[sdiy] Two ways of mixing modulation routes

David G Dixon dixon at mail.ubc.ca
Fri Jan 6 22:54:10 CET 2017

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.

> -----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
> (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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