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 Forum index » DIY Hardware and Software » Circuit Bending
(mis)Using the PT2399 delay chip as a high-speed oscillator?
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Hashtag Octothorpe



Joined: Jun 11, 2017
Posts: 50
Location: Grand Rapids MI

PostPosted: Fri Jan 18, 2019 9:22 pm    Post subject: (mis)Using the PT2399 delay chip as a high-speed oscillator? Reply with quote  Mark this post and the followings unread

RIGHT after I ordered some dedicated "precision adjustable oscillators" for a circuit bend, I learned that the much-loved PT2399's "clock" pin (5) is the output of the clock it uses to run the ADC-delay-DAC magic it performs. It's a 5V part, and according to the datasheet, runs from 22MHz to 2MHz, which would be ridiculously perfect for replacing the 12MHz crystal.

So... anybody done this?

Here's the reverb module I'm going to mod, by the way. It's an INCREDIBLE module for the price, even without all the goodies I'm planning to add to the second one I build. Goodies like adjustable clock, a feedback circuit with gain for runaway crazieness, and dry/wet adjustment. And maybe a resonant low-pass filter in the feedback loop because why not.
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Hashtag Octothorpe



Joined: Jun 11, 2017
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Location: Grand Rapids MI

PostPosted: Fri Jan 18, 2019 9:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

I just checked: PT2399s are $0.16 each and the LTC1799 I ordered are nearly a dollar per chip. US dollars, ordering from AliExpress. Plus, I have lots of the reverb chips in my parts bin and the dedicated oscillators are crawling across the Pacific.
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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Sat Jan 19, 2019 3:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Nice idea Very Happy
I have only used that output as an indicator for the delay time but I think it could be used as an oscillator although it might require an extra buffer.

Instead of the LTC1799 I have use the 74HCT4046 to replace x-tals which gives you voltage control over the clock speed.

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ixtern



Joined: Jun 25, 2018
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Location: Poland

PostPosted: Sat Jan 19, 2019 1:03 pm    Post subject: Re: (mis)Using the PT2399 delay chip as a high-speed oscillator? Reply with quote  Mark this post and the followings unread

Hashtag Octothorpe wrote:
RIGHT after I ordered some dedicated "precision adjustable oscillators" for a circuit bend, I learned that the much-loved PT2399's "clock" pin (5) is the output of the clock it uses to run the ADC-delay-DAC magic it performs. It's a 5V part, and according to the datasheet, runs from 22MHz to 2MHz, which would be ridiculously perfect for replacing the 12MHz crystal.

So... anybody done this?

Here's the reverb module I'm going to mod, by the way. It's an INCREDIBLE module for the price, even without all the goodies I'm planning to add to the second one I build. Goodies like adjustable clock, a feedback circuit with gain for runaway crazieness, and dry/wet adjustment. And maybe a resonant low-pass filter in the feedback loop because why not.
[/url]

I am very interested in your mode of this module as I have the same or similar (although I even haven't tested it yet). I'm curious how you want to mod digital DSP reverb module - I don't think that changing a system clock is a good idea but who knows...
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Hashtag Octothorpe



Joined: Jun 11, 2017
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Location: Grand Rapids MI

PostPosted: Sat Jan 19, 2019 10:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

That reverb module is just amazing. So many very cool effects. My favorite might be 8, which is a nice lush reverb. Other really good ones are... well, there's gated reverb, "reverse" reverb, phasers and flangers, delays and choruses, pitch changers...

Okay, the module doesn't have "wet/dry" mix, so everything you feed to the input gets processed and you don't hear any of the original sound. I will use a reverse fader type circuit for that. It also lacks any way to feed the output back to the input, which I'll include with a basic amplifier circuit (although I might include a Korg MS-20 style low pass filter to the feedback circuit if I have room).

Changing the clock speed should be okay. My other reverb builds based on Spin Semiconductor FV-1 chips and my delay builds based on the PT2399 have adjustable clock speeds. The only problem might be if the microcontroller on the cheap reverb module crashes with a change in clock speed. If the DSP chip and the microcontroller share a the clock speed it shouldn't be a problem!
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Hashtag Octothorpe



Joined: Jun 11, 2017
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Location: Grand Rapids MI

PostPosted: Sat Jan 19, 2019 10:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

I drew a schematic... it uses five op-amps (I recommend TL047 quad op-amps) which is awkward. You MIIIGGHHTT be able to eliminate the bottom amp, instead connecting the two 10K resistors that originally connected to the output of that op-amp to the leg of the wet/dry potentiometer.


