: 2.51V (with slight movement)

I do not see any obvious solder bridges near the PT:



And here are the new resistors in place, in case hou spot something off (R22 is removed on purpose):



Help is always appreciated!

Felipe

[jfrabat]

By the way, prior to taking out R22, the PT was getting pretty hot..  about as hot as when you touch a joint after soldering.

[chuckd666]

Felipe I think at this point it might be best to get out your multimeter and do a continuity check on every trace around the PT - sometimes when you make a PCB you can get cuts in the trace that aren't visible and can only be discovered by use of a multimeter.

[EBK]

Felipe,
I just want you to know that I'm still following this thread, silently cheering you on.  I really want this pedal to work. 

[bluebunny]

the PT was getting pretty hot

It's locking up, and probably toast.  Throw it in the bin.  (Although Pink Jimi claims he can bring them back to life!)  This is down to the resistance at pin 6 being way too low, as Jim has said.

[anotherjim]

Pin 1: 4.97V
Pin 2: 2.48V
Pin 3: 0V
Pin 4 : 0V
Pin 5: 2.73V (IMPROVEMENT!)
Pin 6: 2.4V (PROBLEM!)
Pin 7: 0.461V
Pin 8: 0.520V
Pins 9 to 16: 2.51V (with slight movement)

These value might (only might) indicate the chip is ok. There could be another problem.

[jfrabat]

Felipe I think at this point it might be best to get out your multimeter and do a continuity check on every trace around the PT - sometimes when you make a PCB you can get cuts in the trace that aren't visible and can only be discovered by use of a multimeter.

I did this before soldering components, but I will do it again to be sure all signals that are supposed to be there are, and those that are not are not there.  I think I will also measure voltages without the PT in.  Maybe I am getting voltage from somewhere else and that's messing things up?

Felipe,
I just want you to know that I'm still following this thread, silently cheering you on.  I really want this pedal to work. 

Thanks!

Pin 1: 4.97V
Pin 2: 2.48V
Pin 3: 0V
Pin 4 : 0V
Pin 5: 2.73V (IMPROVEMENT!)
Pin 6: 2.4V (PROBLEM!)
Pin 7: 0.461V
Pin 8: 0.520V
Pins 9 to 16: 2.51V (with slight movement)

These value might (only might) indicate the chip is ok. There could be another problem.

Yeah, I don't think it's toast either.  It may be, but it is not going into the trash bin until I can confirm that it is...

OK, so my next steps should be:

1. Checking voltage at the socket (without PT in) to make sure no voltage from outside is hitting pin 6
2. Checking continuity
3. Taking out Q2
4. Swapping R21 to a 47K

Is this right?

By the way, when I connect the guitar, I can hear the guitar playing; there is just no chorus effect of any kind.  There is just a tiny little bit of clean boost.  So it seems the problem is in the lower half of the schematic...

[anotherjim]

It might help to take out R20 (10k). That will disconnect the dry feed to the output then any sound your hear MUST have come from the PT2399. It may help to know that audio out of the chip first comes out from pin 12. It will also be found on pin 14.

[jfrabat]

It might help to take out R20 (10k). That will disconnect the dry feed to the output then any sound your hear MUST have come from the PT2399. It may help to know that audio out of the chip first comes out from pin 12. It will also be found on pin 14.

OK, so, the process to follow tonight is:

1. Disconnect R20 (one pin, just to break the dry feed from the output). 
2. Checking voltage at the socket (without PT in) to make sure no voltage from outside is hitting pin 6
3. Checking continuity
4. Taking out Q2
5. Swapping R21 to a 47K

Is this correct?

I am posting the schematics and layout for anyone in the future who needs it as reference to troubleshooting...

[anotherjim]

Yes, and check the op-amp pin 1 with slow speed pot to see there is a constantly changing voltage to prove the LFO is running. At full depth you should hear a strong pitch warble as well as the delay.

[jfrabat]

Yes, and check the op-amp pin 1 with slow speed pot to see there is a constantly changing voltage to prove the LFO is running.

You lost me there...  can you expand on this one?

[anotherjim]

Pin1 of the 5532 should have a constantly changing voltage. This wobbles the voltage on Pin2 of the 2399 and causes the delay time to rise and fall. It is the reason for the cyclic effect of a chorus. The speed of it is s l o w  - low-frequency-oscillator - you shouldn't hear it directly. On the slowest speed setting, it's easier to see on the DMM. On fastest, the meter won't keep up but might show an average voltage instead. At any rate, it should never appear stuck at a high or low voltage.

[jfrabat]

And I assume it is the same on the TL082 I amnusing instead of the 5532, right?  Or could that be the issue?

[anotherjim]

082 should work just the same.

[jfrabat]

OK, got it.  Now, from what I read in your 2 previous post, in slow speed, a Digital Multi Meter should be able to pick up the oscillation, but in high speed, it will not.  Now, the only issue is that I am not sure which way is slow and which is fast on my pot, as I can't test it because there is no chorus effect (I am sure there is a way, I just don't know it!).  Usually I wire pots, try them, and if I need to, I invert #1 & #3 to get them moving the right way...  Yeah, I know, that's probably not the best way to do it, but that's what I have done so far (I have only made 2 pedals, and one I still need to re-do because it sounds awful!).

So if I put it in a mid level, will the DMM be able to pick it up?

[jfrabat]

Disconnect R20 (one pin, just to break the dry feed from the output).

No sound coming out

Checked voltage at the socket (without PT in) to make sure no voltage from outside is hitting pin 6

Voltage was OK

3. Checking continuity

All the leads that are suppossed to have continuity check out.  Also cleaned up some areas where I had a bit of continuity where there was none suppossed to be.

Measured voltage at pin 1 of 082

Varies from under 1V to over 5V

Voltage readings at PT:

1. 5.03V
2. 2.50V
3. 0V
4. 0V
5. 1.95V
6. 2.43V
7. 0.311V
8. 0.496V
9-16: 2.51V (starts a bit higher and comes down)

Put in a fresh PT.  Not much changes (except voltage at pins 5 and 6 increase slightly).  Put old PT back in.

I am officially stuck!  I still got plan C (the printed board from Canada), but that has taken FOREVER to arrive at the freight forwarder in Miami!  Anyway, what else should I check?

Remove the transistor?

[bluebunny]

Is the PT still getting hot?