[Pharmaboy]

  Been in here for a while 

 
Anyway yes, 49990 brings mstage to a whole new level and next step would apparently be to bypass its DC decoupling input caps FWIR.....anyway, I got a spare mstage for crazy experiments that'll soon see some action goin'

 
FWIR? What's that?
 
By "bypass DC coupling input caps," do you mean solder other/better caps to, or instead of, the existing capacitors? Or do you mean taking DC coupling caps out of the circult entirely?
 
If it's the 2nd, I'm wondering if the HPA-1 would be able to pass DC on to headphones or powered speakers (not a pretty thought).

 

[Mad Max]

It would multiply the DC voltage AND THEN pass it on.
 
But that's after removing both the big blue DC input caps and the little green WIMAs before the opamp which serve to filter RFI.  The green WIMAs also block DC to some extent.
 
In my case, all of my DACs have zero DC offset at their outputs, so I have nothing to worry about by removing the input caps, and the sound quality improvement rules.  As mentioned earlier in the thread, if you are unsure, just leave the input caps alone, better safe than sorry.

 

[thyname]

hi,
 

MATRIX M-Stage HPA-3B Class

this was strongly recommended by Audeze CTO, as a cheaper alternative to Deckard.
 
How does this pair with HD 800? Enough juice to drive them?
 
Also, the 3U seems to be DAC / Amp combo, and the specs seem to be very close in terms of power. For the same price with 3B.

 

[Mad Max]

The Deckard amplifier looks like an HPA-3U with a different chassis that Matrix must be making for Audeze.  HPA-3B is the balanced version without an internal DAC.

 

[lowrider007]

I recently bought an original HPA-1 in mint condition for only £80, fell in love with it when I plugged my AKG's into it but with all my other lower impedance headphones Grado's, Sony's, IEMs etc I get a distinct humming noise, really gutted as I love the amp and it was my first ever proper headphone amp , is there anything I can do to fix this or is a bin job? 

 

[Spiral Out]

  I recently bought an original HPA-1 in mint condition for only £80, feel in love with it when I plugged my AKG's into but with all my other lower impedance headphones Grado's, Sony's, IEMs etc I get a distinct humming noise, really gutted as I love the amp and it was my first ever proper headphone amp , is there anything I can do to fix this or is a bin job? 

Try unplugging all your inputs and plug in your headphones and see if you still have the hum. It could be a ground loop.

 

[Pharmaboy]

  I recently bought an original HPA-1 in mint condition for only £80, fell in love with it when I plugged my AKG's into it but with all my other lower impedance headphones Grado's, Sony's, IEMs etc I get a distinct humming noise, really gutted as I love the amp and it was my first ever proper headphone amp , is there anything I can do to fix this or is a bin job? 

 
I own 2 of these fine little units (gave 1 as a gift)--both purchased used, both work perfectly. I found the stock volume knob inadequate (because it was impossible to easily see what volume was), so I replaced it on both units. Perfect!
 
Never experienced this humming you describe--and all my headphones until very recently were ~32 ohm, efficient closed back designs.
 
What impedance are your AKG's? Which model?
 
I recently tried a power-hungry 32 ohm planar headphone on the HPA-1 (ZMF Ori). Plenty of volume, no hum, but it didn't sound as good as the other headphones (and the Ori sounds spectacularly good on an amp w/lots of power). That was literally the only thing I ever did w/my HPA-1 that didn't totally work out...
 
I only use the lowest of the 4 gain settings, BTW.

 

[Spider fan]

@lowrider007
 
Maybe try lowering the gain if you arent at the lowest.

 

[lowrider007]

Try unplugging all your inputs and plug in your headphones and see if you still have the hum. It could be a ground loop.

It's works perfect with my akg k612pro, they've never sounded so good but I mainly bought the amp for my Grado 225e to tone it down a little but it hums with that and all my other easy to power cans, I've tried unplugging everything, still hums, I even took the opamp out and powered it on, still the same

 

[Spiral Out]

Try loosening the hex screw for the transformer on the bottom and re tightening it. I remember reading a few other people on this thread mentioning that fixed some noise issues they were having. Try searching this thread for "transformer". 
 