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Hashtag Octothorpe



Joined: Jun 11, 2017
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Location: Grand Rapids MI

PostPosted: Sat Jan 19, 2019 10:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

Whoops, no, there's problems with that schematic..... don't use it. I'll draw a better one tomorrow...
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PHOBoS



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PostPosted: Sun Jan 20, 2019 7:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Apart from the inverted feedback that actually looks quite ok although it might need some AC coulping caps depending on the power supply.
Interesting to see the wet/dry mix at the beginning of the audio chain, I've always just added it at the end but this might be a better idea
especially with delays.

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ixtern



Joined: Jun 25, 2018
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Location: Poland

PostPosted: Sun Jan 20, 2019 1:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hashtag Octothorpe wrote:
I drew a schematic... it uses five op-amps (I recommend TL047 quad op-amps) which is awkward. You MIIIGGHHTT be able to eliminate the bottom amp, instead connecting the two 10K resistors that originally connected to the output of that op-amp to the leg of the wet/dry potentiometer.

Remember that the codec on the module input/output has limited input and output voltage range. In my case it is CS4220-KS and according to datasheet it has 2V rms (means about 5.5V peak-to-peak for sine wave and 4 V for square). Output is almost the same (1.9V rms).
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Hashtag Octothorpe



Joined: Jun 11, 2017
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Location: Grand Rapids MI

PostPosted: Sun Jan 20, 2019 4:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

The inverting feedback shouldn't be a problem because the signal gets thoroughly mixed up in the guts of the reverb so polarity isn't an issue...

...except in that schematic where the dry signal also makes it into the feedback loop, that's my biggest error...

So here's a better one! With the TL074 pinout and bypass caps!

You're on your own to get the 5V the module needs. Maybe your build has a 5V rail? Use a 7805?

Oh! When I build this, I'll totally experiment with that "10K?" resistor. There's already gain coming from the buffer in the feedback loop, and getting the reverb overdriven into infinite repeats or hums or howls can be an amazing feature, but you don't want it going overboard. So higher values like 15K will reduce the signal level of the feedback, while lower values like 7.5K will increase the signal level.


I like including the wet/dry before the effect because then you can have the dry signal going through and "ping" it with a quick twist of the knob and get a chunk of sound into the effect and have it ring until the effect module is done doing its thing. Very Happy I think it's called "tails".


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Hashtag Octothorpe



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PostPosted: Sun Jan 20, 2019 4:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

Okay, change the feedback resistors on the output amps (the only 20K resistors on there) to 30K resistors and you'll get almost unity (well... inverting unity) out of the dry signal, which is good. The wet signal will be processed by the effects module and the one I'm using has its own volume knob, so...?
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ixtern



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PostPosted: Mon Jan 21, 2019 3:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Hashtag Octothorpe wrote:
The inverting feedback shouldn't be a problem because the signal gets thoroughly mixed up in the guts of the reverb so polarity isn't an issue...

...except in that schematic where the dry signal also makes it into the feedback loop, that's my biggest error...

So here's a better one! With the TL074 pinout and bypass caps!

You're on your own to get the 5V the module needs. Maybe your build has a 5V rail? Use a 7805?

Oh! When I build this, I'll totally experiment with that "10K?" resistor. There's already gain coming from the buffer in the feedback loop, and getting the reverb overdriven into infinite repeats or hums or howls can be an amazing feature, but you don't want it going overboard. So higher values like 15K will reduce the signal level of the feedback, while lower values like 7.5K will increase the signal level.


I like including the wet/dry before the effect because then you can have the dry signal going through and "ping" it with a quick twist of the knob and get a chunk of sound into the effect and have it ring until the effect module is done doing its thing. Very Happy I think it's called "tails".

