PT2399 Noise Generator - Help with schematic to vero.

[noisette]

Interesting circuit, I like crazy 2399 stuff, like the "Sewer Pipes Ringverb", anyone remember?
The 2399 has erratic noisy output at delay times > 50k(100k?) to GND on pin6, if that is fed back it might result in noise output even without an input. I think best is to take the idea and redevelop the circuit?

[moid]

OK everybody, in the interests and advancement of scientific progress... I breadboarded it. It works, but don't get excited. Like John already found, it sounds nothing like the video It ticks. Squarewave tick (quite loud) that can be made to get faster as you turn the 1M pot clockwise. Interestingly, if you leave it in any position on the sweep except for maximum CW, the ticks repeat at one rate and then slowly speed up and then slow down... sometimes they just stop, and I have to reconnect the battery to start everything up again (sweeping the pot doesn't work). That could be caused by my breadboarding of course. If the pot is swept fully CW, just before the maximum extent the audio becomes super fast and very quiet, then silent and then finally is replaced by a churning digital noise sound. if the pot is jiggled back and forth a bit at the CW end of the sweep it will make a brief other noisy sound that fades very quickly. The ticks are all the same pitch I think (maybe as the pot goes to near full clockwise they might raise in pitch, but if so it's not by much. My son who has decent hearing is in an online game with his friends so I can't ask him to listen to it at the moment)

I swapped out the 100K resistor that duck mentioned for a 250K log pot (because it was lying on the desk unused, that's why!) and that resulted in the ability to mute the ticks at full counter clockwise and also made the ticks a bit louder when I turned the pot clockwise.

I also tried to pipe in a guitar on pin 16 of the PT2399, but that deactivates the ticks completely - and the guitar audio doesn't come through unless (and this is really odd) I detach the ground connection from the battery to the breadboard - and then I get clean guitar happily, but no ticking.

So clever people, what do we try next? I suspect that the missing IC3 in the schematic is rather important.

[anotherjim]

Try this...

... I have not!
Notes:
C1 & C2 are stock values. As I understand it, these are the ADC & DAC modulator & demodulator and I think we want those working.
No cap on pin 2 -  we want the chips self-noise, so no filtering there - but it may be needed if it's too feisty.
No filter caps on 9,10,11 &12 - we want max noise there too.
Delay output from pin 12 direct back to input on pin16.
Spare opamp between pins 13 & 14 not used. Can be linked out as shown or left open.
You can't give it an external input. Pin 12 is an output with low impedance, it will just short out any signal you try to give it. If you must replace the link from pin12 to 16 with a 100k resistor (the original 22R would be too low anyway) then pin16 should accept a signal.
C5 can be 100nF or 1uF - no point being 100uF. Vol pot can be 100k or more.

[anotherjim]

Well, I've tried it now as I had 1 PT2399 to sacrifice...
Got the same results with my scheme - clicks.
So, I got something going eventually...
Had to build a proper input around pins 15 & 16. 1M feedback and the input from pin 12 via 47k and 4n7 cap. That may change.
Been messing with it a lot. Mute button, LDR time control, Green limit LED on pin 7. Currently have no caps at all on pins 7 & 8 or 2. A 22n between pins 11 & 12. No cap on pins 9 & 10.
Output is too loud into a guitar amp - 100k output pot is barely up.

[John Lyons]

How would you describe what you have going now
soundwise Jim? (Short of a sound clip) Anythng interesting?

[moid]

Yes I'm interested too! Does it make different textures of noise or just a pitch change / speed change of the same audio pattern? I would like to fade this sort of noise into cleaner guitar playing (like some sort of tremolo that fades the noise up and down while the guitar plays at the same time). I was definitely thinking of an LED/LDR combination to make the pot sweep back and forth all the time to keep the noise changing.

