04-12-11: Dracule1
I'm not too certain on about how the length of the interconnects affects this. But I think longer interconnects will decrease the amount of effective volts the amp sees from the source. So I try to keep my interconnects as short as possible which also helps to prevent significantly losing high frequency response. If anyone more technical can find any error in my explaination, please correct me. I'm not that technical.
04-12-11: Ts0711
@dracule1
What am I missing? My amp has a sensitivity of 775mV (VTL compact 100), and I've been running 20 foot interconnects between the amps and various passive pre's with great results.
With resistive and LDR-based passive preamps, the need for short interconnects derives from their high output impedance, and applies to the cable between preamp and power amp. I can't envision a reason why the length of the cable between source and preamp would be any more critical than with an active preamp.
The reason cable length on the output side matters is that its capacitance forms a low-pass filter in conjunction with the output impedance of the preamp. Cable capacitance, besides being dependent on the cable type, is proportional to cable length. If it is too high, the bandwidth of the low-pass filter will be low enough to fall within the audible spectrum, resulting in some amount of roll-off of the upper treble.
The degree to which that is significant will also depend on where the volume control is set, since the volume control setting will have a major effect on the preamp's output impedance. For a passive preamp consisting of a potentiometer or a resistive stepped attenuator, the worst case output impedance will occur at a setting corresponding to 6db of attenuation, which will typically be very loud if the source is a cdp or dac.
As was noted, it is also important for the output impedance of the source to be low (in relation to preamp input impedance), and for the input impedance of the amp to be high (in relation to preamp output impedance). Otherwise frequency response irregularities will result, to the extent that the impedances that are involved are not constant as a function of frequency.
TVC's are a completely different story, that I'm not particularly familiar with. But since a transformer provides an impedance transformation corresponding to the square of the turns ratio (with attenuation or gain being directly proportional to the turns ratio), I would expect that as long as the volume control position that is used corresponds to a significant amount of attenuation (i.e., it is not near the top of its range), cable length and component impedance matching would be much less critical than for a resistive passive preamp.
Regards,
-- Al
