[sdiy] Unknown VCF PCB

[rsdio at audiobanshee.com]

It looks like the trimmers are labeled with their values. e.g.: 223 would be 22 kΩ, 215 would be 2.1 MΩ. The image is too blurry to see what the actual numbers are.

Brian


On Jul 5, 2014, at 5:37 AM, Terje Winther wrote:
> I recently got some modules/PCBs. Most of them was digisound modules, but also a Tau VCO, some old Thomas Henry stuff and some PAiA stuff.
> All of them without any ICs, so it will be some work to get this playing.
> 
> However, one of the PCBs was an unknown filter, see this very bad mobile photo:
> http://www.wintherstormer.no/VCF.jpg
> 
> It is marked "VC - State variable filter", and the next line reads "ARTS  85"
> There are spaces for "coarse", "fine" and "Q", and the power connections are spread out over the PCB, so no typical power connector to identify this, but it is labelled av +/- 15 volt.
> Also of interest is the fact that there are 3 trimmers (missing, so I don´t know their values), no transistors on the board, and some 100pF polystyrene cap used.
> I have followed the traces, and the bottom 14-pin IC is clearly a quad op-amp of some kind, probably to buffer input/outputs and/or make the various filter types.
> 
> So my guess is that the top IC is the filter core. However, I have tried all the various suspects: CEM-chips, LM13600/13700, various op-amps, even CMOS-chips, but none of them fits into the required 18-pin required socket configuration. Also of note is that leg numbers 5, 7, 10 and 14 on this IC are not soldered in, and consequently not connected to anything.
> It also seems that none of the legs are in direct contact with +/- 15 volt, so could this IC be some matched transistor device?