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Scott bernardi PT2399 VC delay
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211



Joined: Jul 18, 2006
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Location: Marseille - France

PostPosted: Sun Feb 11, 2007 8:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Trying to remember... At fastest clock setting, you can get chorus like effects, but not flang-ish effect..

At lower setting, lofi textures were funnier.

Yesterday I picked some 7805, I'll try to repair it soon (And finish the second one I began to get a stereo delay Razz )
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bugbrand



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PostPosted: Sun Feb 11, 2007 9:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Fernando wrote:
thanks bugbrand

I asked assuming someone tried to explore the limits using faster clock rate...


hehe - yeah, I kind of guessed that - I don't know much about really hi-speed clocking, so... well, the figures on the datasheet suggest that probably 30ms is about the shortest, though I seem to recall seeing somewhere about some details of those other unused pins (5, 7 & 8)

ahhh -- here we go more detailed datasheet but that doesn't directly help....

so.. what exactly are CC0 (pin8) and CC1 (pin7) used for - mod & demod?? Know the terms, but don't know what they really refer to...

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shawn



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PostPosted: Sun Feb 11, 2007 10:32 am    Post subject: Reply with quote  Mark this post and the followings unread

hrm bugbrand. you do have a good question regarding CC0 and CC1. Wonder what modulation and demodulation you could do....experiment? One of these days I'm going to have to actually mess with this chip!
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Uncle Krunkus
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PostPosted: Sun Feb 11, 2007 1:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

Current control, hmmmm,....
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bugbrand



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PostPosted: Sun Feb 11, 2007 2:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

....current control?? oh.....
...just been reading thomas henry articles about getting 566 chips to work well....
..click..click..brrrr.
Hmmmmm

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Fernando



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PostPosted: Sun Feb 11, 2007 2:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

bugbrand wrote:
Fernando wrote:
thanks bugbrand

I asked assuming someone tried to explore the limits using faster clock rate...


hehe - yeah, I kind of guessed that - I don't know much about really hi-speed clocking, so... well, the figures on the datasheet suggest that probably 30ms is about the shortest, though I seem to recall seeing somewhere about some details of those other unused pins (5, 7 & 8)

ahhh -- here we go more detailed datasheet but that doesn't directly help....

so.. what exactly are CC0 (pin8) and CC1 (pin7) used for - mod & demod?? Know the terms, but don't know what they really refer to...


Here Ken Stone suggests a path to follow for faster speeds (other than overclocking) but I don't have a clue of how to do it...
http://www.cgs.synth.net/modules/cgs44_ddb.html
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bugbrand



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PostPosted: Sun Feb 11, 2007 2:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

Nah, that's for the PT23955 which works kind-of differently...
..but the companding (NE570) info on there is no doubt very useful

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a.b.o.z.



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PostPosted: Wed Mar 28, 2007 2:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

i've build tonepad layout rebote delay 2.5. it worked but i accidentally delivered +9 to tl072 pin 1. i was trying to do more feedback but with no hi-pass. now it just repeats once really quietly? and 1000$ question is: what's burned? pt2399? i gues..coz its the only component i don't have spare Smile


edit: it was actualy +12v.
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macumbista



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PostPosted: Wed Sep 12, 2007 8:49 am    Post subject: Reply with quote  Mark this post and the followings unread

So I got excited about this Rebote2.5 design and I etched a bunch of them and built them up. The idea is to do a complex delay network where the signal gets bounced around between different delay lines. But now that I've listened to it a bit more, I realized (like others on this thread) that the low pass filter is too aggressive. I'm losing too much signal on each pass of the delay.

In the build reports for the Rebote2, I noticed someone suggested replacing the op-amp feedback cap to reduce the filtering to the overall signal. In version 2, it was 100 pF, and this builder suggested 5 or 10pF. In the Rebote2.5, that cap is 5pF, but the filter is still too sharp! I tried removing it entirely but the filtering is still the same. So the culprit must be someplace else in the circuit.

I'm also trying to get very long delay times out of it (2-3 seconds with a 500k pot for the delay time), so I can imagine that the resampling of each pass also successively knocks out a lot of the high freqs, and there's nothing to do about that except get a different delay IC with a higher sampling rate Wink

But as it stands now, at any time length my delay network quickly turns to mud when I start summing the signals up or passing them between delay lines. Can anyone suggest a mod to the Rebote2.5 that will reduce the low pass filtering?

