TapLFO envelope controlled? How to do?

[Mr. Lime]

Once again the Druid's chips got me awake.
At this point I have to thank Tom for his inspiring work which keeps my brain struggling at nights.. 

I'm currently thinking about some kind of envelope follower to feed 0-5V to one of the controls of a StompLFO or TAPLFO chip.

The idea is to have a seperate pedal which could be the first in the signal chain to get the most natural envelope of the guitar controlling the modulation effects (Rate, Offset etc.) in the fx loop of an amp.

How could such an envelope follower look like? Has anybody tried something like that before?

Thanks a lot.

[Mark Hammer]

The stock circuit for the TapLFO has a pot for the base control voltage for each parameter, and a pot for an incoming control voltage to be mixed/summed with the base voltage.  This would let you have a basic LFO rate and add to it with the envelope follower voltage.  The datasheet indicates, however, that the secondary input for each parameter can accept -5 to +5V, such that your envelope could actually subtract from the base LFO rate.  That is, you could technically slow the rate down by playing harder, assuming you have a means of inverting the envelope voltage.

Having said that, the datasheet circuit assumes control voltages that are pretty stable.  And if you are only using the one pot for base rate, or feeding the secondary input with something from a function generator, that would be true.  Sadly, most envelope followers, mostly because of the properties of the guitar signal they're tracking, are imperfect and have some ripple in them.  In that spirit, I suggest that whatever envelope follower you end up using, you also include a feedback cap in parallel with the 100k feedback resistance in the op-amp that mixes the base and secondary control voltages.  This will smooth the final combined control voltage a bit more.  A value of 100nf seems about right to me, though other folks might suggest a different value.

[Mr. Lime]

Accepting +/-5V would offer a whole new dimension!
Yeah, phase inverting of the envelope follower is definitely a good point.

Well Harry Bissel's envelope detector seems to offer low ripple and fast response.
I got the advice to use diodes for limiting the voltage output..
More info about the follower here: https://www.muffwiggler.com/forum/viewtopic.php?p=1511975
Article here: https://m.eet.com/media/1141271/18042-122602di.pdf


Am I on the right tracks?

[Ben N]

Standard necropost apologies.
Hey, Mr. Lime, ever get anywhere with this?
BTW, I think the idea of tapping a buffered pure envelope at the beginning of the signal chain would have lots of uses, such as controlling downstream noise gates, filters and compressor/limiters--no need to put those things first just to capture a useable envelope. For single coil use, I would add a hum filter as well--it screws with your tone in the signal chain, but not (presumably) in a sidechain.

[Mr. Lime]

Hi Ben,

i'm afraid I had a bunch of project fails that kept me away from new pedal design stuff.
At the moment I'm rather busy with guitar amp builds and I do not know when I'll get back to pedal circuits..

Sorry for that.
Maybe some other clever fellow could jump in?

[Kipper4]

Let me have a look in my drawings and see what I did to envelope control of the Stomplfo.

[strungout]

I just connected the envolope follower of the MXR Envelope Filter to the offset in.  Keeping the filter that's there, in the Filter FX, for the footpedal. The envelope goes through the chip to activate the LEDs. Didn't mess with the rate or depth, though. Technically, I can have all three (EF, LFO, foot) active at the same time. How useful that is... I'll soon find out.

EDIT: I did that with the StompLFO chip. Dunno if that's different...

[telebiker]

Very interesting thread!