Wednesday, 30 June 2010

DIY Boss PC-2 / Amdek PCK100 Analog Percussion Synth

Back at the end of the 80's I went in a music shop in London and on impulse I bought this wierd BOSS box that made weird bloopy noises... a PC-2 Percussion Synthesizer. It wasn't a difficult decision at the time since it only cost me £10 brand new boxed (I think they were trying to get rid of them) and it came with a free brand new BOSS HC-2 Hand Clapper pedal, although that seemed even less useful (though the guy did a good sales pitch involving a tale about a friend with no arms who had trouble applauding at gigs... :o)

Apart from a bit of novelty value I gotta be honest they didn't get a lot of use... I think the HC-2 got chucked during a house cleanout and the PC-2 was sold on ebay a few years back (and was amazed to get £100 for it). Well now I am kicking myself and wished I'd held on to these two collectables.

So when I saw the schematic of the Amdek PCK100 online (actually a kit form of the PC-2 sold by a Roland affiliate) I decided to try to make one and once again re-live boingy noise heaven.

On the page where I found the schematic I also found a photo of the PCB and decided to try to use it directly. With some manipulation in Paint Shop Pro and the use of Press'n'Peel PCB etching film I was able to make a copy of the board and after working out some workarounds (e.g. using BA6110 instead of ultra-rare BA662A VCA chip) I actually got it to work.. So in case you're interested is how I did it

1) I started off with this photo of the track side of the original PCB

2) Turned to mono, upped the contrast, then very carefully use the "eraser" tool to ensure there are good clean gaps between all the tracks

3) Marked drill holes with circles

4) Drop colour depth to 2 colours

5) Negative image and a few embellishments and its ready to press'n'peel

6) Laser printed etch-resist transferred to copper clad board using a hot iron

7) Etched, drilled and trimmed ready for components

I mounted the board inside a project box from Maplin. By the way I have a thing for Dymo embossed label tape :)

The Amdek user guide gives info on some mods to the board (VCO wave form change, mod waveform change) which I added toggle switches for. Usually the Sweep control is a center tap pot.. I didn't have one so I instead rigged up a DPDT toggle and a resistor to a normal pot so that the same effect could be acheived (although I am not sure it works so well)

The original board calls for a Roland BA662A VCA chip... you won't find one! you can use a similar BA6110 chip but the pinout is different. I found the following worked

  • socket 1 connect to BA6110 pin# 4
  • socket 2 connect to BA6110 pin# 2
  • socket 3 connect to BA6110 pin# 1
  • socket 4 no connection. BA6110 pin#3 connected to GND (pin 5)
  • socket 5 connect to BA6110 pin#5
  • socket 6 connect to BA6110 pin#6
  • socket 7 connect to BA6110 pin#7
  • socket 8 connect to BA6110 pin#8
  • socket 9 connect to BA6110 pin#9
Click below to get the full size PCB template to use directly. See the link at start of article for schematic, photo of top of the board and original PCK100 kit instructions