Review and Measurements of Benchmark HPA4 Headphone Amp/Pre

[mackman]

I just got my HPA4 with two AHB2.
I see that even with +10db setting the volume is not the high.
I find that I am at almost 90%.
Previously on my Denon PMA-A110 I could not go much above 40% top 50% (depends on the recording dynamic range and mstering).
My souce in from HoloAudio May DAC KTE.
All connections are XLR.
Any idea?

I don’t know what you mean by +10db. The AHB2 has an input level setting on the back with three options, 8.2, 14.2, and 22. Maybe try one step lower on that (lower input level means higher gain).

 

[dlovesmusic]

I don’t know what you mean by +10db. The AHB2 has an input level setting on the back with three options, 8.2, 14.2, and 22. Maybe try one step lower on that (lower input level means higher gain).

He is referring to the input gain settings on his hpa4 that can boost input by 10db

 

[ObiWanKenobi]

He is referring to the input gain settings on his hpa4 that can boost input by 10db

The +10db is on the HPA4 per each input and not on the AHB2.
I asked Benchmark and they said that the settings from HPA4 to AHB2 have to be on 22.
They said that for 4vrms XLR I need to add +10db on that input.

 

[dlovesmusic]

The +10db is on the HPA4 per each input and not on the AHB2.
I asked Benchmark and they said that the settings from HPA4 to AHB2 have to be on 22.
They said that for 4vrms XLR I need to add +10db on that input.

Yes, customer service with Benchmark is second to none!!! I recalled hopping on to a call to discuss my setup with my 2 subs and the LP4 due to mismatch in output voltage for over an hour.

If you have a dac xlr output at 4v you should add 10db input boost. Not for rca, LPA4 automatically bumped up the input gain on that.

As I mentioned in my earlier post, you will need to be setting your abh2 to high gain, unless you have a dac that outputs 11v xlr like the benchmark dac or my ifi pro idsd

 

[ObiWanKenobi]

Yes, customer service with Benchmark is second to none!!! I recalled hopping on to a call to discuss my setup with my 2 subs and the LP4 due to mismatch in output voltage for over an hour.

If you have a dac xlr output at 4v you should add 10db input boost. Not for rca, LPA4 automatically bumped up the input gain on that.

As I mentioned in my earlier post, you will need to be setting your abh2 to high gain, unless you have a dac that outputs 11v xlr like the benchmark dac or my ifi pro idsd

I don't have RCA connected to my HPA4.
I only have HoloAudio May DAC KTE which outputs 4v on XLR thus I've added +10db on that input.

Rory Rall from Benchmark wrote to me on a that same question:
"The HPA4 is at unity gain at ‘0’ on the dial.

I cannot find a spec sheet on the Holo but my guess is that its XLR output is around 4V. If you have the AHB2’s sensitivity switch in the middle (4V) setting, you’ll not reach full output of the amp until you are at ‘0’ on the volume dial. So if you’re using it at 80-90% of the dial, this is correct. You’re normal listening is about 10-20dB below full output.

Suggestion: Verify the output of the Holo. If 4V, add 10dB of ‘boost’ in the HPA4 setup for that input. Then, set the AHB2 switch all the way down to 9.8. You’ll then reach full output of the amps at about -2. It really doesn’t matter where you are on the volume dial, it will be clean."

 

[dlovesmusic]

I don't have RCA connected to my HPA4.
I only have HoloAudio May DAC KTE which outputs 4v on XLR thus I've added +10db on that input.

Rory Rall from Benchmark wrote to me on a that same question:
"The HPA4 is at unity gain at ‘0’ on the dial.

I cannot find a spec sheet on the Holo but my guess is that its XLR output is around 4V. If you have the AHB2’s sensitivity switch in the middle (4V) setting, you’ll not reach full output of the amp until you are at ‘0’ on the volume dial. So if you’re using it at 80-90% of the dial, this is correct. You’re normal listening is about 10-20dB below full output.

Suggestion: Verify the output of the Holo. If 4V, add 10dB of ‘boost’ in the HPA4 setup for that input. Then, set the AHB2 switch all the way down to 9.8. You’ll then reach full output of the amps at about -2. It really doesn’t matter where you are on the volume dial, it will be clean."

For pcm playback, may kte xlr output voltage is 5.8vrms, rca output voltage is 2.9vrms. Take half of that for dsd playback

 

[ObiWanKenobi]

For pcm playback, may kte xlr output voltage is 5.8vrms, rca output voltage is 2.9vrms. Take half of that for dsd playback

Interesting.
I don’t hear much of a level difference between PCM and DSD.
Maybe I’ll try to sample my PCM to DSD just to see if there’s any difference.

 

[Sean_S]

Nevertheless, the $150,000 Dan D'Agostino Relentless Preamp is a true work of art. The focus is on unique casework and exotic components, but not on audio performance.

The LA4 cannot compete with the Relentless when both systems are turned off.

I love the last line!

 

[sojer2005]

Hi, I am using an Eversolo A6 gen 2 and according to the specifications there is 5 V on the XLR output. So what „boost” value should I enter in LA4 at the XLR input?

 

[reddavin]

Hi, I am using an Eversolo A6 gen 2 and according to the specifications there is 5 V on the XLR output. So what „boost” value should I enter in LA4 at the XLR input?

You could always ask the guys at Benchmark. And report back. They’re very helpful.

