Passive preamps and poweramp's input impeadance

Thank you all for your help, and you in particular, Newbee. I will go ahead and try this unit out in my system.

Is my face red!!!!!!!!!!!!!!!!!! I had my head where there is no sun when i breezed thru the initial post and for some reason thought we were considering the OBH 12 passive preamp (my excuse is the several recent posts on this unit). The manufacturer's specs on the OBH14 show the following output impedences: DAC - 620 Ohm, Non-adjustible 10 Ohm, and the Variable/adjustible is a fixed 5K Ohm. The original post said the Rotel imput impedence is 33K, not the 23k so we have a 6.5 to 1 ratio. It might well work with some minor rolling of the frequency extremes. He could always buy one at retail from audio advisor, which has a 30day return policy, and send it back if it doesn't work out.

There you have it! Newbee has given us some insight on how the impedance curve behaves. Sounds like what we said is right afterall. You'll have to experiment with this one! Arthur

Another thing to calculate, that no one seems to be considering, is the actual output impedence of the passive which changes with the setting of the volume control (which will vary depending of the output of the source). The output impedence of the creek, according to its manual, swings from 50K to 0. This is too complex for me - math wasn't my best subject, but logic tells me that with the variable output impedence of the Creek you should listen to it in your system before you reach any conclusions.

I will third Symphony and Unsound. 10k into 23k is not too good. HOWEVER, it is not the numbers that need to be matched but the impedance curves. I am not familiar enough to know how linear amps' impedances change with frequency to give you many details but if you can find the curves for your two pieces, all you have to do is superimpose them on each other and make sure that they don't hit (the axes will have to be similar of course). Theoretically you could have the preamp's lowest Z equal to the amps highest and still be ok if they don't hit (i.e., are offset). Otherwise the signal will be reduced audibly. So, Pass is right in some situations but if you change the amps or preamps, all bets may be off. Good luck on this tough one. You may just have to experiment and see what you think with your ears since that is what counts in the end anyway. Arthur

Arni, please forgive me. I made a huge error in my previous post. It should have read as: "the Rotel's input impedance does *NOT* make for a classic candidate for a passive pre."

I think Symphony Sound is right. Working and optimizing are birds of a different feather. Arni, the Rotel's input impedance does make for a classic candidate for a passive pre. Not knowing the source specs or cableing prohibits a defintive answer. The fact that it will be driving a sub amp as well, doesn't bode well.

Well maybe Nelson pass says it's ok but I sure as hell wouldn't run a 10k ohm preamp into a 23k ohm amp. Just my two cents worth. Sure it'll work - but it's not going to sound as good as if the impedance were matched better.

Two comments: (1) I've successfully used a 10K ohm passive with a Pass Aleph power amp, input impedance 23K ohms, and Nelson Pass told me that others report the same success, (2) if you can rig up a simple resistor network, you could find out whether a passive will work with your Rotel amp. Details on request if you're interested. A little soldering would be required, and four RCA jacks, and two or three pairs of resistors.