"Little Angel" - Super Simple PT2399 Mini Chorus

[jfrabat]

Capacitors, transistors, sockets and diode are in.  The hole size does make it easier to solder components without making a mess.  Here's how its looking prior to resistors and pots and other stuff outside the PCB:



Definetely looking better than last one.  Gonna check continuity now before putting in resistors.  Hopefully, everything will be as it should!

[stallik]

Looking much better than the last one. Bit late now but you'll find it easier to solder in the components in hight order. Links, resistors and diodes first then small caps, large caps etc. Saves you struggling to hold the things in place when you solder.
You may find that a piece of sponge may help to keep the resistors in place now that the large caps are on the board

[EBK]

I agree that this one looks much better.  There are still a few joints that look like you didn't heat the pad on the board enough, but much progress is being made.  I hope it works when you finish.

[jfrabat]

OK.  Finished soldering.  Signal is going through (with a bit of clean boost), but no chorus effect.  So I am further along, but not quite there yet...

Voltages read as follows (have not yet compared them to the others posted here):

IC1 (PT2399)
1. 5.03V
2. 2.50V
3. 1 mV (gonna call it 0, as even disconneed the reader shows that)
4. 1 mV (again, gonna call it 0)
5. 5.01V
6. 0.74 V
7. 151 mV and starts to go up
8. 126 mV and goes up
9 to 16. 2.51 V

IC2 (TL082)
1. 2.68 to 3.25 V (fluctuates)
2. 2.95 to 2.98 V
3. 2.78 to 2.83 V
4. 0 (1 mV)
5. 4.21 V
6. 4.34 V
7. 4.34 V
8. 8.65 V

Q1 (78L05)
In. 8.4 V
GND. 0 (1 mV)
Out. 5.01 V

Q2 (forgot to mention I replaced this one with a 2N2222A)
C: 78.4 mV
E: 1 mV
B: 0.68 V





Let me know if you guys spot anything out of order...

By the way, I tried replacing the PT, but readings did not change.

Felipe

[jfrabat]

Here are voltages just taken from my Little Angel, which sounds the same as the breadboarded version I did you soundclips on. Speed at 3 o'clock, Depth at 12 o'clock:

PT2399

1:  5
2:  2.38 to 2.42
3:  0
4:  0
5:  2.75
6:  0.61
7:  0.88
8:  0.88
9 through to 16:  2.41 (slight movement)


NE5532

1:  0.13 to 4.9
2:  2.9 to 3.2
3:  2.7 to 3.1
4:  0v
5:  4.79
6.  4.9
7:  5.14
8:  9

So it seems I have significant diferences at:
IC1, pins 5, 7 & 8
IC2, pin 7

Battery is a bit worn; did not check direct voltage, but reading from pin 8 of IC2, maybe its time for a change.  Could that be causing the issues?

[EBK]

I'm wondering about that copper trace across the bottom of your board that appears to disintegrate as it nears the corner.  I'd have to take a look at the original pattern vs. what you ended up with.  Haven't had time to look at your voltages though.

[anotherjim]

PT2399 pins 5 & 6 voltages suggest the chip is "locked up". Don't worry about the 5532, it could well be ok.

Pin 5 should be somewhere around 2.5v. Actually it's a very high frequency, the clock of the delay and your meter will average it as an about halfway voltage, but this is not related to and can differ to the 2.5V found on the other pins. Pin5 either at 5v or 0v suggests the delay clock VCO isn't running.

Pin 6 is the clock VCO frequency control current. A low voltage here suggests excessive current "might" be being drawn from this pin. Possible short to 0v or too low resistance to 0v. The PT2399 clock VCO can fail to start if Pin6 resistance is less than 1k at power on. This sensitivity does vary from chip to chip. Some examples always work, some sometimes work and some never work.

Sometimes the PT2399 can lock up due to static. You can take it out and press all the pins on some metal foil for 10seconds to clear any static charge that might be in it. That bit sounds like hocus-pocus I know, but I swear it's happened to me and this trick fixed it.