 

[ObiWanKenobi]

You could always ask the guys at Benchmark. And report back. They’re very helpful.

I’ve asked Benchmark and they suggest +10db as my Holo Audio MAY DAC output is also 5Vrms.

 

[Luvchampagne]

There have been a few responses on the best way to connect multiple subwoofers to the HPA4 when using it as a preamp. The comments I have found recommend using the RCA output jacks. In my use case I need to use the balanced out and the RCA out for my biamping setup. I have not found any mention of using the Mono out on the rear or the headphone jack on the front. Will that work or are there problems with doing so? Can you control the output separately from the balanced and rca?

 

[John_Siau]

There have been a few responses on the best way to connect multiple subwoofers to the HPA4 when using it as a preamp. The comments I have found recommend using the RCA output jacks. In my use case I need to use the balanced out and the RCA out for my biamping setup. I have not found any mention of using the Mono out on the rear or the headphone jack on the front. Will that work or are there problems with doing so? Can you control the output separately from the balanced and rca?

The balanced mono output will be the same level as balanced stereo outputs if both channels are driven with the same signal. The RCA outputs are 16 dB lower than the balanced outputs. These numbers apply at any volume setting.

The headphone output is independently controlled and it could be used for purposes other than headphones.

In general, multiple subs (or single subs) should be driven from the mono sum output.

 

[Luvchampagne]

The balanced mono output will be the same level as balanced stereo outputs if both channels are driven with the same signal. The RCA outputs are 16 dB lower than the balanced outputs. These numbers apply at any volume setting.

The headphone output is independently controlled and it could be used for purposes other than headphones.

In general, multiple subs (or single subs) should be driven from the mono sum output.

Thank you very much for your reply.

When connecting 2 different amps to balanced and RCA, how do you compensate for 16db of output difference? My limited understanding is that the difference between balanced and rca is usually 6db.
In my use case, the amps with adjustable gain are RCA only. My amp that I want to connect with XLR has no adjustable gain.

 

[John_Siau]

Thank you very much for your reply.

When connecting 2 different amps to balanced and RCA, how do you compensate for 16db of output difference? My limited understanding is that the difference between balanced and rca is usually 6db.
In my use case, the amps with adjustable gain are RCA only. My amp that I want to connect with XLR has no adjustable gain.

Professional XLR outputs are typically 10 dB hotter than consumer-grade XLR outputs. RCA outputs are typically calibrated to 2 Vrms at 0 dBFS. Consumer products with XLR outputs, take this 2V signal and invert it and send it to pin 3 of the XLR. This is not the best way to make a balanced output, but it is cheap and easy. This gives a calibration of 4 Vrms at 0 dBFS which is exactly 6.02 dB higher than the RCA outputs. Recording studios are often calibrated at +24 dBu at 0 dBFS. +24 dBu is 12.28 Vrms which is about 10 dB (9.74 dB to be more exact) higher than 4 Vrms. Benchmark DACs, the LA4 preamplifier, the HPA4 headphone amplifier, and the AHB2 power amplifier are equipped with switches, jumpers, or control settings that allow them to adapt to a mix of pro and consumer signal levels. The LA4 and HPA4 can take any mix of levels on the inputs while normalizing them with a volume offset setting. But the XLR and RCA outputs have a fixed 16 dB ratio to each other. This would not be a problem if you were driving a Benchmark AHB2, but it is a problem if you want to use a mix of balanced and unbalanced consumer devices when these devices are not equipped with gain controls. Benchmark strongly recommends the use of balanced interfaces running at true studio levels. These professional interfaces have a 10 dB advantage over consumer-grade balanced interfaces.

 

[Luvchampagne]

Greatly appreciate the detailed response. I think I understand the issue but like you stated, the solution is running the balanced interfaces as I would highly prefer not to replace my RCA only amps. My use case is self induced complicated and not necessarily for pure audio measurement reasons.

 

[ObiWanKenobi]

Professional XLR outputs are typically 10 dB hotter than consumer-grade XLR outputs. RCA outputs are typically calibrated to 2 Vrms at 0 dBFS. Consumer products with XLR outputs, take this 2V signal and invert it and send it to pin 3 of the XLR. This is not the best way to make a balanced output, but it is cheap and easy. This gives a calibration of 4 Vrms at 0 dBFS which is exactly 6.02 dB higher than the RCA outputs. Recording studios are often calibrated at +24 dBu at 0 dBFS. +24 dBu is 12.28 Vrms which is about 10 dB (9.74 dB to be more exact) higher than 4 Vrms. Benchmark DACs, the LA4 preamplifier, the HPA4 headphone amplifier, and the AHB2 power amplifier are equipped with switches, jumpers, or control settings that allow them to adapt to a mix of pro and consumer signal levels. The LA4 and HPA4 can take any mix of levels on the inputs while normalizing them with a volume offset setting. But the XLR and RCA outputs have a fixed 16 dB ratio to each other. This would not be a problem if you were driving a Benchmark AHB2, but it is a problem if you want to use a mix of balanced and unbalanced consumer devices when these devices are not equipped with gain controls. Benchmark strongly recommends the use of balanced interfaces running at true studio levels. These professional interfaces have a 10 dB advantage over consumer-grade balanced interfaces.

Is there a step-up from consumer-grade XLR to professional XLR that is transparent at the level of Benchmark?