"Little Angel" - Super Simple PT2399 Mini Chorus

[rankot]

It covers only values down to 288 ohms, which gives 32.6ms. That is quite a lot for chorus. 2k2 gives 54ms, which is even more, and 4k7 is around 84ms.

I will try to put 1k pot there and listen what happens.

[rankot]

I've had the idea to try a PT2399 chorus ever since I modded my Clari into a Clari Cubed. The challenge with the PT2399 is to get the delay time as short as possible while still having some wiggle room for the LFO injected into pin 6. I've tried PNP, NPN, FET and LDR - fail! The delay time is either too short for the LFO to have any wiggle, or too long and latency is obvious.

So, screw using pin 6, just ground the MF for the shortest possible delay time and instead modulate the vref at pin2. Shortest possible delay with as much LFO wiggle as you want. In fact it has to be tamed down or you're into tape wobble type effects.

If I understand this well (the very first post of this thread  ), pin 6 is not important at all, since LA uses modulation of a pin 2, so maybe it will not affect anything? I'll see.

[ElectricDruid]

The problem you'll likely hit is that the PT2399 won't start up with a very low resistance on Pin 6. It stops the oscillator, so no sound comes out. Generally, once the chip is going, it can handle the low resistance better. Plus there's considerable between-chips variation - some do it, others don't. Some delay designs have taken measures to avoid the minimum delay setting at start-up.

HTH,
Tom

[gasboss775]

This works really nicely for such a simple circuit...all praise to the creator!

There is the latchup problem with pin 6 which was easily remedied with the following addition...

[jhsa]

Hi guys, I can see that this thread is quite old. I am building a chorus based on the little angel but I am having some annoying noises. Please check the little video I made.
If the resistance from pin 6 of the PT2399 is less than 1.2K, it will make some his noise that will be modulated by the LFO. If i remove the depth pot, or the buffer I am using after it, there is a continuous hiss. If I increase the resistance value, There is no noise. I don't know what causes this, and I am starting to think that the chip doesn't like to operate at really short delay times..
Here is the video

João

https://www.youtube.com/watch?v=tvzi1v-HmH0&t

[rankot]

Little Angel works quite different from datasheet normal operation. In datasheet, you vary Rvco value to get different delay times. Here, Rvco is fixed, and reference voltage is varied to get shorter delays, e.g. in chorus domain. I use 4k7 for Rvco, together with additional circuitry that switch to 47 ohm once chip is started, and it works fine.

Also, this circuit is very sensitive to digital noise produced by PT2399, all the connections must be as close as possible to IC pins, especially filtering caps. So I suggest you build this on some kind of vero board or PCB and then experiment.

[jhsa]

Thanks, the problem is that with breadboard I can experiment. But will probably end up doing that.


By the way, you use the 4K7 resistor on pin 6 to kick start the chip only. When the transistor start conducting it uses the 47 ohm resistor plus the resistance from the transistor itself.. My problem is only the noise, all the rest seems to work really nice..

João

[rankot]

Then you will have to try without breadboard. Before that try to add 10uF tantalum or low ESR electrolytic cap across V+ and GND pins, as close as possible to PT2399.

[jhsa]

OK, tried tantalum 47uF.. Same, no difference at all.. Still the same noise you can hear on the video. A continuous  digital whining is heard even if i remove the LFO and  if the delay resistor is less than 1.2K. Of course, with the LFO this noise gets modulated as you can hear on the video..

João

[rankot]

I had this problem: https://www.diystompboxes.com/smfforum/index.php?topic=86297.msg1117367#msg1117367 and solved it with that power filtering cap. I also used wrong values for filter caps (pins 9 to 16).

