PT2399 sound generator idea

SineHacker · Joined: Mar 09, 2010 Posts: 99 Location: United Kingdom

Hello all, I was wondering, has anyone tried using the PT2399 as a kind of sound generator before? there are endless iterations of cool delays, but I was thinking of maybe a karplus-strong kind of approach, I think the ingredients are there

In software (as always) it's super simple, if you don't know the karplus strong idea then it's all here: http://www.youtube.com/watch?v=5RYy8Cvgkqk

I am going to try making a minimal component project over the next month or so, I will post up results here - but just looking for thoughts at the moment,

GO!

SineHacker · Joined: Mar 09, 2010 Posts: 99 Location: United Kingdom

Ok, I did a bit of a search in the EM forums and it looks like people think the PT2399 has too long a delay time (at minimum) for the KS application, I will still have a fiddle anyway because that's what I do.

The MN3209 looks like a possible option but they are about £5 a pop!

TBC...

Cynosure · Posted: Wed May 29, 2013 3:53 pm Post subject:

I have seen people do KS on modular synths using BBD delay modules.

http://www.youtube.com/watch?v=42Mgzf8-rqs

ejr27233 · Joined: Feb 08, 2010 Posts: 52 Location: UK

I was thinking about this myself. The 'little angel' DIY chorus pedal uses quite a clever way of getting shorter variable delays from a PT2399.

JovianPyx · Posted: Thu May 30, 2013 7:28 am Post subject:

Inventor designed a Karplus-Strong system using a BBD here: http://electro-music.com/forum/topic-36165.html The thread is very long, as it chronicles the development. The initial schematics show more primitive versions and don't have the filter that needs to be there, so make sure to look through the whole thread.

The PT2399 indeed has too long a delay for this purpose. Another problem is that the VCO frequency needs to be in a range from 2 MHz to 22 MHz. This range will present a challenge to make a musically linear VCO.

IMO, the BBD chosen by Inventor is the better choice.

Then again, one can always go back to the original Karplus-Strong idea which used a digital delay. I've done it this way in both an FPGA and in a dsPIC.

SineHacker · Joined: Mar 09, 2010 Posts: 99 Location: United Kingdom

Ok thanks, I definitely want to explore karplus-strong, but I also want to explore the potential of the PT2399 as a low-cost weird sound making device - I will check out the BBD link now

ejr27233, the "Little Angel" is mental! I never even thought of touching the ref pin! can't wait to get home tonight for some mad science Smile

Cynosure · Posted: Fri Oct 11, 2013 11:27 pm Post subject:

I was bored tonight and the pt2399 is a pretty easy thing to breadboard, so i tested it out.

The angel chorus trick only works for lfo modulation. The chip quickly adjusts when the reference is changed, so you can't get it to hold a steady faster rate.

As long as there is at least 1k on pin 6 when you power on the chip, you can dial it down to a faster rate. However, the fastest rate possible only produces a maximum frequency of 78Hz.

It makes some cool drum sounds and could be used for very low bass, but not as versatile as you probably want.

An interesting thing is that the pt2399 has two free opamps in the chip. The second one pretty much has to be used in order to remove the high frequency noise added by the chip, but the first is free to use as you would like. I used that for a variable lowpass filter to do the KS synthesis.

Also, you can borrow the vref and use it for external opamps Smile

Cynosure · Posted: Sat Oct 12, 2013 12:18 am Post subject:

I increased the voltage supply to 8V (beyond the max rating). That allowed it to get up to 114.53Hz. That range is just barely usable for a bass synth.

The chip got a little warm, but seemed to hold up ok.

I wonder how far I can push it and it still be ok...

SineHacker · Joined: Mar 09, 2010 Posts: 99 Location: United Kingdom

I'm surprised you didn't cook it at 9v!! The chips aren't particularly robust so I don't imagine they would live long if you push them like that. Let us know what happens though!

P.S I have been working on a simple cheap delay kit aimed towards circuit benders / dub sirens / cmos synths basically for people who want a quick easy delay module to add to something: aidanrichardtaylor.wordpress.com should be good to go in a couple of weeks if these boards are good Smile

Cynosure · Posted: Sat Oct 12, 2013 8:42 am Post subject:

I used 8V, not 9V. The max rating is 6.5V, so it is only 1.5V above the max. I would have tried 9V too, but I don't have a regulator at that voltage. My next regulator is 12V and I think that is too high to even try.

SineHacker · Joined: Mar 09, 2010 Posts: 99 Location: United Kingdom

Yep, sorry I did see you said 8v straight after I posted Razz

You could use a 9v battery, no need for a regulator there, but one of my friends almost certainly cooked a couple of PT2399's trying to power them from a 9v battery

new voodoo · Joined: May 06, 2013 Posts: 94 Location: RVA USA

you could also check out the other princeton 2395? pr 6? cant remember..thats like the 320x/310x BBD system & requires a DRAM-those (i think) can be used for what yu want..i think.
Theres also the erso es56033, es56029e, mitsubishi ms65831 and holtek ht8955 & 8970 (70 requires DRAM too)
There are lots of comps, oscillators, filters, amps, etc in a lot of the various chips-the erso have surround sound so mixers, etc that can do a LOT of things I think have been relatively unexplored.
I wish you luck with the ideas tho-id sure like to see someone do smething really new and inventive like that!!

They might be hard to find, unless you were to look in some AWESOME poster's signature for a link to a store that carries ALL OF THEM...

(sorry, bit shameless)