In Reply to: passive preamp question posted by Randy Bey on January 20, 2001 at 06:36:22:
The minimum rule of thumb is that the source's impedance should be lower than the receiver's impedance. This is why passives impedance are between 300 ohms and 100K ohms. The passive is both a receiver and a source. When dealing with passive attenuators, the main issues to consider are:A. Required Gain (not an issue, apparently, in your set up)
B. Low resistance/capacitance of the interconnect
C. Relatively short length of the interconnect (under 10 feet)If these are not issues, the selection of the overall impedance of the attenuation circuit is a tradeoff. 10K is a very popular value for Solid State systems and 50K is more popular for tube systems. This has to do with tube circuits liking to see a higher impedance.
From a subjective standpoint, some people hear less "punchy" bass with passives. This could be due to the extra current available from line amps over what is available from the playback component. There could also be some built in bass reinforcement in certain line amps. On the other end, if you have long "complex" interconnects, there could be some high frequency roll-off.
With a high quality source component, short runs of interconnects and an amp with full output sensitivity of around 1v, you should be very happy with passives. This is especially true with a ladder stepped attenuator like Ron's.
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