7
4) Low Jitter Master Clock – The CD55 electronics
are synchronized by a low jitter master clock. In
Resolution CD players, the clock is located close
to the D/A converters to keep timing as accurate
as possible. By contrast, many common designs
locate the master clock at the CD mechanism.
These designs must pipe the clock to the convert-
ers, sometimes over very long lines, and typically
exhibit a great deal of jitter at the D/A converters.
5) Balanced D/A Conversion – The CD55 uses two
D/A converters per channel to achieve balanced
conversion.The primary benefit of balanced con-
version is that it eliminates noise introduced in the
conversionprocess,aphenomenonknownascom-
mon mode rejection. In short, both the right and
left channels are split into plus and minus signals
(180degreesout of phase)prior toconversion and
decoded by separate converters. As a result, any
noise introduced disappears when the plus and
minus phases are later combined.
To enjoy the benefits of balanced conversion, bal-
anced connectors (XLR) are used to connect to
the preamplifier.Most units with balanced conver-
sion also offer single-ended outputs (RCA). Many
manufacturers will simply discard the minus out-
put of balanced conversion and connect the posi-
tive output to the single ended connector. While
this approach is inexpensive, it usually results in a
sonicdifferencebetweenthesingle-ended andbal-
ancedconnectors.Toreduce this difference,Reso-
lutionsumsthe plus andminussignalsbeforecon-
necting to the single-ended connectors. As a re-
sult,oursingle-ended output performsatthesame
high level as our balanced outputs. Any sonic dif-
ference noted between the outputs is often due to
the cables or the preamplifier interface.
6) Low Noise Analog Output w/AnalogVolume Con-
trol–Thehigh resolution of the24-bitD/Aconvert-
ers requires an equally detailed analog output
stage.To keepunnecessarycircuitry toaminimum,
we chose to use passive current-to-voltage (I/V)
conversion. Passive I/V maintains linearity and a
constantimpedance throughthecircuitwhileavoid-
ing problems inherent in active stage designs.
The analog output contains a volume attenuator
that provides precision volume control with mini-
mal signal degradation. In contrast to digital-do-
mainvolumecontrol, noconverterresolutionislost.
In addition, the 6 dB boost required for some
HDCDsources is automatically detected and ac-
tivated using the analog attenuator.While digital-
domain attenuation reduces effective converter
resolution by 1 bit for non HDCDsources, and
analog-domain approaches require signal switch-
ing, this approach avoids both these limitations.
Volume level is indicated on the front panel as a
number between 0 (mute) and 99 (full scale).The
output level is adjustable by 0.5 dB steps from full
scale to -30 dB (40-99).From -31 dB to -69 dB (1-
39) the level is adjustable in 1 dB steps.
7) Robust Power Supply – Power supply design is
important for two reasons. First, a well designed
supplyshouldnotcontribute anyextraneousnoise
to the system.If power supply noise leaks into the
digitaldecoding oranalogoutput circuitry, thenoise
floor will be much higher and power supply har-
monics will degrade sonic performance.
The power supply must also be able to deliver re-
quired power levels to the circuitry over a wide
rangeof voltages(100-240) and50/60Hz frequen-
cies. An inadequate supply can cause behavior
ranging from poor performance, to system failure.
Consequently, we have dedicated three separate
transformers to guarantee that the supply is both
robust and low-noise. Toroidal transformers are
particularlysuitedforhigh-endaudioapplications.
8) A/C Filtering – The power entry module incorpo-
rates a master power switch, fusing, and A/C line
filtering. The A/C filter serves a dual purpose in
that it cleans the incoming power while also pre-
venting digital noise from escaping the unit. The
power entrymoduleusesa standard IEC interface
to the power cord, allowing the customer to use
the player in multiple countries.
9) Miscellaneous – The CD55 also contains many
otherdesign features.Forexample,wiring hasbeen
kept to a minimum to improve manufacturability,
reliability, and performance.Where wiring is used,
lengths are kept short to prevent noise pickup.
From a structural point of view, the chassis and
top are fabricated from 16-guage steel.Steel pro-
vides a good RF shield that reduces interference.
The chassis bottom includes two additional foot
mountsthatallowthecustomer to arrangethe sup-
ports in a tripod configuration, or add isolation ac-
cessories using standard 1/4-20 threads.
Resolution Audio •(415) 643-6971 •www.resolutionaudio.com •info@resolutionaudio.com
