Yamaha CS80

kent_spong wrote:
> So in therory, if you put all 7 triggers to 2 X 4019 and put it low -
6.5 say and join all the out's together and connect it to the trig 9
wire. You should have your ringmod back....on paper. I think :) I will
give this a go tomorrow and see.

Kent,

I'm looking at the KAS schematic, and it seems like it should be much
easier. Just lift the end of the 33k register going from the base of Tr8
to IC8 pin 15 and tied it to +8.5v.  

NOTE: the gates/trigger signals are active-low.  That is, one/on is
-6.5v while zero/off is +8.5v.  TR9 is the mono trigger for the ring-mod
EG.  It's the "OR" of TR1 through TR8, just using eight diodes (D1-D8)
as the OR gate.  However, the diodes look like they go the wrong
direction. This is because is actually a NAND gate, which if you've done
any digital design and studied De Morgan's theorem
(http://en.wikipedia.org/wiki/De_Morgan%27s_laws), is the negative logic
equivalent of an OR gate.

Anyway, that's more than enough digital stuff for a CS80 discussion :^)

 David

>
>
>
> --- In yamahacs80@yahoogroups.com, "David Rogoff" <david@...> wrote:
>> --- In yamahacs80@yahoogroups.com, "billwolfer" <bill.wolfer@> wrote:
>>> Someone mentioned modding the CS80 to 7 voices if you have a dead or
troublesome voice. I just had this done, courtesy of David Rogoff, our
moderator and list-owner. One of the VCO chips was misbehaving, so David
asked me if he could change the keyboard circuit to 7 voices. It sounded
like a reasonable, albeit temporary solution, but when I got the machine
home again, now the EG for the ring modulator is not functioning. I know
that this EG is monophonic, and that it was working before the
modification, so my theory is that by crippling one of the voices,
somehow we are bypassing the EG circuit for the ring modulator. Can
anyone verify this?
>> Here's the details on what's happening.  Based on the KAS chip
datasheet, I changed the MODE pins from a one (-6.5v) to a zero (8.5v),
which puts the chip in 7-note mode. A side-effect of the way the KAS
works is that in this mode it jams the KO8 gate output active.
>>
>> This caused the 8th voice cards to drone, which I "fixed" by removing
the VCO chips (one of which was bad, anyway). The other side-effect is
that the TR9 gate signal, which is an OR of the other 8 gates, is always
on. This is the gate used to trigger the EG for the ring-mod.
>>
>> If this was a longer-term fix, it would be easy to disconnect the 8th
gate buffer (IC8 / TR8 on the KAS board), which would remove both
side-effects.
>>
>> It is handy that the KAS chip can be set for any number of voices, up
to 8, for emergencies like dead voice cards (and because it was also
used on the 4-voice CS50), although the dead cards have to be the
highest number voices.  You can disable, for example, just voice 3, like
some poly-synths were able to do.
>>