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24.126.150.150
Does anyone know the output impedance of a CAT ultimate preamp and the input impedance of the Pass X350.5 amp?I believe they are quite different - if that is the case how would you get the preamp output closer to the amp's input impedance and how would that affest the sound?
Follow Ups:
For all the reviews of the CAT preamp on-line, there is zero mention of the output impedance. The circuit topology is also obscure. All I can find out with Google and the review in TAS 123 is that it sounds OK but lacks some air, and that it uses 6922 triodes.This is frustrating, since the output impedance is probably the single most important technical spec for a line stage. It determines how much trouble the user will have in driving interconnect cables, and should be clearly stated at the beginning of any subjective review along with the other equipment used, IMHO.
Cliff is correct below that you do not have to worry about matching impedances with the power amp. The preamp output impedance should be low and the power amp's input impedance should be high UNLESS you are willing to entertain use of the 600 ohm professional standard. Atma-Sphere preamps are capable of driving 600 ohms, and if you use a balanced cable and terminate it with 600 ohms at the power amp end, you will greatly reduce susceptibility to noise in even very long runs of cable. Most tube preamps, and certainly those using 6922 triodes, are NOT capable of driving 600 ohms, so don't try this if you are not sure.
In general, a PRE should have the lowest output impedance practical for the circuit.An AMP should have the highest input impedance, ditto. This svoids the AMP loading the PRE signal.
Impedance matching is only relevant for POWER transfer (not voltage) in tube amplifiers, or for tramsmission lines at high frequency to avoid signal reflections.
Thanks guys. The info has been most helpful.
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