Pre/Power Amplifiers

Unlike the vast majority of DAC/headphone amplifiers where all inputs end up 'digitised', the analogue input to Ferrum's ERCO remains analogue right through the fine ALPS volume control to the very capable Linear Technology-based headphone amp. The circuit design and performance show clear parallels with the dedicated Ferrum OOR [HFN Dec '21] although the ERCO also has a digital heart that handles its upsampling and digital filtering (inc. MQA if required) of all S/PDIF and USB inputs before conversion back to analogue and routing to the headphone amp. Thus, power output notwithstanding, the performance via the ERCO's analogue and digital inputs is distinct and will likely sound different.

Tested with the Hypsos PSU [HFN Mar '21], the ERCO's 'analogue' noise is low, enabling a healthy 96dB A-wtd S/N ratio (re. 0dBV) alongside a mere 0.000250.00075% distortion (20Hz-20kHz, re. 0dBV) – the latter broadly unaffected by headphone loading down to 32ohm. The response is also resilient, extending out to +0.6dB/100kHz from a very low 0.45-0.51ohm source impedance (a loss of just ~0.08dB into a 32ohm headphone load). The ERCO's gain settings are +11.9dB for a 9.8V max. output ('+dB' setting), 0.0dB ('0') and –11.9dB ('–dB'), but what of power? Here the ERCO does not disappoint, offering a full 157mW into 600ohm [black trace, inset Graph], a huge 2.45W/32ohm [orange trace] while still mustering sufficient current to support 1.6W into a low 8ohm load [red trace]. This latter figure is higher even than that achieved by the OOR, putting the ERCO into the top drawer of headphone amps. PM