Balanced vs. Unbalanced - What does it mean?

Balanced connections mean that there are two signal wires per channel, each carrying a different polarity of the same signal and twisted together. There is no ground, per se, as any ground lead is only to shield the wires and the two signal leads, only, are connected between the two components. The most significant result is that any RF or electrical noise picked up by these leads is effectively canceled because of the differential termination that subtracts one from the other at the (differential) termiantion. This will make for less noise in electrically noisy environments or with VERY long runs.

Unbalanced consists of a signal lead and ground lead.

In practice, there is no real difference unless you have unusual conditions such as RF noise and/or runs of many meters. My interconnects are 10 meters and there is no audible difference between balanced and unbalanced except that the XLR connectors on the balanced lines are more secure and durable.

Kal

I would add that XLR circuits use higher signal levels - so better signal to noise or more dynamic range.

Balanced circuits are needed when there is a noise problem. If using a preamp of suitable gain, running RCA shielded cable for 30ft. should be no problem. When Sheffield Lab did their recordings, they used a shielded coax cable to run from Wiley Chapel to the electronics some 300ft. And we all know how quiet and good those recordings are. I prefer the XLR connector, and use them with the +(2) gnd(1) or pin 1 and pin 2, and not use pin 3 (-). RCA's seem to stretch and get loose over time. I just use the two wire rca cable and put on XLR connectors. My preference is the USA made switchcraft or Vampire. Jallen

Thanks for the information so far.

Can I use RCA out of my preamp with XLR into the amp? Do such interconnects exist and if so, any recommendations? I am using a Linn preamp into the MC402.

See this paper regarding interfacing a single-ended preamp output to the balanced input of your power amp. It's a bit technical, but well worth reading. As you'll see on page 2 of this paper, and as JAllen suggested, an adapter cable can be used. But alternatively, for better noise rejection, a QUALITY transformer (such as the ones made by Jensen Transformers) can also be used.

http://www.jensen-transformers.com/an/an003.pdf

You can find lots of adapter cables and adapters here:

http://www.bhphotovideo.com/c/browse/Cables-In-Line-Accessories/ci/1667/N/4294549275

Here is one example:

http://www.bhphotovideo.com/c/product/133649-REG/Comprehensive_XLRP_PP_6ST_EXF_3_Pin_XLR_Male.html#features

More generally, concerning balanced vs. unbalanced, I'll add a few additional thoughts to the excellent comments which have been made.

Besides the noise immunity advantage of balanced interfaces, single-ended (rca) interfaces are far more prone to hum and ground-loop problems than balanced (xlr) interfaces. That is because a single-ended interface uses the shield of the interconnect cable to both carry the signal return current, and to connect the chassis of each of the two components together (which are in turn connected to both signal ground and ac safety ground). So any voltage offset or noise differential between the ac safety grounds of the two pieces of equipment will result in an extraneous current flowing through the shield, which the receiving component cannot distinguish from signal current. Besides sometimes causing problems which are difficult to troubleshoot (as evidenced by many threads here at Audiogon), that can limit your flexibility in providing separate filtering of the ac delivered to different components, and using multiple dedicated ac lines to prevent cross-coupling of, for instance, digital noise into analog components.

Also, it is important to distinguish between components which are "fully balanced," and those which are not. A fully balanced amplifier or preamplifier provides a completely separate signal path internally for each of the two polarities of the input and output of each channel. A component which is not fully balanced just has a differential input and/or output stage, but has a single-ended signal path internally. Your MC402 appears to be fully balanced, as indicated by this statement in the manual:

Exclusive Double Balanced Circuity: Each channel of the MC402 consists of two balanced power amplifiers operating in push-pull with their outputs combined in a McIntosh Autoformer. This double balanced configuration from input to output cancels virtually all distortion.

An amplifier which is not fully balanced would typically cost less, would not provide the (at least partial) cancellation of internally generated distortion which this paragraph refers to, and might actually sound worse with the balanced interface than with an unbalanced one, because of the extra stage which is introduced into the signal path at the input and/or output, to do the single-ended to balanced conversion. It would, however, provide some degree of rejection of noise pickup, which may or may not be important in the particular setup.

Finally, re long cables, it should be kept in mind that regardless of whether the interface is single-ended or balanced, if both the output impedance of the preamp (or other driving component) and the capacitance of the cable (which is proportional to length) are too high, upper treble rolloff will result. That's not a concern under most circumstances, particularly with solid state gear, but if the driving component's output impedance were say upwards of 500 ohms, and the run were say 30 feet or more, I would make a point of avoiding high capacitance cables (e.g., choose cables that are around 20 or 30 picofarads per foot, and definitely avoid those that are around 100 pf/foot or more).

Regards,
-- Al