Outboard DACs

We are accustomed to valve pre and integrated amplifiers running at significantly higher voltages than their transistor counterparts but the potential offered by this increased headroom and more 'contained' operating area are not exclusive to tubes. For over a decade [HFN Sep '13 to HFN Oct '20], T+A has engineered its 'HV' series to include a 'High Voltage' preamp topology where specially selected J-FETs run at uncommonly high, up to 100V, PSU voltages. With only a very small proportion of this 'swing' used in practice, the FETs can be operated in Class A over a limited but highly linear portion of their range. The result is distortion that's largely unchanging with either output or frequency without employing anything more than the absolute minimum of corrective feedback.

SPL's proprietary VOLTAiR line/gain stages, realised in its single-ended and balanced Supra op-amps [see inset picture], adhere to similar principles, albeit in a more compact 120V (±60V) form-factor. Based around complementary MJD340/MJD350 transistors from STMicroelectronics, SPL's Supra modules bestow very high voltage headroom on its product's buffer/line stages. This is utilised in full with the maximum 45V output of its Phonitor xe amp [HFN Jul '21 and see p112] but is sensibly restricted to a 4.2V (balanced) feed for both the Diamond's 'fixed' and 'variable' output modes. PM