how to start making a bugs/frac module?

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Veteran Wiggler
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how to start making a bugs/frac module?

Post by odditymedium » Wed Aug 14, 2019 8:37 am

my friend said he would make a rob hordijk benjolin for me in frac/bugbrand format, but i don't know where to point him for dimensions, power requirements, etc

is there some canonical information somewhere? does being banana mean some special things have to be considered?

tom, batchas, and other bugzzz guruzzz, i beseech you

if its popular then i will tell my friend he wants to make more modules he is very skilled with electronics

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Post by BugBrand » Wed Aug 14, 2019 8:49 am

Frac size is 5.25" tall (3U - no lip unlike eurorack)
Then multiples of 1.5" wide

Frac came from Blacet & Paia so they're good for specs in theory.
But their frames were super deeeeeep (like 7") so eventually I made my own - first 4" deep but then moving to shallower 2.3" when I began doing parallel PCBs.

Power +/-15V on MTA connectors - I use MTA100, Blacet uses MTA156 (same as MOTM, I think).


If following my ways use these colours for bananas:
Yellow = audio (or main functional) input
Green = audio (or main functional) output
Blue = control input
Red = control output

Respond here if there are more questions -- I probably overlooked something!

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Post by soup » Wed Aug 14, 2019 12:00 pm

In addition to what Tom wrote, I've attached John Blacet's panel spec drawing that used to be hosted on his site. This is the closest thing I've found to a frac panel spec. It will at least give you the positions for mounting holes but be aware that large components like 16mm pots, rotary switches or 1/4" jacks will not fit in the top or bottom row.

Are you making your own pcb's or using an existing one? If using an existing pcb's ... pcb's must be less than 4.25" to fit between top and bottom rails. To fit in a bug rack with parallel pcb on standoffs and a MTA156 power connector you have to be careful about the positioning of the pcb/power connector as to not get in the way of the bug power distro that runs down the center as the MTA156 male+female is quite tall.

Bananas usually make doing flying wires easier but you will have to add toggle switches in the place of any switched jacks.
FPtyp.jpg (313.85 KiB) Viewed 260 times

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Post by johnchantler » Sat Aug 17, 2019 1:00 pm

I recently made a FRAC benjolin panel at Formulor (Ponoko equivalent in Berlin).

files can be downloaded in case it's helpful: ... ... e.eps?dl=0

the furtherest right knob should be labelled 'res' or 'resonance' instead of vcf... but I know what it does so not so bothered with the mistake.

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