That said is there any significant performance hit from using a single ended preamp with RCA/XLR conversion cables?
You might read starting at page 12
here. 12.2 Input configuration
The second major cause of extraneous noise and distortion is common-impedance coupling between
power wiring and signal connections. This is caused by the use of ground-referenced signalling (aka
single-ended or unbalanced transmission), which unfortunately is the predominant method of
interfacing consumer-grade audio equipment. As a result the ground circuit becomes an inseparable
part of the signal path and any currents flowing through the ground circuit affect the audio signal.
Ground loops cannot fundamentally be avoided. Star grounding only works at low frequencies. The
longer the wires to the “star”, the lower the frequency at which supply decoupling becomes
ineffective. The maximum permissible trace length of decoupling capacitors in class D amplifiers is
measured in millimetres and the value of the decoupling capacitances is large. To make a long story
short: you cannot connect the audio signal using a single wire and hope to solve the ensuing drama
using star grounding. It won’t work.
12.2.1 Way of looking at it when you’re only familiar with unbalanced wiring.
The solution adopted by the NC400 is a floating input, consisting of a “hot” and a “cold” connection,
which can be connected to the source like the primary of an isolation transformer. This breaks any
current flow that might otherwise flow in the audio cable. You would never directly connect the cold
pin of the input connector to the ground pin in the same way as you would never locally ground
input of an isolation transformer because it would no longer provide isolation.
Note that this isolation is not absolute. Differentials of more than a few 100mV should be avoided.
Because of this, some current path should be provided using a third wire. Any current that flows
through that wire is current that’s no longer flowing through your audio cable, and which is now
harmless.
Source Amp
Figure 1: The basic idea behind a differential (floating) input.
12.2.2 Way of looking at it if you’re used to working with balanced connections.
The NC400 has a balanced input.
12.3 Acceptable wiring schemes for amplifier chassis
The differential input permits a wide range of robust scenarios for hum-free connection, of which
three will be shown. We would like to urge users not to venture into the unknown before having tried
one of the proven good ones.
12.3.1 Vastly preferred setup: XLR input.
Regardless of whether the remainder of your audio system has balanced connections or not, the very
best way to wire the input of the NC400 is to leverage the advantage of its balanced input. You can
get almost all of the quality improvement afforded by balanced connections even with an
unbalanced source, provided that you have a balanced input.
