+ - 15 volt supply Soft Sync???

[Harry Bissell]

Hi JH...

The oscillators could possibly soft sync to the supply but it isn't likely if
the switcher is a quality unit. A few ohms of series resistance and capacitors
to ground should cure that entirely if that happened. I'm playing with TomG's
VCO4d and a switcher and have no problems at all with the switcher.

Poor layout techniques, daisy chain grounds and power supply runs... lack of
decoupling caps and (oh my) sharing components like quad op-amps among
different VCOs will be far more damaging.

With some modern SMPS... the switching frequency is so high that I doubt you
could hear the sync effect. I expect that the beating would stop at very close
frequencies if there was a sync problem... right ???

:^) Harry

jhaible wrote:

> > Although I will agree that linear supplies are better suited for our
> > particular application, it should be noted that many of today's
> top-quality
> > professional synthesizers have switching power supplies.  For instance,
> the
> > Yamaha TX-816, the DX7-II, the Roland XP-80, most Akai samplers, and many
> > others.  I have used these instruments in many studios and have never had
> > problems with noise (OK... the TX-816 was a little hissy, but that was
> 12-bit
> > FM hash, not power supply noise!)
>
> None of these boxes has VCOs. I wonder if there would be a soft sync
> effect between VCOs and switching PSUs. Mind you, I don't really know
> because i've never tried, but when VCO -> VCO soft sync over the supply
> rails can be a problem in ordinary synths, there might be reason to fear
> that all your precious VCOs get soft synced to a switcher frequency.
> Remember the Minimoog trick to avoid unwanted soft sync ? Noisy
> power supplies. Now imagine a noise that is not random anymore, but
> the power supply rails polluted with 100k switcher frequency ...
>
> JH.