Preamplifier power supply

I am a firm believer in over-specified power supplies in audio, for several reasons:

Large transformers tend to have high primary inductance, this acts as a RF filter, no garbage in, no garbage out.

An over-specified transformer will not distort or limit its voltage going to the PS caps, due to the HUGE current spikes generated by the rectifiers (more than 10 times the average current).

Large capacitors generally have low ESR (equivalent series resistance). PS caps are effectively in series with the output signal, the less ESR the more transparent and "fast" the sound quality. This seems couter-intuitive because conventionally circuit diagrams are drawn with caps in paralell to ground and transistors or tubes in series with the output, however, if we mentally re-draw the circuit, it makes sense.
There are three main "loops" in a typical amplifier circuit:
1- The power transformer secondary + rectifiers form an AC loop that gets rectified and feeds>
2- The PS capacitors, which feeds DC to the control devices (tubes or transistors), which modulate the PS with an AC fac-simile of the input signal (music is variable-frequency/intensity AC), which generates>
3 - The output AC loop, formed by electrons flowing from PS ground to the PS capacitor (+) terminal, then through the tubes and transistors, then to the output. The output AC loop is closed through the load (speakers or the next component input impedance.

In other words:
A preamp or power amp uses tubes or transistors to AC-modulate (to the tune of the music) voltage coming from a power supply, which is the source of all power delivered to the load.
Transistors or tubes act as "control valves", allowing more or less of the PS voltage to pass to the output, hence the term "valve" adopted in the UK for tubes. Also, a FET's control element is called gate for the same reason.

A good listen to any Naim CD player with the Super Cap optional power supplies will convert the non-believer. Or a Musical Fidelity heaphone amp with the high-current PS.
Another example: ARC preamplifier's power supplies are over-specified by at least a factor of ten. ARC's tube preamps are known to sound as good or better than many transistor preamps in the bass.
P.S. I am not associated with Naim, MF or ARC...but I used to own an ASR Emmitter II amp with 1,000,000 uF (yes, one Farad) in the double-mono power supplies. Its bass quality, soundstaging and dead-quiet background are unsurpassed in my experience.

Casouza, there are many experts who don't agree with you, the passive preamplifier proponents included. There is a clear dichotomy I suppose.

Chris

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