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Review and Measurements of Benchmark HPA4 Headphone Amp/Pre

ObjectiveSubjectivist

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I got some spare money to spend and I am considering buying HPA4. But I wonder. Given it isn't cheap (even if I will get small discount) is it worth it compared to anything else on the market? I currently have Monolith THX AAA headphone amp and I wonder if I am may be missing something and it would be "worth" to upgrade it once and for all to HPA4. Or maybe there is something cheaper/better?
You won't hear sny difference.
But is it worth it? That's you have to answer yourself.

It's very nice built has tons of options and I really liked using it. Just feel of volume knob was good ;)

But I switched to cheaper Topping, did I miss something? Soundwise? No not really.


Ps. support and longevity is also something to consider. And with topping it could be bumpy road.
 
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enricoclaudio

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I owned several Topping units, including A90 and A90D, but after getting the HPA4, I stopped looking at headphone amps/pre amps. For me, the HPA4 is end game, period.

1700336910229.jpeg
 
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Matthew87

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I owned several Topping units, including A90 and A90D, but after getting the HPA4, I stopped looking at headphone amps/pre amps. For me, the HPA4 is end game, period.
What are the differences between Topping units and HPA4? Other than Topping may have QA issues? I don't need much from headphone amp in terms of functionality. XLR input and headphone output, on/off switch and volume knob is enough for me. I would like to know more about audio differences.
 

enricoclaudio

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Benchmark products are for those who appreciate exceptional build quality, long 5 years warranty and post sales support no questions asked and very good resell value. If none of those qualities matter to you, then any of the amps from Topping should work for you. Personally, after owning 5 Topping products and reading all the complaints about dead amps and bad customer service, I decided to not purchase any product from Topping and that’s why I sold all of them for good, some at less than 50% the price I paid, not to mention that the A90D took me like 3 months to sell it for $250.
 

John_Siau

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The HPA4 has one very special feature that is not found on any of the other headphone amplifiers. This feature is the 256-step fully-balanced relay-switched volume control. There are actually two of these in the HPA4 - one stereo pair for the headphone amp and one stereo pair for the line outputs. Each stereo pair is controlled independently and each can provide an independent balance control. The volume control provides very precise 0.5 dB steps over a gain range of -127.5 to +15 dB. The advantages include low distortion, low noise, and precise L/R balance tracking over the entire 142.5 dB control range. No other fully-analog volume control approaches the performance of the system that is built into the HPA4.

This relay-switched volume control was something that I had wanted to build into a product for many years. The flagship THX-888 headphone amplifier deserves the best-possible volume control, and I decided to build the HPA4 with what I believe is the best analog volume control ever built.

You can buy a THX headphone amplifier with an ordinary analog pot as a volume control or you can spend a bit more and get something really special. The HPA4 is not just another THX headphone amplifier.
 

staticV3

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True, having two stepped attenuators, one for HP out and one for Line out, is something I haven't seen elsewhere.

Though what's the point unless you want to output to headphones and an external Amp simultaneously?

Per-output volume memorisation can just as well be done with one attenuator.

Here's a list of headphone Amps that also use a stepped attenuator for volume:
 
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John_Siau

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True, having two stepped attenuators, one for HP out and one for Line out, is something I haven't seen elsewhere.

Though what's the point unless you want to output to headphones and an external Amp simultaneously?

Per-output volume memorisation can just as well be done with one attenuator.

Here's a list of headphone Amps that also use a stepped attenuator for volume:
Great question, here is the answer:

We have a large number of professional customers that need simultaneous outputs. They need to be able to monitor with headphones without interrupting the line-level feed. We chose to make one product that would work for pro and hi-fi customers.

As for the list of products with "stepped attenuators", these are distinctly different from the attenuators in the HPA4. You will find that they use ladder network ICs and not relays with low-impedance metal-film resistors. The performance is not the same, but the IC approach is much less expensive.
 

staticV3

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As for the list of products with "stepped attenuators", these are distinctly different from the attenuators in the HPA4. You will find that they use ladder network ICs and not relays with low-impedance metal-film resistors. The performance is not the same, but the IC approach is much less expensive.
Actually, most of the Amps on that list use relays instead of ladder network ICs :)
 

enricoclaudio

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Great question, here is the answer:

We have a large number of professional customers that need simultaneous outputs. They need to be able to monitor with headphones without interrupting the line-level feed. We chose to make one product that would work for pro and hi-fi customers.

As for the list of products with "stepped attenuators", these are distinctly different from the attenuators in the HPA4. You will find that they use ladder network ICs and not relays with low-impedance metal-film resistors. The performance is not the same, but the IC approach is much less expensive.
I’m one of those ;)
 

ObjectiveSubjectivist

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Of course hpa4 is a great device.
In the future when my budget won't be so freakin tight (a lot of stuff happening in my life right now) I'm pretty sure I'll be back to using on of them ;)

Ps. Oh also I love possiblity of setting 'pre gain' for each input so you can level match various DACs and make a comparisons.
Oh don't even ask about faces of my friends when I did such comparison to them :D it was priceless.
 

spindrift1414

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Regarding the volume control of the HPA4 - I had a question about using it as a preset for another amp - in this case a headphone tube amp.

I have a DAC3B in front of the HPA via XLR at with output pads at 0db per recommendations.

My tube amp (which I listen to only occasionally) has xlr inputs (4 vrms) - but I can't connect the DAC3B unless I change the output pads to -20db . . . and I would rather not go back and forth every time I want to change amps.

So I thought I might set the HPA volume to -10db (for 14dBu) and feed the tube amp via the HPA xlr outputs. My question is - is this the same as if I connected the DAC3 (output adjusted of course) to the tube amp? Am I compromsing signal quality by putting the HPA between the DAC and the tube amp? Normal I wouldn't think of doing this but the HPA distortion levels are so low . . I thought I'd ask.