[anotherjim]

There's a lot of different noises. I find most of the tonal squeaks & chirps happen while wiggling in the low resistance end of the time pot. As the resistance goes to the high end, it becomes more of a dirty noise loop (think NiN) - but as you sweep it back, the sounds tend to vanish. I think this is because the low-speed recorded audio becomes ultrasonic at some point when speeded up.
When the only delay resistance is the fixed 1k it hits a tonal feedback state as I think the chips VCO is then running as fast as it can.
Adding a mute switch and tapping it imparts some rhythm.
On power-up, it makes a useful tone in the loop for wiggling, but to get rid of it, holding the mute down long enough replaces it with noise.
It can also sound like tape recorder feedback - which would be expected.

It's a rabbit hole, there's a lot of tweaks I could do - but there's only so much time!

[anotherjim]

Here's what I had last night...

[anotherjim]

In its latest state, C2 has become 2n2 and C1 is 22n.
Reducing C1 increases hf content, so when the delay time is increased, audible bleeps & chirps happen.

The delay pot has become a 250k log. The longest delay with 1M doesn't seem all that useful and the last 50% with linear pot doesn't change that much anyway. Also, the most interesting noises happen in the short ranges. YMMV.

The output is so loud I changed to 100k fixed into a 10k log volume pot.

The mute switch is useful but some good things happen if you can press it on & off quickly to add some rhythm. A spring-biased toggle switch could be better than a button.

The external input idea doesn't work well - the delay repeats are just too loud. A preamp is needed. The unused opamp between pins 13 & 14 could be used for that, but I want to keep it simple. Also, without a bypass cap, pin2 isn't strong enough to mute against a louder external input - but pin2 needs to be used to stop the switch causing a might thump.

If left to run, the loops can maintain content that's more than just noise (albeit very lo-fi) for a surprisingly long time, so the idea of allowing external audio to be recorded is tempting.

[John Lyons]

Thanks Jim
I'm going to breadboard what you have
and compre it to the original with the ways
I've been using it. (Shorting pins and brushing
across pins while the "sample" plays... and manipulating
the delay time)

[anotherjim]

Actually, it's pretty hard to get away from that saturated tape echo feedback sound that any PT2399 scheme, including the databook standard can do. Only by removing most of the filtering can it get into proper noise machine territory.
And I can't quite get the rubbery squelches and squeaks the demo of the original had.

[moid]

In its latest state, C2 has become 2n2 and C1 is 22n.
Reducing C1 increases hf content, so when the delay time is increased, audible bleeps & chirps happen.

The delay pot has become a 250k log. The longest delay with 1M doesn't seem all that useful and the last 50% with linear pot doesn't change that much anyway. Also, the most interesting noises happen in the short ranges. YMMV.

The output is so loud I changed to 100k fixed into a 10k log volume pot.

The mute switch is useful but some good things happen if you can press it on & off quickly to add some rhythm. A spring-biased toggle switch could be better than a button.

The external input idea doesn't work well - the delay repeats are just too loud. A preamp is needed. The unused opamp between pins 13 & 14 could be used for that, but I want to keep it simple. Also, without a bypass cap, pin2 isn't strong enough to mute against a louder external input - but pin2 needs to be used to stop the switch causing a might thump.

If left to run, the loops can maintain content that's more than just noise (albeit very lo-fi) for a surprisingly long time, so the idea of allowing external audio to be recorded is tempting.

Great work anotherjim Thanks for thinking about the external input, but if it doesn't work well in the position you've placed it (without a loud boost beforehand) then could I just feed the noise circuit into a tremolo to vary its volume up and down and then mix that tremolo output with a guitar input? So the mixing would be after the noise circuit volume pot, which would allow me to control how loud it was in relation to the guitar.

Just out of interest, does the guitar input you made actually influence the noise circuit at all or is that pure crazy oscillations and no external source will do anything to it?

I'm definitely thinking of making a daughterboard with an LED LDR combo on it to be switched in to sweep the pot; I reckon that could make some odd noises! especially if the sweep wasn't just a triangle - a sawtooth might make this stutter weirdly?

