Does input impedance double or halve with two amps?

warnerwh · « **on:** 22 Feb 2005, 10:01 pm »

I need to know if I hook two amps to my pre will that increase the input impedance the preamp sees or will it be the total of the two amps divided by two. Thanks

Occam · « **Reply #1 on:** 22 Feb 2005, 10:06 pm »

Assuming they are the same amps, the impedance load seen by the source would be 1/2 the impedance of a single amp.
The generalized formual for impeances/resistances in parallel is
Rt = (R1 x R2) / (R1 + R2)

JoshK · « **Reply #2 on:** 22 Feb 2005, 10:06 pm »

halve (because you are running the amps in parrallel).

WEEZ · « **Reply #3 on:** 22 Feb 2005, 10:07 pm »

The total divided by two. (assuming both amps have the same input z and your pre-amp outputs are not independent outputs- but are paralleled)

WEEZ

warnerwh · « **Reply #4 on:** 23 Feb 2005, 12:33 am »

Appreciate the help. Thanks guys

jeffreybehr · « **Reply #5 on:** 23 Feb 2005, 04:32 pm »

Speaking of resistors in parallel, here http://www.1728.com/resistrs.htm is a site that will calculate the net results of having as many as 10 resistors in parallel. I use it for calculating net gage of multiple-conductor speakercable, among other things.

eico1 · « **Reply #6 on:** 23 Feb 2005, 09:16 pm »

Your capacitive load will double!

steve