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DIY Stompboxes => Building your own stompbox => Topic started by: spectreman on September 09, 2021, 10:36:35 AM

Title: PT2399 Noise Generator - Help with schematic to vero.
Post by: spectreman on September 09, 2021, 10:36:35 AM
Hey everyone,

I recently dug up this schematic for a noise generator using the PT2399 chip.  You can see it in action here:

https://www.youtube.com/watch?v=k810qG5nKXs&t=7s

To me, it sounds great, and I was hoping someone with more advanced skills than myself could make a compact vero of the schematic.

Check it out and let me know what you think!

(https://i.postimg.cc/f3cSNV2F/pt2399noise.jpg) (https://postimg.cc/f3cSNV2F)
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 09, 2021, 03:07:00 PM
That thing's crazy. Me like.
Vero pretty much designs itself doesn't it? Have a strip above and below for ground, link them together. Cut tracks between all chip pins and add parts & links pretty much as drawn on the schematic. That's how I'd do it -  I never plan layout on paper first. Go on - give it a go!
You do need to think about how to get the 5v power. USB power-only cable comes to mind.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: moid on September 09, 2021, 07:43:28 PM
That sounded cool - does the PT2399 need to be connected to IC3 to generate a sound input? Or can IC3 be omitted (if it is required what is it, because a vero layout is no use without it). A 7805 could be placed in the layout so you could run standard 9V to the 7805 and then 5V to the PT2399. I could probably draw something in diylc on vero if you need some help, but I would need to know what IC3 is first (if it is required)
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: mdcmdcmdc on September 09, 2021, 10:29:49 PM
This thing sounds cool as heck, I did a little snooping and found the following:
(https://i.imgur.com/iMTi9Kd.jpg)

Quote
Its part of a larger circuit that I built at a workshop with an artist called Ewa Justka. I'm sure she won't mind if I share it... Ignore the big line that goes to the left. That connected to an oscillator but the box in the video has no input, it just works from self oscillating feedback
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: spectreman on September 10, 2021, 10:17:25 AM
Oh nice!  I was wondering where IC3 went, but it looks like it can be omitted from this layout.  I'm not sure how to set up the regulator for 5V, so I figured a nice little vero layout would clear & clean up everything. 

Thanks for the continued help on this, it's appreciated!
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: duck_arse on September 10, 2021, 10:27:07 AM
sounds good to me. however, as pin 14 on the PT2399 is an opamp output, it will be sitting at 2V5. the circuit needs a DC blocking cap between pin 14 and the outside world, and a pulldown resistor on the end of that wouldn't hurt.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: blackieNYC on September 10, 2021, 01:13:10 PM
Don’t people report that the chip can “lock up” if pin6 is brought to ground?  That pin usually has a 1k in series with the pot, right?
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 10, 2021, 01:51:30 PM
Yes, the speaker needs DC blocking and a minimum resistor in pin6 to the pot.
Not sure if everyone would want a feeble onboard speaker, a volume pot to output jack could be better.

Is it required to work off 9v DC pedal power then?
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: Jdansti on September 10, 2021, 04:12:38 PM
^I made a noise maker for one of my nephews and I put a switched speaker out jack that would disconnect the little internal speaker when a plug was inserted.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: spectreman on September 10, 2021, 04:21:36 PM
^I made a noise maker for one of my nephews and I put a switched speaker out jack that would disconnect the little internal speaker when a plug was inserted.

Very nice!  What noisemaker did you build?  I love this kind of stuff...
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: Jdansti on September 10, 2021, 04:42:23 PM
^ It was a conglomeration of effects stuffed into one box with a bunch of knobs you tweaked to get all kinds of sounds. The front end was an oscillator using a 555 chip. I ran that through a tremolo, then flanger, then delay and finally through a little 386 amp. Just a bunch of small circuits chained together that could be active or bypassed. I had a switch that let the user choose continuous noise or manual control. This caused the unit to only make noise when a momentary button was pressed. I also had an input jack which disconnected the oscillator and let you play an instrument through it. The delay was set up for infinite repeats so you could get some really cool crashing sounds.

