"Little Angel" - Super Simple PT2399 Mini Chorus

[jhsa]

For two reasons. I wanted to separate the 5V from the bypass switching which uses a microcontroller, so it is digital, from the 5V that supply the PT2399 chip. This chip doesn't need more noise that what already produces by itself
The other reason is that I have used  78L05 regulators, which have a max current supply of 100mA. as you know the PT2399 takes about 30mA, and the switching circuit with the relay takes about the same, or a bit more.. Then there are 3 LEDs. With 2 regulators sharing the load, they will run cooler
Let's see how this comes out.. Will print the PCB on photo paper now and etch it.. Fingers crossed that there aren't any mistakes

João

[jhsa]

Something really weird, built a PCB for that schematic and it doesn't work. I don't have modulation. On the breadboard it works. Connected a scope to both and i get exactly the same readings on several points.
Then, started changing stuff on the breadboard to try to find the problem. Found out that the second half of the LFO opamp isn't doing absolutely nothing, but on the breadboard the modulation signal somehow passes through and reaches the PT2399. This doesn't happen on the PCB. Anyway, ended up modifying the circuit using less parts and only one half of the preamp and now it is working. And it was very easy to mod the PCB as well, so, no need to etch another one. Need just to fine tune some resistor and cap values and will probably install it in an enclosure.
Sometimes there are some situations that aren't logical at all

João

[jhsa]

I think I got it to behave and sound quite nice. It will be boxed tomorrow. As you can see, the original little angel values were heavily changed, and some other stuff was added.
I don't know if I can call this a chorus because the PT2399 does not like very short delay times, but it does sound quite nice and it will have a place on my pedalboard. Due to the above, I have decided to name it "Wannabe Chorus"
Might actually build another one for my acoustic guitar.. Or perhaps will try the "Pork Barrel" Chorus, don't know yet.
Here is my schematic.

João

[jhsa]

And finished.. Here are some pictures

João

[duck_arse]

And finished.. Here are some pictures

João

did you shrink wrap your board? why? nice looking build.

[jhsa]

I shrink wrap all my boards to avoid shorts. there are many metalic parts around the board, like pots, jacks, the enclosure itself. If the board touches them, it might create a short and get damaged, and if you are playing, it might ruin your night   And keep things tidy as well.

João

[Vincent64]

Does someone have a copy of the schematics of Little Angel Mini Chorus moded by Earthscum? Care to share it with me?

[wheels1758]

Sorry to bring up an old thread, but I recently built the V2 Little Angel Chorus from TagBoard and I am having an issue with the LFO clicking (I think). I've recorded the sound to hopefully help diagnose the issue.

Audio Probe: https://www.dropbox.com/preview/Little%20Angel%20Chorus%20Click/Little%20Angel%20Chorus%20Clicking%20Probe.wav
(This is probing pins 1, 7, 6, and 5 of the NE5532 op amp. It's definitely quieter on pin 1 (output), but still there! Don't mind the hum, that's in my DAW, not when I direct monitor the pedal)

Dry: https://www.dropbox.com/preview/Little%20Angel%20Chorus%20Click/Little%20Angel%20Chorus%20Clicking%20Dry.wav
Wet:  https://www.dropbox.com/preview/Little%20Angel%20Chorus%20Click/Little%20Angel%20Chorus%20Clicking%20Wet.wav
(Dry and Wet were recorded at the same time using 2 channels on an audio interface)

Here are the pin voltages on the NE5532 and the PT2399:
NE5532
1: 4.85
2:  4.62
3: 4.62
4: 0
5: 2.8-3.25 cyclic
6: 3.0-3.25 cyclic
7: 1.7-4.5 cyclic
8: 9.26

PT2399
1: 5.02
2: 2.5
3: 0
4: 0
5: 5.02
6: 0.45
7: 0.25 (drops to 0 when testing)
8: 0.25 (drops to 0 when testing)
9: 2.5
10: 2.5
11: 2.5
12: 2.5
13: 2.5
14: 2.5
15: 2.5
16: 2.5

Voltages taken without any audio signal being played. Strangely (maybe) when I play something and then probe (with a multimeter) pin 2 of the PT2399, the audio signal is killed and I have to cycle the power supply off, then on, to get it to start again.

