general op amp question

[aziltz]

while i was working on my electronics class project i noticed something interesting that confused me.
i had a few op amp voltage followers hooked up to use like a buffer, powered with 9v and ground. and the input was biased with 4.5v. it worked, that made sense to me. then a little later in the circuit, i had a summing amp hooked up.  2 inputs, both connected to v-, v+ was grounded, gain of 1. powered with 9v and ground, but no 4.5v signal was needed to make it work. (i was using 741's)  is there a quick explaination why the summing amp didnt need the 4.5 bias? is it because the feedback loop is connected to the input at V-?

[Sir H C]

I can not really visualize what you are saying, could you post a schematic?

[aziltz]

nvm, i think i figured it out.  i thought the thread would just die off.

[aziltz]

would inserting a buffer after the signal split but before a tuner out type jack fix the tone sucking problems?

(input) ---------------buffer----tuner out
               |
               |
               |
           effect--------output

(switching has been left out)

[Sir H C]

If the tuner is causing the tone suck then yest.  But usually they are quite high impedance and do not really suck that much from the input.

[aziltz]

i just thought in general, a unbuffered signal split was a bad idea.  i was using a tuner as an example.

[Peter Snowberg]

It's a very good example. To be scpecfic, you can split the signal without problem, the problem comes from the terminating impedances at the signal destinations.

With most opamp stompboxes you'll see an input impedance of 500K. if you put two of those in parallel you'll now have only 250K across the input and tone sucking will be in full effect.

Transistor fuzzes and some boosters can be as low as 10K so there isn't any room for a split.

The best deal is if you can add the buffer to an existing pedal where you can take advantage of the existing input resistor. All you need to add is a simple JFET buffer which has an input impedance of something over 1000000 MEGS (!).