Pt2399 8 step sequencer

[jghfslk]

I would like to use my electro harmonic 8 step program to control the delay time of a pt2399 delay? Does anyone know if this is possible or can point me in the right direction?

[HamSandwich]

Do you mean you want to use it like an LFO? Or to tap in a tempo and have it set the delay time? One is infinitely more easy than the other!

[jghfslk]

I don't need tap tempo. The goal is to use the sliders on the sequencer to set the delay time and have the sequencer cycle through the various settings.

[gtr2]

Look how CV is implemented for delay time in the PT2399 designs used in synth.

[HamSandwich]

I'd think the synth stuff would use a bipolar supply? At least the MFOS one does.

The 8 step kajjiger puts out 0-5V. I think it'd be easy enough to strap and LDR onto the delay pot, then have an LED light up with the 8 step CV out.

[jghfslk]

Do you happen to have examples of projects that have implemented this method?

[zombie_rock123]

Complete shot in the dark but Id be surprised if the MFOS Pt2399 Echo didnt have CV controlled delay times

[gtr2]

You can do it without using a bi-polar supply.

Grab a breadboard and search google for some PT2399 circuits utilizing CV and work it out

[jghfslk]

I tried a method using an led and ldr.  I connected the tip of my trs cable from the output of the sequencer to the positive side of the led. The negative side of the led is connected to the sleeve of the trs cable. One side of the ldr is connected to pin 6 of the pt2399 and the other side to ground.  The led and ldr are in heat shrink tubing.
The control of the delay time on the sequencer isn't good.  For about 2/3 of the slider control I get no change in delay time. Within the last third of the slider there is still only a portion of it where most of the delay time is changing.  The ldr is from tayda and led is a diffused red.  I may try a different led and ldr combo.  It was tough to tell if the delay time changes happen instantaneously, which is goal, because it was difficult to dial in specific delay times. 
I'm also thinking method may be a little too simplistic.  Looking into other pt2399 circuits with cv, there seem to be much more complex things going on.

[madbean]

Is anything else connected to pin6 besides the LDR...like a delay pot?

[jghfslk]

Yes. I left the delay pot connected.

[jghfslk]

I tried disconnecting the time out and only using the led and ldr to control the delay time. I still have the issue with limited range of usable control from the sliders on the sequencer.  The 8 step program has the ability to decrease the depth of the sliders but no matter which setting I tried nothing seemed to work great. 

[madbean]

The reason that's happening is because the dark resistance of the photocell is too high for the application here. The ideal resistance range should be very small - typically 1k through 50k (even smaller for more musical results). The photocell could have a dark resistance of 1M or even up to 10M. IOW, probably only 5% of that range is useful here and that's why you have such limited control.

EHX says the CV output range is 2v to 9v on its website. I'd take some voltage measurements on the CV and see if that's true (i.e. measure the voltage output versus slider position). It's possible you could modify it well enough to limit the minimum darkness of the LED driver in the LDR so it's limited to a more useful range.

[jghfslk]

Thank you! It seems obvious once having it explained to me..
I measured the voltage between the tip and ring from the output of the sequencer and the max range I got was 0-5V.  If I set it to a smaller range the minimum voltage stays the same but max voltage is reduced.  I'm not sure how to modify it to have the LEDs minimum brightness brighter.  Would the easiest way be to add an additional voltage source to the LED so the minimum is something greater than 0V? Could that lead to additional problems or potentially damaging anything?
Regarding ldrs: do they typically have a relatively fast response time? For example if I want to change from a large resistance to a smaller one, will the ldr detect the light change quick enough to seem almost instantaneous?

[madbean]

The response time varies with the device part #. For example, a vactrol designed for a really fast response time is the VTL5C9 (I forget exactly what it is). The NSL-32 and H11F1 do as well, with the added bonus of ridiculously low on resistance (on the order of a few hundred Ohms).

What I would try first is this (schem below). This is the depth pot setup from the Tremulus Lune. With this your LED actually doesn't go dark (exactly what we want): as you turn it down the pulsing stops and it stays a constant brightness. You may have to modify some values here to make it work but it would be a good starting point. There are two places to try the photocell connection - across the delay pot and stopper resistor or just the stopper resistor. They'll produce different ranges so you'll have to see what works best for you. Again, this is guesswork at this point.