Question for moderators: is this better as a new thread?

Thanks!
derek

Last edited by macumbista on Wed Sep 12, 2007 9:50 am; edited 1 time in total
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Peake



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PostPosted: Wed Sep 12, 2007 9:26 am    Post subject: Reply with quote  Mark this post and the followings unread

I agree, it's really nice to jam the thing to zero with no hint of clock noise, but a mod for less filtration would be nice too, for different applications.

Anyone think about a version with two (or more) chips for longer clean delays?
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macumbista



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PostPosted: Wed Sep 12, 2007 9:54 am    Post subject: Reply with quote  Mark this post and the followings unread

I guess the main place to look is in the caps bridging pins 13/14 and 15/16. These are the bridges from the output of the LPF opamps back to the negative inputs of those same op amps in the delay chip itself. I might try throwing some different values in there, but of course this is also tied to the resistor values. Guess it's time to hit the books and find some formulas!

Question to any engineers in the group: is there a standard formula for computing the LPF cutoff frequency in this situation? The configuration appears to be an inverting op amp. In the meantime I'll hit Google and "The Art of Electronics" for suggestions...
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revtor



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PostPosted: Wed Sep 12, 2007 6:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

PT-80 soundclips a bit down on this page.. Built as a guitar effect, with a joystick for delay time and regen..

http://bizzofaction.com/prod.htm

~Steve

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bugbrand



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PostPosted: Thu Sep 13, 2007 2:05 am    Post subject: Reply with quote  Mark this post and the followings unread

revtor wrote:
PT-80 soundclips a bit down on this page.. Built as a guitar effect, with a joystick for delay time and regen..

Nice!


Derek -- first off, nice to see you here!

I think that it may be 1/(pi x R x C)
& I reckon you need to look most at the RC networks around the Delay Out label at the base of the Rebote2.5 schem (so probably you mainly want to look around pins 13/14) --- 12k / 10n gives me 3kHz if I'm on the right track.. Halving 12k to 6k (just for calculation's sake) would raise that to 6kHz

10 delays? Yr freaking nuts.
Did you get the 60 sin gens going yet?!!?


Here's a pic of Derek's wonderful work from a workshop we did together in Sweden recently:::: (didn't Ellinor do a good job painting it!)

Posted Image, might have been reduced in size. Click Image to view fullscreen.

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macumbista



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PostPosted: Thu Sep 13, 2007 3:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Tom! I'll have to hire you on as my publicity agent! Wink Ten delays was nothing! Took 45 minutes each by the end. Wait till I do a hundred Thomas Henry VCOs!!!! Yeah, I'm a bit Obsessive-Compulsive sometimes...

I looked through one of my op-amp books and discovered that the type of low pass filter is a "multiple feedback" one. What followed was a huge pile of Greek letters and Arabic formulas that didn't do me a lot of good. But at least I know what it's called now Wink

Pins 9 -12 are modulated and demodulated op amp outputs. What gets used is the demodulated one. The more informative spec sheet you posted here on this thread a while back shows the block structure. Beyond knowing what *these* are called, I don't really know what they would be used for.
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Scott Stites
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PostPosted: Thu Sep 13, 2007 10:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Anyone think about a version with two (or more) chips for longer clean delays?


I got back into synth DIY through playing with PT2399s back in 2002. I had a couple of them rigged up in either series or parallel. In series, one could actually get a decent long delay out of them. I was controlling them with an MPF102 Fet.

The tricky thing about the PT2399 is that there is no way I know of to precisely synch their clocks, which (not having looked at the DS for a long time) is available at one of the pins. As a side note, this signal might be handy for controlling a clocked filter a-la-Blacet Time Machine.

Anyway, not being able to synch the clocks opens the door for heterodyning, so you have to be careful about that.

As for minimum delay, when I returned to the PT2399 out of necessity (not having an echo box then) in November 2004 I put one on breadboard with an expo control. Here's a sample I made pushing the PT2399 to its limit - still a bit long for a flanger, but some comb filtering is definitely happening. It's a simple modular patch going through the PT2399 flirting with the max clock using an LFO. Very touchy setup, IIRC.

Cheers,
Scott

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Peake



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PostPosted: Thu Sep 13, 2007 12:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Scott Stites wrote:
The tricky thing about the PT2399 is that there is no way I know of to precisely synch their clocks, which (not having looked at the DS for a long time) is available at one of the pins. As a side note, this signal might be handy for controlling a clocked filter a-la-Blacet Time Machine.