Which particular LA circuit is this built to? There have been various changes to the pin6 control.
Is that PT2399 the same part used in the earlier fail?

[jfrabat]

Sometimes the PT2399 can lock up due to static. You can take it out and press all the pins on some metal foil for 10seconds to clear any static charge that might be in it. That bit sounds like hocus-pocus I know, but I swear it's happened to me and this trick fixed it.

Which particular LA circuit is this built to? There have been various changes to the pin6 control.
Is that PT2399 the same part used in the earlier fail?

I will give that a shot.  The PT I started the test wit was the same one of the failed experiment.  It is the one example I found locally.  But I then replaced it with a new one I ordered from Amazon (or was it eBay?).  I would have to re check the voltages of pins 5 & 6 to be sure they are also the same still (I just woke up!), and will do so shortly.  But I will also do the metal trick just in case...

The LA is the Birthday Edition.  I will repost the schematic I followed so you guys dont tneed to search back to it.

[jfrabat]

^^^

Well I was gonna save this as a surprise for LA's 1st birthday in August, but........




I wanted to keep it 1590A-able, but also add good things like the Pin 6 Fix and a seperate vref for the audio path. Here's the lowdown:

• Pin 6 Fix: D1/C16/Q2/R21/R22
  I did add a little Pin 6 Fix subcircuit to a PT2399 that I know won't work without. It still has issues, but I think raising R22 to 100R and C16 to 47uF will sort it
• Audio vref: R23/R24/C17 - suggested by merlinb as a way to reduce noise dumped into the older version's 5v vref supply by the PT2399
• C4 changed to 3.3nF - might be a bit darker but will be less hissy

   
As it's planned to be 1590A-able, hopefully all the electro caps should be able to be bend over 90⁰ to lie flat against the PCB. C16 might be the trickiest.

I PM'ed this layout last week to a couple of people who expressed interest in verifying it, so you never know, it could be verified within a day or so. The layout does need a little tidy up, as I notice the pad sizes are not all the same size.

This is the one I am using

[jfrabat]

Voltages of new PT after grounding all legs

1. 5.01 V
2. 2.50V
3. 1 mV
4. 1 mV
5. 5.01V
6. 0.708 V
7. 4.58 V
8. 4.58 V
9. 4.83 V
10. 0.403
11. 0.402
12. 4.78 V
13. 2.5 V
14. 0.235 V
15. 2.5V
16. 2.5 V

[jfrabat]

I just notice if I take the chip out, ground it, and  put it back in, pin 5 goes to 2.3V.  When that happens, pins 9 to 18 go to 2.51V and pin 7 goes to 0.434V.  But if I connect the guitar...  back to square 1.

[anotherjim]

Ok, that really looks like the PT2399 is locking up.
I think this is the schematic...


Do check R21 is 2k2 (red/red/red) and R22 is 100R (brown/black/brown) - can't see those well in the photo.

To test if it's due to too much current out of pin6, remove the 100R resistor R22 (only need to take one lead out of its hole).
Without R22, it should work but with a noticeable short time delay, which will show the PT2399 is running.

[jfrabat]

I think the resistors are right:



checked with the multimeter, resistance seems OK on both as well (98.9 ohms and 2.18K Ohms).

Here is another shot of the entire board, in case it helps figure out what wrong...

[stallik]

The chip socket for the pt2399 is placed the wrong way round. The little semi circular notch should be on the left side. This is only to indicate which way round the chip should be inserted but if you haven't got that in the right way.....
Having said that, I see in a previous picture that you have the chip inserted correctly but it's worth checking

[jfrabat]

The chip socket for the pt2399 is placed the wrong way round. The little semi circular notch should be on the left side. This is only to indicate which way round the chip should be inserted but if you haven't got that in the right way.....
Having said that, I see in a previous picture that you have the chip inserted correctly but it's worth checking

To be honest, this is the first time I notice that notch!  LOL!  Nothing like the bliss of ignorance, right?  But the chip I did insert the right way, so I do not think that is the cause.