Many thanks!
 

Matthew87

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Well... I wanted black version of HPA4, but there was promotion for silver one (in reality it looks much better than on pictures). So I pulled a trigger, thinking that worst case scenario I will be able to tell everyone there is little to no difference and you don't need to spend that much money.
20231124_190501.jpg


Thing is there is a difference. At least between HPA4 and RME ADI-2 DAC. I need longer cables to test it against Monolith THX AAA as cables I am using are super short and switching headphone amps would be problematic. Also I don't remember that much of a difference between ADI-2 and Monolith when I added it do my setup. If I remember correctly difference between ADI-2 and Monolith was very small (if any).

I need to do proper testing with volume matching, but from very simple test it seems like there is much better separation between instruments (and maybe slightly more details?) on HPA4, while ADI-2 sounds more messy.

I wouldn't say that difference is worth the price, but if someone has expendable income, then go for it - there is (some) sonic upgrade here. At least now I can say that I have reached endgame in headphone amp area.

At least until HPA5 comes out, which I hope would be much cooler. HPA4 is very warm (at least more than I expected) to the touch.
 

Dealux

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Are there any amps in Amir's database that measure as clean as the HPA4? It doesn't seem like it. Even the top of the line Topping stuff has 4-5 dB worse distortion across the board.
 

staticV3

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Are there any amps in Amir's database that measure as clean as the HPA4? It doesn't seem like it. Even the top of the line Topping stuff has 4-5 dB worse distortion across the board.
I'm not sure what graphs you're looking at. Comparing Amir's default 1kHz FFT, even Topping's basic $150 L30II has less distortion than the HPA4:
Topping L30 II Headphone Amplifier Measurements.png Benchmark HPA4 Preamplifier and Headphone Amp Preamp Dashboard Audio Measurements.png
(Not that it matters at these levels)

Same is true for the L50, L70, A70, A90:
Topping L50 Measurements Balanced Headphone Amplifier.pngTopping L70 Balanced Headphone Amplifier Balanced measurements.pngTopping A70 Pro Headphone Amplifier Balanced Preamplifier XLR Measurement.pngTopping A90 Headphone Amplifier Unbalanced Audio Measurements.png
 

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  • Topping A70 Pro Headphone Amplifier Balanced THD 300 Measurement.png
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John_Siau

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One HPA4 feature that is often overlooked it the fact that it uses a 256-step fully-balanced relay-controlled attenuator to adjust the output volume. The result is that the measured performance is available at a wide range of volume settings, not just where the volume control is maxed out (as it always is when these headphone amplifiers are being measured). It would be tedious and time consuming to perform measurements at various volume settings, but this is where the HPA4 would really shine.
 

RichB

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One HPA4 feature that is often overlooked it the fact that it uses a 256-step fully-balanced relay-controlled attenuator to adjust the output volume. The result is that the measured performance is available at a wide range of volume settings, not just where the volume control is maxed out (as it always is when these headphone amplifiers are being measured). It would be tedious and time consuming to perform measurements at various volume settings, but this is where the HPA4 would really shine.

The performance is excellent.

But, do you know what would be nice?
A firmware update to the HPA4/LA4 for direct input select IR codes....
Even better, have input selection also power on the unit then switch to the proper input to be absolutely family proof. :D

I can't tell you how tiring it is to have the input selection sequence go wrong, only to find that the reason the volume is low is that the front Salons directly connected to the LA4 are not getting the signal.

- Rich
 

John_Siau

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The performance is excellent.

But, do you know what would be nice?
A firmware update to the HPA4/LA4 for direct input select IR codes....
Even better, have input selection also power on the unit then switch to the proper input to be absolutely family proof. :D

I can't tell you how tiring it is to have the input selection sequence go wrong, only to find that the reason the volume is low is that the front Salons directly connected to the LA4 are not getting the signal.

- Rich
Thanks for the feedback. We are out of buttons on the Benchmark remote control, but we may be able to add codes that are not on the control.

This may be helpful:

You can disable unused inputs and you can set inputs to a fixed volume.

Or, you may be able to do this:

If you select the DAC ON INPUT1 option, you can send the remote code for any digital input and this will set the HPA4/LA4 to input 1.
 
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RichB

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Thanks for the feedback. We are out of buttons on the Benchmark remote control, but we may be able to add codes that are not on the control.

This may be helpful:

You can disable unused inputs and you can set inputs to a fixed volume.

Or, you may be able to do this:

If you select the DAC ON INPUT1 option, you can send the remote code for any digital input and this will set the HPA4/LA4 to input 1.

The LA4 has two remote modes, one when paired with a Benchmark DAC and another when not.
For this, consider the stand-alone remote configuration.

The HPA4/LA4 has 4 analog inputs and no USB or digital inputs.
The DAC/LA4/HPA4 Benchmark remote is sold as an option.
When not using a Benchmark companion DAC, the D1, D2, D3, D4 buttons do nothing at all, and it is not possible to discretely select inputs.

The solution seems straight-forward, allow the LA4/HPA4 configured in stand-alone remote mode, use the D1, D2, D3, D4 buttons to directly select the numerically corresponding analog input.

When controlling the DAC2/DAC3, they the Dn stands for Digital, selecting the digital input.
When controlling the LA4/HPA4, the Dn stands for Direct, selecting the analog input.

Perhaps, this is difficult, but it does not seem like it should be.
This solution is backward compatible and removes deficiency.

LA4FrontWithRemote.jpg
LA4Rear.jpg


4 numbered buttons on the remote, 4 analog inputs.... ;)

- Rich
 
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