effect of an amplifier input impedance

read my friend audionote DAC user manual. Its written there not to match with a preamp with input impedance lower than 100k ohm as it will cause alteration in bass roll off (or whatever technical jargon i am not familiar with)

having search around the net, some preamp / int amp have input impedance as low as 20k ohm(ayre, marantz etc) while some have up to 100k ohm (eg. pathos amp). My own valve amp have input impedance of 47k ohm.

is it that important to match a DAC/cd player with amp with certain input impendance? what is the effect on the sound?

some cables like the MIT one have option to toggle with the impendance. anyone who own this mit cable try the effect of switching the cable's impendance?

miss match can lead to humming. been there.

Its about power transfer, afaik. The larger the input impedance and the lower the output impedance, the more efficient the signal transfer.

Then again, there's the argument that the impedances should be the same, so that you get maximum power transfer. I've heard that this is the approach taken in Jeff Rowland's preamp/power amp combos.

http://en.wikipedia.org/wiki/Maximum_power_theorem for more info.

azri wrote:miss match can lead to humming. been there.

I wonder if this is the problem I had pairing Maverick D1 in preamp mode with Rotel power amp. No matter what I do the humm never go away. The D1 didn't hum with my Yamaha int amp though when used as DAC.

azri wrote:miss match can lead to humming. been there.

that's not what causes humming.

i think it is more to impedance matching.
1 of the alternative way is change the value of grid/signal to ground's resistor in output of the DAC, or input of preamp.

for futher info can search net, the lampizator website got some info on this.

the use of resistor depend on type of your DAC chip as well.

yes, it can