[Tobes]

That’s a good suggestion.

Now, would you, or somebody else, be able to just check whether the neutrals on your rca inputs are floating or if they are earthed (to the mains earth pin, or to the rca outputs for example)? (Mine are not and it seems to cause problems). Would be much appreciated!

John Siau of Benchmark has previously stated this:

"The incoming RCA ground is connected to HPA4 chassis ground through a 30-Ohm resistor. This resistor limits the current flowing through the RCA shield between the two audio devices. This greatly reduces the ground-loop currents between the two connected devices and minimises the ground-loop-induced voltage across the two ends of the RCA shield. "

FWIW, I have an AVR and a tube phono stage connected to the RCA inputs of my HPA4 and don't have any issues. As John suggests above the 30ohm resistor should make the RCA shield path far less inviting for ground loop currents.

 

[YooperAudio]

That’s a good suggestion.

Now, would you, or somebody else, be able to just check whether the neutrals on your rca inputs are floating or if they are earthed (to the mains earth pin, or to the rca outputs for example)? (Mine are not and it seems to cause problems). Would be much appreciated!

Sorry - I just listen to music. I have no clue what you’re talking about.

 

[Tonybo]

No problem YooperAudio, and thanks Tobes, that could explain it. Trouble is it seems to exacerbate the problem with a Pi DAC..

 

[Tobes]

No problem YooperAudio, and thanks Tobes, that could explain it. Trouble is it seems to exacerbate the problem with a Pi DAC..

Probably best to contact Benchmark and seek their advice. Maybe the HPA4 expects a certain level of ground integrity in the source component?
I suspect Benchmark have tested the HPA4 pretty rigorously in this regard, given it may end up in complicated pro installations - though balanced operation is probably a given in such installs.

 

[M Siau]

No problem YooperAudio, and thanks Tobes, that could explain it. Trouble is it seems to exacerbate the problem with a Pi DAC..

If your Pi DAC is causing a hum while using the RCA input, its most likly because the power supply is leaking voltage to the ground. Try using our RCA to XLR cables and use the XLR inputs on the HPA4.

 

[flyte3333]

Hi @jsiau

I have MrSpeakers planar headphones that have a ruler flat 13 ohms impedance.

What is the power (and separately the current) output of the HPA4 at 13 ohms, for both 6.3mm and XLR4 headphone outputs?

Many thanks

Hi @M Siau

Can you kindly help with this?

 

[M Siau]

at 13 ohms the HPA4 can produce between 7 and 7.5 W with a current of up to 0.75 A.

 

[SeanS]

Hello. @jsiau or @M Siau, has Benchmark considered applying the principles of feed forward error correction to, say, the low level outputs of its DAC? I would be interested on your take. Thanks. Sean

 

[flyte3333]

at 13 ohms the HPA4 can produce between 7 and 7.5 W with a current of up to 0.75 A.

Many thanks.

Is it also stable with flat 10 ohms impedance headphones? There is no increase in distortion for ultra low impedance like 10 ohms flat impedance?

For high sensitivity headphones, my understanding from reading the manual is there is no gain adjustment possible with HPA4. But there is also no channel imbalance issues say below 9 o'clock with the volume knob. Is that correct?

With other headphone amps they often have recommended using > 10 o'clock on the volume knob to avoid channel imbalance issues but this is no issue for the HPA4?

Appreciate your help with these 2 final but critical questions I have before ordering.

Many thanks again.

 

[Tsyer]

at 13 ohms the HPA4 can produce between 7 and 7.5 W with a current of up to 0.75 A.

Would appreciate if you could advise if HPA4 can drive the Abyss Phi headphones well.

