Sunday, 26 August 2018

DIY-101 synth voice - part 1

I bought a Doepfer DIY synth nearly two years ago.
It was lying on my shelf ever since.  
This month I made a eurorack module with it.  I'll document it's making in two parts.

Close-up of the finished panel

The Doepfer DIY synth is an assembled printed circuit board that includes all the necessary functions to build a basic analog synthesizer: VCO, VCF, VCA, EG, LFO, you name it.  You can design your own synth.  All you have to do is to provide a case and all the connections to the mandatory controls : jacks and potentiometers. 

Before I could get to a finished product I'm proud of, I went into a lengthy thought process.
My first idea was to make a semi-modular synth whose functions are as close as possible to an Roland SH-101.

I tried several panel designs before deciding on the final one.

XAOC Karl Marx Stadt module provided the necessary faith that I could build a 42 HP (about 21 cm) module to house the Doepfer DIY synth.

Moreover, I was inspired by the Motherfucker-19 work from YokoBoko.  It helped me making some decisions on jack placement and avoiding some mistakes during cabling (not that I didn't do any…).  You can find description and instructions on the module modulagrid page.

As usual, I prototyped the panel on cardboard to check my placement hypothesis.  It seemed critical here.  I wanted to specifically check  the density of jacks on the low part and the room for the spacers to hold the board.
Back side of the early cardboard prototype.

Annotated paper and cardboard proto
I used my traditional way for panels : punching to locate the holes, drilling, then printing the panel, laminating and glueing it.

This time, I chose to drill the holes with a wood block beneath the panel.    It proves to be way more comfortable than my usual technique of maintaining the panel over the edge of the bench.  The panel is firmly clamped and I move the drill freely to get to the next hole.  I know, I should get a drilling press…
Holes are 6 mm for LEDS, jacks and switches and 8 mm for pots.  It is a bit large for the pots.  But it proved helpful later.

Bob cleans-up
This generated a lot of chips and dirt. Fortunately, Bob helped me to clean the mess.

Given the panel is 3U 42HP, or 212 mm x 128,5 mm, it fits nicely on an A4 sheet of paper.
It's a large sheet.  So placing it parallel to the panel edges is essential.  A small deviation could give an awful result.
I'm quite happy with the final result except the paper is one millimeter too much on the right and could have been half a millimeter lower.

Bob cuts holes

I cut the holes with an X-Acto knife.   Here again Bob gave me a hand.

This is the time to place all pots, jacks, switches and LEDs.  There are 51 of them (23 pots, 23 jacks, 3 switches and 2 LEDs).
As the holes for pots were a bit larger than needed I corrected the most obvious alignment problems by moving the pot half a millimeter here, a millimeter there.

Sorted potentiometers

Here is the final panel before cabling.

Final before cabling
Go to part 2.

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