[raoultrifan]

So, I did a bit of "modding" last night:

- 1) I had replaced WIMA MKS 4 (Metallized Polyster) with JB JFX Premium Film Cap (Polypropylene Film) bought recently from TME.
I might be inclined to tell that trebles are a bit more upfront and detailed now, but to be honest without proper A/B testing it's quite hard to tell if any real difference occured. Anyway, acording to audiophile forums & resources Polypropylene is better than Polyester, so I'm pleased that I swaped Wima with JB (I was tempted to use MIFLEX MKP10 or MKP11, but they were too big to fit properly). Caps links: 1, 2, 3, 4, 5, 6.

​

-2) I had installed G.O.S.S. (Grain Oriented Silicon Steel) to shield the toroidal transformer.
Initially, with my sensitive AKG K550 and without any source connected to XLR inputs, when using +20dB gain setting I was able to hear a bit of a hum noise when volume pot was at 3 o'clock or more, especially on the right channel. Now after partially shielding the transformer that noise is COMPLETELY gone!

​

-3) EMI/RFI noise suppression filter got installed as well, but that made the amp to get a bit of hum noise again, perhaps because the AC lines were too close to XLR inputs (also, PCB traces from XLR were right besides the noise suppression filter). So, I moved the filter from right to the left side, just above the 120/230V selector, as the red arrow shows (sorry for not providing a picture of the actual noise suppression filter positioning, but I was quite struggling with fitting the filter inside the case and I totally forgot to get another picture). Also, please ignore the big red wire, it was connected to the 2 Y-capacitors, but it's not really needed, so I removed it from lack of space (it also did a quite nice short-circuit with flame, so next time I'll be more careful).

​

​

-4) Arctic Silver MX4 thermal paste has been correctly applied between transistors heatsinks and the case, just to be sure thermal transfer is OK (just realized that outer side of both heatsinks were not perfectly flat, so thermal paste should help a little bit here).

Burdie, feel free to have a look to my DT880/600. Now that's what I call shiny headphones!
Perhaps on Friday I'll receive some decent mash sleeving from Distrelec/Austria and I'll see if I'll dress those phones or not.

​

L.E.: Re-edited few pictures for better understanding of what I've did.

WARNING: Mod 3) is really dangerous to DIY and electric hazard might happen, so I don't recommend it! Instead, please use a power strip with common-mode filter inside or change the inside power outlet with one containing common-mode filter within.

 

[burdie]

 
Burdie, feel free to have a look to my DT880/600. Now that's what I call shiny headphones!
Perhaps on Friday I'll receive some decent mash sleeving from Distrelec/Austria and I'll see if I'll dress those phones or not.

Very good looking cable, suggest to retain the shiny look by adding tranparent heat shrink (just like lapp kable ÖLFLEX CLASSIC 100 CY), instead of mash sleeve.If still prefer mash sleeve then must go with multifilament type to reduce microphonic noise caused by those expandable sleeve.
By the way, since you started to mod HPA-3B, are you considering to add permanant 0.1uf bypass cap to pin 4 and pin 8 of the opamps? Or may be you able to find out the earth/ground point so that 2 bypass cap can add to each pin. I really have no time to mod it. 

 

[raoultrifan]

  Very good looking cable, suggest to retain the shiny look by adding tranparent heat shrink (just like lapp kable ÖLFLEX CLASSIC 100 CY), instead of mash sleeve.If still prefer mash sleeve then must go with multifilament type to reduce microphonic noise caused by those expandable sleeve.

Thank you, I couldn't find transparent heat shrink easily, but I'll probably give it a 2'nd chance...I'll see about it soon.

  By the way, since you started to mod HPA-3B, are you considering to add permanant 0.1uf bypass cap to pin 4 and pin 8 of the opamps? Or may be you able to find out the earth/ground point so that 2 bypass cap can add to each pin. I really have no time to mod it. 

I was actually thinking of this one myself the other day, especially that even Burson is recommending this easy mod, but AFAIK this decoupling technique should reduce OPAMP oscillations (if any) and not really improve sound in our case, but perhaps I'm wrong, so I'll keep reading about it. I had prepared  the other day a couple of WIMA MKP 0.1uF for this task and I'm also interested in adding a couple of 1uF tantalums as well in parallel with existing 1uF caps, but I'm not sure I'll gain anything out of this mod because PSU looks OK, no AC ripple issues, OPAMPs are not oscillating, so I'll think about it perhaps soon. Thanks!