 

[SeanS]

Page 25 of the manual has some info relevant to some questions asked here: https://cdn.shopify.com/s/files/1/0321/7609/files/HPA4_Manual_-_REV_B.pdf?640602437357059139

"Powerful Headphone Output
The THX-888 amplifier in the HPA4 can cleanly deliver high power and current into low-impedance headphones. It can also deliver the high voltage required by very lowsensitivity headphones.
High Power
The HPA4 delivers 6 Watts into 16 Ohms. Best of all, there is no increase in THD when driving low-impedance headphones. The THX AAA™ technology keeps the output distortion free while driving very difficult low-impedance loads.
High Current
Low-impedance headphones may also require high current due to difficult phase angles presented by non-resistive driver loading. The HPA4 can provide peak currents exceeding 1.5 amps. This is more than enough current to drive difficult headphones with ease.
High Voltage
High-impedance headphones may not draw much power or much current, but they may demand high drive voltages. The HPA4 delivers 11.9 Vrms into 300-Ohm headphones. This is plenty of voltage to drive headphones with very low sensitivities.
Input Level Matching
By default, the unbalanced inputs on the HPA4 are automatically boosted by 15.8 dB so that they will match the level of the professional-grade balanced inputs. If the 15.8 dB default boost doesn't work in your system, individual inputs can be trimmed by +/- 10 dB in 0.5 dB steps using the BOOST function. The boost value does not impact the audio performance. It is equivalent to automatically rotating the volume control when the input is changed. The boost value changes the way the volume is numerically displayed."

 

[Tsyer]

Page 25 of the manual has some info relevant to some questions asked here: https://cdn.shopify.com/s/files/1/0321/7609/files/HPA4_Manual_-_REV_B.pdf?640602437357059139

"Powerful Headphone Output
The THX-888 amplifier in the HPA4 can cleanly deliver high power and current into low-impedance headphones. It can also deliver the high voltage required by very lowsensitivity headphones.
High Power
The HPA4 delivers 6 Watts into 16 Ohms. Best of all, there is no increase in THD when driving low-impedance headphones. The THX AAA™ technology keeps the output distortion free while driving very difficult low-impedance loads.
High Current
Low-impedance headphones may also require high current due to difficult phase angles presented by non-resistive driver loading. The HPA4 can provide peak currents exceeding 1.5 amps. This is more than enough current to drive difficult headphones with ease.
High Voltage
High-impedance headphones may not draw much power or much current, but they may demand high drive voltages. The HPA4 delivers 11.9 Vrms into 300-Ohm headphones. This is plenty of voltage to drive headphones with very low sensitivities.
Input Level Matching
By default, the unbalanced inputs on the HPA4 are automatically boosted by 15.8 dB so that they will match the level of the professional-grade balanced inputs. If the 15.8 dB default boost doesn't work in your system, individual inputs can be trimmed by +/- 10 dB in 0.5 dB steps using the BOOST function. The boost value does not impact the audio performance. It is equivalent to automatically rotating the volume control when the input is changed. The boost value changes the way the volume is numerically displayed."

Thanks for the information. I was asking as i just got both the Abyss and the HPA4 yesterday. Of course viewers would say test it yourself then. Well i spent most of today doing just that. I must preface that i am totally unfamiliar with the HPA4 and have only tested the Abyss on Dave + Blu2 + Woo Audio WA33 before. Using my Qutest into HPA4 via rca and to Abyss via xlr, i had to set volume to between -10 and -17 which a bit disconcerting as you start from -100. With the hd800s the volume setting was -17 to -22. However using XLR from Denafrips Terminator using Ayre CX7 as transport, the volume setting for Abyss was -6 to -10 and for hd800s -12 to -16. Sorry i dont know what the numbers represent as i just picked it off the HPA4 display on volume. Initially i was surprised that there was no sound until i really cranked it right up.
However, after i reached those volume levels i got sound that i was not familiar with. It sounded different from my existing IHA6 Cayin and R28 AudioGd. Very black background and transparent with no addon sound artifacts. I suppose it was because every piece in the chain is very revealing/clinical. Well the end result was that the sound was glorious. Musical, deep, transparent and natural. I fell asleep listening to it and woke up happy. I was listening to mainly orchestral pieces.

