Alan Langford from DEQX Australia has viewed this forum topic and emailed me as below:
"....Andrew, Just noticed your last few posts, it would be good to point out that your HDP3 used DACs from Analog Devices AD1853. The New HDP-4 & PreMate use a DAC by Burr Brown PCM-1795 and completely new I/V and analog output stages that has completely changed the sound when compared to the HDP-3. All the latest models are complete redesigns other than the DSP and some logic...."
I will only find out when I eventually change to an HDP4, it is quite possible that I may prefer this DAC over the HDP3
"....Andrew, Just noticed your last few posts, it would be good to point out that your HDP3 used DACs from Analog Devices AD1853. The New HDP-4 & PreMate use a DAC by Burr Brown PCM-1795 and completely new I/V and analog output stages that has completely changed the sound when compared to the HDP-3. All the latest models are complete redesigns other than the DSP and some logic...."
I will only find out when I eventually change to an HDP4, it is quite possible that I may prefer this DAC over the HDP3