9V Sample and Hold

[soggybag]

for more range try a vtl5c4.  i believe the vtl5c3's like to see a lot more current.

I used the VTL5C3 since I had some on hand. I ordered a few VTL5C9s from Small Bear to test with. I'm still waiting on these. I have not tried VTL5C4 before. They don't have them at most places. Heck vactrols in any form are a specialty item. I'll keep a look out for these and get a few for testing if I see them.

I tried using some home made LED/LDR combos. These were a little hit and miss. I seemed to get the best results with the VTL5C3 so far.

I think the on/off time and the resistance range has big effect. It's hard to find the perfect device for this application.

I had been thinking about using a FET in place of the Vactrol. I stuck one in there for a quick test, but I couldn't get it to work at all. I couldn't figure out how to bias it correctly.

[soggybag]

Here's the latest version of the 9v sample and hold. This one works pretty well.

It needs some adjustment in the range of the effect. As it is the effect spends too much time in the low range of the wah. Otherwise it gets a pretty good range of random bubbly wah sounds with a good selections of speed.

I tested both VTL5C3 and VTL5C9 optocouplers and both seemed to work well. In the last incarnation I used the VTL5C9.

I haven't built this on a circuit board yet. As is it's still on the breadboard. The clock noise bleed is minimal but you can hear some ticking. I used 1458 for the clock and a TL072 for the other op-amps.

[Brian Marshall]

just curious, and forgot to mention this before.  What are you using as your Vr.

I ask, because when i designed the original one i was using an opamp buffered voltage divider.  Seems like some of your earlier problems were worked out, but that may have been the source of some of the problems, if you were just using a voltage divider directly.

[soggybag]

Hey that's a good question. I did not draw the voltage divider. I think I used two 39K resisters and a 100u cap. I'll check when I get home. I think I still have a spare op-amp available if I use two dual op-amps. Though, it might not be a good idea to have the voltage divider share an op-amp with the clock.

[Joe Kramer]

The clock noise bleed is minimal but you can hear some ticking. I used 1458 for the clock and a TL072 for the other op-amps.

That's a nice looking circuit--I especially like your short signal path.  FWIW, you might get a bit more depth and a bit less ticking if you use TL062s for your clock/control circuitry.  I think the 062 will swing closer to the rails than the 1458, as well as deliver less impact to the supply, which may be the source of some ticking.  Just my two-cents.   

Regards,
Joe

[flo]

Not trying to be a pain but did you perhaps also consider using a dedicated cheap sample-and-hold ic like LF398?
Futurlec has them for $1.79 as a DIP8: http://www.futurlec.com/Linear/LF398N.shtml
The functionality of it looks like what you need.

[soggybag]

Thanks, I had the TL062 in mind for experimentation.

I'll have to look into the LF398N. I hadn't consider this.

[Brian Marshall]

Not trying to be a pain but did you perhaps also consider using a dedicated cheap sample-and-hold ic like LF398?
Futurlec has them for $1.79 as a DIP8: http://www.futurlec.com/Linear/LF398N.shtml
The functionality of it looks like what you need.

I'm pretty sure it's unstable at 9 volts.  it's rated at +/-5 volts.  the whole point is to make it work at 9 volts.

[flo]

LF398:
http://www.datasheetcatalog.org/datasheet/philips/LF398_2.pdf
"Operates from ±5V to ±18V supplies"

[slacker]

The problem for us is that the LF398 is designed to work off a bipolar supply ie: +5, ground, -5. I don't know if it can be made to run of a single supply, and even if it could 9 volts isn't enough as it expects at least 10 volts in total.

Might be worth playing with though.

[markusw]

The problem for us is that the LF398 is designed to work off a bipolar supply ie: +5, ground, -5. I don't know if it can be made to run of a single supply, and even if it could 9 volts isn't enough as it expects at least 10 volts in total.

Might be worth playing with though.

I've used it at single 12V. Worked nicely. Didn't check it at 9V single though.

[flo]

The problem for us is that the LF398 is designed to work off a bipolar supply ie: +5, ground, -5. I don't know if it can be made to run of a single supply, and even if it could 9 volts isn't enough as it expects at least 10 volts in total.

Ah, yeah right. My mistake. 9V = not 10V... sorry   
Perhaps in combination with a MAX1044 kind of bipolar power / voltage doubler maker then? That will keep it stable when the battery gets low. Would still make a sample & hold with less complexity, more compact, probably better performance at comparable cost.

Ok, I'll leave it here then. Don't want to push...
Much success in your effords!