MOTM

Hey, noobie here. I'm wondering what "unity gain" is. I thought it
meant that when two or more signals are mixed together, unity gain
will stop signals from overloading the circut. I know that you
shouldn't use multiples as mixers. Is that because a multiple doesn't
have unity gain?

-Elan

On Feb 27, 2009, at 3:10 AM, Argitoth wrote:
> I know that you shouldn't use multiples as mixers.

is that a hard-and-fast rule, though?

i thought MOTM modules were pretty ironclad ... could you use an MOTM  
multiple as a mixer?
---
Suit & Tie Guy
suitandtieguy.com
stgsoundlabs.com

At 04:26 AM 2/27/2009, Suit & Tie Guy wrote:
>On Feb 27, 2009, at 3:10 AM, Argitoth wrote:
> > I know that you shouldn't use multiples as mixers.
>
>is that a hard-and-fast rule, though?

Just about. I have read that it's usually okay to mix gate/trigger 
signals together -- maybe "bus" them together is a better term -- but 
that's the only possible exception that I'm aware of.


>i thought MOTM modules were pretty ironclad ... could you use an MOTM
>multiple as a mixer?

MOTM multiples are passive, just like everyone else's multiples.

John

>
> i thought MOTM modules were pretty ironclad ... could you use an MOTM
> multiple as a mixer?

a) Unity gain means a gain of 1 (unity) or no *overall* gain. Now, in 
electronics the term is *context sensitive*.

- a "unity gain mixer" means if I add 4 1 volt signals, I get 4 volts out 
(1+1+1+1)

- a "unity gain stage" is also called a "buffer" has a gain of 1. so if I 
put in 3V I get out 3V.

b) by *definition*, a multiple has no circuitry, it is just jacks wired in 
parallel. If  you plug 2 outputs into a mult, there will be *some* "mixed" 
signals, that will depend on what the output impedances of the 2 driving 
circuits are with respect to each other AND assuming there is an input also 
plugged in, the input impedance of THAT. Adding more inputs or outputs will 
*drastically* change the resulting signal.

This is NOT a recommended thing to do. That is why MOTM modules have 
built-in CV and audio mixers in them.

Paul S>

Mixing signals in a multiple was, I believe, one of Bernie Hutchins's 
reasons for putting a 1K series resistor on all outputs.  Paul makes a 
good point that results depend on the output impedances of the modules.  
While most MOTM do have 1K outputs, some have as low as 100 ohm.  On 
this topic Tony Allgood (Oakley) has pointed out that power supply 
current use is higher when jamming outputs together.  Having said all of 
that, the fact is it's not dangerous to do if the outputs are from op 
amps.  A typical op amp can stand being shorted to ground or any other 
voltage within its power rails without damage, because the outputs are 
current-limited.  Isn't this true, Paul?  I've never heard of a module 
being destroyed because a patch cord shorted out.

By the way, if you patch two 1K outputs together, they do not form an 
additive mix.  Each is seeing a 2K load, but the mix is drawn from the 
half-way point, so each signal will be attenuated to half strength.

Richard Brewster
http://www.pugix.com

Paul Schreiber wrote:

>> i thought MOTM modules were pretty ironclad ... could you use an MOTM
>> multiple as a mixer?
>>     
>
> a) Unity gain means a gain of 1 (unity) or no *overall* gain. Now, in 
> electronics the term is *context sensitive*.
>
> - a "unity gain mixer" means if I add 4 1 volt signals, I get 4 volts out 
> (1+1+1+1)
>
> - a "unity gain stage" is also called a "buffer" has a gain of 1. so if I 
> put in 3V I get out 3V.
>
> b) by *definition*, a multiple has no circuitry, it is just jacks wired in 
> parallel. If  you plug 2 outputs into a mult, there will be *some* "mixed" 
> signals, that will depend on what the output impedances of the 2 driving 
> circuits are with respect to each other AND assuming there is an input also 
> plugged in, the input impedance of THAT. Adding more inputs or outputs will 
> *drastically* change the resulting signal.
>
> This is NOT a recommended thing to do. That is why MOTM modules have 
> built-in CV and audio mixers in them.
>
> Paul S>
>
>