[ DAC AH hacking may be yesterdays news, but I'll describe my sucessfully completed project anyway. Acknowledgements: the project is heavily inspired by the many postings by HeadFi users including recca
]
A couple a years ago, I bought a DAC AH from the Pacific Valve company. I had the clipping problem reported on this forums and decided to fix it knowing that I would risk ending up with a useless brick. After having successfully modded the unit, fixing the problems, I couldn't resist doing further hacking.
My goals was:
i) to have the DAC run on a single, high quality power supply.
ii) To improve on component quality.
iii) To see if I as a 100% software guy by profession could succeed without breaking the unit :-)
As a consequence of i), the analogue section had to go. I considered buying a SLA battery to provide power to the unit, but decided that was too tedious and messy.
I settled on ordering an SR1 PSU from Paul Hynes design. This solution is used by Altmann Attraction DAC users and is claimed to superior to using a RedTop battery.
I didn't want to use the money for the SR1 if I broke the DAC before having the need for it, so I started out using a cheap 7V switchmode PSU. 7V gives enough drop voltage for the 7805 feeding the SPDIF reciever. I feed it directly to the DAC chips.
After having got things working, I decided to stay at 7V and had Paul build me a custom "SR1-7" PSU.
I heatsinked the DAC chips to be sure that they would not overheat. I had troubles getting originals sinks but finally had a technician at work make me some by cutting up a CPU heat sink. I attach them using thermal tape.
As per ii), I ordered 4.7uF Jupiter Beeswax capacitors and 270 ohms Shinkoh resistors from the HifiCollective in the UK. 270 ohm may not be the optimal value for 7V operation but having adjusted for 3.8V across the resistors, I experience no clipping problems.
iii) Mission accomplished . The DAC sings like a charm.
The only - a little strange problem - I've had was that initially, I had to power the SR1 PSU on, off and then on in order to have the DAC work. I found that out that this was
because I had been too lazy to remove C25 (2200uF). This probably generated an power-on surge strong enough to activate overload protection circuitry in the SR1. After having removed C25 too, the problem is gone. Now all I lack is to replace the Pacific Valve sticker with an "Modified by aysabtu" one.
Edited by aysabtu - 7/31/10 at 2:32pm
