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Simaudio Technical Education
Updated: May 25, 2008
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Simaudio Preamplification Technologies
M-Ray Volume (Simaudio Ltd. Proprietary Technology)
This volume control circuit is based on the R-2R resistor array configuration and uses high-quality thin metal film surface mount
resistors with 0.1% tolerances. The entire process is microcomputer controlled via a discrete relay network. The audio signal is
never converted to digital, nor is it processed in any way. As well, with this type of circuitry, we can physically place the gain
section at the optimal spot on the circuit board, regardless of the actual location of the volume control, thus helping to shorten the
overall length of the signal path. This is a fully discrete circuit design and therefore, one of the contributing factors to the MOON
P-8 Preamplfier's 2-chassis design.
Image #1
The M-Ray circuit provides for 0.1db incremental adjustments and is considered amongst the most accurate volume control in the
marketplace today. Providing absolutely no sonic degradation of the audio signal regardless of the chosen volume setting
resulting, it also adds no colorations whatsoever. Two additional benefits of this volume control circuit are a previously
unattainable signal-to-noise ratio and a plethora of unique volume settings – a staggering 530 unique steps respectively in
the case of the P-8.
Furthermore, since there are no internal moving parts, as is the case with potentiometers whose internal contacts and moving
parts eventually oxidize, long-term reliability is not an issue.
M-eVOL Volume (Simaudio Ltd. Proprietary Technology)
This volume circuit is based on a resistive array configuration and employs a pair (for
balanced circuitry) of highly-regarded BurrBrown PGA2310 volume control circuits found
in both the MOON i-7 and P-7. Level matching between channels is significantly
more accurate over the entire volume range as compared to using a potentiometer type volume.
The M-eVOL circuit providess 0.5dB incremental adjustments for a high-level of accuracy
and yields absolutely no measureaable sonic degradation of the audio signal regardless
of the chosen volume setting.
Crosstalk
Crosstalk typically increases as a function of frequency; the higher the frequency, the greater the amount of crosstalk.
This is a behavioural chracteristic common to all volume controls, regardless of the circuit topology. Higher quality
volume circuits will have a significantly lower crosstalk measurement throughout the entire bandwidth:
Figure #10
In figure 10 above, the perfect scenario would have an identical crosstalk measurement of -140dB
(green)
across the entire frequency spectrum, but this is not realistic. The fully discrete M-Ray volume circuit found in
the MOON P-8 Preamplifier yields an astonishing -135dB
(blue)
at 1kHz. The MOON P-7 Preamplifier uses our M-eVOL circuit and produces a remarkably low -126dB
(orange)
of crosstalk at 1kHz. A very high quality potentiometer based volume circuit will have a crosstalk level -118db
(red)
at best and a ordinary poteniometer circuit may reach -82dB
(grey).
As crosstalk increases in the upper frequencies, the width of the soundstage becomes
compromised and consequently diminshes the accuracy of sonic reproduction.
Virtually perfect soundstage reproduction ... a genuine sense that the musicians are playing right in front of you.
Signal Level Matching
All volume control circuits suffer from imperfect level matching between the left and right
channels, especially at low and high output levels. In simple terms this means that the actual
volume level is not identical for both channels at various settings:
Figure #11
A high quality potentiometer-based volume circuit will typically have a variance of as much as 1.5dB
(red)
between the left and right channels at the volume extremeties as shown in figure 11 above. Both the MOON M-Ray and
M-eVOL volume circuits maintain an extremely low and consistent variance across the entire volume range of less that 0.05dB
(blue).
Perfect level matching between channels that no other volume control can achieve ... Recorded music heard
as it was intended to be - pure, natural and uncolored.
M-LOCK (Simaudio Ltd. Proprietary Technology)
This is our in-house developed maximum volume lockout circuit. It is a software based design
that is end-user configurable for each individual input on the MOON i-7, P-7
and P-8. The purpose of M-LOCK is to protect your amplifier(s) and your speakers
from possible signal overload; The logic being that different source components vary with
respect to their output voltage levels.
The days of accidentally over-loading your system are over!
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