[sdiy] Unknown VCF PCB

[crystal]

that definitely looks homemade, can you post a photo of the other side?





On 7/5/2014 5:37 AM, Terje Winther wrote:
>
> 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?
>
> Any response appreciated.
>
>
>
> Terje Winther
> terje.winther at wintherstormer.no
> http://wintherstormer.no/
>
>
>
>
>
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>


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