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Review and Measurements of Benchmark HPA4 Headphone Amp/Pre

ShiZo

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Nothing is wrong with it. It sounds pretty good, in fact. I'm running my ADI-2 currently into the Bottlehead Crack and I feel that provides a good tube experience. I've heard great things about the HPA4 and the possibility that it will take my ZMF headphones to their true potential. I don't believe the ADI-2 does this (however I could be wrong). Hoping to learn and get some input. Would you suggest the headphone out of the ADI-2 will perform comparably to the HPA4?
I had them paired and the worked perfectly. I have the d90se now though. But the rme was no slouch. I like the older version of the rme strangely enough
 

Strumbringer

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I had them paired and the worked perfectly. I have the d90se now though. But the rme was no slouch. I like the older version of the rme strangely enough
Thank you! Before I spend $3K on the HPA4, I was curious if it would sound pretty much like the ADI-2 headphone amp section.
 

trl

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Guys- Very interested in in the HPA4 after someone highly recommended it to me. He says it pairs beautifully with ZMF headphones, of which I own two, the Verite Open and Auteur. Can anyone confirm that the HPA4 will pair well with the RME ADI-2 DAC FS? Some guys on another forum stated the ADI-2 is best paired with a tube amp, but I can't see how I could go wrong pairing with the HPA4. Thoughts are most appreciated.
Will pair perfectly, no worry. I see that HPA4 has a bit better SINAD, a fancy look a higher output power, in case this is what you are looking for. Although, if you don't need more power you could save your money and leave it as it is.
 

ShiZo

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Will pair perfectly, no worry. I see that HPA4 has a bit better SINAD, a fancy look a higher output power, in case this is what you are looking for. Although, if you don't need more power you could save your money and leave it as it is.
Personally, I felt the HPA4 was a better amp/preamp but scientifically I know that's not supposed to be possible lol
 

Strumbringer

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Will pair perfectly, no worry. I see that HPA4 has a bit better SINAD, a fancy look a higher output power, in case this is what you are looking for. Although, if you don't need more power you could save your money and leave it as it is.
Thanks- This was really my big question and I appreciate your answer to leave it as-is. I feel the ADI-2 is driving my ZMF headphones well and I didn't know if there was going to be a significant tonal benefit with adding the HPA4. It sounds like definitely more power with the HPA4, but I don't think I need more power.
 

MattHooper

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I've had my Benchmark LA4 in my system for a couple of months now. I've used it in place of my Conrad Johnson Premier 16SL2 tube preamp.
My Thiel 2.7 speakers are being driven by CJ Premier 12 tube monoblocks. I use a Benchmark DAC 2L as my digital source, and a good turntable/phono stage for vinyl.

My impressions so far:

Negatives:

1. I share some of the list of gripes posted by Rich B so won't repeat them. I also find the volume knob a bit plasticy and clicky, feels more toy-like than I'd want. I actually find the volume knob on the DAC 2L preamp section to be more luxurious - it's turns smoothly and quietly yet also provides a subtle clicking sensation as I dial the volume, which I like. I really love the minute volume steps offered by this product as I HATE pre-amps with coarse volume steps. On the other hand I've found the remote control of the volume to be more fussy than my CJ remote controlled pre-amp. It seems like I start pressing the volume up, barely hear a change and then suddenly it increases quickly and I can over-shoot. My CJ remote operates more smoothly. Also, the CJ remote offers discrete input selection, very helpful when I'm switching between my digital and LP source. (And sometimes I'm doing it to compare the two). Where the LA4 forces me to toggle through "dead" inputs to get back to a source.

Finally, I'm not very big on the aesthetics of the plain looking box. I do like a bit of audio jewellery and love the look (and glow) of the CJ preamp.

Positives

2. Operation/Sound!

First, while I'd like a smoother feeling volume knob, I nonetheless do appreciate a volume knob over my CJ pre-amps volume, which use"down" and "up" volume buttons. A knob is much simpler to use, and was one of the attractions of the LA4 for me.

I also like, if conceptually, the synergy of having a Benchmark DAC hooked up to a Benchmark preamp. Feeling of confidence. I also enjoy on a conceptual level - or a pride of ownership level - that the LA4 represents such a high level of no-B.S. engineering, and that it seems to be at about the top of the heap in terms of objectively verifiable performance (neutrality/low distortion etc).

As I said, some of that is "conceptual" pleasure because, given I use some old tube amps and often listen to vinyl as well, my system isn't going to be taking full advantage of the performance of the LA4. But my motivation in buyin the LA4 wasn't to achieve best possible (and likely inaudible to me) transparency, but rather "more neutrality/transparency than my tube preamp" which is a lower bar to clear, it seems to me.
In other words, it just had to give me something more neutral than my preamp in my system.

Beyond all that I have nothing technical to offer - all that is in Amirm and other people's measurements, and that's not my expertise anyway.
So on to my subjective uncontrolled listening impressions - my advice is to stop reading now if such things annoy you :)

My listening impressions are that the LA4 is a damned impressive addition to my system! All this is in the category of "subtle differences" but (presuming FTSOA they are there) these can make large subjective impact to those who care about such things.

I'd always found the CJ preamp added a slight bloom to the sound (images seem to expand a little bit) and a sense of roundness and body (where a voice sounds a bit more corporeal and occupying solid space between the speakers, rather then a see-through apparition). Also a tiny bit of "sheen" and "texture" that seems to make voices and instruments a bit more vivid and present (and to my ears slightly more "reminiscent of the real thing."). Though it all came at the cost of a very slight generalization, a mild coloration I was aware of, even though I love it.

