Update 9-23-22: I was unhappy with the way I laid out the bias+ and bias- buffers subcircuits in the circuit below, so I redesigned the attenuverter PCB. Build the newer one--not this one--I think it improves things in terms of flexibility. Post about the rev 2 PCB is here.
"Skiff" in synthesizer terms means the module is about 30-40mm deep or less.
That's the thing about AudiDIWhy, I can do this any way I want. The world is moving away from depth?
First, I used my SEM inspired attenuverter schematic in Eagle, capturing the strip board mock up to create a PCB for the project. The Thonk 3.5mm jacks for Eagle come from the very useful MusicMachineModular lbr file, which you can get here. (Thonk you).
After about 8 tries: the paper mock up fits.
I initially put this SMD stuff off because I was scared to try something new. Turns out it's probably easier and quicker to fab your DIY projects this way in some situations instead of using through hole and hook-up wire.
OK that's it, until next time: don't skiff the fumes.
I already bought some tools for SMD one-off fab--read about that here....
This time I build an SEM style attenuverter. Blog post part one, where I stripboarded an ugly but functional (and highly skiff unfriendly) Tom Oberhiem inspired attenuverter is here.
Today's post may not make a lot of sense if you don't skim through that first--the CTPOT is an interesting component, and I added some bias offset tricks to the original design.
First, I used my SEM inspired attenuverter schematic in Eagle, capturing the strip board mock up to create a PCB for the project. The Thonk 3.5mm jacks for Eagle come from the very useful MusicMachineModular lbr file, which you can get here. (Thonk you).
The only slightly tricky thing was finding an Eagle device definition for the center tap pot. I searched high and low and couldn't find one so I had to create the device myself, a tutorial about how to do that is here:
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| The center tap pot.... |
In Eagle the CTPOT now looks like this:
OK with this Eagle part good to go, I created the board:
Also, I had to fabricate a small daughter board for the Centertap Potentiometer since it sat too low on the PCB:
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| The board accommodates 2x CTPOTS; for this project I sawed the board in half. |
Now what? I realized after sending the gerbers off to China that I should have laid out in the pots and jacks for the main PCB in a more logical way--say every 200 mils. That would have made laying out the front panel a lot easier. But I was in a rush and I didn't. I'll deal with that later....
PCB is back from China, let's get the board going--I laid in the op amps and a few resistors:
With Skiff there is no hook up wiring so it's a fast build.
But the board didn't work first time because the TL084 was soldered in upside down. I wicked it out, and soldered in a correctly oriented replacement. Joy: now the attenuverter works.
Independent bias offset on each channel; normals for easy inverting. The joy of fuming!
Front Panel Fu: Since I didn't lay the pots and jacks out in a smart way, they landed on the PCB where ever, I took caliper readings of all the dimensions of the completed skiff PCB, laid out a potential front panel in Illustrator, and printed out a mock up on a paper sheet, then cut it out with an Xacto knife.
After about 8 tries: the paper mock up fits.
Final step is a FPE panel for this.
Ten days later it's back and yes, it fits.
Done! You can get Eagle files, etc etc for this on my webpage, here.
Done! You can get Eagle files, etc etc for this on my webpage, here.
I initially put this SMD stuff off because I was scared to try something new. Turns out it's probably easier and quicker to fab your DIY projects this way in some situations instead of using through hole and hook-up wire.
OK that's it, until next time: don't skiff the fumes.
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