s trig

[rarecomponent]

Is it possible for the s trig to affect the application of the 911's ?
I wonder if my V to S trig unit is under powering ?
Or is the S trig simply on/off ? I notice the modular keyboard circuit has quite a few components with a relay and + 12\-6 power.

[thealien666]

S-Trigger (short trigger) is by definition a short, a momentary on-off-on switch. But maybe the time is is maintained low isn't long enough, or it's not shorting completely ?

[Rarecomponent1]

Yes...all the 911's work fine however I'm wondering if they need a certain " strength" S trig....

My Mididac C V convertor doesn't generate S trig so I've incorporated a V to S trig circuit in there.
But is this giving a correct strength Moog S trig.?

What I really really could do with is knowing what voltage/? the 950 kicks out between H and G in the schematic.

I know the S trig two terminals are shorted on the 911's but is there any minus voltage there that's pulled up or anything via the Moog keyboard ?

In a nutshell can a weak S trig produce a weak 911 output.?

[rarecomponent]

Yes ..all my 911's work fine. ( I think !)

What I'm trying to find out is does the 950 keyboard controller have any " pull up" voltage associated with the S trig output.

I realise the S trig is simply two terminals shorted but would there be any difference by say shorting a 911 with a screwdriver than with a 950 keyboard .Would the result be the same or would the 950 deliver more " punch" ?

My V to S trig consists of a 2N3904 and resistors...but I notice one of Moogs inverters has similar but with a voltage to the 2N3904 collector....ie the Moog Accesories ..its confusing me.

In a nutshell can the "strength" of the S trig affect the output of the 911?

[analogmonster]

Yes ..all my 911's work fine. ( I think !)

What I'm trying to find out is does the 950 keyboard controller have any " pull up" voltage associated with the S trig output.

Not a pull up, but a pull down to -12V. Q6 (NPN) of the 950 Interface works as current sink to ground if a positive voltage initiated by a key press opens the base / the transistor Q6. The collector of Q6 (=STrig connection) is preset to -12V via a high resistance of 470k. In closed mode (no key pressed) the STrig out of the 911 (yes, indeed, the 911 STrig 'input' is an 'output' in reality) provides a voltage of 12V, which is shortened to ground via Q6 of the 950 interface if a key is pressed. This voltage drop at the STrig connector of the 911 initiates the envelope. Please refer to the original circuit or check out my 950 clone site http://www.analog-monster.de/mmt950_en.html for further details.

I realise the S trig is simply two terminals shorted but would there be any difference by say shorting a 911 with a screwdriver than with a 950 keyboard .Would the result be the same or would the 950 deliver more " punch" ?

No. I've just cloned the 911 (not documented yet) and for my tests I shortened the 911 STrig connector of my board to ground of the same board. It works fine. The tests with my 950 clone and the shortening process via Q6 of the 950 interface were fine also.

My V to S trig consists of a 2N3904 and resistors...but I notice one of Moogs inverters has similar but with a voltage to the 2N3904 collector....ie the Moog Accesories ..its confusing me.

In a nutshell can the "strength" of the S trig affect the output of the 911?

No. The STrig event sets a flip flop on the 911 board which initiates an voltage independant envelope generation process. As long as the voltage drop at the STrig connector oft the 911 is close enough to zero the envelope will start. There is no dependancy between the "rest" voltage at the STrig connector and the envelope out.

[rarecomponent]

Thanks AM for taking the time to answer my query and supplying some good info and links.

Well I think that's answered my problem or at least stopped me worrying about it.

By the way your 950 project looks pretty good, I too was considering a keyboard project but not with midi features. In fact it was an old Crumar keyboard using contact springs. Its on the project list.

By the way apologies for double posting...the site logged me out and would not let me back in.

[thealien666]

Welcome to the Moog forum Rarecomponent1 !

[analogmonster]

By the way your 950 project looks pretty good, I too was considering a keyboard project but not with midi features. In fact it was an old Crumar keyboard using contact springs. Its on the project list.

Thank you Your question was interesting. I made some more tests with my 950 clone and there is a small difference between an "STrig - zero voltage" created by a 950 and a screwdriver shorting indeed: The STrig voltage has a small dc offset of about 40 millivolts when a key is pressed, which is obviously close enough to zero to initiate the 911 envelope.
Then I did some spice simulation of the 911 and found a maximum value of this dc voltage for proper 911 operation: 1V is ok, the envelope is still initiated, more prevents the internal flip flop from switching to DECAY Phase and the result is a kind of AR behaviour instead of an ADSR operation.