I’ve had a couple of conversations the past couple of years with mastering engineer Dave Collins about the D/A processor he was designing for Manley Labs, the company run by his wife EveAnna Manley. The 2014 CES saw the consumer debut of the Heart Monitor Controller 24/192 DSP ΔΣ [Delta-Sigma] DAC, which was being demmed in a system featuring Manley’s 25th Anniversary monoblocks, which use KT120 tubes. There are four digital inputs and Dave has kept the fully differential signal path as short as possible. Silicon includes a SHARC DSP and AD1955 DAC chips and harmonic distortion has been kept to a superbly low –120dB, and even that is the subjectively benign second. Price has yet to be decided.
What I found particularly interesting is that the Heart’s co-designer was Paul Frindle, a pro-audio engineer with whom I had become acquainted back in the days of Usenet. At very low signal levels, delta-sigma DACs suffer from what are called “limit cycle” spuriae—there is insufficient data in the delta-sigma loop and this leads to instability and the appearance of low-level enharmonic tones in the decoded analog signal. (You can see these in some of the spectra I publish in Stereophile’s DAC reviews.) Frindle’s patented topology adds low-level noise at the input of the loop to keep it busy and eliminate limit cycles. However, as the overall DAC circuit is differential but the noise is common-mode, it is canceled out in the reconstructed analog signal. Neat.