I almost didn’t give it to my nephew!  I plan to make another one for myself.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: moid on September 10, 2021, 06:54:04 PM
Hello spectreman

I had a go at a vero layout for you

(https://i.imgur.com/cQmnSS5.png)

Don't build any of it until someone with more knowledge than me has checked it! I'm no expert at this sort of thing. I added duck's suggestion about the DC cap and pulldown resistor, but I'm not sure if I've put them in the right place, and I also added a minimum 1K resistor for the pot as suggested by anotherjim. I made the output to an audio jack. The power is a standard 9v like you use on any effects pedal, but it goes through a 7805 to turn it into 5V for the IC.

Edit: I think I can get rid of the long jumper on the right of the board and make the board smaller... I need some sleep first, it has been a long day...
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: mdcmdcmdc on September 11, 2021, 12:22:51 AM
I could be wildly mistaken, but I think the LM7805 needs a few caps attached to make it function as a regulator per the datasheet?

(https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRAsrGC7ZVUB8wfAYRnCav2OxS8Qzt_1aF5Hg&usqp=CAU)
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 11, 2021, 04:32:11 AM
I knew Moid would have a go at it! Ah, the universe turns in its expected order.
The output cap shouldn't go to 0v though, and you don't need that r/h long link.
If you cut the track below pin 9 (K8) then move the 1M pull-down to the bottom track bridging that track cut (K7-K9), the output wire also moves down to the bottom track (K14). The polarity of the output cap is negative to the bottom trace.

If you make the long link under the chip in 3 pieces, it can call in at pins 3 & 4 and you don't need the 2 links on the left.

This is a noise machine, so noise and audio quality are not on the agenda. All the nF value caps can be cheap ceramic discs or mlcc as they can better fit over adjacent tracks.
Any constant supply noise/hum from a less than perfect PSU might be objectionable. Another 100uF cap between the top 2 tracks would deal with that.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: duck_arse on September 11, 2021, 10:02:04 AM
I don't think we should take the speaker symbol to mean connect a speaker here [it shows no impedance, either], but rather this is where you connect for output to something else, not a speaker.

moidy, you have a DC bypass cap, we want a DC blocking cap - they go in series with signal. 100uF is probably way too much, maybe 100nF would suffice from all the screeching sounds in the clip. and 1M could be 100k, or an A100k or A50k pot. all this will become clear once you breadboard it, tho.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: spectreman on September 11, 2021, 10:46:45 AM
Amazing!  I'm super amped that you all are into this!  Thanks for all the input & work (thanks moid, for the initial layout!).  I'm excited for the future posts...looks like we're getting real close to a working layout.  Awesome!

Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: John Lyons on September 11, 2021, 01:31:44 PM
In my experience with this circuit (as drawn) I get almost none of
the sounds in the video. Shorting pin 16 to 15,9,10 briefly, not all at once
but randomly glitches the repeat to get some of the sounds though.
It's hit or miss depending on the knob setting. Wildly variable and unpredictable...
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: moid on September 11, 2021, 06:45:32 PM
Hi everyone, round two!

(https://i.imgur.com/wDtWNDw.png)

I've tried to add everyone's suggestions, so please point out anything I missed or stuck in the wrong place.

I could be wildly mistaken, but I think the LM7805 needs a few caps attached to make it function as a regulator per the datasheet?

(https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRAsrGC7ZVUB8wfAYRnCav2OxS8Qzt_1aF5Hg&usqp=CAU)
I think you could be wildly correct :) Thank you for reminding me that drawing layouts at midnight is not the best plan I ever had!

I knew Moid would have a go at it! Ah, the universe turns in its expected order.
Wow, I had no idea that I had that level of reliability :) Sadly it won't last, work is picking up for me now and will be stupidly crazy until Christmas, which means my chances of fixing that Sentinel Reverb are looking slim... but I haven't forgotten it!

The output cap shouldn't go to 0v though, and you don't need that r/h long link.
If you cut the track below pin 9 (K8) then move the 1M pull-down to the bottom track bridging that track cut (K7-K9), the output wire also moves down to the bottom track (K14). The polarity of the output cap is negative to the bottom trace.

If you make the long link under the chip in 3 pieces, it can call in at pins 3 & 4 and you don't need the 2 links on the left.

This is a noise machine, so noise and audio quality are not on the agenda. All the nF value caps can be cheap ceramic discs or mlcc as they can better fit over adjacent tracks.
Any constant supply noise/hum from a less than perfect PSU might be objectionable. Another 100uF cap between the top 2 tracks would deal with that.

