I bought Matrix M-stage three months ago. In stock condition it is fully capable to drive AKG 701. But BB OPA2134 is not something spectacular. It behaves almost like mono. My opinion is that this OPAMP is not worth listening. So I tried BB OPA 2107 which has huge sound stage (real stereo, very deep and wide) but it was slightly "metallic" (artificial). Next OPAMP which I tried, was BB OPA 627. It has less wide sound stage, but more deep than OPA BB 2107. And it sounds relaxing and very natural. I also tried AD797. It is faster than OPA62 and not so laid back. Sound stage is wide, but very shallow. Bass is tight. (OPA 627 has soft and warm bass). AD 797 is very sensitive to gain and voltage regulation. So if someone wants to play wit this opamp, then he must replace Cadj (WIMA - 150nF) with something slower and bigger (for example electrolytic cap 10 - 22 uF). And avoid LOW ESR caps like Panasonic FM...
Opamp (OPA627) is biased into class A with JFET and two resistors. My suggestion is to use 1000 Ohm resistor between Source and -Vcc. Why 1000 Ohm? Because when I used 470 Ohm, JFET died after two days. So 1000 Ohm is more safe solution. Resistor between opamp output and Drain is also 1000 Ohm . JFET is 2N5484.
After opamp rolling I tried to roll capacitors in output stage and in opamp stage. I tried Panasonic FC, Panasonic FM, (and combination of both). I seems that AD797 doesn't like LOW ESR Panasonic FM (mentioned before) because it makes buzzing noise when they are in the circuit. With Panasonic FC there is no problem. For OPA 627 it doesn't matter which capacitors are used. Replacing stock output capacitors with Panasonic FC makes sound stage more deep, and replacing capacitors (electrolytes) near opamp with Panasonic FM makes sound more defined (wider treble and deeper bass).
I removed bulk capacitors after rectifier (Nichicon KG) with Mundorf Mylitic. Mundorf Mylitic has better "punch" and more defined bass.
Changes were:
Opamp: Burr Brown OPA627 biased in class A, with JFET
Input capacitors: Mundorf Mylitic 63V, 4700uF
Output capacitors: Panasonic FC 25V, 680uF
Opamp capacitors: Panasonic FM 35V, 470uF
Regulator ADJ cap: "Crappy" 50V, 10uF
Difference between stock amplifier and modded, is about 70%. The biggest improvement was achieved with opamp replacement and capacitor combination. My advice to everyone is to try to combine different capacitors (opamp stage and output stage) for the best result. For example, all Panasonic FC made sound stage too rounded, all FM made sound stage too flat (and painful highs). But combination both of them was real deal.
Rest of equipment:
- PC source: Prodigy 7.1 LT
- DAC: Matrix Mini I (optical link)
Edited by BlaBlaBla - 9/27/10 at 3:19am