[geeks] Stupid recording engineers

[Tim H.]

On Wed, 24 Jul 2002 14:55:19 -0400
Joshua D Boyd <jdboyd at cs.millersville.edu> wrote:

> I understand that it is bad. But the difference between that design,
> and the official Rane design for summing to mono is 3 resistors, are
> one output.  So instead of
> Vr -------------
>          |
>          |
> Vl -------------
> 
> V- -------------

My problem occurs here, (and I'm not looking to get a running flame war
going) From working with 1/8 inch phone plugs, I know that some mono
plugs actually touch the barrel of the jack far enough down to make
contact with what you are calling Vr.  If your headphones actually
switch as you say, then if you plugged them into a piece of mono
equipment with one of these jacks it would drop a dead short across the
output.  

What should happen to make a stereo plug mono is this

Vl -------------------
		|
		|
Vr ------x    x-------
	|
	|
V- ---------------

with the "x"s signifying a break in the circuit.

so the entire barrel of the jack, composed of common and what is Vr on a
stereo jack is now common, and the tip or Vl connects to both speakers+
connection.  In any case there is no way to conveniently sum 2 channels
passively without taking a big hit in signal strength, if there was
there would be no reason to build your op amp mixer we were discussing
last week.

I am curious what the headphone was supposed to do, was it supposed to
sum channels of a stereo source, or was it supposed to plug into a mono
source and still use both speakers?

Tim