"Newps" wrote:

I have the PS Engineering PM 1000 II, the specs say the headphone
impedance range is 150-1000 ohms.

That's right. When you use that Radio Shack adapter cable, you're plugging
an eight-ohm load into your headphone jack. Eight is not between 150 and
1000. Consequently you're asking your amp to drive nearly 20 times its
rated output on that jack.

I don't know what the load is. The cable isn't relavant, it's the mic
jack off the camera that matters. And looking thru the camera manual it
does not list the load for that jack.

The cable is totally relevant. It determines your load.
Radio Shack provides the spec for the cable:

http://support.radioshack.com/suppor...oc33/33094.htm

It places a 10 ohm resistor directly across the plug contacts, in parallel
with the voltage divider (attenuator). This is to provide the proper load
to consumer audio devices which are designed to drive eight ohm speakers and
headsets. When you put a low impedance in parallel with a much larger
impedance, the lower impedance prevails and you can essentially ignore the
large impedance; the effective impedance of the circuit will be just
slightly less than the smaller parallel impedance. The impedance of the
camera's mic input basically doesn't matter at all. All the amp sees is
that tiny little 10 ohm resistor.

Another concern would be the amount of power dissipated in that 10 ohm
resistor. The intercom can put 70 mW into a 150 ohm load. If you
extrapolate, then that 10 ohm resistor ought to be rated for about a watt or
so, and would therefore be somewhat physically large. The actual resistor
in that patch cord is probably rated no more than a quarter of a watt.


In any event I don't care.

Your personal experience notwithstanding, it's poor advice to recommend this
product to others for this application. EE101 says that something is likely
to get hot.