First, to explain the difference of detection principle between the optical cartridge and MM / MC cartridge.
Both the MM / MC cartridge and the optical cartridge read the record groove through the needle, but the usual MM / MC cartridge detects the music signal by vibrating the magnet (or coil) in the magnetic field.
On the other hand, optical cartridges detect music signals by capturing shadow changes (brightness changes) using LEDs and PD (photo cells). Because MM / MC cartridges generate electricity by cutting off the magnetic field, magnetic resistance always occurs when the magnet (or coil) moves. However, the optical cartridge detects only the change in brightness (shadow movement), so no magnetic resistance is generated when the vibration system moves.
Since there is no magnetic resistance applied to the vibration system, the tip of the needle can move smoothly.
This is the primary advantage of optical cartridge technology
To detect music signals, the MM / MC cartridge must move the magnet or the core and the coil. However, in the case of optical cartridges, it is only necessary to move a light shading plate with a thickness of only 100 microns, so the moving mass is very low.
This is an additional advantage of optical cartridge technology
・What is the detection principle of the optical cartridge?
The optical cartridge detects movement of the needle using infrared LED, light shielding plate and two PD (photo cells). The operating principle is simple, the shading plate vibrates in front of the LED, and the PD (photo cells) behind it detects the change in brightness.
When the groove of the record vibrates (oblique 45 degrees), the vibration is transmitted from the tip of the needle to the cantilever, and the shading plate also vibrates together.
Since the shading plate vibrates in such a way as to block the light of the front LED, the brightness entering PD (photo cells) changes continuously from bright → dark → bright → dark.
As the photo cells detect changes in brightness created by record groove movement, the output voltage changes accordingly The movement of the shielding plate will be read as 2 separate stereo channels, by 2 independent photo detectors. The angular movement of the shielding plate ensures that each photo detector can only pick up information from its corresponding channel. Information from the parallel movement of the opposite channel will not be read, ensuring accurate channel balance and channel separation. ※Since the brightness of the photo cell does not change because the motion of the light shielding plate becomes a parallel movement on the side of the reverse PD (photo cells) side, it is possible to detect audio signals of the left and right channels with one light shielding plate.
・The reason why you need a dedicated equalizer
With an optical cartridge, you can not use a phono equalizer for MM / MC, you must use a phono equalizer dedicated to the DS Audio optical cartridge. There are two reasons for this
Voltage is required in order to power the internal LED inside the cartridge, and this voltage is supplied by the equalizer
Power is supplied to the LEDs of the optical cartridge using the tone arm ground (blue and green lines). For that reason, in order to use the optical cartridge, it is essential that the four cables of the tone arm are properly independent. (There is no problem with most arms that are currently on the market.)
The standard RIAA equalization curve required for MM/MC is completely different from equalization required for optical cartridges.
Because the output of an MM / MC cartridge is proportional to its speed, the output increases as the speed rises (= higher frequency). However, the optical cartridge has an amplitude proportional output that outputs flat from the low frequency to the high frequency (same as the old crystal type and capacitor type).
Since the optical cartridge is classified as amplitude proportional and is not affected by changes in speed, even on the same record, it has totally different output properties. Much less EQ correction is required for the amplitude proportional output compared to traditional MM / MC. Because of this, the RIAA correction circuit of the optical cartridge requires much less manipulation of the signal compared to a speed proportional type MM / MC cartridge. The RIAA correction circuit of the optical cartridge becomes an overwhelmingly simple circuit. This is yet another advantage of optical cartridge technology
The amplitude proportional type optical cartridge can output the movement of the groove flat from the low frequency to the high frequency, so the RIAA correction circuit of the optical cartridge becomes an overwhelmingly simple circuit compared to the RIAA correction circuit of the speed proportional type. The RIAA correction circuit of the optical cartridge becomes an overwhelmingly simple circuit. This is also big merit of the optical cartridge.
The biggest reason why DS Audio was able to successfully bring the optical cartridge back after 40 years is that technologies have evolved for both the light source and for the light detector.
Today the problem of “Heat” is not an issue, because very small and high power LED can be used. Unlike traditional incandescent or fluorescent bulbs, LEDs do not generate heat.
And since it uses a highly sensitive photodiode with its sensitivity characteristics well matched to the wavelength of the light source, it is possible to achieve a very high output. The optical cartridge has about 40 mV output, which is about 10 to 100 times higher than MM / MC cartridges, so high output can be obtained from an extremely low mass system. This is an advantage over MM / MC systems which require a very low voltage to pass through the tonearm wires, becoming vulnerable to interference and signal loss. The high output of the DS Audio cartridge is much more robust and less sensitive to interference.
Mix And Match
All DS Audio cartridges are fully compatible with any of the company’s accompanying phono stages/equalisers, so you can mix and match them, the price breakdown being DS Audio Master 1 cartridge plus phono stage/equaliser at £19,995, the cartridge at £8,150 and the phono stage/equaliser £12,695 on its own.
Significant when discussing a system that’s five times the cost of its later sibling are the physical differences. I realise ‘Never mind the quality, feel the width’ is a silly basis for an argument, but the less expensive of the two EQ units weighs 4.7kg, occupies a space of 310x92x235mm (whd) and offers only one output configuration via single-ended RCAs. The Master 1 equaliser box weighs 24kg, its size is 436x161x395mm (whd), and the box is filled with a PSU larger than you might find in a power amplifier.
Moreover, it offers three stages of subsonic filtering and both single-ended and balanced outputs for each. Balanced is better in every case – more robust and controlled – but the preferred filtering had to be determined by ear on a speaker-to-speaker basis.
Turning The Screw
Cartridge vs cartridge and not just equaliser is the other issue to address when comparing the Master 1 to the DS-002. Both share identical tracking forces (ideally 1.7g) and both weigh 8.1g. Construction, however, is where they part ways. The DS-002 employs aluminium for its body, the cantilever is aluminium and stylus has a Shibata profile. The Master 1 uses Super Duralumin for its body, has a sapphire cantilever and a ‘micro-ridge’ stylus.
What listeners, when first hearing DS cartridges, find most disorienting is this absolute absence of grunge, hum or other background annoyances.