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Gustard H10 Headphone Amplifier

Posted 14th February 2015 at 12:47 PM by rjm
Updated 12th April 2015 at 02:59 AM by rjm

Technical Specifications:

Signal Input : 2x XLR female , balance
2x RCA, unbalanced
Maximum input level : +21 dBu, impedance 10kΩ
Input impedance : XLR: 10kΩ, RCA: 68kΩ
Input Sensitivity : +6 dBu
Main amplifier gain : +8 dB
Main amplifier gain adjustment range : -4 / +2 / +8 / +14 / +20 dB
Frequency response : 0-55kHz (-0.5dB)
Damping Factor :> 400 @ 50Ω
Dynamic range :> 128dB (A -weighted )

THD + N (1kHz 1W @ 100Ω): <0.00035%
THD + N (1kHz 0.5W @ 32Ω): <0.0007%
Crosstalk :-110db (1kHz)

Each channel has a BB OPA134PA - socketed - for voltage amplification and an eight transistor discrete buffer with 2 ea. 2SA1837. 2SC4793, C546B, C556B. Dual mono layout - more or less ... the circuit board itself is shared and not completely symmetric. There's a pair of NE5532s at back for balanced-unbalanced input conversion, and a pair of transistors (TIP122 TIP127) with trim pots and circuitry between the input and the main amplifier which looks a bit like voltage regulators to me but I can't see where they fit in the scheme of things.

Pretty decent quality for the price. (I paid $350/delivered)

First impressions of the sound are quite positive, plenty of depth and decent smoothness. Letting it cook overnight now and will put it in the main system tomorrow.


Comparison notes vs. Sapphire 2.0 (with Sennheiser HD600s)

H10 immediately impresses with huge soundstage, deep and controlled bass, and low noise floor. The midrange is smooth, with just a hint of extra warmth which gives a pleasant burr to vocals. Lyrical, with a sweet touch for melody. The high frequencies are extended, again smooth, but a bit mild. I would say the amp only falls down in one area: it starts to come apart as the going gets tough. On big, loud, complex tracks the details start to smear and run into each other, and the dynamics stall out. All around excellent performance though.

In contrast the Sapphire (which I still prefer, I'm addicted to its visceral thrill) is the literal embodiment of the saying "when the going gets tough, the tough get going". There is no muddiness or congestion or strain no matter how loud its playing or how complex the source. Indeed it plays better loud. I admit though that the H10 has blacker backgrounds and generally better resolution, both spacial and tonal.


Comparison notes vs. Sapphire 3.0 (with Sennheiser HD600s)

The new Sapphire circuit is smoother and quieter than the previous version. It ups the game, in other words, in those areas where I felt it was weak against the H10 before. I also switched the coupling caps from the splashy Multicap PPFXS to the warmer, more restrained Mundorf Supreme.

With these changes, the Sapphire reaches parity with the H10 on resolution and transparency. In terms of differences then, what remains is the impression of the H10 as a musically-engaging headphone amp with a well-defined but slightly thin soundstage, and a tendency to soften up transients and stumble during heavy dynamic passages. The Sapphire3, meanwhile, rigidly locks onto the HD600 drivers down to infrasonic whatever the signal: more dynamic snap, and a huge sense of impact and rhythmic drive.


Last change: Sapphire3 coupling caps changed again from 0.47 uF Mundorf to 0.33 uF Multicap PPFXS. Less bass "thunder", more focused soundstage, cleaner overall.


The final word: The H10 is a velvet glove, the Sapphire is a steel fist. I find there are things to like about both though my overall preference is now pretty solidly with the Sapphire3. Given the level of polish on the H10 (selectable gain switch, soft-start relay, overall fit'n'finish) and the low price I'd happily recommend** it as a point-of-entry pre-built "working" reference. By this I mean it is sufficiently neutral and sufficiently musical to use as a reference against which to judge and compare other headphone amps. That's not a distinction I award lightly.

