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minimoog glide
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author minimoog glide
Dimitree
as far as I know, the minimoog glide circuit is really particular since it would give you different glide times for "glide up" and "glide down".
So I'd like to integrate this circuit to my minimoog clone.

Currently I'm using a simple 1V/oct keyboard as key CV, with 5V gate and 5V short pulse (trigger).

Can you tell me if I can simply take the minimoog glide circuit (posted) and put it between my keyboard CV out and the VCOs CV mix?
Or maybe this circuit is altering someway the 1V/oct tracking, since it is expecting the original minimoog keyboard?

guest
im not sure what the glide trig signal looks like, but the circuit is a simple version of the DUSG. it will have offset issues due to the limited gain inside the feedback loop, and the offset in the diffpair, but that should be fixable with the tune knob on the VCO. it will also have some CV drift when the glide trig is off. but it should work.
Dimitree
thank you!

"glide_trig" is a -10V(off) to +10V(on) gate
so I guess I need to adapt this one too to my 0V to 5V gate.

can the offset be fixed before the tune on the VCO, without major modifications of the circuit?

Quote:
it will also have some CV drift when the glide trig is off.

due to what? easily fixable?
guest
the JFET labelled "glide up" acts as an analog switch. the JFET labelled "glide down" is a track and hold buffer. so when the switch is off, the capacitors before the track and hold buffer can leak, and the CV out will move slightly. im not sure how bad this will be, depends upon the caps and the JFETs. its probably not too bad.

i have no idea why the JFETs are labelled the way they are. its not like one is only used for positive going CV or anything. im also wondering where the different glide times come from that you mention. perhaps the "glide up" JFET conducts differently on positive and negative currents.
Dimitree
So is the purpose of the npn pair just to buffer the pitch cv? If so I can remove that since my kbd already has a buffer on its output
guest
no, the npn diffpair and following pnp act as an opamp, with the JFETs completing the feedback loop, just the same as in the DUSG. you might be able to replace those transistors with an opamp, but i cant say for certain it would be stable. i would guess it would be, as the delay in the feedback is quite large. quite frankly, im not certain how its stable as it is.
Dimitree
ok, no problem then
I will simply copy this circuit as-is (with all its defects, after all it's a minimoog)
and connect it to my 1V/oct kbd.

do you think my 0V to 5V gate could correctly engage the JFET?
guest
no, that will need to be +/-10V
cygmu
guest wrote:
im also wondering where the different glide times come from that you mention. perhaps the "glide up" JFET conducts differently on positive and negative currents.


Is it because the follower transistor (T45) can source current but not sink? As usual I could be miles off the mark here.
guest
T45 is biased to 5mA, so i dont think it ever shuts off. its output impedance should be pretty consistent, and low with that 1.3k there.
Dimitree
guest wrote:
no, that will need to be +/-10V

what if I use a comparator to shift 0/5V to +/-10V?
like this: http://tinyurl.com/y9lt6nng

or using some transistors:
http://tinyurl.com/y9ssfqmv
guest
either would be fine.
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