Sonic Frontiers SFD-2

1 9 9 3 1993
1 9 9 5 1995

Sonic Frontiers' first digital-to-analogue converter and very much at the frontier of the somewhat affordable as it cost 4700$ !

SF spent then a lot of time testing all that was available around and prototyping along the way : one-bit or multi-bit, Crystal, Burr-Brown, Analog Devices, Philips or UltraAnalog for the actual d/a, Yamaha, Cristal, Burr-Brown or NPC for signal shaping and filtering as well specific programs à la Theta or Wadia.

The final choice went for Dick Powers' dual UltraAnalog D20400A converter (two of them), one AES20 input receiver and an NPC SM5803AP digital filter.

Jitter reduction is processed before the d/a stage with the AES20 input receiver : another UltrAnalog module offering less than 40ps of jitter.

The D20400A converting the signal is a 20bit dual module offering increased bandwidth, lower noise, superior settling time, lower impedance and improved internal layout than the 5-year old D20400.
There are two inside the SFD-2 for phase+ / phase- treatement of each stereo channel and redundancy correction.

Output of the D20400A modules is done by an output buffer stage of two Sovtek 6922 in cathode follower configuration with a low 50 Ohm output impedance.

The analogue output stage contines with SF's motto : "passive parts quality is of paramount importance" : silver wiring, Vishay and Caddock resistors, MIT caps, Kimber RCA and silver-plated Neutrik balanced terminals.

The power-supply section holds three split-bobbin transformers, high-speed rectifiers, Panasonic HFQ low-impedance caps, Solen/Wima/MIT shunt film caps in a mix of IC and discrete regulation.
Among the sixteen regulation feeds are a ±5V for digital, ±15V for the two D20400A and another, two-stage, for the AES20 module.

Like the SFC-1 but in a more ambitious way, the SFD-2 makes music... but was nevertheless updated in 1995 as SFD-2 MKII.
It is however the original version which got Stereophile's "Digital Source of 1994" award.

Sonic Frontiers SFD-2, image 1 Sonic Frontiers SFD-2, image 2 Sonic Frontiers SFD-2, image 3
Sonic Frontiers SFD-2 specifications
Title Value
Input receiver : 1x UltraAnalog AES20 AES/EBU
Digital filter : 1x NPC SM5803 with 8fs
D/A converters : 2x dual UltraAnalog D20400A
Low pass analog filter : proprietary passive configuration
Frequency response : 50Hz...20Khz (+ 0,5dB)
20Khz (- 0,1dB)
Intrinsic jitter : < 40 picoseconds
Jitter rejection : from 1Khz and above
S/N ratio : > 110dB (IHF-A)
Crosstalk : > 105dB (1Khz)
> 85dB (10Khz)
THD : < 0,05%
Output voltage : 3.5V (single-ended)
7.0V (balanced)
Output stage : fully balanced for AC and DC parameters
high speed tube buffer
Digital inputs : 1x coaxial (RCA)
1x optical (AT&T ST glass)
Digital output : 1x coaxial (RCA)
Tubes : 2x Sovtek 6922 (E88CC)
PC : 75VA max.
Dimensions : 48 x 10 x 33cm
Weight : 12kg.
List price : 4695$ (1993)
5895$ (1995, with digital board upgrade to SFD-2 MKII)
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