** I feel I should however note a more-than-passing resemblance of the H10 with the Violectric products. I don't know the story, and will update this entry as needed if more details become available.
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Views 8551 Comments 10
Total Comments 10


  1. Old Comment
    abraxalito's Avatar
    Impressive array of caps there - seems to have a loyal following over on Headfi. Is it a pure classA output stage? If so with the opamps I wonder if they remembered to bias them into classA too - if not that could be the reason it falls over with higher crest factors.
    Posted 16th February 2015 at 02:58 AM by abraxalito abraxalito is offline
  2. Old Comment
    rjm's Avatar
    It's a push-pull output, so class AB in principle though its probably biased such that transition out of class A is extremely rare. The exact circuit is a bit of a mystery to me, with four output devices per channel, four smaller transistors, as well as some LEDs and diodes ... the buffer topology does not immediately jump out at me.

    Can't comment about the op amp bias. What you see in the photos is all I know about this amp. There's an unusual level of sophistication to the design compared the usual ebay stuff. I can't even find the rectifiers, let alone decode the voltage regulation! Its troubling resemblance to the Violectric V200 (reverse engineering or ... ?) is no doubt all part of the reason.
    Posted 16th February 2015 at 09:11 AM by rjm rjm is offline
    Updated 16th February 2015 at 09:13 AM by rjm
  3. Old Comment
    Hi. Thanks for writing down your impressions. I've been looking at the H10 for some time, as it is quite affordable. I have a pair of Dexa NE5532s which I used in an Eastern Electric Minimax Dac. But I sold the dac and would like to use the Dexa opamps elsewhere. Do you think it would be an improvement putting them in the H10?
    Posted 22nd February 2015 at 02:24 PM by asaifa asaifa is offline
  4. Old Comment
    rjm's Avatar
    The NE5532 are dual op amps, they won't replace the main OPA134s, only the NE5532 already used in the balanced-to-single-ended conversion for the input XLR.
    Posted 22nd February 2015 at 11:32 PM by rjm rjm is offline
  5. Old Comment
    Thanks for replying. My knowledge of all this is absolutely minimal. But that raises two questions, if you don't mind. First, would sticking the NE5532 in the balanced-to-single-ended conversion for the input XLR make a difference to the sound--assuming you would then use XLR imput?
    Second, can you see any easy ways of upgrading the H10, for example by replacing the OPA134s with better ones?
    Thanks again...
    Posted 23rd February 2015 at 08:59 AM by asaifa asaifa is offline
  6. Old Comment
    rjm's Avatar
    I doubt it would make much of a difference replacing either the NE5532s or the OPA134s. Both are pretty solid choices.
    Posted 23rd February 2015 at 12:18 PM by rjm rjm is offline
  7. Old Comment
    SSaudio's Avatar
    Thanks for the post rjm. On the Headfi thread they have been using different op amp combinations with the H10, a thing i like about this little beast.
    Posted 21st July 2015 at 05:16 AM by SSaudio SSaudio is offline
  8. Old Comment
    Rhamnetin's Avatar
    In case anyone is interested, I see people on Head-fi have replaced the OPA134s with AD797ANZs and are very pleased with the results. Someone else replaced the NE5532s with Muses02s and recommended it as well.

    I don't have the H10 yet but when I get it I'll probably try replacing the OPA134s with LME49710HAs, AD797ANZs, and OPA627SMs. I'll also try replacing the NE5532s with OPA2111AMs and Muses02s. I'll mix and match each combo.
    Posted 10th September 2015 at 01:55 PM by Rhamnetin Rhamnetin is offline
  9. Old Comment
    Dumb, but basic question: How do you remove the case from the H10? I removed the four corner screws from the back, and the four screws on the side (near the front) but the wraparound metal case doesn't slide off. What other screws must be removed to get inside?
    Posted 20th May 2017 at 02:08 PM by output555 output555 is offline
  10. Old Comment
    rjm's Avatar
    I don't remember it being difficult to remove to top lid. It is held in place by two screws on the rear plate, and one screw on each side just behind the front panel.
    Posted 3rd June 2017 at 10:46 PM by rjm rjm is offline

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