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TVCs and the subjective loudness curve (Fletcher/Munson)

I am posting this again because it became lost in a previous thread. I think it deserves some constructive debate.
On a previous post I wrote:

"a transformer volume control, which lowers impedance by a factor of as it reduces gain by a factor of 2 (do a search on TVC)"

The correct phrase is:

A transformer volume control lowers impedance by a factor of 4 as it reduces gain by a factor of 2 (3 db).

Impedance change is the square of voltage change, a basic transformer law. Or impedance ratio = turns ratio squared.

This means that if one plays music at one tenth of CDP output( let's suppose about 200 mV signal on the power amp input - pretty loud with today's speakers) the output impedance of a CDP source will be divided by 100!
That's what I call a powerful drive!

This is the reason why TVC preamps seem to INCREASE bass definition and punch as one lowers the volume control.
IMHO they are the ideal line stage for today's combination of high output sources, sensitive neighbors and late-night listening sessions. One can easily follow a double bass solo at very low volume levels (around 55 db).
Of course a TVC will sound much more open and "alive" at the correct listening level, however low level listening with a TVC is NOT a source of frustration.

If I may be so bold, I believe that the Loudness curve developped by Fletcher & Munson is off by several decibels, due to the use of resistive attenuators (the only ones available at the time).
All the best
Carlos




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Topic - TVCs and the subjective loudness curve (Fletcher/Munson) - Carlos 21:37:11 10/18/03 (15)


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