As for the voltage, I took out my trusty multi-meter, and went to check resistances...  Got some surprises.  Here's the resistor list with what should be in and what I measured:

                       Listed Value                Measured Value
R1                           68K                           66.6K
R2                           10K                           9.53K
R3                           10K                           9.84K
R4                           10K                           9.80K
R5                           10K                           9.79K
R6                           10K                           9.77K
R7                           330K                           321K
R8                           47K                           318K
R9                           100K                   39.7K
R10                           220K                   Did not get a measurement
R11                           220K                   212K
R12                           4.7K                      4.6K
R13                           33K                           66.6K
R14                           100K                   97.8K
R15                           1M                           2.09M
R16                           470K                   462K
R17                           10K                           9.79K
R18                           10K                           9.80K
R19                           1M                           Did not get a measurement
R20                           10K                           9.79K
R21                           2.2K                           2.18K
R22                           100                           98.8
R23                           10K                           9.20K
R24                           10K                           9.32K

The ones that have no measure is because I was getting no indication on the multi-meter.  Correct me if I am wrong, but:
47K = Yellow-Violet-Orange
100K = Brown-Black-Yellow
Is this right?  If so, I got the right resistors in place for R8 and R9, right?

I did notice that the 1M resistors I accidentally put 2.2M resistors, but I also noticed my 2,2M resistors have resistance all over the place (from 700K to 3M!).  I also have the wrong resistor for R13, so I have to swap out 3 resistors and see what's up with the other 2.  Does this sound about right?

[anotherjim]

You might have to tried to measure resistance with power on? It has to be power off for that, and preferably with IC's removed as they can make connections to other parts of the circuit. Also any capacitors must have time after power off to discharge.

It can take a noticeable time for resistance readings to "resolve" to a true value when there are significantly large value capacitors also connected, because the meters own test voltage supply will have to charge the capacitor as well as inject its test current through the part you are measuring. You will notice then that if you reverse the meter probes , it will first have to discharge the capacitor then recharge it to the reverse polarity, taking even longer to resolve. For the small value capacitors, this can be too fast to notice, but with the larger ones over 1uF, it's a handy way to tell if it is acting like a capacitor should. Incidentally, you cannot damage an electrolytic capacitor if you connect the meter resistance test to it with wrong polarity as there is very little current.

Ideally, resistors should have at least one leg lifted out of contact so it can be measured without the rest of circuit affecting the reading, but that is tedious unless you have a good idea that its value is wrong. So we probe around with the resistors in circuit and when we find something that looks wrong, we unsolder one end and test again to be sure.

I've a suspicion that there is nothing seriously wrong with your resistors. Do check if it works without R22. If it still don't work, try again without Q2. If it still don't work, replace R21 with something higher like 47k - there should be a really obvious delayed signal out of the PT2399. If there still isn't -  it's a bad PT2399.

[bluebunny]

You can't really measure resistors in-circuit.  The chances that a resistor has no DC connection to anything else is slim.  As Jim says, lift a leg and measure (with the power off - that would really upset your DMM!).  Ideally, measuring resistors is something you do before you assemble.   

[jfrabat]

Thanks, guys.  So this means that R8 and R9 are correct.  I still need to change R15, R19 (the two 1M ones, which are the green ones in the photos, which I used 2.2M instead of 1M) and R13 (I put a 68K resistor by mistake).  Could these 3 resistors be the cause of my problems?

Here are the resistors in the schematic and in the picture:





33K should be Orange Orange Orange (obviusly it is not! Blue Gray Orange is 68K) and 1M (the green resistors) should be Red Black Green, and these are Red Red Green (2.2M)

I will try removing R22 tonight, and see how it goes.  But out of the 2 PT2399 I have tested, none have worked (different sources).  I have 4 additional PT's I can test as well.  Is it worth swapping it out at this time?  The 2399 is already out at this time...

[anotherjim]

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.

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.

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.

[stallik]

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