Wadia S7i direct to amp

Paperw8: a 3dB reduction in voltage corresponds to a 6dB reduction in power.

Bombaywalla: wrong! a 3dB reduction in POWER corresponds to a 6dB reduction in VOLTAGE.

I haven't taken the time to read through most of this thread, but I'll just say with respect to the quoted comments that neither is correct.

A 3db reduction in power corresponds to a 3db reduction in voltage, for a given impedance. A 6db reduction in power corresponds to a 6db reduction in voltage, for a given impedance.

To see that, consider that a 3db reduction in voltage corresponds to the voltage being reduced by a factor of 0.707. Since, as I think we all agree, P = Esquared/R, that 3db reduction in voltage results in power being reduced by a factor of 0.707 x 0.707 = 0.5, which is also 3db.

Regards,
-- Al

12-05-10: Bombaywalla
wrong! a 3dB reduction in POWER corresponds to a 6dB reduction in VOLTAGE.

unlike much of the subjective discussion in this forum, this is a factual matter; your *opinion* on the matter is irrelevent to the actual *facts*.

12-05-10: Almarg
I haven't taken the time to read through most of this thread, but I'll just say with respect to the quoted comments that neither is correct.

A 3db reduction in power corresponds to a 3db reduction in voltage, for a given impedance. A 6db reduction in power corresponds to a 6db reduction in voltage, for a given impedance.

the reason why impedance is not considered is because you are generally looking at power at a given point. for example, when you measure output power, you are always measuring power at the output terminals, so there is no difference in impedance. in this case, what we are describing is the effect of the wadia digital volume control on either the voltage output level or on power output level. so if you do a decibel measurement on voltage, the voltage level is halved at each 3dB increment; if you do a decibel measurement on the power level, that too is halved at each 3dB measurement, but if you look at power as a function of voltage and perform the power measurement AS A RATIO OF THE CORRESPONDING VOLTAGE LEVELS, then each halving of voltage level corresponds to a 6dB redunction in power level (you need to pay particular attention to the capitalized section).

at this point i have to say that i think that i have explained this as best i can. so if someone still isn't following this, then i can't help them and they will have to refer to other sources for further discussion.

Paperw8: If you look at power as a function of voltage and perform the power measurement AS A RATIO OF THE CORRESPONDING VOLTAGE LEVELS, then each halving of voltage level corresponds to a 6dB reduction in power level

Yes, absolutely. But note that each halving of voltage ALSO corresponds to a 6dB reduction in voltage level.

the voltage level is halved at each 3dB increment

I haven't taken the time to follow the parts of the thread that may be behind that statement, but an increment that results in voltage being halved is not in fact a 3db increment, regardless of the wording that may be used to refer to it. It is a 6db increment.

db = 20log(V1/V2) = 10log(P1/P2)

20log(0.5) = -6.02

Best regards,
-- Al

A 3db reduction in power corresponds to a 3db reduction in voltage, for a given impedance. A 6db reduction in power corresponds to a 6db reduction in voltage, for a given impedance.

Almarg, you are correct. Guys, I stand corrected on this.

P1 = V1^2/R1 & P2 = V2^2/R2
P2 = 0.5*P1 & R1 = R2 = R because we are looking at the power reduction at the same location hence impedance at that point remains unchanged.
So, if we take the ratios: P2/P1 = 0.5 = (V2^2/R)/(V2^2/R)
or V2^2/V1^2 = 0.5
or V2/V1 = sqrt(0.5) = 0.707

I should have done this calc before I wrote my post - my bad. ;-O
Yeah, so if we want half the amplitude, we will find it at 6dB lower power where we'll have 6dB reduction in ampl as well. So, my earlier post on 12/04/10 is correct where I showed the digital volume versus full-scale amplitude - you will get 1/2 the voltage amplitude at setting 88 & at setting 65, you will get approx 1/8 full-scale meaning that you will lose 3 bits. If you start from 21-bits, you'll be down to 18-bits at digital volume setting 65. You will lose 6 bits at digital volume setting 28.

Dennis_the_menace, I apologize for hijacking your thread. If it is any solace to you, I think, that you already got your answer to your question (which is depends on the quality of your preamp & on your personal preferences -> cannot remember right now which members wrote these 2 apt replies).