Passive Stage preamp vs Active Stage Preamp

It has been said many times that simpler is better. I believe that to be true in a lot of situations but is not always true in passive preamp. Albert talks about impedance matching being a problem in passives. It is a misnomer to talk about matching impedances because in a standard pre / power combination the output impedance of the preamp is many times smaller than the input impedance of the amp. It is the desirable low (~100 ohms) output impedance of the active preamp designs that allows the pre to drive the capacitance of interconnects without frequency degradation.
If one was to match the output impedance of the preamp to the input impedance of the poweramp you would only get half of the open circuit voltage output of the preamp into the amp. Tube amps typically have a higher input impedance that solid state but the designer is free to set the value to practically any value within reason. With the higher input impedance of a tube design it MAY be more sucessful with a passive pre. The biggest problem with a passive preamp is the higher output impedance (1000 ohms or greater) can react with the capacitance of long cables and dull the top end. I use a buffered passive design most of the time. It has a gain of one but an extremly low output impedance. I find that it can drive most power amps to full output and has the ability to drive a capacitive load with ease.

Several of the variable output CD players have a low output impedance. If they have enough voltage output to drive your amplifier to full output, I would believe you could do no better. I feel that the best sounding preamp is no preamp at all! If the system does not require the added gain or a lower output impedance, I do not feel the added switches and circuitry can improve the sound.

Chris

It has been shown that any realtime electrical signal (music)can be broken down into a series of sine waves of varying amplitude, frequency, and phase using the Fourier transform. Fourier analysis shows that music is composed of a linear sum of many sine waves. If an amplifier is linear and has sufficient bandwidth to pass all audio harmonics, then it will clip with a sine wave at the same peak to peak value as it does with music. The confusion can result when comparing the RMS value of a sine wave to the RMS value of music. This is usually not a problem in a CDP because the voltage output is usually specified as an RMS value at 1 KHz and at 0 db recording level. I agree that the 0 db output level must be greater than the input sensitivity of the amp because music is not recorded at 0 db on a disc.