Diamond DAC

The SPL Diamond DAC is a digital-to-analogue converter with connections for 6 digital stereo sources and an external word clock. It combines VOLTAiR technology, the AKM AK4490 Velvet Sound™ DAC chip and the SPL DLP120 Dual Low-Pass filter with an analogue volume control, allowing the output level to be adjusted without reducing digital resolution.

The front-panel volume control uses a solid, milled aluminium rotary knob and an Alps RK27 “Big Blue” potentiometer. Both stereo output pairs carry the same signal, with their level controlled by this volume control.

Diamond has 1 stereo USB input, 1 AES/EBU input, 2 optical stereo inputs and 2 coaxial stereo inputs. USB accepts PCM and DSD audio. PCM audio is also received in S/PDIF format through the coaxial RCA, optical Toslink F06 and balanced AES/EBU inputs.

Input selection is made with the front-panel control. The dot matrix LED display identifies the selected source as USB, COA1, COA2, OPT1, OPT2 or AES. After approximately 2 seconds, it shows the clock source and detected sampling rate. The DAC automatically detects the sampling rate and resolution from a streamer, computer, CD player or external word clock. For example, U768 indicates a 768 kHz clock signal in the USB stream.

The clock source is selected with the CLOCK switch. With Source selected, Diamond synchronises to the digital clock in the incoming source signal. With Word selected, it synchronises to the digital clock connected to WORD IN. The external word clock input allows Diamond to synchronise with a clock signal separate from the digital audio source.

Two stereo output pairs are provided for power amplifiers, active loudspeakers or other equipment. One pair uses XLR connections and the other uses RCA connections. The volume control can be removed from either output pair’s signal path with the DIP switch on the rear panel. This allows, for example, a headphone amplifier with its own volume control to be connected to one output.

The AKM AK4490 Velvet Sound™ DAC chip converts PCM audio at up to 32-bit resolution and a sampling rate of 768 kHz, equivalent to 16 times CD resolution. DSD is supported up to DSD4 or DSD256. Unlike the DAC 768xs, the DAC768 design includes an AES/EBU digital input and the SPL DLP120 with VOLTAiR technology.

The DLP120, or Dual Low-Pass filter, uses separate analogue filters for PCM and DSD audio because the 2 formats require different roll-off frequencies. These filters use VOLTAiR technology, which operates with a higher audio voltage and provides additional headroom and dynamic performance.

SPL develops the Professional Fidelity series both according to the circuit design and through listening. Many important components are fitted to the circuit boards using Through-hole technology, allowing SPL to select the components used in the design.

VOLTAiR is SPL’s 120V reference technology. It operates at a DC voltage of 120 volts, which is 4 times the voltage used by IC-based semiconductor operational amplifiers. The audio circuitry operates at +/-60 V through proprietary SPL 120V SUPRA operational amplifiers designed to handle this voltage. Conventional components and operational amplifiers would be damaged by it.

The 120V operating voltage supports the technical performance of the circuit in areas including dynamic range, signal-to-noise ratio and headroom. SPL also specifies benefits in detail reproduction and listening comfort. The 120V designation refers to the internal audio operating voltage, not the local mains voltage from the power socket.

The internal linear power supply uses a toroidal transformer to convert the mains voltage to the required secondary voltage. Rectifiers then convert this AC voltage into the DC voltage required by the audio circuitry.