You're on the right track!
Hello Chris,
I think you are on to something here. I have removed the diode, fuse, big cap, 5V regulator and 220uF+ bypass cap, and replaced that with a diy dual voltage external power supply based on LD1085.
The interesting part was 'tuning' the psu, It has a really big impact on the sound IMHO. 12 to 15V is not critical if you have the passive mod, but the 5V is very sensitive to every little change made. At the moment I have 2x12Vac >> 2x Hexfred (for me more detail) >> 2200uF Panasonic FC bypassed with 0,1 uF Pe >> LD1085 referenced by 100r to two LED's bypassed by 10uF foil bypassed by 6,8nF Polystyrene. (This is the trick! LEDs are a quiet current source, and the bypass caps are in the feedback of the regulator, they invert on your frequency response) >> 470uF 6,3V (tunes bass responce, but at a cost. 150uF minimum according to data sheet) >> XLR cable to box, connected at output of removed 7805 >> 10uF Foil >> 100uF Panasonic FM at the converter. This results in the clearest, most balanced sound so far, after a week of experimenting with the power supply.
I personally feel that this is the biggest upgrade yo can do after the passive mod, without exotic components that is. I have ordered some fixed 5V LD1085 regulators to experiment on a caiman. only decent 15V according to description and the regulators on the board swapped, so I can tell how much difference that alone made, since my DAC is completely hotrodded now.
It was one of the biggest improvements in terms of harshness, my main issue with the 7520. I think I will trade mine for a caiman now and see where that will lead me...very pleased with my little DAC now!
For anybody reading: If you have a linear PSU based on LM317 you can replace the regulator with a LD or LT1085, they are pin compatible, or you can start by bypassing the LM317 according to previous directions first, and zener reference it. This alone will make a difference!
Well Chris, I felt so sorry for you I joined this bunch Thanks for having me guys!
Marc
Last edited by Bassie; 23-03-2011 at 06:10.
Learn from other people's mistakes, you don't have time to make all of them yourself!