Cgs synth

I'm working on a Sequential Switch for sequencing. Each of the eight
steps having an LED, a Gate Out jack, and a pot.

If I use +15v off the PCB (right after the bead), should there be a
resistor between that voltage and the pot? What size?

I'm guessing there should be since I wired it up without one and it
blew up the bead (a 10R resistor).

Magic Smoke Drew

At 03:51 PM 8/13/2007, Andrew wrote:

>I'm working on a Sequential Switch for sequencing. Each of the eight
>steps having an LED, a Gate Out jack, and a pot.
>
>If I use +15v off the PCB (right after the bead), should there be a
>resistor between that voltage and the pot? What size?
>
>I'm guessing there should be since I wired it up without one and it
>blew up the bead (a 10R resistor).
>
>Magic Smoke Drew

IMHO, you shouldn't use the 15 volt rail to be a "reference quality"
voltage source. A sequencer should have a precision voltage reference
(as should a VCO, for example). Not that I can recommend one.*
--
john (of Magic Smoke Electronics, ahem! ;-)

* You can see why Tim Servo handles our engineering.


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Something definitely NOT right here!
100k pot with one end to +15V and the other end to 0V or -15V. The wiper
goes through a 220k resistor to the input to limit the range a bit.

Ken

Hi All.. I've been lurking for awhile waiting for something like this to
come up...

I have a similar project that I've been neglecting over the past couple
years... its an old Tom G design, a midi controlled gate module, outfitted
with pots to turn it into a sequencer. I've had the thing built for a
couple years and just recently (about 6 months ago) decided to finish it up
and put it into the case with my ASM-1...

The original module just has 16 gate outputs, each at 5v. I put an LED and
a pot on each of these. I have 2 outputs connected directly to the front as
triggers and all the pot wipers go to a little CV mixer I hacked together on
perfboard. The whole thing is powered on a +-15v supply along with the rest
of the synth (although this module only uses the + side of that IIRC).

My problem is that I keep blowing up my little CV mixer and various other
parts of my synth. I was able to get it running and had great fun with it
for about a week, but I turned it off and left if alone for a couple weeks,
came back, and now its toast... I don't know if this is because its poorly
designed or just poorly implemented, or if my kids or my cat got in it and
shorted something out...

I'm wondering if anyone has any tips or a better design for the mixer part
that will prevent this from happening... its just a simple thing with
whatever opamp I had laying around and some resistors. I think i may have
made the opamp amplify the input voltage x3 to bring it up to 15v or I may
have decided against this and kept it at unity but I don't remember now.
Also, any ideas on tying up loose ends, securing the modules to the
underside of the panels and making the whole thing more robust would be
helpful. Its a mess or flying wires with the boards hanging loose
underneath right now...

Is anybody here familiar with the old Tom G designs? He's out of the
business now and I've got a bunch of those modules and it would be nice to
be able to discuss them with someone.

Many thanks.
Christian Oncken


[Non-text portions of this message have been removed]

Would 50k pots work? Maybe with a different resistor? (I've got a whole bunch of 50k pots sitting here but only *7* 100k...)

And just to make sure I'm understanding correctly:
(from the backside with connections on the downside)
the pot's left connection to +15
the pot's right connection to ground
the pot's center connection goes to a resistor and then on to the "I" connection on the PCB (I1, I2, I3, I4, etc)

Thanks for putting up with my limited brain :)

Drew

sasami@... wrote:
Something definitely NOT right here!
100k pot with one end to +15V and the other end to 0V or -15V. The wiper
goes through a 220k resistor to the input to limit the range a bit.

Ken

>Would 50k pots work?

Yes.

Maybe with a different resistor?

No need to change the resistors. Probably around 180k. If you have too much
range still, go up to somthing higher. Not enough, drop down to something
like 100k.

> And just to make sure I'm understanding correctly:
> (from the backside with connections on the downside)
> the pot's left connection to +15
> the pot's right connection to ground
> the pot's center connection goes to a resistor and then on to the "I"

connection on the PCB (I1, I2, I3, I4, etc)

Correct.

_______________________________________________________________________
Ken Stone sasami@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>
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