THis unit is well laid out. I took a look inside it, and it is using standard opamps, so 2132/2134, etc can be swapped in. The supporting and coupling caps are electrolytic through-hole types, so that's a go there, as far as the op-amps go..
I can post a image or two tomorrow, if anyone is interested. I bought it for the office, and it looks MUCH better laid out than the Pioneer unit I last started a thread on. It's a single board design. The usual warnings about fragile traces apply.
Standard pulse power supply, not much can be done about that these days.
I can post a image or two tomorrow, if anyone is interested. I bought it for the office, and it looks MUCH better laid out than the Pioneer unit I last started a thread on. It's a single board design. The usual warnings about fragile traces apply.
Standard pulse power supply, not much can be done about that these days.
I did series of mods on HD841 and this player is a killer. I don't see that much difference between modified version and ML31.5 transport/NOS DAC combo, I'm using as a reference.
I made a completely new output stage with dedicated PS and separate transformer. Major caps were also replaced with BG and OsCons. The bottom is reinforced with acrylic plate.
Swapping just the opamps and coupling caps don't do much justice to the potential of this player
I made a completely new output stage with dedicated PS and separate transformer. Major caps were also replaced with BG and OsCons. The bottom is reinforced with acrylic plate.
Swapping just the opamps and coupling caps don't do much justice to the potential of this player
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An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I have an HD931 and it's a complete piece of ****. It has a sample slip/repeat problem when playing CDs. The clock starts to drift with temperature and as time goes on, you get more and more slipped or repeated samples. This player is a completely incompetent design, and I wouldn't waste your time modifying it with anything other than a hydraulic press.
markp said:
The unit by itself is not bad sounding at all. Changing coupling caps (before and after output stage) and upgrading op amps (let's say to OPA627AU or AD8620) brings a substantial improvement, but you can still perceive the sort of softening/veiling and lack of dynamics and bass depth.
I went a step further, and decided to use separate PS in the output stage. The small trandformer is mounted in a far corner, raw filtering based on 4 x MUR860 and 2 x BG STD 1000/25. From here it goes to LM 2990 and LM2937 regulators (those reg are much better than 78xx/79xx variety). I only use 4.7 BG N as bypass on the op amps, but it seems to be enough. Two separate OPA627 chips are used (to my surprise AP worked here better than BP) with only 2 resistors left from the original circuit. No low pass filtering implemented, as this filter was reducing extention and feeling of air. The player is not bright at all. I'm also using 4.7 BG N for coupling. That about all, and new output RCAs were fitted in a rear panel.
Beside that, I implemented new bypass caps from Rubycon (ZL) in after regulators filtering (original PS). On the DAC and some other chips, BG N and OsCon caps were installed.
The player sounds very good, and basically, comparing to ML 31.5 and NOS DAC combo it shows some strengths and some weak points, but overall, it keeps its ground and I could easily live with it as my main source.
If somebody needs schematic, contact me by e-mail.
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