Scott bernardi PT2399 VC delay

vtl5c3 · Posted: Tue Feb 17, 2009 7:29 pm Post subject:

So, I finished my first one of these units yesterday. I found it annoying when the delay cuts out when the delay pot is turned beyond a certain point. I found a simple solution:

1) Turn the pot right to the point where the delay cuts out

2) disconnect the power lead from the pot

3) measure the resistance between the middle pin of the pot and the pin you just removed the power connection from.

4) Solder a resistor that matches the value from step 3) to the power pin on the pot. Solder the power wire to the other end of the resistor.

I ended up putting a 4.7K resistor on mine, but yours may be a different value, depending on what pot you're using and what value you used for the "free" resistor.

And now that I'm looking at the PCB layout, I see that I could have just replaced the free resistor with one that is 1.5K + 4.7K... 6.2K.

211 · Joined: Jul 18, 2006 Posts: 50 Location: Marseille - France

Nice feedback vtl5c3.

Perhaps should I edit the shematics to add this info, or add a 10K Trimer in place of this *free* resistor on the PCB ?

Did you feel the feedback loop was too lowpass ?

vtl5c3 · Posted: Thu Feb 19, 2009 8:18 am Post subject:

I don't feel like the feedback is too lowpass. If anything, it adds a nice analog quality to the otherwise digital delay.

I'm now debugging a second unit. Right now it just makes farty motorboat noises. Seems to be an assembly error somewhere.

fluxmonkey · Joined: Jun 24, 2005 Posts: 708 Location: cleve

vtl5c3 · Posted: Thu Feb 19, 2009 9:09 am Post subject:

Fixed it 5 minutes after my last post. It was an etch error. Two traces had merged that shouldn't have. Bye-bye farty motorboat!

211 · Joined: Jul 18, 2006 Posts: 50 Location: Marseille - France

Good news ! Lucky the one who own a stereo device !

6079smith · Posted: Mon Mar 09, 2009 11:21 am Post subject:

This may be a dumb question, but what's the 100k trimmer for?

211 · Joined: Jul 18, 2006 Posts: 50 Location: Marseille - France

Hello 6079smith
the trimmer is used for VCA adjustment (CV feedback)
It must be set to prevent VCA clicks

6079smith · Posted: Mon Mar 09, 2009 3:29 pm Post subject:

Thanks for that... I just got a couple of the 2399 chips from Small Bear so I'll give this circuit a try. Might even make a dual version...

And thanks 211 for the PCB/schematic.

johans121 · Posted: Tue Mar 17, 2009 9:56 am Post subject:

tommi · Posted: Wed Jul 08, 2009 8:02 am Post subject:

Hi,
I am building this module, I got the Pcb almost populated and I am designing the panel..
I 've seen that there are two separated grounds (analog and digital) but I couldn't see a way to separate them and I planned to link them together.
Any suggestion?
thanks.

creatorlars · Posted: Wed Jul 08, 2009 8:16 am Post subject:

The grounds must be connected together at a single point, so you're fine I think. Smile

tommi · Posted: Tue Jul 14, 2009 6:24 am Post subject:

Thanks Creatorlars. I 've linked digital ground to the alalog ground on the spot where they are closest.
I post some picture. I still have to test it. This evening is testing time!

delay_tommaso.jpg

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creatorlars · Posted: Tue Jul 14, 2009 7:27 am Post subject:

Please let us know how it sounds. I found the output level on mine was a little low.

tommi · Posted: Tue Jul 14, 2009 12:40 pm Post subject:

GREAT MODULE! I 've done just a little bit of testing here and I really love it.
I inserted an lfo in the delay cv and in this configuration, when the voltage control goes over (under?) a certain level, the unit stops.
I am sure this was discussed before in this thread. And the solution could be to use a higher value resistor for the one marked as 'free'.
But I really like those weird sounds that it does when stopping. They should be used in a creative fashion for sure.

Creatorlars: I can confirm that sounds are lowered passing through this unit. It's clear tweaking the mix knob from wet to dry. The dry signal is higher in amplitude (and also brighter) than the wet one.

One weird thing about constructing it was that I thought that the pots on the layout were seen by the top. But, in fact, they was represented on a bottom view.
Now I got to reverse all pots wirings ( except for delay CV attenuator... strange..)

By the way thanks to 211 for posting this circuit Very Happy

Sebo · Joined: Apr 27, 2007 Posts: 564 Location: Argentina

Hi:
I just finished a module using this PCB and is working OK. Thanks for sharing it!!!
I didn't calibrated the DC offset of the VCA yet, as I don't have an oscilloscope,
and I didn't found a practical way to do it. At this point I set the trimmer to have 0VA at the middle leg.
The delay time was hard to control with the Delay pot (100KA lin) as at most of the travel of
the pot, the delay time was too short, and all the action happens in the last 25% of it. As I didn't have a antilog pot,
I soldered a 20K resistor between legs 1 & 2 of the pot (the one connected to the free resistor and the middle one).
This mod give me a better response of the pot but could be improved.
Another thing I noted is that the feedback losses low frequency in every repeat, as if passing thought a hi-pass filter. At first I tried to fix this, but in the end I liked it, I think it gives the delay
it's particular sound.
The voltage control of the delay is great!!!
Thanks again.

TekniK · Joined: Aug 10, 2008 Posts: 1059

Sebo · Joined: Apr 27, 2007 Posts: 564 Location: Argentina

Minimalist · Joined: Nov 21, 2008 Posts: 9 Location: NZ

I've built one of these and its working well. I have one problem though, when the recirculation pot is at minimum I still get about 4 echoes, is there a simple change I can make to get the minimum recirculation down to 1 or no echoes ?
Just starting on the second to go stereo.
Thanks to all who shared the design, pcb and modifications advice.

xi-boy · Joined: Dec 16, 2008 Posts: 18 Location: germany

i want to use this with +/- 12 volt
do i need to change anything ?

thanks

edit: got it successfully to run with +/- 12 volt

Peake · Posted: Wed Jan 19, 2011 4:44 pm Post subject:

Hi, I've got one of these up and running but had a question or two...how to get it to go out to delay times such as two seconds, as mentioned here? I've tried a 1M pot on the delay time and got more, swapped the free trimmer (10K) out with a 10M resistor and lost all signal...where is it and what to do? Thanks for the project!

Sebo · Joined: Apr 27, 2007 Posts: 564 Location: Argentina

Hi Peake:
I used the 100K pot as in the original circuit, and reeplaced the free resistor
for a 2K trimpot (as someone suggested). With the trimpot at the middle I
got about 1.5 seconds of delay. With the trimpot about 3/4, the delay stop
working. I ended setting it to a maximum delay of aprox. 1.8 seconds.

Peake · Posted: Thu Jan 20, 2011 3:29 pm Post subject:

Hi Sebo, thanks for the advice. Odd that my attempts didn't work...

brother303 · Joined: Nov 02, 2010 Posts: 139 Location: ruhr-area/germany

Hi all,

I have two Tonepad Rebote 2.5 pcbs and the ics around here.

Now I found this nice thread here and my question is : Is there a way to add cv-control to the tonepad pcbs?

Any ideas?

Thanks and best regards!
Greg

Sebo · Joined: Apr 27, 2007 Posts: 564 Location: Argentina

I think is possible, but you better go with the PCBs posted here, as the mods
you have to do to the Tonepad PCBs are too extensive.