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 Forum index » DIY Hardware and Software
Three unusual things in late Roland SH-3A 3080 VCA
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Ricko



Joined: Dec 25, 2007
Posts: 199
Location: Sydney, Australia
Audio files: 17

PostPosted: Tue Feb 13, 2018 7:47 pm    Post subject: Three unusual things in late Roland SH-3A 3080 VCA Reply with quote  Mark this post and the followings unread

Roland's SH-3A went through several revisions: one was a board layout that justified the rename from SH-3 to SH-3A, but the main boards had a couple of revisions each.

Looking at the last revision of the waveshaping/Filter/VCA/output board, at the VCA, I can see three unusual things that perhaps people building VCAs could take note of. They are circled in the attached file.

1. The op-amp that provides the control current for the 3080 OTA has a chain of diodes on the power supplies. I think this reduces the supply to +/- 12.5V. The same chip also drives the ladder VCF. The diodes were not there in earlier versions of the board. So I guess the reason is to protect the 3080.

2. The Tremolo is implemented using a diode arrangement on the VC, so it limits/unlimits the CV signal but (am I right?) low tremolo will stop at the end of the Release tail due to the diode drop: subtle but slick. Very simple and (sonically) works well. I'd love for Eurorack VCA implementers to provide this kind of tremolo input.

3. The Hold control has a resistor to tailor the response.


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