Anyone have any ideas on what to check or what could be causing this issue?

Thanks!

[garcho]

Ye olde LFO ticking. The first thing to try would be a TL072 in place of the NE5532, as it is in the original. There's a lot of misinformation online that the 5532 are "better" than the TL072. Yes, they can be better. But that's a long, long way from always better. Often enough, the 5532 is worse.
What layout are you using? If you're making your own layout, you can buffer the LFO signal with an emitter follower or another op amp, you could use a different op amp for the LFO, you can use some of the "anti-latching" tricks people have come up with to deal with the finicky PT2399, etc. Keep in mind the PT2399 is a quick & dirty karaoke machine IC, it's not intended for "professional" use, despite the legion of pedal makers and behringer type crooks using them in their designs. Some finessing is required.
Your voltages look fine.
EDIT: bravo on a great troubleshooting post, you did your homework

[patrick398]

Welcome to the forum!
If trying a TL072 doesn't solve it maybe try a TL062, they're often used to cure LFO ticking problems as they're low current draw. I think they have more noise than the 072 but see how you get on.
Ordinarily i'd suggest providing the lfo with 'isolated' power via a low value R and high value cap to ground but since this circuit using a dual op amp for both the LFO and audio it won't work.
How is your off-board wiring?

[wheels1758]

Ye olde LFO ticking. The first thing to try would be a TL072 in place of the NE5532, as it is in the original. There's a lot of misinformation online that the 5532 are "better" than the TL072. Yes, they can be better. But that's a long, long way from always better. Often enough, the 5532 is worse.
What layout are you using? If you're making your own layout, you can buffer the LFO signal with an emitter follower or another op amp, you could use a different op amp for the LFO, you can use some of the "anti-latching" tricks people have come up with to deal with the finicky PT2399, etc. Keep in mind the PT2399 is a quick & dirty karaoke machine IC, it's not intended for "professional" use, despite the legion of pedal makers and behringer type crooks using them in their designs. Some finessing is required.
Your voltages look fine.
EDIT: bravo on a great troubleshooting post, you did your homework

Thanks for the tips! I don't have any 072 or 062 op amps but I did have similar results with an LM833N (what I had on hand). I am using the V2 layout that IvIark posted on tag board effects.

How is your off-board wiring?

Uhh, I just poked the input/output wires from the circuit through the enclosure and plugged them into jacks on a breadboard. No stomp installed yet.

[anotherjim]

If you can read wobbling voltage from the LFO, you should see wobble on the PT2399 pin2 unless the depth is turned down.
Pin 5 is the delay clock. It ought to read closer to 2.5v. That it is reading 5v suggests the delay is locked up,  or at least it was when you took the measurement.

[wheels1758]

If you can read wobbling voltage from the LFO, you should see wobble on the PT2399 pin2 unless the depth is turned down.
Pin 5 is the delay clock. It ought to read closer to 2.5v. That it is reading 5v suggests the delay is locked up,  or at least it was when you took the measurement.

I think it might have locked up when I touched pin 2, so when I subsequently checked pin 5, it was at 5V. I can check that again tonight. Should it be locking up when pin 2 voltage is measured?

[anotherjim]

Taking voltage readings from pin2 should not cause lockup.
If you have not included the anti-lockup circuit, I'd recommend temporarily replacing the 100R resistor between pin6 and 3 of the PT2399 with something larger like 1k until the problem with the LFO is sorted out, that way you shouldn't be troubled with the lock-up problem confusing things.

