Originally Posted by EJD
Thanks Don. Two follow up questions for you (or someone else)
1) I know balanced outputs are supposed to reduce "noise", but does that noise mean interference-related noise (say from cable boxes or dimmers) AND the inherent noise from an amp with a high noise floor/high gain. Or is it just the former?
2) When a preout voltage spec is given (1.2V, 2.4V, whatever), I assume that is a maximum output - correct? If so, do preamps generally increase from zero to that maximum in a linear fashion - i.e. does 50% on the volume dial equate to 50% of preamp output voltage?
1. The former -- the balanced connection tends to reject noise and hum since external signals couple equally to both wires in the cable. A quick explanation: There are positive (Vp) and negative (Vn) outputs from the source, so the signals on each wire are 180 deg out of phase. At the source and load, common-mode signals like noise get cancelled since the components effectively perform (Vp - Vn) = Vdiff. That is, the signal gets doubled since Vp - Vn = 2V, but noise is the same on each side and gets cancelled: Vnoise = Vnoise = 0.
2. Our hearing is not linear and so most volume controls are not either. Old-style controls used to have different "tapers". A linear taper went 1, 2, 3 etc. A log taper would (for example) double the level for each step from e.g. 1 to 10. Note that in power, to our ears, it takes 10 times the level to sound twice as loud. Audio taper controls were most common for audio systems, a special type of log control that put most of the change in the last half to match the way we hear. That is, the change is smaller at lower levels, and faster as it gets loud. This correspond to the way we hear. 50% on the dial of an audio taper control is only 10% of the total.http://en.wikipedia.org/wiki/Potentiometer
These days, volume controls are often designed to provide steps in dB, another logarithmic term. 1 dB is barely noticeable*, 3 dB is a significant step, and +10 dB is twice as loud.
HTH - Don
* Sitting there listening to music 1 dB is a pretty small step, just noticeable to most people. However, if you are comparing two sources, you can actually resolve much smaller steps, to perhaps 0.1 dB or less. Since "louder" almost always sounds "better" to us for various reasons, this is why level-matching is so important in comparisons. That is, with no reference, a 1 dB change does not seem large, but when comparing one source to another, 0.1 dB is routinely detected, with the source 0.1 dB louder sounding better.