Another thing to try is moving the amp to another room and see if you get noise . It may be an EMI issue.

 

[lowrider007]

I've tried loosening and tightening the hex screw but there is still hum there with my Grado's 225e's, Sony MDRv55's and IEMs etc, it doesn't increase with volume, it doesn't matter if I unplug all the RCA's, change dip switches etc, yet the AKG 612pro nothing at all, like I said I've fallen in love with this amp, I'm still glad I bought it because it has introduced me to a lot higher audio quality, I'm now considering grabbing a HPA-2 brand new for £145, can you guys give a me bit of assurance that these amps do work with sensitive headphones with no hum at all? 

 

[Spiral Out]

The M-Stage has a 5 ohm output impedance. I don't think it is ideal with 32 ohm headphones. Ideally the headphone impedance to output impedance ratio should be 8:1. If you are going to use a lot of 32 ohm headphones, I would look at an amp with less than a 2 ohm output impedance. I have noticed that my M-Stage tends to be noisier with 32 ohm headphones. With my K7XX I hear no noise and a perfectly black background.
 
Since you are looking for a new amp, maybe you could keep the M-Stage for use with your AKG's and get something with a lower output impedance with your low resistance headphones. 32 ohm headphones typically don't  require that much power so a super high powered/expensive amp isn't necessary.

 

[Pharmaboy]

  The M-Stage has a 5 ohm output impedance. I don't think it is ideal with 32 ohm headphones. Ideally the headphone impedance to output impedance ratio should be 8:1. If you are going to use a lot of 32 ohm headphones, I would look at an amp with less than a 2 ohm output impedance. I have noticed that my M-Stage tends to be noisier with 32 ohm headphones. With my K7XX I hear no noise and a perfectly black background.
 
Since you are looking for a new amp, maybe you could keep the M-Stage for use with your AKG's and get something with a lower output impedance with your low resistance headphones. 32 ohm headphones typically don't  require that much power so a super high powered/expensive amp isn't necessary.

 
Didn't realize any of this. Maybe it's better, because my experience runs contrary to yours: for awhile the HPA-1 was my go-to amp (+ system pre-amp), and the only headphones I listened to on it were 32 ohm, efficient designs (1 open, 2 closed back). They sounded terrific, and it got even better when I upgraded the opamp.
 
I've never heard noise of any kind through the HPA-1...

 

[Spiral Out]

   
Didn't realize any of this. Maybe it's better, because my experience runs contrary to yours: for awhile the HPA-1 was my go-to amp (+ system pre-amp), and the only headphones I listened to on it were 32 ohm, efficient designs (1 open, 2 closed back). They sounded terrific, and it got even better when I upgraded the opamp.
 
I've never heard noise of any kind through the HPA-1...

I haven't listened to many low impedance headphones with the M-Stage. The lowest I have owned is the Grado Sr-225, which is so old that I ended up giving to a friend. It really depends on the impedance curve on the headphones. If it is flat at all frequencies there should be no issue with the output impedance, other than a lower than optimal damping factor. Whether this is a big deal with the drivers being relatively small in headphones is debatable. At 32 ohm, the M-Stage can manage a 6:1 ratio, which may be fine. I'm kind of grasping at straws as to why his amp is making noise with lower impedance headphones. Probably shouldn't be happening and there may be something wrong with his amp.
 
On another topic, I just installed a Burson V5 dual opamp in my HPA-1. It's soooo much better than the class A biased 627 I had in it before. I'm shocked how much of an improvement this opamp makes.

 

[Andreeas1978]

Mine used to have a hum because of the volume knob touching the case. You could also feel a subtile scratching when twisting. Changed the knob for aesthetic reasons also. Fixed. However, it has a slight different type of buzz with too low impedance iems. That's how it's built. And on USB it takes and amplifies some of the PC noises.