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Introducing the Matrix M-Stage HPA-3U and HPA-3B, review to follow!

Discussion in 'Headphone Amps (full-size)' started by keanex, Jun 5, 2015.
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  1. canthearyou

    You are correct. But I wanted to lower the voltage to allow me to swap to other op-amps. The Bursons are a Max 17v and tend to run a bit hot at that number.

    Now I can try any op-amp on the market without worry of overvoltage.

    Before the mod the amp ran on the warm side. I know this is due to its class-a topology, but I still wanted it a bit cooler. This led me to install the case fan, which dropped temps dramatically. After I lowered the voltage the amp runs much cooler and negates the purpose of the fan. But I already installed it so now it's gonna stay put.
  2. alpovs
    I wonder if anyone compared the HPA-3B to Schiit's Jotunheim? The prices are similar.
  3. loserica
    It is a worth upgrade, this affect the sound. The sound is better indubitable. A better, refined texture, strooong bass!!, voices are more realistic. [​IMG] 
  4. loserica
    I replaced all 6 Nichicon capacitors. [​IMG]
  5. lowrider007
    Thinking of grabbing the HPA-3U, can someone assure me unlike the HPA-1 it has no problems running IEMS and low impedance headphones, humming etc? 
  6. trybeingarun
    I have a HPA-3u+. I have a $5 iem & I din't hear any hiss with it when I tried it on. My lowest impedance over ear is M50x, which doesn't seem to pick up any noise either.
  7. Mark R-S
    I just bought a used HPA-3U. All works well, but I get humming on the lowest gain (5db) setting with my T5p headphones. It gets worse when I touch the input or gain selector toggle switches. The other gain settings are fine, and have no humming.

    This problem is only with my T5p's, which have an impedance of 32ohms, and with the lowest gain setting. My 600ohm T1's don't have any problem, and neither do any of my other low impedance cans.

    All inputs are disconnected, and I've tried swapping cables on the T5p's.

    I've heard of humming issues with the HPA-3U, but this is strange. Anybody got any ideas how to fix it?

  8. raoultrifan
    Try using an isolation transformer to power up your HPA-3U or at least a dedicated ground-loop eliminator device (for mains outlet).
    You could also try to shield the inside transformer, but this means a bit of tinkering (http://www.head-fi.org/t/770610/introducing-the-matrix-m-stage-hpa-3u-and-hpa-3b-review-to-follow/45#post_12120336).
  9. Mark R-S
    Hi. Thanks for the tips. I saw your earlier posts, and I like the mods you have done. I noticed that turning it upside down, can affect the hum or even make it go away completely for a while. So can putting a little pressure on the power connector or phono inputs. All of the screws seem to be tight. I wondered if it could be to do with the toroidal transformer or something being lose.
  10. raoultrifan
    PCB traces for rear audio plugs from the rear are placed on main PCB, at the bottom of the DAC, so if there's any noise getting in there then it will go straight to the input caps and then to potentiometer. If the hum is not caused by a ground-loop or a noisy earth/ground then you could probably use some sort of shielding between DAC's bottom and main PCB, then connect the shield to the ground. Though, I'm almost sure this is do to a ground-loop or some inside grounding issue that should be double-checked prior to start any DIY tasks, especially if device is still under warranty.
  11. Mark R-S
    Thanks for the pointers, raoultrifan. I tried a few things and noticed that connecting the phono, USB or headphone output ground to the chassis eliminates the buzz. I also measured that there's 100ohms between the chassis ground and signal ground, which I guess was done to prevent ground loops but in this case it might be causing one, unless there's some other root cause. I bought the amp used on ebay.
  12. mickerru
    Any impressions on matrix quattro amp vs mstage 3b? Im from the Philippines and quattro is still available here. The 3b would be purchased on aliexpress. I would be using it with the hd800. Need help
  13. Mark R-S
    I'm still trying to resolve the buzzing issue with my HPA-3U.

    I noticed that removing the DAC module make the buzzing go away, so it plays a roll. Perhaps as you said, raoultrifan, adding shielding under the DAC would help.

    I also noticed that there are a couple of resistors soldered on the underside of the opamp and sealed with hot glue - Ive added a photo below. Are these original, or a modification? According to the text on the top side of the PCB the revision is 1.6.

  14. raoultrifan
    If I'm not mistaken those 2 resistors are 6.04K and they're soldered between both the inverting inputs of the opamp and the V+ from those 2 caps (330uF I guess). Doesn't looks like a Matrix job, but only someone with HPA-3U can confirm that (I own HPA-3B).

    O picture from above the opamp might help, just inca se someone did upgraded the default opamp with something else the original resistors from the front of the PCB got burned. We should see some smoked resistors perhaps. Also, if you can measure those 8 resistors it would be great; if you'll find 6.04Kohm on 2 of them then those are burnt (and you're actually measuring the resistors values from the back of the PCB).

    Anyway, if amplifier sound great, then maybe you should just ignore those 2 resistors.

    If there's a way for you use some protective shielding, without creating short-circuit, it could help in lowering the buzzing sound.

    L.E.: Hope I'm right with the resistor's value: https://www.digikey.com/en/resource...version-calculator-resistor-color-code-5-band
  15. Mark R-S
    You're right about the resistor values, and they are to pins 2 & 6, so the inverting inputs. Ive attached a photo of both sides of the pcb. I'll test the other resistors later. Could anybody confirm if this is original work, or a modification?

    HPA opamp.jpg
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