Micromega CD 20 MM CD20SILVER User Manual
Product codes
MM CD20SILVER
The drive mechanism
The MICROMEGA team’s wish was to be innovative in this field, and it was the case for some very
good reasons. Due to the success of DVD, DVD mechanisms produced today are of top, reliable
quality, simply because they are mass produced and therefore subject to extremely tough quality
control procedures inherent to mass production. It is for this reason that we took the wise decision to
equip the CD20 with the latest generation SONY KHM313 or SANYO SFH850 DVD mechanism.
The mechanism control is ensured by a Philips SAA78247 circuit and a MICROMEGA proprietary
software program featuring error correction algorithms which are particularly efficient and designed for
audio reproduction. At present and in many cases, CD players are optimized to read CD ROM. Indeed,
audio CD is read at nominal speed, whereas in the case of CD ROM, some players reach up to 52
times nominal speed. It’s a different aspect but it is not the most significant. When reading CD ROM, it
is possible, if a batch of data contains errors, to go back and to re-read the passage, before choosing
the best remaining error interpolation strategy. This solution is absolutely unthinkable in audio terms,
because in the event of errors the aim is to privilege continuity of the musical message so that the
listener doesn’t realize that the player is correcting inaccurate data. Obviously, it’s impossible to stop
the reading and to repeat a passage several times to remove a scratch, a finger mark or anything else
which could have triggered the error correction system. In light of this, we can see how important it is to
adopt a specific strategy to audio reading and why the MICROMEGA team invested so much energy
and time into developing the most appropriate solution in terms of musical reproduction.
good reasons. Due to the success of DVD, DVD mechanisms produced today are of top, reliable
quality, simply because they are mass produced and therefore subject to extremely tough quality
control procedures inherent to mass production. It is for this reason that we took the wise decision to
equip the CD20 with the latest generation SONY KHM313 or SANYO SFH850 DVD mechanism.
The mechanism control is ensured by a Philips SAA78247 circuit and a MICROMEGA proprietary
software program featuring error correction algorithms which are particularly efficient and designed for
audio reproduction. At present and in many cases, CD players are optimized to read CD ROM. Indeed,
audio CD is read at nominal speed, whereas in the case of CD ROM, some players reach up to 52
times nominal speed. It’s a different aspect but it is not the most significant. When reading CD ROM, it
is possible, if a batch of data contains errors, to go back and to re-read the passage, before choosing
the best remaining error interpolation strategy. This solution is absolutely unthinkable in audio terms,
because in the event of errors the aim is to privilege continuity of the musical message so that the
listener doesn’t realize that the player is correcting inaccurate data. Obviously, it’s impossible to stop
the reading and to repeat a passage several times to remove a scratch, a finger mark or anything else
which could have triggered the error correction system. In light of this, we can see how important it is to
adopt a specific strategy to audio reading and why the MICROMEGA team invested so much energy
and time into developing the most appropriate solution in terms of musical reproduction.
Digital to analog conversion: AD1853
CD20 calls upon one of the best dedicated digital-analog converters currently available. We chose the
Analog Devices AD1853 because of its unbeatable value for money. This converter with its dynamics of
110dB, its signal to noise ratio of 112dB and its THD + Noise figure of < -100dB is the ideal converter
for treating signals from the SAA7824 as accurately as possible. The power supply with constant
current source and shunt regulators ensures total immunity from external disturbances. The local
decoupling ensured by very low inductance, very low series resistance capacitors, guarantees better
signal integrity for the analog stages. The signals generated by the SAA7824 enter the AD1853 at 44.1
kHz. They are converted internally and oversampled 8 times in a digital filter whose out of band
rejection is higher than 115 dB, pushing very far back from the audio band the first images of the digital
filters. That makes it possible to have analog filters of a relatively low order while minimizing the energy
transmitted out of the band. The design of the printed circuit is critically important and the MICROMEGA
team put all its know-how into this part, which represented a challenge in more ways than one. The
circuit, which was designed using the most modern software, is optimized to take into account the
extraordinary possibilities of the selected components. Any design error can be costly, both in terms of
measurements and listening quality. The AD1853’s current outputs in differential mode enable it to
preserve the intrinsic dynamics of the signal and to reject in common mode any disturbance which
could have affected the signal. Despite all the precautions taken in terms of the layout, it may be that at
certain times some external phenomena affect the signal. In this particular case, the differential mode
proves to be extremely effective. Indeed, the principle of differential mode consists of conveying a
signal in two separate branches, one of which is in opposite phase to the other. If a disturbance affects
the signal it will simultaneously affect the phase of the two branches. When the differentiator comes into
play between the two signals, this disturbance will be totally cancelled. It is what we call in technical
jargon the common mode. Therefore, we can affirm that a differential signal saves 6 dB of dynamics
and totally rejects any signal in common mode, taking into account the differentiator’s common mode
rejection factor. A subject often discussed is that of symmetrical connections. These were invented in
the past in the professional field to transmit low level signals such as microphone signals, to eliminate
ambient disturbances and in particular, hum due to mains cable radiation at 50 Hz.
Analog Devices AD1853 because of its unbeatable value for money. This converter with its dynamics of
110dB, its signal to noise ratio of 112dB and its THD + Noise figure of < -100dB is the ideal converter
for treating signals from the SAA7824 as accurately as possible. The power supply with constant
current source and shunt regulators ensures total immunity from external disturbances. The local
decoupling ensured by very low inductance, very low series resistance capacitors, guarantees better
signal integrity for the analog stages. The signals generated by the SAA7824 enter the AD1853 at 44.1
kHz. They are converted internally and oversampled 8 times in a digital filter whose out of band
rejection is higher than 115 dB, pushing very far back from the audio band the first images of the digital
filters. That makes it possible to have analog filters of a relatively low order while minimizing the energy
transmitted out of the band. The design of the printed circuit is critically important and the MICROMEGA
team put all its know-how into this part, which represented a challenge in more ways than one. The
circuit, which was designed using the most modern software, is optimized to take into account the
extraordinary possibilities of the selected components. Any design error can be costly, both in terms of
measurements and listening quality. The AD1853’s current outputs in differential mode enable it to
preserve the intrinsic dynamics of the signal and to reject in common mode any disturbance which
could have affected the signal. Despite all the precautions taken in terms of the layout, it may be that at
certain times some external phenomena affect the signal. In this particular case, the differential mode
proves to be extremely effective. Indeed, the principle of differential mode consists of conveying a
signal in two separate branches, one of which is in opposite phase to the other. If a disturbance affects
the signal it will simultaneously affect the phase of the two branches. When the differentiator comes into
play between the two signals, this disturbance will be totally cancelled. It is what we call in technical
jargon the common mode. Therefore, we can affirm that a differential signal saves 6 dB of dynamics
and totally rejects any signal in common mode, taking into account the differentiator’s common mode
rejection factor. A subject often discussed is that of symmetrical connections. These were invented in
the past in the professional field to transmit low level signals such as microphone signals, to eliminate
ambient disturbances and in particular, hum due to mains cable radiation at 50 Hz.