yet another 'has anyone ever built...'

[rutabaga bob]

Am wondering if any of you have built the Music From Outer Space Envelope Follower Filter?  If so, do you have any layouts/build docs, etc.?

Edit: a search shows me that some of you have, but nothing comes up re layouts for the thing.

[Kipper4]

Is this any help Larry

http://musicfromouterspace.com/analogsynth_new/ENVELOPE_FOLLOWER/efpg4.html

[rutabaga bob]

Yeah, thanks Rich...I've had all that printed out for a while, but was wondering if anyone did their own perf for the thing.  Doing the Penfold got me interested in this again.  Drat this hobby!  You can build yourself right into the poorhouse! 

[Kipper4]

I'll see what I can do regarding doing a perf layout for you mate.

[Mark Hammer]

have they re-opened the store since Ray's passing?  I know they were closed, as one would expect, but I get a message that they're still closed when I go there with my tablet, and on my desktop, the website is ambiguous, suggesting they're open again.

[rutabaga bob]

Rich...maybe I'll try and see what I can adapt from the pcb diagram.

[ElectricDruid]

Yeah, thanks Rich...I've had all that printed out for a while, but was wondering if anyone did their own perf for the thing.  Doing the Penfold got me interested in this again.  Drat this hobby!  You can build yourself right into the poorhouse! 

It's quite interesting to compare those two schematics side by side. The filters are pretty much identical - 13700-based SVF. The MFOS version doesn't have the variable resonance, but that'd be easy to add if you wanted it. Even the initial values going in  are broadly similar (10K/1K vs 15K/1K) so there won't be a lot in it in terms of "filter drive". Both filters use the on-chip darlington buffers. That's one place you could have made a difference as a designer - use a FET maybe, or an op-amp I-to-V stage.

So basically any differences boil down to the envelope follower, and they differ a lot more. The MFOS one looks like it uses a PNP exponential convertor for the current source, whereas the Penfold one goes minimal and uses...a resistor! So one responds linearly, and the other exponentially. Pretty big difference. And that's only the current source.

There's lots more to say if you keep digging into them, I'm sure.

Tom

[bluebunny]

have they re-opened the store since Ray's passing?  I know they were closed, as one would expect, but I get a message that they're still closed when I go there with my tablet, and on my desktop, the website is ambiguous, suggesting they're open again.

I don't think the store is open yet, but Muff Wiggler member synthcube has taken over the maintenance of the website, with Debra Wilson's blessing and support.  Check out this thread at MW.  Ray's designs are available at synthCube (Concord, MA), and they're also at Soundtronics in the UK.