Try those values:

[jhsa]

Yeah, it looks like this might actually get to be a pedal after all.. 
Managed to greatly reduce the noise by decreasing the values of the caps on the pins 9/10 and 11/12. Instead of 10nF, I now have 6.8nF, but this is still not definitive. There is still a little noise but I guess I will have to reach some compromise, after all the PT2399 is very noisy.
One thing I have noticed now is that when I increase the delay time I get some noise when the guitar sound is fading.. I believe I can tame this changing the caps on pins 15/16 and 13/14.. Still playing with them.. I do like the way the increased delay  with some modulation sounds   

I have just freed some other breadboard and will try a different approach as well, which consists in using pin6 for both delay time and modulation..

João

[rankot]

Try with 3n3 (c5 on my schematic) between 15 and 16, it did the whole trick for me.

[jhsa]

That is what I have at the moment.. And have 10nF between 13 and 14..
I think I have it more or less working on the breadboard. I am just adjusting values at the moment. It doesn't look like a little angel anymore.. It is an angel on steroids now When I'm happy with it, if i ever will  I will post the schematics and a sound sample..
What I can say is this is too much work on a pedal that will probably never make it to my pedalboard, who knows

João

[jhsa]

Unbelievable, it seems I can't decrease the resistance on pin 6 to less than about 1K as I get lots of hiss that oscillates with the modulation.. No, it is not caused by the LFO. If I remove the LFO completely out of the circuit, there is a continuous hiss. I can't believe that you guys are not having the same. Perhaps this happens due to the fact I bought my PT2399 at Aliexpress, so they aren't for sure originals. But I guess there aren't anymore original chips being produced??
Will try to post some sound sample tomorrow..

João

[rankot]

I have few PT2399 which came from Ali, and few of them which came from Tayda. Not sure if there's a difference. I have also ordered few HT8970 from Ali yesteday, hoping to get even shorter delay times with them.

[jhsa]

Cool, please let us know how you get on with the new chip. Might get some as well.. I will see if Musikding has it as well. Actually, I might also try the pork barrel chorus. need to get some ICs for it.. I don't know why I am doing this as I am not really into chorus Ha ha ha
But working on this circuit I found out that if i use a pot for the delay time, I can get some really nice tones, so it might be good to have such a circuit on my pedalboard.
I didn't manage to remove the noise completely, but I did manage to reduce it a lot. That increased the chances of being actually built and perhaps go on my pedalboard
Again, sound sample later in a while

João

[rankot]

Try to add that "Space" mod, it really makes things interesting!

[jhsa]

Here is the link to an mp3 file of a little demo I have made.
I originally spoke while I was recording the guitar, but the microphone wasn't loud enough, so I have edited the file to remove the speaking and leave only the guitar.
It was recorded by my Soundcraft Ui12 mixer directly onto the USB thumb drive. I then used Audacity to remove my talking and normalize the audio. No other effect was applied.

I have recorded the clean sound at the beginning and also several times during the recording. Then played with the different pots (speed, Depth, Delay and mix (Wet/dry) ). I started with the shortest Delay setting, then pot (5K) at half, then full Delay, and at the end again the shortest delay. Please don't mind my guitar playing as i wasn't trying to play anything in particular, only some loose chords.
Please let me know if you are not able to download the file..

https://drive.google.com/file/d/18wCaHOaIclLoMxWJAfujh3sX8OOrDWzn/view?usp=sharing

Constructive comments are very welcome
I will try to also implement a "Tone" pot.

EDIT: Didn't like the "Space" feature SO, less components on my board.. I already have too many Need to draw a schematic to have a better overview of what I have done

[jhsa]

Ok guys, this is where I am at. I have only tested the Chorus circuit itself on the breadboard, but the bypass circuit is the same I use on all my other pedals, so that should be working. Didn't test it all together though.. I am designing a PCB for it. Might etch it tomorrow. it gave me a huge amount of work so far to make it fit on a 54mm x 54mm double sided PCB, but I think i managed it, I hope
Comments and constructive criticism is welcome

João

[rankot]

Why do you have two linear regulators for 5V?

LFO rate LED is a cool add on!