Is this circuit at the point that it would be worth me drawing into a vero layout for spectreman?

[anotherjim]

Well, it's having problems at the moment. My one & only PT2399 keeps locking up on power up and I have to discharge the chip by shorting out all its pins together to get it going again. Bizarrely, this has nothing to do with a too low delay resistance and can happen if the delay pot resistance is high when it's switched on. It only started doing this today and reversing the last changes I made doesn't cure it. When it's running it won't fail.
Hmmmm.........

[John Lyons]

Mine locks up as well
with the original schematic.

[rutabaga bob]

Brings to memory Anchovie's 'Noise Ensemble'...

[anotherjim]

https://www.parasitstudio.se/stripboard-layouts/noise-ensemble
It is the same, but different. This thing's meant to self run. If you need to process external audio, Anchovies' invention could be the one for you.

I think I was getting that old breadboarditus. It wasn't locking up, just not starting. So I'll post the "final" soon. I've gone back to a 1M log for the delay pot. Log feels better than a lin to me. Also put a 1uF cap on pin 2 as it seems to give the VCO a gentle start.

I don't know about an external input. It will probably need a blend control to get decent balance with the repeats.

I'd be happy though to know of any other breadboard adventures with what I posted last.

[anotherjim]

I've made the output strong enough to drive a mixer or powered speaker - a guitar amp may not be the likely destination for this kind of thing.

Personally, I like to start it with minimum delay time then slowly extend the time right down and listen to the noise loop evolving. The loop time can be quite long so be patient. Adding gaps introduces new artifacts, starting with silence, then a sample rate tone that degenerates each time around.

If you switch on with time minimum, slowing the junk down creates FSK modem like random beeps which degrade nicely over time. You might want to add a power switch to the box.

It can create a lush but solid noise if you let it that's a bit more interesting than a proper noise generator. Would make a good module for a Lunetta-type synth if that's your thing.

[duck_arse]

here's a funny story - I couldn't stand not knowing anymore, so I cleaned off a breadbord and tried the circuit as shown.


and it worked first go. I had 2M instead of 22R, but made no diff. I have output cap, feeding computer speakers at the moment. I had 47uF at pin 8, 500k pot.

I have made some findings and scribbles, will need to draw them proper, for tomoz. stay tuned.

[anotherjim]

That resistor should make absolutely no difference. Maybe the developer didn't have any link wires left and used a handy l resistor instead? Pin 12 is actually an opamp output and it doesn't need a resistor to drive the inputs at pin13 & pin16. Those opamps have no feedback resistor so are pretty much comparator fuzzes.

Note, I haven't actually tried that original - I thought it had been proved to have problems -  seems not!

[duck_arse]

[image deleted - updated below]

here's where I'm at so far. you need a power reset push-switch, just cuts power and clears the mess. and you need a load push-switch, for when nothing happens. this sags the V/2 pin with the emptied-when-not-in-use C4. C3 & 4 need to be equal values, not critical, or larger on the switch.

at switch on, you need to waggle the delay pot to make something happen. you have until the orange LED1 lights to load your mess, to some extent. the speed switch selects a faster or slower delay string. the sweep switch add an ldr across larger or lesser part of the delay string, for some self modulation. the problem is tho, the led is on mostly, and only dims a bit, so the ldr is mostly lit. but on/off switching the sweep can do interesting things to the gurgle in progress. [you want a dim diffuse led and a not low swooping ldr, or maybe an opto coupler instead - to be decided.]

C5 can be switched out and in, out gives a different bassy sound, but all the information seems to drain out of the stack and you end up w/ ticks. I haven't gotten to the opamp section yet, so they are fairly stock, but I'm thinking of a percussive piezo input or something. output level pot value not critical, plenty of volume.

I've found that you need to crank/vary/wobble the delay pot/string switches as you release the reset push, up until the led lights, or nothing much happens. and if nothing happens, bump the load key and hope for a squeel. if you get the ticking, just hit the reset button for a while.