 

[YooperAudio]

Yep - I look at those dB volume indicators/numbers just as relative info - and even then, they're kind of not worth much to me other than when I see that one track is playing back at a different volume level as a previous track. I've owned the HPA4 for a bit over a month and I still can't derive much usable value out of them. Whatever. I like the sound that I get out of it, and I've got it configured so that most of the time the display auto-dims completely anyway within a few seconds of me adjusting the volume with the remote..

 

[bluenight]

Some years ago, I owned a Headamp GS-X mk2. I sold it, because:
a) its form-factor. It needed too much space. The cable between its power supply and the actual amp is rather huge and hardly bendable, In the end the amp needed about 60cm depth on the desk (or shelf).
b) While sound quality as a headphone amp was really excellent, I found it less convincing as preamp (sound quality and noisy preamp on/off switch).

Later I owned the V281 for about 3 years. This had a better form-factor for my needs. Sound quality as a headphone amp is also excellent.
As a preamp, sound quality was about the same as the GS-X, In both cases I preferred the direct connection DAC to active speakers. In addition, the clicking noise of the V281 volume knob always disturbed me to some extend.

Now I have a Benchmark HPA4:
Sound quality of the headphone amp is on the same level as the GS-X mk2 and V281. Maybe even a bit better compared to the V281, I think it creates slightly more space around each instument and separates them better.
As a preamp the Benchmark is the best of three. The difference is significant to me. I clearly prefer the connection: DAC > HPA4 > active speakers.
The volume adjustment is excellent, very small steps, very precise (also on low levels). I find this implementation better than the volume controls of the other two amps.

Considering only the sound quality of the headphone output, these three amps are very close together. It also depends on the headphone you are using. All my comparisons are based on:
DAC: Resonessence Mirus Pro OR Crane Song Solaris. Headphones: Sennheiser HD800 and HD800S. Speakers: previously: Genelec 8040, now: 8341. I only used balanced outputs & inputs an all devices.

How do you mean that HPA4 and V281 are close? Do they sound similar with HD800S.

I read alot of people mention V281 drive HD800S and other HP with authority is that the case with HPA4 as well when driving HD800S? Are they similar in bass peformence. Prefer a strong deep bass with impact with alot of texture. Drums should have attack and dont sound thin.

I find Hugo 2 DAC/AMP is to thin and bright for HD800S, making the music somewhat distant, feeding it to my Lake people RS 02 HPA brings more bass thickness and warmth to the sound more pleasure, probebly a wider sound as well.

Hugo 2 like HPA4 is also a clean amp with low distortion THD: <0.0001% 1kHz 3v RMS 300Ω but what i understand is that HPA4 is not to bright with HD800S. Good.

The only high end amp i have heard is Sennheiser HDV 820 with balanced output, and it was a big step up in bass amount over my current SE 600$ Lake people RS 02 HPA. Im all about HP listening btw. And own the HD800S. Im only talking about bass here but i am sure it got the other parts sorted?

 

[jsiau]

Yep - I look at those dB volume indicators/numbers just as relative info - and even then, they're kind of not worth much to me other than when I see that one track is playing back at a different volume level as a previous track. I've owned the HPA4 for a bit over a month and I still can't derive much usable value out of them. Whatever. I like the sound that I get out of it, and I've got it configured so that most of the time the display auto-dims completely anyway within a few seconds of me adjusting the volume with the remote..

For the line amplifier, 0 dB is unity gain from XLR in to XLR out or from RCA in to RCA out.

For the headphone amplifier, 0 dB is unity gain from the XLR input to the headphone output.

The HPA4 provides 256 gain steps in 0.5 dB increments. The line and headphone gain controls are independent.

In all cases, the actual output level is a function of the output level of your DAC (or other upstream analog signal source) and the gain shown on the display.