Thanks anotherjim. I've incorporated all your suggestions (I think). Would you mind checking I put them in the right places please?

moidy, you have a DC bypass cap, we want a DC blocking cap - they go in series with signal. 100uF is probably way too much, maybe 100nF would suffice from all the screeching sounds in the clip. and 1M could be 100k, or an A100k or A50k pot. all this will become clear once you breadboard it, tho.

Well luckily my head is still screwed on or I'd forget that too! Thanks Duck - I've changed those values you suggested too. Haven't added  the pot yet, because I'm not sure if spectreman wants that. Spectreman, let me know if you want another pot; I'm not sure what it will do, but Duck knows his stuff so it'll probably something fun.

Amazing!  I'm super amped that you all are into this!  Thanks for all the input & work (thanks moid, for the initial layout!).  I'm excited for the future posts...looks like we're getting real close to a working layout.  Awesome!

That's no problem, this does sound like something I'd like to build at some point and I would do it on vero anyway. It's doubtful I'll get the chance to make this until Christmas though :( So if you build it I would like to know if it works. It does sound like you should probably breadboard this first if John's comments are anything to go by.

In my experience with this circuit (as drawn) I get almost none of
the sounds in the video. Shorting pin 16 to 15,9,10 briefly, not all at once
but randomly glitches the repeat to get some of the sounds though.
It's hit or miss depending on the knob setting. Wildly variable and unpredictable...

I wonder if the missing IC3 is actually an opamp or other IC (a PLL?) that generates a loud tone to feed into the PT2399 to get it oscillating? So it might work without it, but not very well as you have found? I wonder if just piping guitar audio into pin 16 might be enough?

Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: John Lyons on September 11, 2021, 08:19:10 PM
In my experience with this circuit (as drawn) I get almost none of
the sounds in the video. Shorting pin 16 to 15,9,10 briefly, not all at once
but randomly glitches the repeat to get some of the sounds though.
It's hit or miss depending on the knob setting. Wildly variable and unpredictable...

I wonder if the missing IC3 is actually an opamp or other IC (a PLL?) that generates a loud tone to feed into the PT2399 to get it oscillating? So it might work without it, but not very well as you have found? I wonder if just piping guitar audio into pin 16 might be enough?

There has got to be more to it, I agree.
My PT2399 theory is week. I need to look
a some schematics and figure out some stuff...
This look like a good place to start.
https://www.electrosmash.com/pt2399-analysis (https://www.electrosmash.com/pt2399-analysis)
A little more info here.
https://www.facebook.com/chrismenessound/posts/2012014219074621 (https://www.facebook.com/chrismenessound/posts/2012014219074621)
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 12, 2021, 04:20:57 AM
^Latest layout looking good I think.

This thing has been "designed" at a circuit bending workshop. Therefore there is a lack of proper development. It raises concerns & questions...
Why is the feedback resistor only 22R? Pin 16 is a hiZ input, that resistor there may not do anything - and 22R is more like a value you might choose to allow an 8R speaker to run off an output pin. Is it in the right place?
Without the resistor we've added to the delay pot, the chip can lock up & ceases working. Could that be why some report failure with it as it was?

Somebody needs to breadboard it!
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: noisette on September 12, 2021, 04:40:08 AM
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?
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: moid on September 12, 2021, 03:09:42 PM
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.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 13, 2021, 09:22:54 AM
Try this...
(https://i.postimg.cc/tRYLwJC9/PT2399-regen.png)
... 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.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 13, 2021, 05:02:08 PM
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.

Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: John Lyons on September 13, 2021, 05:14:38 PM
How would you describe what you have going now
soundwise Jim? (Short of a sound clip) Anythng interesting?
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: moid on September 13, 2021, 06:24:53 PM
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.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 14, 2021, 04:41:07 AM
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!
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 14, 2021, 08:25:57 AM
Here's what I had last night...
(https://i.postimg.cc/SxDC6nfF/PT2399-regen2.png)
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 15, 2021, 01:39:51 PM
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.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: John Lyons on September 15, 2021, 08:47:59 PM
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)
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 16, 2021, 08:49:35 AM
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.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: moid on September 16, 2021, 07:12:58 PM
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?
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 17, 2021, 04:58:26 PM
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.........
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: John Lyons on September 17, 2021, 09:44:49 PM
Mine locks up as well
with the original schematic.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: rutabaga bob on September 18, 2021, 02:01:12 PM
Brings to memory Anchovie’s ‘Noise Ensemble’...
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 18, 2021, 04:58:33 PM
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.

Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 19, 2021, 02:00:18 PM
(https://i.postimg.cc/CLGG8PJ7/PT2399-regen2.png)
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.

Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: duck_arse on September 21, 2021, 11:14:38 AM
(https://i.postimg.cc/wBPXDJh6/pt2399noise.jpg)

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.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 21, 2021, 11:52:43 AM
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!
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: duck_arse on September 22, 2021, 10:41:36 AM
[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.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 22, 2021, 04:07:52 PM
Wow Ducky! You've gone a long way with that one.
I see you've avoided the shortest delay range - it is just a buzz no matter what's in the loop.
I've got mine built & boxed. Hasn't locked up once. Delay knob and gap switch are it's most useful tools. Doesn't really need a volume knob if you plug into something that already has one.
I've scoped the audio. Tones are square waves, noise portions are trains of pulses either positive or negative.

I like the idea of a piezo impulse input. It should do the opposite of my Gap switch. "Musical" input probably won't live long enough although it should be useful if it's only modulating the delay time.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: duck_arse on September 23, 2021, 10:14:42 AM
(https://i.imgur.com/8i2Z51A.png)

updated - still not finished.

I can't prove it, but the size of the load cap might influence the noise, so you might be able to use a sprung both ways centre off rewrite toggle (hasn't everyone got one?) and a same-size and larger-size to get different bumps, but I don't know if they would discharge in a reliably re-usable manner.

I've added the smooth toggle - this is used (waggle it, then on) on loading, as the smaller cap produces a more off/on signal at that pin - which produces a different tone, odd phasery outputs, and maybe different drive for the opto led.

the step switch values are tricky, but this is used for both loading and running, to give steps. the sweep switch now switches an opto transistor shunting some/more of the delay string. it works, not terribly convincingly, the resistor values are tricky.


AJ - any pointers on adding the piezo? or even maybe an electret mic? I should be able to use the OP2 for gain and then take output from OP1, no? I might be able to wrangle the piezo as modulation somewhere along the string, too, maybe. my intended build will have a wooden front panel, I was planning on a toothbrush drumstick.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 23, 2021, 04:24:28 PM
Hmmm now - you've used the spare opamp (13-14) but pin12 can drive output without it - or do you like the extra comparator fuzz effect the opamp brings? Whatever, a piezo pulse can probably hit one of the inputs directly only if it happens when the thing is already in full clip it may not be noticed. Piezo is capacitive. It may need a high >1M bias resistor from pin2 but it wouldn't need a blocking cap unless you find it helps with the pulse shape. Then again you might just hook the piezo to pin16 and get something useful. It will have signal on it though from the 1M - I don't if it will be audible from the disc like that. Or you might split the 1M in two and feed the piezo in the middle or if the 1M was a pot to the wiper?

Electret setup is easy. 5v supply and pick a bias resistor to the mic+ that gives *2v; just like setting a JFET drain which is what it actually is. However, the thing full clips so the mic needs a preamp and if you allow it to be monitored "live" it will probably howl by itself with nothing to do with the delay. It might be best if fed to the delay input and only be heard after delay.
*2v as that's what I saw in a Panasonic electret datasheet long ago.


Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: John Lyons on September 23, 2021, 05:28:36 PM
Interesting tweaks Duck!
Here's what I get out of the original schmatic as outlined
in my post above (touching different pins somewhat at random
to pin 16). I added a strong low pass tone knob to get more thump
or sizzle, depending...

Sound Clip
https://soundcloud.com/john-lyons1/pt2399-noise-circuit (https://soundcloud.com/john-lyons1/pt2399-noise-circuit)
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: duck_arse on September 24, 2021, 10:35:35 AM
John, your audio is exactly the rubbish I've been listening to all week. except more musical. I want that tone control. I've found the step switch is very useful for getting from here to there, and back again.

