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In Reply to: pre-amp output posted by thad6000 on November 09, 2002 at 21:28:17:
Most power amps can be driven to full power by 1 volt or less, so 3.5V may be plenty. However, you also need to look at gain (ratio of output to input voltage), especially for phono preamps where the input signal is small (a few millivolts or even less with moving coil cartridges.) Other than that, the output impedance needs to be about a factor of 10 lower than the input impedance of the driven amplifier. This is rarely an issue with most amps.
Follow Ups:
But say as if in my case where the pre-amp has significantly more voltage output- will that affect the perceived loudness our output of the device? Or is that due to some other factor?
On the output, percieved loudness is usually a factor of gain. It might take a volt(rms, so the waveforme will be 2.8 v peak to peak)to drive an amp clipping or distortion onset. So if one pre will do it by the time the volume know is turned a quarter turn v a pre that takes half turn, it is probably a gain difference. If you can get to highest listening levels with all of your inputs, you have enough gain.
Output impedance is a bit more difficult to measure. Lower output impedance will allow the pre to drive more difficult loads-read:capacitance of interconnects. The old SS pre Kenwood L-07c had advertised output impedance of ten ohms and was designed to work with 5000 pF cables. A pre whose output is taken from the plate of a 12AX7 will have output impedance of something like 60-80 kOhm, and will be very cable sensitive.
regards,
Douglas
The situation with 12ax7s is not so bad if the final 12ax7 is a cathode follower. Otherwise I agree.
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