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Review and Measurements of Benchmark HPA4 Headphone Amp/Pre

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Also, do y'all ground anything together by standard practice? Or only if you hear problems?

The Oppo, Yamaha, Moon, and Monoprice pieces all have grounding posts, but nothing is connected.
 

RichB

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Also, do y'all ground anything together by standard practice? Or only if you hear problems?

The Oppo, Yamaha, Moon, and Monoprice pieces all have grounding posts, but nothing is connected.
It is commonly reported that cable installations that are not problem grounded can cause hum. The best solution is to get the cable installer to use the common ground.

Another noise source is amplifier transformer hum which cannot easily be solved. For that Monoprice amp, Gene at Audioholics was able to cure using an Emotiva CMX-2 power strip.

When I had ATI AT6000 amps, I had intermittent hum which I was able reduce that by putting my DC fans on a HumX filter that I had hanging around.

Ultimately, I switched the AHB2's which do not have any discernible noise at the speaker nor any mechanical noise. The reduction in heat allowed the fans to be removed. My equipment rack got lighter as did my wallet :p

- Rich
 
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I wasn't really having issues, just curious. The cable did cause ground loops a long time ago, so it has one of those Jensen transformers on the back of the cable box.

The cable outside is grounded tot he electric meter. Don't know if that counts as proper, buts that's all they do here generally.
 

Djjez

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Can someone please explain the power specs to me cause in the review it says its 3 times more powerful than the thx789 but when i look at the specs i dont see it. The 789 is 6w and it looks like the hpa4 is as well? What am i missing lol
 

JohnYang1997

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Can someone please explain the power specs to me cause in the review it says its 3 times more powerful than the thx789 but when i look at the specs i dont see it. The 789 is 6w and it looks like the hpa4 is as well? What am i missing lol
If you don't put lol in the end....

In the review, it's 300ohm load with single ended output. In single eneded 789 has less power at high impedance load. 789 has the benefit of balanced output, when being used, has more power than hpa4. The 6W is not 300ohm load so it's a irrelevant number here.
 

JohnYang1997

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Is channel frequency not being 1.00000 hz exactly a problem?
Firstly, no.

That's a headphone amplifier. There's an option on AP called precision tune to tune the oscillator to exact frequency. The frequency is only an small issue for DACs. Meaning their clock isn't so precise. But the difference is never to be heard ever.
 

Kami-san

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Does anyone know how they managed such a low crosstalk number? Absolutely inaudible but very impressive nonetheless, it's a good 13dB lower than the ADI-2 DAC and 28dB compared to the A90.
 

John_Siau

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John, That's mean LOL
OK, here is the long answer: ;)

80% of this is achieved through a set of circuit board layout rules that we have developed. Low crosstalk can be achieved through physical separation, but the real trick is to achieve low crosstalk when signals must be closely spaced. We use 6-layer boards and 3-dimensional shielding. We basically create a grounded box on all sides of sensitive signals (ground trace on either side, ground plane above and below, ground traces stitched to ground planes). If the trace will be carrying high current (i.e. output of a power amplifier), we use star-quad distribution of the signal and its return current, inside the circuit board. We also use star-quad traces for microphone signals to provide immunity to magnetic interference. The AHB2 power amplifier even uses star-quad send and return lines for the power supply rails to eliminate the magnetic fields that would normally be emitted by these traces. Electrostatic shielding (ground traces and ground planes) have no effect on magnetic fields. Star-quad conductors are the only effective means of achieving magnetic immunity. Also, we often use separate power distribution for the left and right channels.

The remaining 20% to design the circuits so that they have a very high power supply rejection ratio (PSRR). This can be tested by applying interfering signals on each of the power supply rails.

In many cases, crosstalk is almost always harmonic distortion. This is especially true when a power supply rail interferes with a signal.

It is nearly impossible to achieve low THD if you have crosstalk problems.
 

tomchr

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Welcome to precision design. The layout is part of the circuit.

Tom
 

MC_RME

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