Multi-bit DACs

Philips TDA1540 | Top
The evolution in the use of digital filters and DACs, which greatly influence the sound quality of Super Audio CD/CD players, is also a fascinating topic. In the Red Book, which defines CD standards, the resolution is quoted as being 16 bit.

However, the first DAC used in the first Marantz CD player, the Marantz CD-63, and the Philips LHH-2000, was the 14-bit resolution Philips TDA1540. Since Japanese CD players all employ 16-bit resolution DACs, the Marantz/Philips specification would seem inferior, but according to data taken from actual performance situations and among audiophiles with a good ear for sound quality, the performance of the TDA1540 CD player with its 14-bit DAC is rated outstandingly high.

In actual fact, the secret to the excellent sound produced by the Philips SAA7030 digital filter incorporated into the TDA1540 is not obvious at first. The SAA7030 with a 4x over sampling filter capacity utilizes a top quality noise shaping circuit called a secondary noise shaper. When the Marantz CD-63 went on the market, the effect of noise shaping (imposing frequency characteristics onto distribution of quantized noise in order to shift noise component to an ultra-high ranges that are difficult to hear with the naked ear) was lagerly unknown. The combination of the SAA7030 and TDA1540 used noise shaping to achieve a resolution equivalent to 16-bit.

That's not all. Analog filters built into the analog output circuits after the DACs were set for smooth 3rd order slopes with particular attention given to regularity of the phase characteristics.

At the time, the filter characteristics of Japanese products were set as high as the 9th or 11th order, and the superb sound quality of the Marantz products was overwhelming. The sound quality of the Marantz CD-34 was given high praise as being nearly equal to that of the ultra high-end Philips LHH-2000.

Philips TDA1541 | Top
The next DAC developed after the TDA1540 was the 16-bit resolution multi-bit DAC TDA1541, well known among audiophiles. As with the TDA1540, the TDA1541 series are multi-bit DACs employing a DEM (dynamic ekement matching) circuit.

To put it simply, DEM is a superior system developed by Philips technicians that employes 4 to 5 current sources inside the DAC applied in turn to achieve a 1/4 to 1/5 reduction in DAC conversion errors. At first, the TDA1541 was used in combination with the Philips-made SAA7220P/A 4x over sampling digital filter (a noise shaper circuit was not required and was not used).

Philips TDA1541A | Top
The SAA7220P/A digital filters and TDA1541 were slightly improved and re-released as the SAA7220P/B and TDA1541A. These new digital filters conformed to the 28kHz DAT sampling rate, and plans were implemented to improve the precision of DACs. These were incorporated into the Marantz CD-94 after its initial release and also used in the Marantz CD94ltd and Marantz CDA-94.

Philips TDA1541A S1 | Top
While the value of Philips multi-bit DACs increased day-by-day, Marantz technicians were trying to achieve an even better sound quality. At about the same time, Philips, who was manufacturing the devices, proposed a special "select" version of the TDA1541A that had a particularly high rate of conversion precision. (Makers often release these kinds of special "select" devices.) Thus, the ultimate 16-bit resolution mutli-bit DAC, the TDA1541A S1, with a carved crown, was born and installed in the Marantz CD-80, Marantz CD-95, Marantz CD-99SE and the Philips LHH-1000. Naturally, the digital filter used in was the SAA7220P/B, which had already gained quite a reputation.

From the audiophile point of view, the TDA1541A S1 was a unique experiment that tested the performance limits of current device technology.

Philips TDA1541A S2 | Top
The "select" version TDA1541A S1 progressed to become the TDA1541A S2, with an even stricter selective standard and a so-called double crown mark. In fact, previous "select" product levels were ealisy exceeded through improvements in the manufacturing process and manufacturing precision of the device. The TDA1541A S2 was installed in the Marantz CD-95Ltd together with the SAA7220P/B. Later, Marantz successfully employed the TDA1541A S2 16-bit D/A converter as a finishing touch in the Marantz Project D-1.

Production of the SAA7220P/B digital filter had stopped long before this, so Marantz technicians programmed an 8x over sampling digital filter circuit for use as a high speed DSP.

The legendary 16-bit CD player Marantz CD-7, which is still highly praised, was the last Marantz CD player to feature the TDA1541A S2. Since actual production of the TDA1541A S2 has stopped long before, the number of players that could be produced using this device was limited from the start. Marantz used their precious stock of TDA1541A S2 to design digital filter circuits with high-speed DSPs in the same way as the Marantz Project D-1. The Marantz CD-7 however used 4x over sampling equivalent to the SAA7220P/B and a primary noise shaping circuit modeled on the secondary noise shaping circuitry in the digital filter SAA7030 (used with the first 14-bit DAC TDA1540) but fitted with an on/off function.

Actually, since the phase characteristic could also be calculated, the digital filter was used to calculate the pass-through characteristics of the analog low-pass filter and its phase correction. In other words, the unit was engineered on the premise that the signal output from the CD player would be completely linear and receive no phase correction. In addition, a variety of other technologies have been used during the process of converting the digital signal back to analog. This concludes the history of the Philips multi-bit digital audio DACs.

