Preamplifier power supply

Dazzdax, just for the sake of friendly discussion, the purpose of a preamp is to present a proper load to the source(s), switch inputs, adjust volume and drive properly the amplifier.

A resistive passive preamp is basically made of a 10 K ohms potentiometer used as a voltage divider. The potentiometer attenuates the incoming signal.

As a load for the preceding component, it performs poorly, the 10 K amplifier input impedance in paralell with the passive preamp's internal resistance add up to an equivalent ~5-6K ohms load, too low for most CD players and even worse for phono stages.

As a driver, its average output impedance is 5 k ohms, plainly unsuitable for driving a 10 K ohms power amp* input impedance and incompatible with long or high capacitance cables.

* Most engineerring textbooks and many audiophiles agree that the preamp output impedance must be lower than one tenth of the driven component's input impedance, for optimum transfer of signal and no loss of bass/treble/dynamics. 10 K amp needs a 1 K source (or lower).

The symptoms of low input impedance (poor load) and high output impedance(poor driver) are lack of punch, dynamics and weak bass.
Also, if the ICs are high-capacitance ones or longer than 1 meter, the 5K internal impedance will form an RC low-pass filter that will attenuate treble.
All of the above is measurable and not subjective at all.

Of course there is one advantage to a resistive passive preamp: lack of active circuits, therefore one hears purer midrange and zero noise.
However, IMHO, passive resistive preamps are a flawed design and do not play music (specially rhythm) well.
Because rhythm and dynamics are so important to the kind of music that I like, I use an active preamp.

TVCs are a different ball game, they present a high input impedance to the source and a low output impedance to the load, because they are transformers.
The role of a transformer is to step up or down AC voltages (great as an attenuator) and to match impedances (great as a sorce AND a driver).
Provided that a TVC is well designed and has enough inductance, it will have no measurable frequency response roll-off from ~20 Hz to ~50 Khz. You can read the data sheets at the Steve & Billington, Sowther and Bent Audio sites.
All IMHO and IME, take my comments for what they are worth.

Casouza, thx for your precious input. It leads certainly to a greater understanding of this matter. Why do some digital front end manufacturers like Wadia advocate the use of passive (digital) built in preamplifier? If transformer based preamplifier is the answer, why are most preamplifiers still built in the conventional way?

Chris

What do you think of the so called passive preamp with buffer?

Chris

I'm wondering myself, like the Pass First Watt B-1.

Chris, my comments were regarding resistive passive preamps versus transformer passive preamps. Between those, I prefer TVCs.

Most preamplifiers are built the traditional way because people need gain, specially audiophiles with phono front ends, low gain amps and low efficiency speakers. A preamp must be (ideally) able to cope with all kinds of sources, amps and speakers, no easy task.

As for Wadia's integrated preamp, it is active, not passive (I have seen the opamps inside a Wadia). Its attenuation is partly analog, partly digital. It sounds great and it replaces handsomely a preamp + PC + IC, as long as one adjusts the internal analog gain DIP switches in order to use a MINIMUM of digital attenuation. If one goes deep into digital attenuation, there is a clear loss of resolution/detail/soundstaging.
As for active preamps, there are excellent ones, some with gain, some with unity-gain buffers. I am not familiar with the Pass buffered preamp.

In summary, there is no clear-cut BEST solution.

In general, I follow these rules-of-thumb:

-If your system lacks dynamics and punch or you need to use the preamp above 3 in the dial, you need more gain, therefore no passive preamp will do the trick. Buy an active preamp that drives your system to VERY LOUD levels and still has about 6 db spare gain for those quiet recordings.

-If your system has too much gain ( volume pot stays around 8 in the dial, "jumpy" volume control near 9) or you can hear noise/tube hiss, you need a preamp with less gain or a TVC preamp IMHO.

-If you want a minimalist solution, a Wadia or Audio Aero CD player connected directly to the power amp will sound great IME.
Audio Aero has an internal active analog, tube-based preamp followed by a buffer to lower output impedance.
Opus 21 also has an internal solid state active analog preamp (SS) and it sounds great for the money.
There may be other brands of CDPs with internal preamps.

Anyway, my original point about the cap-charging current peaks in a preamp DC power supply reaching 10 times the average current remains (and is validated by engineering textbooks). A transformer that is specified for 10 times the preamp continuous power draw is NOt overkill, it is just sensible design.

I hope this helps