JK Acoustics JK DAC 1

The digital signal is received by a Sony chip, the CX23053, which can lock at 32, 44.1 and 48 kHz. The digital audio signal is stripped of all further unnecessary transmission information, then fed to a Philips digital filter, an SAA7220P with /A suffix, the latest version. This performs a four-fold resampling, which brings the output signal to a clock speed of 176 kHz. This signal is added to a pair of now classic Burr-Brown converters, PCM56's, but in their highest (K-) selection and equipped with an MSB trim potentiometer. What is special is that the converters are not powered with /- 5 V (which is in principle sufficient and what everyone else obediently does) but with a much more generous /- 12 V. The converter and digital filter are electrically separated via a quartet of HP optocouplers. But that's not the end of it. The 7220 digital filter assumes an integrated 1541 dual-DAC (from Philips) and cannot simply be connected to two separate Burr-Browns. A handful of logic ICs from the 74-series (mostly fast HCx types) encrypt the digital information into the correct format. However, Ketelaar and his boys have come up with another trick here, whereby the converters are driven differently than usual, something that initially completely threw me into the woods during measurement. During a subsequent puzzle hunt, under the watchful eye of (a by the way silent) JK himself, I suddenly had a lightbulb moment, but I have promised not to reveal the secret. Immediately after the converters follows the current/voltage converter in the form of a discreetly built op-amp, no IC so. After that, the signal passes through two potted blocks that contain a final version of the (active) JK analog filter. These filters are plug-in modules and can easily be updated if necessary. The board with the converters (and the conversion electronics) also stands on gold pins, so if you want a version with a TD/A1541 or another converter, that is possible. The two-stage tube line stage is built around an E188CC per channel. Instead of anode resistors, current sources are used, something that leads to optimal functioning of the triodes. Through cathode degeneration, the overall negative feedback has been kept low. The coupling capacitors used are manufactured to specification (by Ropel), the output capacitor measures 5 cm in diameter.

Digital format S/PDIF Type D/A conversion 4 x oversampling, 16 bit Number of D/A converters 2 Type D/A converter Burr Brown PCM5U/K Demodulator Sony CX23053 / Yamaha YM3623B Digital filter Philips SAA7220P/A Frequency response flat within 0.2 dB from 20 Hz - 20 kHz Channel separation 84 dB , 1 kHz Quantization noise (linear) 93.5 dB Dynamic range 97 dB THD noise -82 dB, < 0.01 % Resolution 18 bit L/R Output voltage 2 V; 6 dBV Output impedance 3.5 Ohm (line 185 Ohm) Sample frequencies 32, 44.1 and 48 kHz Indicators warm up, operating, digital lock, emphasis Digital inputs 3, 2 coaxial and 1 optical Analog inputs 2, 1 fixed and 1 adjustable via line stage Line inputs 2 Dimensions (h x w x d) 85 x 435 x 380 mm Weight 5 kg