1-bit DACs | Top
The 1-bit DAC, also referred to as the Bitstream DAC, is based on a completely different concept to that of the multi-bit DACs. Multi-bit DAC rely heavliy on LSI manufacturing precision, Bitstream DACs by and large are not infuenced by such factors, and are characterized by the simplicity of the circuit itsef. Although the linearity of 16-bit DACs is impeccable, production costs are a big drawback. Thus, the current worldwide trend towards cost reduction supports the development of Bitstream DAC.

Philips SAA7320 & Philips SAA7321 | Top
Philips developed their first Bitstream DAC, the SAA7320, with a digital filter circuit. This however was not utilized in any Marantz CD players. Their next Bitstream DAC, the SAA7321, featured 4x over sampling and secondary noise shape digital filter circuitry. This was used in the Philips LHH-300 and Philips LHH-500.
Marantz began seriously employing Bitstream DACs from the SAA7350, which incorporated a secondary noise shalping circuit. This DAC was used in conjuction with the newly developed custom made Philips 18-bit output and 8x over sampling digital filter SM5840FP in the Marantz CD-42, Marantz CD-52, Marantz CD-72 and Marantz CD-72a.

Philips DAC7 TDA1547 | Top
Advancementin Bitstream DAC technology kept pace with advancements in peripheral devices. The SM5803APT, an 8x over sampling digital filter capable of 20-bit output, and the newly developed "DAC 7" switched capacitor type Bitstream DAC TDA1547, were used in the Marantz CD-15, Marantz C-16, Marantz CD-16SE, Marantz CD-23, Marantz CD-17, Marantz CD-17D and the Philips LHH-700. A secondary noise shaping circuit, the SAA7350, was positioned between the digital filter and the DAC 7. This added the solid feeling of depth found in the multi-bit DACs to the highly praised smoothness and spaciousness of the Bitstream DAC, making it even more desirable.

Philips DF7 TDA1307 | Top
The last lot of Marantz Bitstream system CD players used newly developed Philips TDA1307 digital filter that incorporated 8x over sampling and secondary noise shaping circuits (the so-called "DF7") together with the DAC7 (TDA1547), like the Marantz CD-14 and Marantz CD-16D.

Even in the Super Audio CD era, this combination of the TDA1307 and TDA1547 displays real audio quality. This combination was employed in the first Marantz Super Audio CD/CD player, the SA-1. However, the SA-1 uses four TDA1547 circuits per channel, each of which performs a single clock data shift in order to move quantized noised components beyond audible frequencies. In addition, the TDA1307 digital filters are only used for CD playback.
During Super Audio CD playback the 2.8MHz 1-bit delta sigma modulated DSD data is sent directly to the DAC 7.

Cirrus Logic CS4397 | Top
Currently, the Cirrus Logic (Crystal Semiconductor) super DAC known as the CS4397 is the main DAC used in new Marantz Super Audio CD/CD players. The CS4397 DAC features a built-in digital filter that enables input of not only Super Audio CD DSD streams but also PCM data up to 192 kHz/24 bits. It also contains a delta sigma modulator and DEM (dynamic element matching) circuitry inherited from the gloriously high fidelity 16-bit DAC TDA1541A S2. A switched capacitor DAC circuit is used in the final stage, and each stage has anti-jitter performance exceeding that of previous 1-bit(Bitstream) DACs. Each CS4397 has a dual channel structure.

Apparently, the same skilled Philips engineers involved in the development of the TDA1541 also participated in the CS4397 DEM circuit. The CS4397 is therefor a super DAC that inherits the tradition of Philips technology.
(source: All about Marantz - stereosound)

Digital filter fs/noise shaper (n/s) DAC Used in model(s)
SAA7030 4fs.secondary n/s TDA1540 (14bit) CD-63 (1982), CD-73 (1983), CD-34 (1985), (LHH2000 (1981)
SAA7220 P/A 4fs (no n/s) TDA1541 (16bit) CD-65 (1985), CD-75 (1986), CD-94Ltd, CD-50 (1989)
SAA7220 P/B 4fs (no n/s) TDA1541A (16bit) CD-94 (from mid-production), CDA-94Ltd, CD-60 (1989)
SAA7220 P/B 4fs (no n/s) TDA1541A S1 (16bit) (LHH1000 <1987>), CD-80
SAA7220 P/B 4fs (no n/s) TDA1541A S2 (16bit) CD-95Ltd
DSP 8fs (no n/s) TDA1541A S2 (16bit) (Project D-1 <1998>)
DSP 4fs (on/off selectable, primary n/s) TDA1541A S2 (16bit) CD-7 (1998)
SM5840FP 8fs (16bit in 18bit out) SAA7350 (2nd n/s BS) CD-42, CD-52, CD-72 (1991)
SM5803APT 8fs (16bit in 20bit out) SAA7350 + TDA1547 (DAC7) (LHH-700 <1991>), CD-15, CD-23 (1994), CD-23D
TDA1307 (DF7) 8fs (secondary n/s) TDA1547 (DAC7) CD-17Da (1994), CD-16D
TDA1307 (DF7) 8fs (secondary n/s) TDA1547 (DAC7) SA-1 (1999)
Cirrus Logic CS4397 (Super Audio CD DAC) SA-14 (2001), SA-12S1 (2001), SA-17S (2002), SA8260(2003)