Moog Music Forum

Is it possible to modify the standard V-trig to S-trig unit (sorry not sure how to include circuit diagram here) but its the one using the 2N3904 --Moog part 74-221.
Using more than 5 x 911's (clones) the unit fails to re set after note on i.e. it gives continuous note on.
I replaced the 10k resistor down to 1k but the extra 2x911's are just too much for the unit to handle.

Does anyone have this problem and is there a solution?

PS ...shorting the terminals manually , of the Jones connector, all 7 x911's operate fine.

Every 911 S-trig input contains a thing known as a pull-up resistor. (it holds it at a positive voltage.)
It's there to keep the S-trig from falsely actuating since they function by being grounded (no voltage.)

But resistance adds up. So the more 911s, the more resistance that converter will see.

The solution (albeit not a perfect one) is to replace all the 911 pull-up resistors with ones of higher value so they don't all add up to some larger, lower resistance.
Please remember that these converter cables with the transistor inside derive their power from a positive gate voltage.
There's only so much current available to them depending on the current provided to them from the V-gate supplied to them.
Once that current is sunk (by too many 911s and their pull-up resistors), they can no longer function.

A 911 normally uses a 1K pull-up resistor.
But it might well still function fine if it was something higher.
Perhaps 2.2K, 3.3K... perhaps even 10K. I don't know.
But the higher you can go without affecting the 911, the better.
Basically you just want a 911 that doesn't trigger when it's just sitting there by itself.

Also, if you have 911s that have an external S-trig buss (as many Moog modulars have), you might consider cutting those lines if you don't use them.
They're all attached to each other either directly or through the "normalling" switches.

Good luck.
Sorry I can't be of more input. (no pun intended.)

Kevin...thanks once more for your time and help which is much appreciated.
Yes this has been an ongoing problem ..too many mouths and not enough porridge but as they all trigger fine with manually shortening the blades I am going to boost the V to S as you mentioned via the buffer in the Moog manual and see if it sorts the problem, so I'll also try the tip with the pull up resistors and that will be the two methods to try out, I'll post results for future reference....again thanks.

Good results from V trig buffer placed before V to S trig. But the 10k resistor on the V to String converter
had to be lowered to 3.3k or even 1k ....so far all 7 x 911's are triggering correctly although I have not given them prolonged tests but I don't think there's going to be any problems. I was about to try Kevin's idea with the pull up resistor but as yet, no need.
I'm using the Oakley Midi DAC with the new V trig buffer and V to S trig on the same 40mm x 25mm board nestled in the unit.

However you get there... you got there.
All good.

Most MIDI to CV converters have enough current sinking capability to drive several 911s, but not all "semi-passive" converter cables do.
Your solution is good.

Now what to do with 7 envelopes firing at the same time?

I'm following along and learning a lot. I built a V-trig to S-trig converter cable recently, using that circuit. I found it on page 69 of the Micromoog owners manual. (Thank you Kevin for hosting those wonderful references!)

For the buffer, was it a 741 op amp you used in front of the V-trig to S-trig converter? If not, could you point me to the right doc?

I'm not exactly sure what the circuit being used is, but wanted to offer a possible warning.

If I'm assuming correctly, an opamp follower has been added to the V trig input to allow more current to flow to the base of a 2N3904. (?)
That's probably all fine.

But using a 2N3904 to sink the current of seven 1K resistors normally tied to +12 volts requires about .085 amps.
That's enough to make things toasty.

So perhaps reconsider the choice in transistor or use some other circuit.
Maybe even a darlington topology would work.

All I know is that I just hooked 142 ohms across +12 volts and things got hot quickly.

Thanks Kevin. So I'm thinking that for a homemade V-trig to S-trig cable carrying that much current, that using a 2N2222 (handles 3X to 5X the current of a 3904) in the converter would be a better choice than a 2N3904. And they both cost just pennies anyway.

That's well anticipated Kevin....yes it does seem the 1k's are taking a bashing or at least some of them are as I've found signs of heat build up.
I'll change the 3904 and let's see what happens.

I've never tried it in this application, but I can recall pinball machines that all used darlington transistors.
Basically they're two transistors in one.
In pinballs, they could take a standard 5 volt digital signal and control a 35 volt paddle or target solenoid directly with one part.
(well, they added a diode across the solenoid coil to keep the tranny from blowing out, but that's not your concern here.)

You're still going to get toasty warm with a Darlington. Darlingtons increase the beta parameter but not the current capacity.

The better approach is moving from the TO-92/18 to the larger TO-220 package which can handle higher currents. There may be Darlingtons in the TO-220 package.

MC, I agree. I didn't mean a small package transistor.
Like the ones in pinballs, something like a TO220 or similar.
Solenoids take a lot more than 85ma too.

I haven't been in an arcade in a looooong time, but I *love* pinball machines. Fixed a few of them when I was a kid and I blame those catastrophic childhood experiences for getting me into synths and engineering