Oh.. Oh well! Thanks for the info, and your mp3 is nice. As you said, not quite to zero, but not bad at all otherwise!

Thanks again.
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synthmonger



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PostPosted: Sun Jan 13, 2008 10:58 am    Post subject: Reply with quote  Mark this post and the followings unread

I built it from the pcb and upon firing it up the first time everything worked except the feedback. After playing with a few settings and then powering it back on the PT2399 and 7805 were hot. I noticed that it didn't knock the 12 volts down to 5v, but about 6v instead while it rose slightly about .01 volts per every couple seconds. However, when I turn it off and back on again about 90% of the time it goes to 5 volts. I'm getting a very low clicking noise from the delay output. I switched out the chips with working ones and still getting the same effect. Anyone else have similar problems?
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PostPosted: Sun Jan 13, 2008 5:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well I figured out my problems. I switched the regulator for the bigger one and I was using the wrong tranny for the vca. Sounds rad!

One thing I noticed though is the max delay isn't as long as the Vactrol version. The vactrol version you can get delays up to about 11 seconds (the sampling is very nasty sounding but in a cool way) unfortunately the delay is a bit droopy as if there is a permanent glide effect. The major benefit the current sinking method is instantaneous delays.
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janvanvolt



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PostPosted: Wed Jan 16, 2008 6:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

I am close to finish the PCB stuffing, however, i am curious what values to
use for the optional onboard regulator ( the capacitor + 2 x elco)

also what to use for the "*free" resistor value ?

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Etaoin



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PostPosted: Thu Jan 17, 2008 2:44 am    Post subject: Reply with quote  Mark this post and the followings unread

unit-sound wrote:
I am close to finish the PCB stuffing, however, i am curious what values to
use for the optional onboard regulator ( the capacitor + 2 x elco)


Anything you'd find in your standard PSU. The input elco value would depend on how much ripple the unregulated supply has. You might get away with something small like 100uF, but you might also need to go up to something like 1000uF. For the input cap I'd use an ordinary 100nF multilayer. Output cap isn't really important. 10uF, 47uF? something like that. It's not critical.

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211



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PostPosted: Thu Jan 17, 2008 9:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
also what to use for the "*free" resistor value ?


This resistor is a part of a voltage divider. It was intend to set input CV scale, as the PT2399 stop to output sound when the delay is too slow.

This resistor could limit the CV input, to prevent this annoying behaviour.

hope this help !
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Fernando



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PostPosted: Thu Jan 17, 2008 3:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

...it's obvious, but it just came to mind:

for those (like me) looking for shorter delays with the PT2399... building two circuits you can achieve a shorter delay between the two delayed signals.

The bad side is that both source and delayed signals will be already degraded by the delay (filters, distortion...), but at least some interestng things (sounds, music) might be done: pseudo physical modeling, inserting it in the feedback loop of other modules, etc

I wonder if, when using a vactrol, another problem could be that both delay vactrols would be working too hard most of the time in order to keep the quality "high" (both signals on the shorter delay region)
So other methods might be better (FET???)



drunken
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janvanvolt



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PostPosted: Sun Jan 20, 2008 7:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

211: i still have issues with the pcb.

i finished your design couple of hours ago, i did connect the
+5V unregulated in directly to +15, used two 47 uF and 100 nf for the 5V regulation.

however, i seem out of luck as i get something out, but it is way different than i know from the pt2395 setup (ken stone one).

it seem to react in some way, but nothing like a delay or such.
*R-free should have which value ? (it's currently not connected).

anything i could check ? i do get an output similar to the original signal, have no double scope to check out. also do i need to adjust something on the preset trim ?

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Etaoin



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PostPosted: Mon Jan 21, 2008 12:57 am    Post subject: Reply with quote  Mark this post and the followings unread

unit-sound wrote:
however, i seem out of luck as i get something out, but it is way different than i know from the pt2395 setup (ken stone one).


The PT2395 is a different chip... You should get delay, but nothing like as long as the PT2395 can produce (with sufficient DRAM).

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janvanvolt



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PostPosted: Mon Jan 21, 2008 3:10 am    Post subject: Reply with quote  Mark this post and the followings unread

Okay, in order to test it correctly, what should i give as input and which result should i get ?
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