On active Pre-Amps (mini-rant warning):
First, a few basics -
A properly designed pre-amp will neither add nor remove artifacts. It will have no color, no shading, no ‘warm’, no ‘cold’, no ‘dry’ sound, and will do neither more nor less than reproduce what it is fed. Describing what it does (or does not) do in terms typically reserved for wine or truffles is pretty much a waste of time for both the victim and the perpetrator.
The typical “Signal Source” will deliver +/- 2V out to the next-in-line component. For the purposes of this rant, all “sources” will be a generic 2V, and all “amps” will require this same generic 2V for full RMS output. This eliminates ‘refutation-by-exception’, one of the seven classical fallacies.
The typical amp will accept a 100% modulated 2V signal and produce its full RMS output indefinitely. Feeding it an over-modulated 2V signal will not increase its output, just cause it to reproduce (faithfully) the trash it is fed. What this means is that transients (as noted previously: Rimshots, hand-claps, knocks and pings) will be over-modulated 2V signals. Distilling it down to its simplest terms: over-modulated signal from source is clipping at the source level as sources are not typically designed for transient-response capacity *BEYOND* the 2V level, but the signal source (vinyl, CD, Tape, Whatever) if well-engineered will have the transients at 2V – maximum modulation. Consider why, for a few moments.
The typical active pre-amp will produce somewhere from about 5V out to as much as 15V out. Much as with amplifiers, call this “headroom”. NOTE: the source, typically at full volume, will produce 0 – 2V, and include the transients at the 2V level.
A dynamic source will have many transients – and the amount of energy in the attack of that rimshot is immense – but momentary.
Most well-designed amplifiers have an RMS capacity, and a transient capacity. The latter is typically defined in XX watts for YY seconds. Back in the day, this capacity was called many things and leveraged by less than scrupulous manufacturers to impute much greater power to their equipment than the reality. c.f. IPP – Instantaneous Peak Power. By comparison, the OEM Dynaco ST70 was rated at 35 wpc/rms with an 80-watt peak capacity, time not specified. My brute-force Citation 16 has an IPP of over 1,200 watts for one second. Generally, this IPP is a function of the power-supply and reserve capacitance. And with that in mind, consider that the VTA line has a much better power-supply than the OEM line.
So, an active pre-amp will deliver transients to the amp at some level above 2V if so-set. This will allow *ACTUAL* signal already embedded in the source to be revealed where a passive attenuator will not. Those not familiar with the process may attribute these revelations to the pre-amp – they are not. They are already there, have always been there, but have been hidden or left below the noise floor for any number of reasons.
Noise Floor: a passive attenuator has only the input signal to work with. There is no real adjustment between ‘too loud’ and ‘too soft’ for a dynamic source that makes everything comfortable at every level. And, if, like me, one is listening in a large room with highly inefficient speakers, it would simply not work. An active pre-amp solves all of those issues at once.
First, a few basics -
A properly designed pre-amp will neither add nor remove artifacts. It will have no color, no shading, no ‘warm’, no ‘cold’, no ‘dry’ sound, and will do neither more nor less than reproduce what it is fed. Describing what it does (or does not) do in terms typically reserved for wine or truffles is pretty much a waste of time for both the victim and the perpetrator.
The typical “Signal Source” will deliver +/- 2V out to the next-in-line component. For the purposes of this rant, all “sources” will be a generic 2V, and all “amps” will require this same generic 2V for full RMS output. This eliminates ‘refutation-by-exception’, one of the seven classical fallacies.
The typical amp will accept a 100% modulated 2V signal and produce its full RMS output indefinitely. Feeding it an over-modulated 2V signal will not increase its output, just cause it to reproduce (faithfully) the trash it is fed. What this means is that transients (as noted previously: Rimshots, hand-claps, knocks and pings) will be over-modulated 2V signals. Distilling it down to its simplest terms: over-modulated signal from source is clipping at the source level as sources are not typically designed for transient-response capacity *BEYOND* the 2V level, but the signal source (vinyl, CD, Tape, Whatever) if well-engineered will have the transients at 2V – maximum modulation. Consider why, for a few moments.
The typical active pre-amp will produce somewhere from about 5V out to as much as 15V out. Much as with amplifiers, call this “headroom”. NOTE: the source, typically at full volume, will produce 0 – 2V, and include the transients at the 2V level.
A dynamic source will have many transients – and the amount of energy in the attack of that rimshot is immense – but momentary.
Most well-designed amplifiers have an RMS capacity, and a transient capacity. The latter is typically defined in XX watts for YY seconds. Back in the day, this capacity was called many things and leveraged by less than scrupulous manufacturers to impute much greater power to their equipment than the reality. c.f. IPP – Instantaneous Peak Power. By comparison, the OEM Dynaco ST70 was rated at 35 wpc/rms with an 80-watt peak capacity, time not specified. My brute-force Citation 16 has an IPP of over 1,200 watts for one second. Generally, this IPP is a function of the power-supply and reserve capacitance. And with that in mind, consider that the VTA line has a much better power-supply than the OEM line.
So, an active pre-amp will deliver transients to the amp at some level above 2V if so-set. This will allow *ACTUAL* signal already embedded in the source to be revealed where a passive attenuator will not. Those not familiar with the process may attribute these revelations to the pre-amp – they are not. They are already there, have always been there, but have been hidden or left below the noise floor for any number of reasons.
Noise Floor: a passive attenuator has only the input signal to work with. There is no real adjustment between ‘too loud’ and ‘too soft’ for a dynamic source that makes everything comfortable at every level. And, if, like me, one is listening in a large room with highly inefficient speakers, it would simply not work. An active pre-amp solves all of those issues at once.