 

[burdie]

  Thank you, I couldn't find transparent heat shrink easily, but I'll probably give it a 2'nd chance...I'll see about it soon.
I was actually thinking of this one myself the other day, especially that even Burson is recommending this easy mod, but AFAIK this decoupling technique should reduce OPAMP oscillations (if any) and not really improve sound in our case, but perhaps I'm wrong, so I'll keep reading about it. I had prepared  the other day a couple of WIMA MKP 0.1uF for this task and I'm also interested in adding a couple of 1uF tantalums as well in parallel with existing 1uF caps, but I'm not sure I'll gain anything out of this mod because PSU looks OK, no AC ripple issues, OPAMPs are not oscillating, so I'll think about it perhaps soon. Thanks!

The transparent heat shrink should be easily source from Europe. Have you tried RS Components Europe or your country?

 

[raoultrifan]

Will try finding some transparent shrink soon, thank you burdie. Right now I finished re-wiring with balanced cables my K701 headphones and "burning in" the new cables.

 

[raoultrifan]

Just measured the DC on XLR output plug (no phones connected, no input signal applied, amp was powered since about 15 minutes):
 
 Gain:    Left   /   Right
 +5dB:  1.20mV/-0.60mV
+10dB: 0.42mV/0.40mV
+20dB: 0.65mV/0.63mV
 
DC was constant, no matter of volume knob position.
 
AFAIK, an output DC lower than 10mV is really safe, even for 8 Ohms IEMs, so less than 1mV I would call this as being perfect.
If speaking about low-sensitivity planars or 600 Ohms headphones, then even 30mV should not have any negative influence at all.
My O2 amplifier has around 3.0-3.5mV of DC and everyone says this is a very good value. Also, my LME49720/LME49600 DIY headamp has between 1.5-3.0mV of output DC.
I was unable to see any DC offset circuit on the PCB, just the protection from output jack/XLR plugs, so I don't know why the DC is so low; perhaps the transistors are all very well matched...who knows...
 
I've also checked the XLR output with my PicoScope and spectrogram was looking very well, with no spikes or anything suspicious from 0Hz to 10MHz. SNR was around 100dB RMS with volume knob to the min. This is not Audio Precision, but if there's something wrong like an oscillation or some voltage spikes then I should be able to observe it with the scope.
 
Temperature on the case, after about 2 hours since powered up, was about 50C; measurement was done with an IR gun and also with a metallic thermometer. Quite hot I'd say, so I'll try to swap the 4 small rubber feet from the bottom with something bigger and higher (1cm height perhaps), because a small part of this heat was probably caused by the warmth of Essence One from below HPA-3B. So, this headamp should probably not be stacked at all.

 

[raoultrifan]

I did a sort of a "in-house RMAA", though I don't have a sound-card with a decent ADC chip inside, I've used my EssenceOne as player and my PicoScope to interpret the results as well.
I trust the ADC from my scope more than the ADC from a sound-card anyway, also PicoScope's input OPAMPs are AD8065A having 7nV/√Hz of noise.
 
I've downloaded a lot of -3 dB 48Khz WAV files from AudioCheck website, played them through Foobar (no plugins used!) and connected the scope to XLR output (only left channel I've used).
I've used for this test 21 WAV files having the following frequencies (Hz): 20, 30, 40, 50, 63, 80, 100, 125, 250, 500, 750, 1000, 2000, 3150, 4000, 5000, 6300, 8000, 10000, 12000, 16000 (usually people does RMAA only from 40Hz to 15KHz).
 
Signal level I choose for testing was 389 mV peak-to-peak; couldn't use more than 400mV because I was loosing graph resolution to my scope and I needed a good resolution to see if the sine-waves are perfect or not. Anyway, at this level with my DT880/600ohms headphones connected this was the highest supportable volume for my ears for the 1KHz frequency; for higher frequencies than 1KHz I was actually unable to keep the headphones on my head! In the end, I've removed my headphones to do this test, because I needed the XLR plug available to connect my scope probe. To get this voltage the head-amp gain was +10 dB and volume knob was around 9 o'clock (I usually listed to music with volume knob between 11 and 13 o'clock with my DT880/600 at gain of +10 dB, but looks like with these pure sine-waves I can't even get over 9 o'clock without starting my ears to bleed).
 