[wheels1758]

I used the V2 layout which does include anti-lock. However, after the first 5 or 10 seconds, pin 6 should be grounded. Does that change whether or not it will lock up when probing?

http://4.bp.blogspot.com/-vh39ImHNIJ0/UVSr6KhaPEI/AAAAAAAAFWA/5Zsre3f8XoU/s1600/Little+Angel+Chorus+V2.png

[wheels1758]

If you can read wobbling voltage from the LFO, you should see wobble on the PT2399 pin2 unless the depth is turned down.
Pin 5 is the delay clock. It ought to read closer to 2.5v. That it is reading 5v suggests the delay is locked up,  or at least it was when you took the measurement.

Measured voltages again. This time waiting until last to measure pin 2 of the PT2399. Pin 2 starts around 1.78V and jumps up to 2.5 almost immediately, with the chip locking up and no sound being produced until the power is cycled. Pins 7 and 8 of the PT2399 don't drop to 0 when the chip is not locked up. This circuit uses an anti-lock transistor for startup, in series with a 47R to ground. There is also a 100R resistor to ground in parallel with the 47R and transistor. Admittedly, the transistor does not fit snug in it's socket, but I don't think that would cause it to lock up when probing. Thoughts?

Voltages below.

NE5532
1: 4.85
2:  4.62
3: 4.62
4: 0
5: 2.8-3.25 cyclic
6: 3.0-3.25 cyclic
7: 1.7-4.5 cyclic
8: 9.26

PT2399
1: 5.02
2: 1.78 (then straight up to 2.5 and the chip locked up)
3: 0
4: 0
5: 2.76
6: 0.45
7: 0.69
8: 0.70
9: 2.5
10: 2.5
11: 2.5
12: 2.5
13: 2.5
14: 2.5
15: 2.5
16: 2.5

[anotherjim]

It's possible that the LFO ticking and the delay lockup are two separate issues.

I would tackle the lockup first since it's not going to give any kind of effect if that keeps happening.

The chorus effect requires a very short delay time and pushes the PT2399 chip beyond its specifications to achieve this.

As I read the tag layout, the delay time control resistor to ground from pin6 is a fixed 100R. This low value already exceeds the recommended 2k for that resistance. Incidentally, I have never known a PT2399 to lock with a 1k minimum.

The anti-lockup transistor, after a time delay, adds a 47R in parallel.

The time control for that chip is intended to be done using the pin6 resistance, but because of the very low pin6 resistance, the LFO is fed to pin2. Pin2 is the chips operating reference supply voltage and will normally have a decoupling capacitor attached and nothing else. Using the LFO to wobble that reference modulates the delay time.

It all adds up to the chip being pushed beyond its design specification with a low time delay at startup that is pushed lower by the anti-lockup and lower again at one extreme of LFO sweep. The lowest delay times are achieved by making the internal timing clock oscillator go really fast -  over 20Mhz and this is what it doesn't much like.

Removing the transistor and replacing the 100R pin6 resistance with 1k should stop the lockup. In addition, check that the LFO depth connection to pin2 has the correct series resistor (33k). This won't give a proper chorus effect, more like a wobbly slap-back echo, but at least you should hear something happening.

Once you can get the thing behaving, you can put things back, but I would leave the pin6 resistor as 1k and change the 47R in the anti-lockup to 100R.

[patrick398]

I have never known a PT2399 to lock with a 1k minimum.

FWIW i have never had any issue with latch up using 510R at pin 6

[anotherjim]

Any advance (or is it retreat?) from 510R? 

Incidentally, I suspect that with the anti-lockup (some say latch-up, same thing) you don't need the fixed pin6 resistor at all. The chip won't mind at switch-on and as the transistor turns on, it will still get a "soft-start" from a high to low resistance. I'd still change that 47R to a 100R though.

[wheels1758]

Incidentally, I suspect that with the anti-lockup (some say latch-up, same thing) you don't need the fixed pin6 resistor at all. The chip won't mind at switch-on and as the transistor turns on, it will still get a "soft-start" from a high to low resistance. I'd still change that 47R to a 100R though.

Removed the 100R from pin 6 to ground. Still locks up when measuring pin 2 voltage. I did find that if I short pin 2 to pin 3 (ground), it resets it most of the time and starts working again. Not sure if that is expected behavior or not.