H11F1 with LFO?

[HamSandwich]

Anyone had success using an H11F1 with an LFO for use in a tremolo or delay mod? Can't seem to find any projects using them for this purpose. I see the multiple. Uses one for the ramp switch, and plenty of bypass schemes. Does it not easily work in pace of a vactrol when fed a LFO?

[somnif]

It would be a bit tricky I imagine. The chip is a photo-FET rather than the simple resistors you typically find in LFO/Envelope driven systems. It has an absolutely massive resistance range, from like 100 ohm (on) to 300 Meg ohm (off), and a time between them of less than 50 microseconds.

If you have an incredibly tightly controlled current I suppose you might be able to reign it in to actually get something resembling a sweep in there, but you'd still need a circuit designed around a several hundred meg-ohm range.

That said I know the (modern) Expandora uses one in its envelope circuit to spike the gain on attack. But the vast majority that I see are used as isolators. LED power off = nothing going through.

[midwayfair]

It also distorts very badly in the signal path so it's not good for most tremolo designs, and it's more expensive and harder to implement than a plain FET if it isn't in the signal path, like in an EA tremolo.

[HamSandwich]

Thanks guys.

Distortion in the audio is no good. That rules out quite a bit.

I did see these two things after posting this thread, that gives me hope that there's some way to shoehorn these seemingly more accurate (and cheaper) devices in place of the VTL photo-couplers.

http://paperpcb.dernulleffekt.de/doku.php?id=paper_bits:pb401_vc_echo
That project uses one as a way to apply a CV input to the delay time of a PT2399.

The 1776 multiplex Deluxe seems to use or at least have an H11F1 on the modulation board, but as it's a commercial product, I don't think they have a schematic anywhere.

[stringsthings]

Just checked out the paperpcb website.  This dude really did his homework!
Full blown modular synth on vero! 

[somnif]

The 1776 multiplex Deluxe seems to use or at least have an H11F1 on the modulation board, but as it's a commercial product, I don't think they have a schematic anywhere.

http://1776effects.com/wp-content/uploads/2015/03/Multiplex-Build-Doc-1.7.pdf

The H11F1 isused a bit oddly in the circuit. Its not used with an LFO, but rather a nifty little bit of circuitry that will brighten the LED steadily over a bit of time when the switch is stomped, speeding up the delays, then dim steadily, slowing them back down when the switch is released. 

[gtr2]

I do recall making a modulation board using the H11F1 once.
It was a one-off that I was just playing with and ended up using it in a build for someone.
It's not a commercial product, it was just a prototype I had laying around at the time.
From what I recall it worked well but it required some tweaking.  I'm fairly certain it used the same oscillator found in most of the pt2399 modulation circuits but it had maybe a 1M resistor in series with the H11F1 on the "resistance" side.  There really wasn't any secret sauce.
I think at the time I didn't make any further PCBs because the fate of the H11Fx series was uncertain with ROHS compliance.
I don't really remember much more than that as it was maybe +5 years ago?
Josh

[electrosonic]

The data sheet shows a circuit for a "distortion free attenuator for low level ac signals". Looking at the transfer function graph, the signals would need to be below 100mV pk - so it looks doable, you might need to attenuate to signal before the h11f1 and then add gain after.

Andrew.

[HamSandwich]

Thanks everybody!