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291r build issues
MUFF WIGGLER Forum Index -> Buchla, EMS & Serge  
Author 291r build issues
I was torn between posting here or the diy section but thought there may be more knowledge here. I'm building a 291r and am having some issues. Things seems to be working for the most part but i dont really want to assess or focus on the other features until the frequency cutoff is working. Right now the frequency cutoff seems very marginal on both halves. They definitely dont act as a low pass at all and definitely dont come close to approaching the 30Hz listed on the panel. I'm wondering if my vactrols are in wrong or if you spot any other issues.


Im open to any suggestions or requests for measurements seriously, i just don't get it [/img]
Im almost completely new to buchla, so please bear with me. I always forget about Dave's amazing site. I saw some waves there and realized its a band pass and not a low pass which I originally thought.

If i send a swept frequency in I see similar results to Dave, except when I move the bandwidth to wide I loose a significant amount of volume.

I also dont see the same wave shaping from square to sine

Also not sure what the trimmers on the back are supposed to do
R22 and its companion component in the other circuit are 1M and can be changed to 4.7M or higher to allow the filter to come down a bit more into the low frequency range.
That resistor changed helped a lot, thanks for that thumbs up I played with a few higher values but there wasn't much difference after the 4.7M.

Any insight into the trimmers on the rear

Edit: I just notice the resistor change seems to have robbed from the bandwidth adjustment. I dont see any effect from this now hmmm.....
Messed up, the resistor to change is R22 in the original schematic, from 1M to 4M7 or so. The bandwidth circuit isn't involved in that change. 0_150.jpg

I don't know offhand what the part number is on the Roman clone.
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