I think I've sorted the sweeping bit of the delay string, in my head at least. switching resistors problem, it seems.

as for piezo - I did standard proper opamp, and the bloody thing wouldn't go sick properly. one thing - whacking the piezo and opening the smooth switch in playback created the exact sound of a pushbike bell, with variable tone. the problem with the piezo tho is the tiny short burst goes in, then gets time shifted into a bip, and nothing results. piezo whacks into pin 2, however, does like a load/bump, depends on how hard.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 24, 2021, 11:13:24 AM
Awww.... mine sounds nothing like Johns. I suppose I will have to post a clip.

A slow LFO to pin 2 might create PWM/Phasey goodness since it's the reference for opamps working like comparators - depends on what the audio is doing - square waves won't change much.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: John Lyons on September 24, 2021, 01:23:47 PM
Post a clip of what you guys have going.
Jim. Yours seemed to get more airy swooshes
and softer noises in the one I breadboarded
from your first schematic.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: anotherjim on September 24, 2021, 04:39:24 PM
https://soundcloud.com/ashdalestudio/noisedegenerator
Try this.
It starts fading in on a loop I had left running for 20mins or so.
I've got an spdt gap switch that is spring-biased one way, latching the other. Outer lugs are joined so it can be flicked for short gaps or held for erase. Funny thing - erase still makes a click. I suspect I'm getting a pulse in the chip when the memory address count bits all flip back to 0 - but that's a guess. Also, have a power switch. It's cool the chip has a soft start so there are no big thumps when you switch power. Oh, and this has no LED on pin7.
Apologies for the length of the clip, but at long delays, it can take a while for things to develop. I've actually swung it about faster and more often than I would for myself.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: PRR on September 24, 2021, 07:12:30 PM
....useful for getting from here to there, and back again.

https://www.youtube.com/watch?v=iab9YKocUcw
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: duck_arse on September 25, 2021, 10:15:20 AM
I've versioned this 1.0, so it must be buildable.
[removed.replaced - another one down, see later post]

some values changed. I've sorted the sweep string and the action makes sense now, is possibly a little extreme. also added a somewhat brute force topcut, at least till John shares his. [tone controls is not my best thing.] I tried AJ's version as well, I thought much the same as JL, softer than mine.

it's a fun thing to do a bump/load and leave the delay set at one or other end of travel, when the led lights you wind slowly to the other end of the pot. zounds!
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: John Lyons on September 25, 2021, 11:45:39 AM
I need to get my head around that schematic Duck.  :icon_redface:
My Hi Cut control is just a 50k pot in series with a .02 cap to ground
just before the volume pot.
If you get a chance I'l love to hear some of the sounds you're getting.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: duck_arse on September 26, 2021, 10:36:03 AM
here, see, don't be scared, it's V1.1, probably the final, some more value changes.

(https://i.imgur.com/PFoQuS4.png)

JL - seems we both used the same tone method. I added R7 and C10 in an effort to reduce the tiks - actually just muddied them a bit.

and, for a short time only, here's some short sound bites of the version above in action. first and second are just switch mashing, demonstrating the step and the sweep functions - no movement on the delay pot at all. third one is the sweep switch and the delay pot tuning bird whistles and bell ringings.

skwrp.one.mp3 - https://www.mediafire.com/file/zls4er85xieqyj1/skwrp.one.mp3/file
skwrp.too.mp3 - https://www.mediafire.com/file/5rm114tvhilq5e9/skwrp.too.mp3/file
skwrp.tree.mp3 - https://www.mediafire.com/file/nlrdpg9rqileylb/skwrp.tree.mp3/file
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: John Lyons on September 26, 2021, 08:32:15 PM
We all get very different sounds.
Pretty cool.
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: rutabaga bob on September 26, 2021, 09:11:16 PM
Impressions: some remind me of the noise you hear when you dial a fax number instead of a phone number.  Others sound like flea-sized jackhammers on metal.  How are those for recommendations?  ;-)
Title: Re: PT2399 Noise Generator - Help with schematic to vero.
Post by: duck_arse on September 27, 2021, 11:00:14 AM
yes indeed, you get a lot of modem noises.

for those without optocouplers wanting to sweep, you could use a photofet thing probably, I've never had one, or a vactrol, but the ldr lag will make for not much effect. the part diagram below shows how you could [probably, I haven't tried it, can't see why it wouldn't work] wire an ordinary transistor. just aboot any silicon npn small signal/switch would suit. a small pF value cap added base to ground might add a little laggy swoop to the action.

(https://i.postimg.cc/Y9PgRwWF/sw-eep-alt.png)