Thursday, November 29, 2018

FrakRac +/- 15V Power Supply, drop in Replacement for the Original

Hi again: Quick one this time.

When it came time to pick a format for my modules, I had a lot of choices: Doepfer's "Eurorack"; "5U"; and so on.  I went a bit outside (I do that sometimes?) and chose PAIA's offering, FracRak.

Maybe because it's about the same physical size as the API 500 "Lunchbox" format; I used 500's a lot during my audio engineering days, and found that the 500 series is a good compromise in size--the knobs aren't super tiny and the panels aren't super huge. With Frak or the 500 series you can throw your rig on the front seat of your car without issue, or just get your girlfriend to carry it on her lap. Just skip the Taco Bell drive thru!  Try doing that with a Moog 55, right?

Or maybe because a PAIA 2700 kit got me into this whole thing to begin with when I was like 12?

Because I spoke to John Simonton in 2005 and he was one of the nicest guys you could ever talk to? 

All of the above I guess.

OK good news is that Fracrak is pretty cheap n easy for the case and power supply (which using their 9700 universal power supply, could be built as +/-12 or +/- 15).

For non-critical apps I wanted something a bit beefier than PAIAs "wing" 9770 supply. So I whipped up my own drop in replacement for powering FraKracs:


The clone board--bolt it right into your FrakRac case.....
My design has the advantage of being able to add heat sinks then screw them down to the PCB vs. have them "flap in the breeze", offers a bit more cap filtering options, slightly better reverse voltage protection for the regulators and some other basics. This is a $5 for 10 PCBs fabbed in china type deal--why not, right? It probably won't work for super-critical applications, say a bank of analog VCO's.  For that you will need better regulation, but for the basics this quick replacement gets the job done.

the original PAIA supplied PCB.  Super low parts count--them Voltage Regulators are looking shabby.....

For this power supply you can get more information on my website including gerbers, PDF of schematic and board layout, BOM etc.



OK, If you go the Frac route like me and want something more stable/better for VCO's let's say, I'd suggest sticking to PAIA's 9771 Psup...maybe I will modify the design above for more beef as well....that said I have built this board a few times and have successfully mounted it inside some of my FracRaks. Works.....no magic smoke after many many hours.

About the board: The cap values are not critical--I have used 1000uF, 2200uF or 1500uF for C3-C4, 470uF or 100uF for C2-C6, left off C1 C5, 100pF for the caps close to the output headers, etc. I mostly use up whatever I have in my junk box that's reasonably close value wise to what's here.  Good enough!

If you are a more advanced DIYer and want to get a freebee of this board, personal message me through the electro-music forum (my handle is cslammy).  My day job deal doesn't allow me to sell any PCB's or my designs (so I can't join the fray of the 1000+ dudes selling synth modules these days?) But maybe we can do a swap.

Coming soon: More noise projects with voltage controlled attenuators.

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