[sdiy] VSM201 Vocorder Question

[Tim Ressel]

I think if an effort was made to make a DIY copy of the VSM201, a case 
could be made for swapping out the switched VCAs for 13700s or something.

Another question:  It looks as though what is being PWMed is the audio 
and not the CV coming from the detectors. The CV signals (I think) are 
labelled 'KK' but I cannot find their source.  It is not helping that 
the schematics are copies and are in a language I don't read.

Also I can't see the values for the filter components. Is there a BOM 
somewhere?

--TimR

On 1/2/2016 2:10 PM, rsdio at audiobanshee.com wrote:
> A PIC that runs at 48 MHz, e.g., for USB, can manage a 46.875 kHz PWM rate. That's enough to just satisfy Nyquist. Unfortunately, the filter would probably cost more than a true VCA, but if there are cheap low-pass filters oriented towards Compact Disc 44.1 kHz sampling then you might be able to pull it off.
>
> WIthout a fancy, brick-wall filter, you'd lose the ideal 20 kHz bandwidth and drop into the audible range, which 31 kHz certainly would require.
>
> Are you using a PIC that runs at only 32 MHz?
>
> Brian
>
>
> On Jan 2, 2016, at 12:44 PM, Tom Wiltshire <tom at electricdruid.net> wrote:
>> I've thought about this a bit because of using the PIC's PWM module so much. The best case output from that is either 8-bit or 10-bit, which means that -60dB is about as good as I'd get using it for a VCA, and that implies having a switching frequency which is much too low (31KHz) for many jobs.
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-- 
--Tim Ressel
Circuit Abbey
timr at circuitabbey.com