[sdiy] Starting my ASM-1

[Jimmy Gogas]

Hello Gene,

Can you scan me page 12 of issue 67 (single bus keyboard interface). I'm not 
quite sure what the difference between a single and a double bus keyboard 
is. I currently have an cheap "(30$ about) portable digital keyboard with 
some effects on it. I was thinking of transforming this into my CV-keyboard. 
Is that considered as a single or double bus?


>From: Gene Stopp <gene at ixiacom.com>
>To: synth-diy at dropmix.xs4all.nl
>Subject: RE: [sdiy] Starting my ASM-1
>Date: Fri, 11 Jan 2002 17:48:02 -0800
>
>Electronotes issue 67 page 12 is a really good digital scanning interface
>for a single bus keyboard. I've build several over the years and they are
>great. If you think about it, converting a switch number to an analog
>voltage and deciding what to do if more than one is pushed at a time is 
>best
>handled by a simple digital circuit. This design uses a low-note priority
>latch plus a simple DAC, which allows you to keep your 
>resistor-string-based
>keyboard legato playing style.
>
>This kind of interface is pretty much immune to dirty contacts. It has zero
>drift over time after you stop playing, so you can drive the same synth 
>with
>a midi-cv converter and not have to worry about it drifting out of tune.
>
>If you have a 2-bus keyboard and you want to get by as simply as possible,
>you can use a current-source/resistor-string/holding-cap/buffer cv output 
>on
>one bus and use the other bus for the gate. This works pretty good and is
>fairly immune to dirty contacts, but it does drift over time after you let
>go of the last key. This would be acceptable in a synth that is never
>intended for midi-cv operation while the keyboard is still hooked up. It
>does require that you adjust the j-wires on all the keys so that the
>contacts hit at the same time.
>
>I would never reccommend a gated sample-and-hold design ever again. It just
>takes one dropped or mis-sampled note to spoil a cool solo to make you
>realize that there's a design you could've gone with that never has that
>problem.
>
>I've noticed there's a bunch of raw keyboard assemblies on ebay right now -
>these would be perfect.
>
>Best Regards,
>
>- Gene
>
>
>-----Original Message-----
>From: Ian Fritz [mailto:ijfritz at earthlink.net]
>Sent: Thursday, January 10, 2002 9:31 PM
>To: Rob Mantel; synth-diy at dropmix.xs4all.nl
>Subject: Re: [sdiy] Starting my ASM-1
>
>
>At 08:18 PM 1/10/2002, Rob Mantel wrote:
> >I built the formant keyboard years ago, and to be honest, I would never 
>do
> >it again. A lot of those keyboards, like the formant one, use double
> >contacts for each key (one for the cv, one for the gate), its a pain to
>keep
> >those contacts work reliable and trigger both at exactly the same time 
>over
> >the years.  So if you want to build your own, try to find something that
> >only uses 1 contact per key, but unless you can find the right 
>schematics,
> >it won't be easy to have a keyboard that you can play both with and 
>without
> >triggering a new gate pulse when you play the keys legato. There might be
>an
> >easy solution for this, but I don't know it.
>
>
>See EN #67 (12)   :)




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