[sdiy] Buffering Busses?

[Dave Kendall]

Hi Seb.

> You should use low output impedance buffers (to avoid voltage drop from
> connecting multiple things), but maybe you have them already in the
> output stages of your midi to CV module?

It's a PAIA Midi2CV8, <http://www.paia.com/midi2sch.pdf> in mono mode with
home-made LAG on the MW AT and PB outputs, and offset/scaling on the
Pitchbend output to give ±5V. How do I work out what the output impedance of
the 1V/OCT is, and what would be a good value to end up with?

I got a tracking error when connecting both oscillators in an EFM VCO3D to
the 1V/oct CV from the Paia. One was fine, but both threw the pitching way
off, that's what started this train of thought. The eventual plan is to have
between 4 and 8 VCOs in total, with one set of 4 driven from a CGS37 CV
cluster, which I hope will provide a measure of buffering, so I guess I need
something that can handle LOTS of VCOs...
> 
> Remember also that any input voltage offsets in your buffer opamps will
> cause errors in your cv voltages - not so bad if the voltage offsets are
> static, but changes with temperature will not be good (choose your opamp
> buffer for pitch carefully .. I would recommend something like LT/MXL
> 1013/1014)

OK seems worth the extra money. Would just the one OPA on the 1V/OCT output
be sufficient to feed up to 8 VCOs? I haven't yet found a really good buffer
design, and was planning on using just a simple voltage follower. Do you
know of a schemo anywhere, perhaps with provision for trimming any input
offset?

Lots of questions, - sorry!......

Cheers,

Dave
.
(I REALLY need to get that Horowitz and Hill book..... :-)
 

> 
> Seb
> 
> 
> Dave Kendall wrote:
> 
>> Hi All.
>> 
>> Am building a Midi 2 CV module with a perfboarded Blacet MIDI sync IC in it,
>> and am thinking about running several Busses  throughout the modular, to
>> minimise on panel jacks, and make set-up faster.
>> 
>> 1/ 1V/octave
>> 2/ Gate
>> 3/ Trigger
>> 4/ Clock *1
>> 5/ Clock *2 (maybe....)
>> 
>> Question is, should I use voltage followers as buffers on these outputs
>> where they come out of the MIDI2CV? I figured that this might help stability
>> when feeding several VCOs from the 1V/oct outputs via the busses. Is it a
>> good thing to do this with the clocks and gates etc........ ? I know Doepfer
>> use a buss system, but I haven't got any of their gear, so don't know how
>> they do it.
>> 
>> Any thoughts appreciated.
>> 
>> Dave (saving up for Horowitz + Hill - £50 in the UK - Yikes!)
>> 
>> P.S. thanks Ryk, Harry and Seb for stuff on tempcos :-)
>> 
>> 
>> 
>> 
>> 
>> 
>