It is a bad idea to put pot in the feedback loop of opamp. After some time, when pot's resistive path would worn, your opamp may go crazy with open feedback loop, generating big clicks (or maybe locking up).
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Hashtag Octothorpe



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PostPosted: Mon Jan 21, 2019 8:23 am    Post subject: Reply with quote  Mark this post and the followings unread

I always tie the wiper to one of the ends, so at most it'll fail at the MAXIMIUM VOLUME 😁 In the 808 all the variable-gain inverting amps also include a big electrolytic cap in series with the potentiometer and a 470K resistor in parallel.

If I ever build modules for sale, I'll do that too.
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noto



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PostPosted: Wed Jan 23, 2019 10:28 am    Post subject: Reply with quote  Mark this post and the followings unread

hi! that reverb module looks like it is using a coolaudio V1000. it is possible to pitch them with an external oscillator, but it may cause the microcontroller to crash. you can disconnect the micro controller and still access the 16 FX with switches. check out the datasheet http://www.coolaudio.com/docs/V1000_DATASHEET.pdf
the mod is great. sounds really good. although i didn't try feedback. https://youtu.be/ybgNFWiQv1U
also, did you get the pt2399 to work as a clock oscillator? sounds like a cool experiment.
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Grumble



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PostPosted: Thu Jan 24, 2019 12:12 am    Post subject: Reply with quote  Mark this post and the followings unread

In my delay module I use a digital potentiometer (AD5144 from Analog Devices) controlled with an Arduino to change the clockfrequency of the PT2399.

Youtube clip

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noto



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PostPosted: Thu Jan 24, 2019 8:38 am    Post subject: Reply with quote  Mark this post and the followings unread

very cool! i really need to make some time for arduino someday.. i have lots of pt2399 laying around, but i don't really like the sound quality for typical delay applications. looking for new ways to use them. always thought it would be cool to try to build a sort of comb filter out of a pt2399. probably not fast enough, but might give some unique quality. Very Happy
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Hashtag Octothorpe



Joined: Jun 11, 2017
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Location: Grand Rapids MI

PostPosted: Thu Jan 24, 2019 3:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

noto wrote:
hi! that reverb module looks like it is using a coolaudio V1000. it is possible to pitch them with an external oscillator, but it may cause the microcontroller to crash. you can disconnect the micro controller and still access the 16 FX with switches. check out the datasheet http://www.coolaudio.com/docs/V1000_DATASHEET.pdf
the mod is great. sounds really good. although i didn't try feedback. https://youtu.be/ybgNFWiQv1U
also, did you get the pt2399 to work as a clock oscillator? sounds like a cool experiment.


I didn't mess with the PT2399 for this use yet... I'm struggling with getting a fully-point-to-point clone of an 808 hi-hat voice, which I JUST finished!!! Very Happy

I'll update this thread with any progress. It would be nice to have fifteen cent chips usable as crystal replacements! With, like, just a decoupling cap and a pot!
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Hashtag Octothorpe



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PostPosted: Fri Apr 12, 2019 10:48 am    Post subject: Reply with quote  Mark this post and the followings unread

I built this with a 1799 oscillator replacing the crystal. It works!!!

The timing range is pretty sensitive, it'll crash if the timing is too fast OR too slow, so if you go this route, trim the end and middle of the speed-setting pot carefully (if that makes any sense).

I did NOT try the PT2399 clock in this build, but I may get another of these modules and give that a try!
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Hashtag Octothorpe



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PostPosted: Sat Jun 15, 2019 7:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

IT WORKS!!!!!

I'm so happy to report that the PT2399 clock will drive other circuits! I feel like with 1799s and the like, there's going to be more precision and consistency, but if that's not something your circuit needs, TOTALLY use them!

I put a 10uF cap between pin 2 and 3, another 10uF cap between 1 and 3, AND a 100nF between 1 and 3, a couple 100nF caps from pins 7 and 8 to ground (not sure if any of these caps are strictly necessary but...?) and grounded pins... um... 10, 12, and 15. All the inputs on the right side of the chip. My particular application needs a 2.7K resistor minimum from pin 6 to ground, and a 50K pot seems to give me the most usable range.
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PHOBoS



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PostPosted: Sat Jun 22, 2019 4:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

great, good to know that works Very Happy
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