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  • Writer's pictureClayton

Groß DAC Design

Updated: Sep 27, 2018

'Groß' - meaning 'big', relates to our classic series of 'Klein' or 'small' DACS.

This DAC is based on the AKM4497EQ DAC chip running in software mode with a onboard micro controller. It is available in a USB only or a 3 - input version which is USB, coax & optical. 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 and only sourced from reputable Australian & US suppliers. The DAC chip runs from multiple ultra low noise Analog Devices ADM7150 series regulators. The output noise level on these is only 1.0 u volt. PSU rejection ratio is also very high which is great to isolate against mains bourn interference. The critical DAC output stage is based on a minimalistic design design using massive top quality Jensen line output transformers & zero feedback. The -3db bandwidth range is from 0.1Hz to 15MHz! Distortion 0.004% typ at 20 Hz and +4 dBu output level. These are the highest quality line output transformer Jensen make with PC mounting. The AK4497EQ is run in a special heavy load mode which enables the chip to directly drive the transformers. 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 Gross 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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