[sdiy] Two ways of mixing modulation routes

Mattias Rickardsson mr at analogue.org
Fri Jan 6 23:09:53 CET 2017


Den 6 jan. 2017 10:54 em skrev "David G Dixon" <dixon at mail.ubc.ca>:

Summing into a buffer gives an average rather than a sum.  Perhaps that's
what they were after here?  The resulting amplitude would be same as the
incoming signals and not twice as large.


True for the LFO waveform mixing, but in the modulation routing the
switches go towards Gnd when off, causing the signal to get weaker if fewer
are on.

/mr - should power up ye olde Pro~One and try it!



> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On
> Behalf Of Tom Wiltshire
> Sent: Friday, January 06, 2017 3:02 AM
> To: synth-diy at synth-diy.org
> Subject: [sdiy] Two ways of mixing modulation routes
>
> Hi all,
>
> I've been looking at the Sequential Pro-One schematics,
> specifically the modulation routes:
>
> http://machines.hyperreal.org/manufacturers/Sequential/Pro-One
/schematics/pro1-schematics-a.gif
>
> (Rotated image, but it's bottom right when it's the right way around).
>
> I noticed that rather than mix the signals using an inverting
> op-amp mixer (as I might have expected), instead they do a
> passive mix, followed by a non-inverting op-amp.
>
> Is there any benefit to this approach, aside from avoiding
> the inversion? Is that the reason it was done this way?
>
> Thanks,
> Tom
>
>
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> Synth-diy at synth-diy.org
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