external audio input voodoo

[Matthias]

Answering Matt:

>Hey,... in my M0D00LAR, is this all I need?

I liked that one. I do not know wht you need, but why don't you call it
MOODOOLAR to call the oldest african spirit? That wood be a even more
powerfool joint than with the spirit of the creator of your TOOL!

My thing is LOOP. It all started with a delay. Then it went LOOP SOOP.
Then I found rhythm and people liked it and soon it will turn into a LOOP
POOL and SCHOOL - It's COOL (don't call me a F...)

Soon I tell you more


Trying to help:
>Thanks for the input. I don't actually want to put a *real* limiter in
>front of the circuit, 'coz that costs money and could be used elsewhere

Very much so.

>Should I put a zener diode in, just for emergencies? If so, where?
>(before the op-amp I would assume) And what value?
>
>Realistically, I'm going to be taking the output of samplers and other
>synths, which are usually in the same range. No mics, no guitars, no
>bassoons. :)

Your first drawing looks very resonable (once I switch to that ugly font...)
The protecting diodes would be ordinary ones to positive and negative rail,
and after a input resistor of about 10k in series, to protect the diodes.
Put 10p in parallel with the 3M3, it might oscilate!
I do not actually see a reason to invert. Straight you get lower values on
feedback, too. It allowes you to put the input cap before the pot which
eliminates scratch noises from the pot in case the output of the feeding
device is not decoupled properly.


                     680k
                 ___/\/\/\_
                 |         |
          22k    | \       |
                 | |\      |
       __/\/\/\__|_| \     |
     __|__         |  \    |
 1my _____         |   \   |
       |      +    |    \__|_____
      GND     |    |    /
             _|_   |   /
             /_\   |  /
 POT __/\/\/\_|____| /   Thats the first time I am using ASCII...
        100k  |    |/
             _|_   /     ...and probably the last...
             /_\
              |
              |
              -
Since the potentiometer is a log one, the range is not very critical.
In mid position its 10 times less sensitive. So if you have a max
sensitivity of 5V/33 = .15V that serves for your instruments, and if you
start at middle position, you have 1.5V which is close to studio level.

>     I would put a shunt series reverse pair of zeners right on the output
>     of the op amp to ground.  You would pick the max voltage you want
>     (hard limit) by adding the forward voltage drop of a diode (0.7V) plus
>     the zener voltage of the diodes.  For example, picking a limit of
>     6.8V, you would pick 5.1V zeners.

I would rather have the OPAMP limiting and in case the output needs to stay
lower, devide the output signal. As I see, you need mixing resistors
anyway, so the value of those define the voltage limit.

Matthias