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 Forum index » DIY Hardware and Software
Buchla 266 SoU -- Eurorack!
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masterofstuff124



Joined: Sep 21, 2015
Posts: 23
Location: Miami, Florida

PostPosted: Fri Dec 30, 2016 4:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

looking through all of the yearly build threads, all of AlanP adaptations and designs look amazing. I want all of them!

208 random
Quadrature function Generator
Source of uncertainty Dunno!


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elmegil



Joined: Mar 20, 2012
Posts: 2177
Location: Chicago
Audio files: 16

PostPosted: Wed Apr 18, 2018 7:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Gotten around to building this, and I wanted to pop in and make a note.

Because of the 5V supply, the eDruid noise chip requires a change to either R176 or R174. Otherwise the level is wrong, and the FRV doesn't do as much as it should. Got this from Dave Brown's build of Roman F's clone of the SOU.

Dave's solution was to replace the 39K R174 (it was different designator on that schematic, but same positionally in the circuit) with a 6.8K resistor.

In my opinion this messes up the passive LPF consisting of R174 and C56. My preferred solution is to replace R176 (a 10K) with a 56K. The whole thing being that there's a voltage divider there, and since the voltage is significantly lower out of the replacement noise chip, you have to adjust it to get the same levels into the next stage of the circuit.

See Dave's notes and modifications for the Roman F version on this page:

https://modularsynthesis.com/roman/buchla266/266sou_pcb2.htm

If you look through his notes on the SOU, he's made some other changes from Roman's version, I haven't gone through and made those changes myself; I'll have to see whether I think they're necessary after I'm done with the build, but I know this particular one definitely is needed.
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AlanP



Joined: Mar 11, 2014
Posts: 746
Location: New Zealand
Audio files: 41

PostPosted: Fri May 11, 2018 4:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

It's been awhile since I did the PCBs, but IIRC, I included a lot of Dave's mods (including protection diodes.)
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