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In Reply to: More on the listening room as an evaluation tool posted by Charles Hansen on January 17, 2007 at 20:19:17:
...many people feel a system sounds better with a preamp in the system, when it can be run without one?Is this a matter of adding favorable colorations to create a more musical sound?
By the way, it is great to see you back on the forums.
Follow Ups:
The more I think of Charles response to this question, the more disatisfied I become with it.To answer this question appropriately you need to consider the an electrical circuit in its basic terms, a device with three basic properties Voltage, Current and Resistance. In a system without an active preamplifier e.g a resistor based attenuator, the voltage of the circuit is varied following the time honoured V=IR formula, if you consider the formula, you will notice that there is cost for this, i.e. increased impedance (or resistance). An 'active' preamplifer on the other hand, introduces an active device (transistor or tube, both functionally equivalent in this application) can vary the voltage without a corresponding increase in output resistance, of course there is a price for this of course, the noise floor of the active device is typical higher than that of the typical passive element such as a resistor, but that penalty pales in a comparison to the advantage the active device brings to the table.
So it is not case of "adding favorable colorations to create a more musical sound". It is a case of less is less without an 'active' preamplifier, as the resistor based less so a transformer based attenuation are restricted devices in comparison to 'active' preamplifiers, as their attenuation comes with a stiff penalty, much higher output impedance. And as an aside, I think RFI has very little relevance in this scenario.
Music making the painting, recording it the photograph
I wish I had a great answer for you, but I don't.When we first started Ayre, we used a passive preamp between our reference CD player and our power amplifier (our first product). We quickly found that different passive preamps yielded different levels of performance, and went through a few of these. By far the best sounding was a custom-made fixed attenuator comprising a pair of rhodium-plated connectors soldered back-to-back with two resistors permanently soldered in place to give a single fixed volume level. No switches, no wires, just two connectors and two resistors. (All of the passive preamps and attenuators were plugged directly into the inputs of the power amp, so there was no issue concerning driving an interconnect cable.)
So when we made our first preamp, I was wondering just how much *worse* it was going to sound compared to our reference fixed attenuators. I was stunned to find that it sounded *better*.
There was a very slight loss of resolution, but that was more than made up for by increased focus of each instrument, improved weight and impact in the bass, a larger soundstage, and a greater sense of musical ease and flow.
I'm really not sure why this was so, but it certainly was. Here are a couple of possibilities:
a) The power amp was more sensitive to RFI than was the preamp. Somehow the preamp was filtering out RFI that was getting through the passive preamp.
b) The output impedance of our reference fixed attenuator was around 900 ohms, while the output impedance of the active preamp was 300 ohms. It may have been that the input stage of the power amp "preferred" seeing the slightly lower source impedance.
I find neither of these explanations to be very satisfying, in that I don't think they are telling the full story. But here it is ten years later, and I still don't have any better idea what is really going on here. However, I am quite confident that (at least in this case) it is *not* a case of "adding favorable colorations to create a more musical sound".
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