PCB for the EFM VC-RADSR

jbeuckm · Posted: Thu Mar 19, 2015 6:09 pm Post subject: PCB for the EFM VC-RADSR

I'm going after the EFM VC-RADSR mentioned here:

http://electro-music.com/forum/post-224210.html#224210
schematic: http://www.modular.fonik.de/files/EFMforum/orgEFMfiles/vcradsr.pdf

I've got a euro-friendly layout pretty close, and I will make a prototype soon. Anyone see any problems with this capture of the schematic? I added the supply decoupling capacitors -- the CMOS are at middle left and opamps are on the bottom left. I did not put in the offset amplifier from the original.

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EFM VC-RADSR

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jbeuckm · Posted: Fri Mar 20, 2015 6:58 pm Post subject:

That first schematic missed a 10k resistor between Q1 and the OTA. Here is my prototype - will try one soon.

Eagle stuff here: https://github.com/jbeuckm/EFM_VC_RADSR/tree/master/eagle

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roglok · Joined: Aug 28, 2010 Posts: 202 Location: uptown

looks great. haven't come across this one yet. the rate parameter seems super useful. please keep us posted!

if you decide to do a PCB run it would be cool if you included mounting holes.

glot · Joined: Jan 25, 2015 Posts: 15 Location: boston

that really does look great Cool

would you add a footprint for the lm13700 the ca3080 is only getting more rare and expensive

roglok · Joined: Aug 28, 2010 Posts: 202 Location: uptown

one thing: why did you leave out the attenuverter? all you need to do is add 2 extra resistors and a pot somewhere... you could make it optional, just the pads for flying wire installation... there's a spare opamp anyway...

btw. are you joe beuckman of beige records fame?

jbeuckm · Posted: Sat Mar 21, 2015 10:49 am Post subject:

@roglok I'll probably add the offset amp back if this works. I usually try to mount on the 16mm right angle pots. Is there a particular way you would do the mounting holes? No production run but my work in Eagle will be open if someone wanted to.

@glot I'll look into that lm13x00 substitution.

Anyone in MSP have an extra 4052? Wink

joe@beigerecords.com

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VC-RADSR prototype in progress

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jbeuckm · Posted: Mon Mar 23, 2015 8:02 pm Post subject:

Everything seems to work. Here is a sample playing with rate, attack and decay in LFO mode. I wish the release could be adjusted longer relative to the attack. To get the release very long at all, the rate has to be drawn out so that the attack is soft. Since it's voltage controlled, I guess I could use a separate EG to change the rate parameter during the release... VC opens up a lot of coolness.

The output is a little less than +5V at +/-12V supply. Offset amp will be nice. If the 3080 gets replaced with a 13700, there will be an extra OTA sitting there. I was thinking of trying to fit a simple VCA onto this board.

vceg_lfo_mode.mp3

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vceg_lfo_mode.mp3

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roglok · Joined: Aug 28, 2010 Posts: 202 Location: uptown

cool. good to hear you got it working.

regarding the gain stage and envelope times, maybe this is of interest to you (in case you haven't seen it):
http://synthdiy.fonitronik.de/files/7413/8288/0912/VC-RADSR_forum.pdf
http://www.modular.fonik.de/files/EFMforum/vc-radsr%20ScottBmod.pdf

you could make C1 switchable to get different overall envelope times.

jbeuckm · Posted: Tue Mar 24, 2015 1:55 pm Post subject:

@roglok Thanks - that's really good info! I will try some of the many mods and possibly JH's discrete VCEG.

jbeuckm · Posted: Fri Mar 27, 2015 9:34 pm Post subject:

Here is an update with LM13700 instead of CA3080, offset amp from the original and an indicator LED with transistor driver. Let me know if you see any problems before I make one tomorrow.

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jbeuckm · Posted: Sun Mar 29, 2015 6:44 pm Post subject:

It works. Here is the layout. Eagle stuff available here:

https://github.com/jbeuckm/EFM_VC_RADSR

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