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Review and measurements of Oppo HA-1 DAC & Amp

MRC01

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#22
Am I reading the channel balance graph properly: the channels match within 0.5 dB from full volume to about -40 dB? Then from -40 and lower it gets all wonky.
 

MRC01

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#24
You should be able to derive current, as P = R*I^2. For example 35 mW into 50 Ohms is 26 mA and 7 W into 50 Ohms is 374 mA. That assumes voltage & current in phase. They would be for a planar headphone, but not for conventional.
So the HA-1 can push 374 mA through a 50 ohm load; that's 18.7 Volts!! It's rated at 3 Watts into 30 Ohms, so in Amir's test it produced over twice its rated power.
 

MRC01

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#26
In phase only if the headphone's impedance vs. frequency curve is flat (it's a resistive load). Planars are like that. But conventional headphones can have wildly varying impedance vs. frequency. Without knowing the particular curve, 80% is sometimes used as a rough approximation for the losses.
You can get actual impedance/frequency plots for many headphones from Inner Fidelity, from the days when Herstens was running it https://www.innerfidelity.com/headphone-measurements
 
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amirm

amirm

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Thread Starter #27
Am I reading the channel balance graph properly: the channels match within 0.5 dB from full volume to about -40 dB? Then from -40 and lower it gets all wonky.
Correct.
 
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amirm

amirm

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Thread Starter #28
The HA-1's volume knob is a conventional analog pot and its fixed output setting bypasses the volume control. Do I understand how Amir tested -- both of the first 2 measurements were done using the line stage XLR outputs (not the headphone output)?
Correct. I have recently separated the topic headings with "DAC Measurements" and "headphone amp measurements." The former is always with pre-amp out, not through the headphone jack.

From what I can tell, if you set the unit to variable, it routes the signal from the DAC completely through the headphone amp as I saw outputs as high as 10 volts out of the rear XLR pre-amp output! It is the combo of the DAC and headphone amp that reduces performance in variable mode then.
 

RayDunzl

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#29
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amirm

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Thread Starter #30
@amirm Are you in general able to measure not only the watts and volts but also the current the headphone amps deliver on the common 30 and 300 ohm marks???
There is no direct current measurements since all probing is done in parallel (voltage) mode. Watts is simply computed from giving the analyzer the resistance of the load. As noted, you can compute the current manually from the graph.
 

MRC01

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#32
Ok, made me look. Back-of-the-napkin estimate ...
That looks like the formula for thermal noise. This excludes current noise, which makes it akin to the theoretical noise of an ideal resistor. Metal film or wire wound might get close to this. It's the same formula I used several years ago when building a stepped attenuator from metal film resistors. But IIRC, other kinds of resistors like potentiometers are noisier than this.
 

RayDunzl

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#33

MRC01

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#34
... the channels match within 0.5 dB from full volume to about -40 dB? Then from -40 and lower it gets all wonky.
That's actually pretty decent for a conventional potentiometer volume knob; I've seen much worse. But in my view, the volume knob is one of the weak points of the HA-1. At that Kilobuck and up price range there's no engineering excuse not to have a fine grained stepped attenuator or a 24-bit dithered digital control.

Correct. ... if you set the unit to variable, it routes the signal from the DAC completely through the headphone amp ...
So the HA-1's line stage, which is opamp based, is cleaner than its headphone amp, which is discrete. I'm not surprised. I can see why they made the headphone amp discrete because if you want that kind of power (7 watts o_O) is it even possible with a typical opamp based headphone amp (something like an OPA209 or AD797 stiffened with BUF634)? It's just a shame they route the line output through the headphone amp when the volume control is being used.
 

JohnYang1997

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#35
That's actually pretty decent for a conventional potentiometer volume knob; I've seen much worse. But in my view, the volume knob is one of the weak points of the HA-1. At that Kilobuck and up price range there's no engineering excuse not to have a fine grained stepped attenuator or a 24-bit dithered digital control.


So the HA-1's line stage, which is opamp based, is cleaner than its headphone amp, which is discrete. I'm not surprised. I can see why they made the headphone amp discrete because if you want that kind of power (7 watts o_O) is it even possible with a typical opamp based headphone amp (something like an OPA209 or AD797 stiffened with BUF634)? It's just a shame they route the line output through the headphone amp when the volume control is being used.
Depends on your definition of typical opamps. opa189+tpa6120a2 composite will give 700ma current, if you parallel it you double that. 7 watts isn't a dream. For 8 ohm load it's voltage limited. For 4 ohm load it's fine. Ada4870 can work under +-20v so in that case it's even better.
 

frogmeat69

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#36
Thanks for the review, not so upset now about selling mine a year or so ago, not that I should be upset, made some money on it, lol.
 
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#37
I had a chance to listen to one of these last Saturday with a pair of Hifiman He1000. Sounded good and I loved the display. However with the custom tube amp the owner used with it, the sound took on a whole new dimension. This was the first time I heard a tube amp and liked what I heard. The notes seemed thicker with more weight and the sound stage was bigger. There was a little noise in the background when no music was playing but once there was wow what energy. I don't know if this can be measured?

Amirm, do you have balanced cables yet? I only ask as most amps with a balanced headphone jack are primarily wired to take full advantage of that connection. Whilst at this price range no doubt the single ended should be terrific as well still the balanced is more than likely better in leaps and bounds.
 

Music1969

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#40
Whilst at this price range no doubt the single ended should be terrific as well still the balanced is more than likely better in leaps and bounds.
Benchmark:

https://benchmarkmedia.com/blogs/application_notes/audio-myth-balanced-headphone-outputs-are-better

This expectation that balanced headphone amplifiers should be superior to single-ended amplifiers, ignores some of the most basic laws of electricity. The current into and out of a two-wire network is always equal and opposite. This means that the two-wire transducers used in headphones always see fully-balanced current. It also means that the headphone drivers are completely ignorant of the difference between single-ended and balanced-drive voltages.

Let me spell this out again: Headphone transducers are balanced devices. They have two wires. The electrons that flow into one wire must flow out of the other. The current is always balanced. The headphone transducers cannot detect the difference between a single-ended drive and a voltage-balanced drive. The system is balanced with either type of voltage drive.

But, this does not mean that balanced and unbalanced headphone amplifiers will sound the same! In many cases, voltage-balanced headphone amplifiers will produce more noise and more distortion than single-ended amplifiers of an identical design. The reason for this is that two separate output amplifiers are required in a voltage-balanced amplifier, and each must drive one half of the transducer's load impedance. The output noise will double because there are two amplifiers instead of one. The damping factor will degrade by a factor of 2 because both amplifiers contribute to the source impedance of the balanced amplifier (output impedance is doubled). Distortion will usually increase because each amplifier is required to drive half of the impedance that would be seen by an unbalanced amplifier. Power consumption will increase by a factor of 4 for a given output level (assuming the power supply voltage rails remain unchanged).

Rob Watts of Chord has similar opinion...

As Benchmark says, balanced headphone output can sound different (subjectively better?) but it might be technically worse...
 
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