Manley REFERENCE PREAMPLIFIER - Manual (Page 9)

BALANCED or UNBALANCED ?
9
The topic of balanced inputs and outputs is relatively new and often confusing to some.
Balanced inputs and outputs are very old stuff to the professional recording business and telephone
systems. It was invented to reduce hum and interferance in systems with very long cables. Shielding is a
good thing but never perfect. Hum can still get in. Balanced cables use the shield the same as unbalanced
wires but they add a second signal wire. These two signal wires are generally driven with equal signals
but of opposite polarity. At the recieving end the input has the job of only accepting the difference of
these signals and rejecting any signal that is the same polarity. Because the 2 signals are opposite
polarity, they get amplified but because each of the two wires get the same hum and RF noise on them
the hum and RF should get cancelled. The standard connector for unbalanced hi-fi is the common RCA.
For balanced it is an XLR. These lines were first used for microphones and it was convenient to have a
female connector at one end and a male at the other to allow a number of cables to be connected together
for really long runs. Outputs are males. Some great uses are to 1) drive an amp in another room, 2) drive
a headphone amp, 3) drive the woofer amp in a biamped system., 4) drive VU meters if you have 'em.
Of course some power amps only have balanced inputs and this is the primary application and some
amps probably have better performance when you have the choice. You should evaluate this for yourself.
Is one form of cable inherantly better than the other ? Theoretically, balanced cables should be
better because hum and some RF will be cancelled. As a practical issue this may be not the primary
factor. Convenience may be. Chances are that most of your gear is not balanced. It is also likely that a
preamp designed to be optimum for balanced signals may be a little compromised for unbalanced and
vice-versa. The Reference Preamplifier is optimised for the much more common unbalanced RCA
interconnect and is slightly compromised in balanced modes. It uses ICs to perform balanced to
unbalanced conversion and then again from unbalanced to balanced. These are very high performance
parts designed expressly for audio but it is a few more parts in the chain.
Can you put unbalanced signals into the balanced inputs or the other way around? The answer is:
usually, but you need the correct adapters. You may also need a "ground wire" between the source and
preamp if you get some hum. Now, whether it is OK to "short" PIN 3 to Ground or PIN 1 or leave PIN 3
floating (unconnected) depends on the source. You probably shouldn't short PIN 3 to ground using the
balanced outputs of this preamplifier, just leave it floating. However if you need more output (6dB) short
PIN 3 to PIN 1 - you won't damage anything. It is what is normally referred to as a "transformer-like"
output. A true transformer output requires connecting PIN 3 to an input or ground.
By the way - You are probably aware that if you have the Phono Version that the phono inputs
are balanced. It will tend to reduce some forms of hum and RF. The main reason we did this is because it
improved the imaging and the soundstage. It was an experiment that worked well enough for us to look
into patenting the circuit. It also allows the easiest way to be sure you have absolute polarity intact - its
on switches. For checking - no wires to change!
We do get a number of calls asking us to recommend brands of interconnects. Tough question.
The best answer is to find a dealer with cables that can be tried out in your system. We have used
Kimber, Van den Hul, Illuminati, and Cardas with success and Audioquest and Goertz are very nice in
many systems. Each is different, has its own personality and should be choosen to complement the
system. A bright cable would likely be the wrong choice in a bright system. Perhaps a smoother, rounder
presentation will be the best overall balance unless you just plain love it scorching. We don't know of
any that cause problems with the preamp. We don't suggest spending more on interconnects than the
preamp or speakers. Some have suggested spending 20% of the budget on cables but we lean towards
10% or less - and listening rather than reading ads. We might suggest labelling them. A year from now it
might save some confusion. Saved you a call.