The Audio Note DAC 4 Signature, c.2002, is a non-oversampling, digital filterless DAC using premium parts, more silver than a Liberace concert, a tube rectified choke filtered power supply, and a pair of E182CC / 7119 dual triodes in the Class A output stage. It was said to sound smooth.
Instead of a digital filter, Audio Note employed a single-pole filter/interstage transformer combination…the gentlest way to bandpass limit the output of a digital/analogue chipset.
The DAC 4 Signature unit in-Barn for Flashback-Fi has been upgraded with an early DAC 5 digital board, which employs the Analog Devices AD1865 18 bit D/A chip. Note: The current production AN DAC 4.1x still uses this same Analog Devices D/A chip.
Premium parts abound including Black Gate caps, AN-Vx silver wire, and selected copper foil paper in oil coupling capacitors. You wouldn’t know it by sight, but the entire chassis is pure copper (painted black), adding to the DAC 4’s heft.
Inputs include 2x Coax S/PDIF (BNC and RCA), while the single-ended RCA output options include a “DE-EMP” or De-Emphasis output which applies a high frequency roll-off filter originally meant to be used when playing back a CD with pre-emphasis, and a “Direct” output.
I was not able to hunt down the DAC 4 Signature’s original price, or the cost of the DAC 5 upgrade, but I think we can safely say it was not inexpensive seeing as the DAC 4, not the Signature version, cost $9000 back in the day and the current production Audio Note DAC 4.1x Balanced Signature DAC lists for $35k.