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  • Writer's pictureClayton

Fein DAC Design

Updated: Sep 27, 2018

This DAC is based on the brand new AK4493EQ chip which has just been released. It is the replacement for the AK4490EQ which was released in 2014. There are a number of improvements over the 4490 including lower THD, higher S/N & full DSD512 decoding. The design is identical to the Gross DAC except using the AK4493 (Gross uses AK4497) & slightly smaller Jensen output transformers. Due to these two changes I can reduce the price quite a bit vs the Gross. On paper the AK4497 still has slightly higher specs but in the real world & with critical listing tests the two sound very similar. Another bonus with the Fein is remote switchable DSD filers. The effect is subtle but definitely noticeable on a good system.

The Fein is available in a USB only or a 3 - input version. The USB input is asynchronous using an Amanero Combo 384 USB board. This is separately powered with its own ultra low noise PSU so does not require USB input power to operate. The parts quality is very high with all components sourced from reputable Australian & US suppliers. Warranty is two years parts & labour on a RTB basis. The DAC chip runs from multiple ultra low noise Analog Devices ADM7150 linear series regulators. The output noise level on these is only 1.0 uV. PSU rejection ratio is also very high which is great to isolate against mains interference. The critical DAC output stage is based on a minimalistic design using top quality Jensen line output transformers & zero feedback. These transformers have a very wide bandwidth which is -3dB from 0.2Hz to 15MHz! Distortion is 0.035% typ at 20 Hz and +4 dBu output level. The DAC output is fully variable (via remote) using the DAC chip internal 256 step attenuator. The maximum output level is 2v RMS. The added bonus with this is that the DAC can drive a power amp directly making for a very simple setup if required. The built in memory function ensures that the DAC output level always remains at the last setting before being power off.

Lower output impedance option

The output impedance of the Fein DAC is 600 ohms which is fine running into a integrated amplifier or pre-amplifier. It also works reasonably well into power amplifiers with a input impedance of 10K ohms or greater.

However in some circumstances eg when using long cable runs, driving dual power amps or a amp/sub combination the 600 ohm output impedance is too high for a good match.

In these situations I can offer an upgrade option which reduces the DAC's output impedance to under a 100 ohms. This involves adding a very high spec fully differential (in/out) op amp between the DAC chip outputs & the Jensen transformers. These also require a dual rail separate PSU's.

It is currently only available on the USB only version.


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