[sdiy] VSM201 Vocorder Question

[Magnus Danielson]

Tim,

If I had component values for the filters, I would have put them up 
along the schematics. Unfortunately I never got those. It has annoyed me 
ever since.

As for replacing the PWM with VCAs, well, it depends on how close a 
clone one would like to have. I would be inclined to agree that NE5517 
or LM13700 would be a modern design-choice.

Cheers,
Magnus

On 01/03/2016 07:45 AM, Tim Ressel wrote:
> 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.
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
>