Darling AutoFilter

[Kipper4]

Just cause you can never have too many AutoWahs
Just an idea so far unverified.

Low parts count autowah with darlington envelope detector. Credit to midwayfairer and Duck Arse. RG for the mfb filter.

The Darling AutoFilter


edited post

[dschwartz]

Looks really nice on paper!
How does it sound?
Maybe a "down" option could be done with an dpdt and an extra diode..just ideas...

[Kipper4]

Oops deleted the wrong image from imgur. I'll reupload.

[Kipper4]

[antonis]

Well done Rich... 

(with a doubt about R16/R17 values..)

[bool]

You could probably delete R6 and R7.

[Kipper4]

Thanks Bool I'll breadboard it at the weekend probably. Now i have made a dual ldr vactrol for the breadboard.

Antonis
What doubt my friend?  Much smaller I presume. 10~22k ?

[EBK]

You won't get as much light spread out of the sides of that led as you do through the lens...

[antonis]

Antonis
What doubt my friend?  Much smaller I presume. 10~22k ?

Yeap Rich..

To make a stiffer voltage divider for more "steady" V_B on non-inverting input..

<gosship on>
Despite Q2 Darlington high beta, don't you think you've overize it's collector feedback resistor..?? 
<gosship off>

[Kipper4]

Stiffer?

I might have to adjust the C feedback Resistor. I stole it from Jon and it worked for me before.
So I copy and paste and see if it works here too.

[Kipper4]

A few adjustments made on the breadboard.
The buffer and darlington envelope detector are working though.
Filter next.

[anotherjim]

I'm sure you can get away with 100k dividers in this case. The only thing feeding signal into Vb is the LDR on the filter and the 10u C11 should send it straight through ground without bothering anything else.
"Stiffer" would be 10k divider resistors, which I go for by default. Lower R uses 450uA of supply current - shocking waste 

[Kipper4]

Verified on the breadboard.
A low parts Envelope Filter
It could probably do with a better filter.

[PRR]

R10 can't be going to ground; suspect VB.

If you have a VB, you may as well bias Q1 from that; better power filtering and one less part.

Since the filter modulation VACT returns to VB, and may be under 1K, I would make the cap on VB much larger than 10uFd, say 100uFd. I may be wrong. However the added cost is less than my brain-pain to figure the possible interaction.

It is probably possible to eliminate IC1_B by putting a divider in IC1_A's NFB loop; however a single opamp is no cheaper than a dual.

I have doubt that ATTACK resistor 470r is needed. C8 can only pull-up through R12 2,200r, so another 470r does little. Likewise 100K DECAY is only effective at an extreme, because the 1K R14 plus LED is more like 2K when LED is on.

[Kipper4]

Thanks Paul.
Appreciate the help I'll do more breadboarding tonight.
It's gonna be a long day. Family visits.....

[Kipper4]

I'm getting chuffed off.
I'll clear the bigger breadboard and redo it tommorow the envelope is intermittantly responding.

[Fancy Lime]

Bump for the auto wah / envelope filter discussion. Nice discrete envelope follower! Makes ideas about an all-discrete envelope filter float to the top again...

We should have us a proper small(ish) envelope filter shootout, me thinks

Cheers,
Andy