[sdiy] Pearl Syncussion VCO

[HOSHUYAMA]

Hello Ben,

Thanks a lot for sharing the info including the schematics.
Almost all the Pearl designs in those days are interesting for me.
In the Syncussion schematic, VCF is also unique and interesting.

> Maybee the VCO inverters are not across the whole supply but rather
> GND to +V?

Exactly.

An inverter can be considered as an opamp with a non-inverting input 
connected to a bias voltage which is determined by the ratio of 
nmos and pmos. (Approximately, Vcc/2)

The same technique is used in my cmos VCF.

http://www5b.biglobe.ne.jp/%7Ehoushu/synth/VcfMos0206.GIF

U1d generates a bias voltage for the inverters.  This bias voltage
cancels out the drift of DC characteristics for the inverters.

Best,

Sam HOSHUYAMA
Saitama, JAPAN

Ben Barwise wrote:
> Thanks, that helped. I suspected that, but didnt know if it was that
> or if it was a trick to tie up a unused inverter. but the thing is
> that it it has a proper GND , the negative voltage is the one that is
> forced- see below
> 
> 
> http://www.gearslutz.com/board/attachments/electronic-music-instruments-electronic-music-production/234092d1305016042-another-syncussion-thread-pearl_syncussion_sy-1_schematic.jpg
> 
> Maybee the VCO inverters are not across the whole supply but rather
> GND to +V? it has a 1u Cap on its output so I guess that means it must
> be floating between GND and +V and thus they needed a reference.
> 
> Cheers!!
> 
> -Ben
> 
> 
> 
> On 5 October 2011 20:47, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> > On 04/10/11 18:15, Ben Barwise wrote:
> >>
> >> Hey,
> >>
> >> I have been exploring lots of drum synthesizer schematics and I am
> >> currently looking at the Pearl syncussion. I was wondering if someone
> >> could give me a few tips on certain parts I am finding confusing in
> >> the VCO.
> >>
> >>
> >> I understand the integrator and schmitt trigger and then sort of get
> >> the CV input but I am just completely lost what is happening with that
> >> inverter stuck on the side of that PNP pair at the top - is that just
> >> a good way to tie up unused pins? does this schematic seem a bit
> >> bonkers? because I have traced it from that well known scan hanging
> >> around the internet (why do people bother scanning schematics you cant
> >> read! ) the inverters are guessed as 4069's they may not be.
> >>
> >> it is an interesting design anyway,
> >>
> >> http://img88.imageshack.us/img88/1884/pearlsyncussionvco.jpg
> >
> > It's a bias voltage source... "buffered" if you so like.
> >
> > Cheers,
> > Magnus
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