From 20Hz to 12KHz I haven't seen even a 0.1mV modification in volume and all the sine-waves were perfectly reproduced (graphs were looking perfect). At 16KHz I've seen around 1mV roll-off and that means less than 0.05dB, so I find this an exceptional value.
 
If someone has a decent sound-card with an acceptable ADC inside, I would also be interested in finding out a real RMAA test. Thanks!
 
P.S.: In case it matters for someone, the R-C input filter of the HPA-3B is created by using 4 x 47KOhm resistors and 4 x 2.2uF capacitors. That means that at 1.5Hz there's a -3dB signal and starting with 15Hz the signal should be 0dB flat line. So, perhaps this is why there's no roll-off at all when applying 0.4V sine-wave with a frequency of 20Hz.

 

[Suopermanni]

Have to ask a stupid question but what is the RCA output for on this unit?

 

[raoultrifan]

It has XLR and RCA inputs only, but based on adapters from XLR 3-pins to RCA. Check the back side of the headamp on pictures from previous pages and you'll see the 2 XLR plugs and also the 2 RCA-XLR metallic adapters.
 
On outputs you can only see XLR 4-pins plug and 6.3mm jack.
 
Cheers!

 

[Suopermanni]

Sorry, should of mentioned i have unbalanced version. Im not sure why it has rca out and what purpose it serves.

 

[WilCox]

Sorry, should of mentioned i have unbalanced version. Im not sure why it has rca out and what purpose it serves.

 
Those are the pre-amp outputs.  You can use them to drive powered speakers or an amplifier.

 

[raoultrifan]

Oh, sorry..
 
Most headamps have IN and OUT, mostly because you may need to connect an external DAC and now you want to listen to your headphones, but latter you might want to listen to your power integrated amplifier + speakers.
 
So, it's quite OK to have RCA In and RCA Out in case you'll need to use external source (DAC, CD whatever) and use HPA-3U and external speakers/amp.
 
L.E.: Please disregard this not so intelligible speech/post and go straight to post_12144919 or to http://www.matrix-digi.com/pdf/HPA-3U_Manual_EN.pdf. Thanks!

 

[Suopermanni]

Wait, this thing is a pre-amp also? I had no idea! Now i can try it.

 

[raoultrifan]

I'm sorry if I wasn't very explicit, but here's the manual: http://www.matrix-digi.com/pdf/HPA-3U_Manual_EN.pdf.
 
Matrix M-Stage 3U has 2 input sources:
- internal DAC
- external RCA input
 
There are also 2 x RCA output plugs are only used in case you want to feed with internal DAC (as source) an external amplifier (another headamp or speakers amp); you can also use headphones plug when feeding audio signal using RCA output (listen to headphones while feeding an external amp/speakers). So, no preamp unfortunatelly...

 

[raoultrifan]

I did a couple of A/B tests today.
- DAC used: ASUS Essence One Muses MKII (internal power source moded + dedicated power source for both PCM1795 DACs).
- Headphone amplifiers used: Essence One's internal amplifier and M-Stage 3B (balanced input).
- Headphones used: 2 x K701 (one balanced and another one unbalanced).
 
- 1) K701+Essence1/SingleEnded against K701+MStage3B/SingleEnded: not much of a difference I'd say, same imaging, same sound...quite similar sounding (perhaps E1 has a bit fuller bass, but this needs to get investigated a bit more latter).
- 2) K701+Essence1/SingleEnded against K701+MStage3B/Balanced: hmmm, how can I put this...it's like mono vs. stereo! Soundstage increased a lot and all scene and voices are all around of you when going balanced; every voice and every sound is much more clear now, it's like a veil just uncovered and now all sound is better and clear, upfront and with a way much better soundstage.
 
Notes:
1'st test was done by using only one single ended headphone and pressing a button to choose between the 2 headamp's outputs.
2'nd test was done by quickly replacing the headphones around the head.
At least 50 tests were done for each of the 2 A/B's from above and 100% of them were conclusive!
 
P.S.: I realized from the first hour of listening to M-Stage 3B that going balanced improved the scene a lot (vs. unbalanced), but I thought it's just a psychological effect of my new headamp. I was almost going to install Meier Corda's foobar plugin for "crossfeed" to diminish the larger scene and bigger stereophonic image created by this balanced upgrade. But to be honest, until today's A/B test I didn't thought the difference is so huge! So, now I strongly recommend to everyone to move to balanced DAC/headamp/headset, because this is a really step up in audiophile's world and you'll never go back to unbalanced/single-ended.