With the LA4 any such suggestion of those colorations from the preamp are gone. It just sounds eerily transparent and neutral, yields a psychological sense of "very quiet" where incredibly subtle details - e.g. a drummer in a quiet passage tapping his hi-hat super softly - seem to just occur in the room with no sense of an artificial haze around the sound. Super, super clean. Similarly, there is the sense of hearing every iota of information in a track, down to the most quiet, distant, subtle detail. That triangle lightly struck, mixed waaaay back and deep in the mix in it's super subtle halo of reverb? Effortless to hear with total clarity. There's also a sense of cleaner timbral character to everything - from how drum cymbals are differentiated, to drum skins, to the character of a sax vs trumpet etc. There isn't that slight sheen added that slightly generalizes the timbre, and so instruments and voices seem that much more differentiated. One of my main gripes with the CJ preamp is that drum cymbals sounded a bit too similar and high hats especially could tend to sound a bit more like "modulated bursts of white noise" where on the LA4 the particular timbre of metal is preserved, making that aspect of drums more convincing. The brassy metallic quality of a trumpet vs the reedy quality of a sax is a little bit more revealed. Which I love.

It's definitely been an audiophile occasion to listening to lots of music again, re-appreciating various aspects with the LA4 in place.

Am I going to fully replace my CJ preamp with the LA4? I'm not sure yet. There are still pluses and minuses to each, subjectively. The CJ is a bit more richer and filled out and seems to produce a slightly more consistent "sense of thereness, density and realism" to my ears, at the expenses that I've noted, the LA4 more neutral, detailed and transparent to the source, which can sound a "bit on the thin side" but which can also often sound "more real" given the recording. It has lots of allure to my ears. I haven't put my CJ pre-amp back in for quite a while, so it will be interesting to see what I think after having lived with the more neutral LA4 for quite a while.

My apologies if all this is a distraction to the thread, but wasn't sure where to put it otherwise.
 
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buttlep

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It is my understanding that the HPA4/LA4 are designed to use ‘professional’ balanced XLR voltages but appears to handle ‘consumer’ balanced XLR levels and RCA.

Benchmark are very clear that using components that use professional level voltages will result in the best performance.

I’m wondering if anyone has had issues with the range or resolution of the gain control when using lower voltage XLR or RCA outputs to power amplifiers?

I hope this isn’t a silly question. I’m interested in purchasing an LA4 amplifier but am hoping to pair it with a power amplifier that is designed for consumer XLR levels.
 

Anonamemouse

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It is my understanding that the HPA4/LA4 are designed to use ‘professional’ balanced XLR voltages but appears to handle ‘consumer’ balanced XLR levels and RCA.

Benchmark are very clear that using components that use professional level voltages will result in the best performance.

I’m wondering if anyone has had issues with the range or resolution of the gain control when using lower voltage XLR or RCA outputs to power amplifiers?

I hope this isn’t a silly question. I’m interested in purchasing an LA4 amplifier but am hoping to pair it with a power amplifier that is designed for consumer XLR levels.
You can only change the voltage to the XLR outputs, and it is no problem whatsoever. The sound only goes a bit less loud.
 

John_Siau

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It is my understanding that the HPA4/LA4 are designed to use ‘professional’ balanced XLR voltages but appears to handle ‘consumer’ balanced XLR levels and RCA.

Benchmark are very clear that using components that use professional level voltages will result in the best performance.

I’m wondering if anyone has had issues with the range or resolution of the gain control when using lower voltage XLR or RCA outputs to power amplifiers?

I hope this isn’t a silly question. I’m interested in purchasing an LA4 amplifier but am hoping to pair it with a power amplifier that is designed for consumer XLR levels.
This is exactly what the HPA4/LA4 is intended to do. It can provide transparent gain reduction to interface professional DACs to Consumer power amplifiers. It can also provide transparent gain to allow consumer DACs to drive professional power amplifiers such as the Benchmark AHB2 power amplifier. The LA4 line amplifier can provide up to 15 dB gain and up to 127.5 dB of gain reduction in precise 0.5 dB steps (286 steps in total). Of these 286 steps, some are reserved for the balance control, so the user has direct access to 256 levels ranging from -112.5 dB to +15 dB in 0.5 dB steps. This is absolutely the state of the art in relay-controlled analog volume.

In short, the HPA4/LA4 line amplifier optimizes the interface between any combination of professional and consumer gear without adding any audible noise or distortion.
 

anmpr1

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I really love the minute volume steps offered by this product as I HATE pre-amps with coarse volume steps.
There was a time when 'stepped' volume controls in consumer gear were popular, as opposed to continuously variable pots. My first encounter with this sort of thing was a Japanese Pioneer SA-9500, which in addition to the stepped volume control, featured a -15dB and -30dB switch, so you could theoretically 'fine tune' the steps as needed. Supposedly the steps were calibrated, but that would have surprised me if calibrations were done very well, at the unit's price point. In any case, I found it rather wonky to use for making fine adjustments.

I remember a Counterpoint SA-3 tube preamp having a stepped volume control. Again, you couldn't make fine adjustments because of the fixed location of the steps. Upon investigating, I found the the 'steps' were simply a toothed gear insert the company used, in order to 'simulate' a calibrated control. You could easily pull it out using a needle nose plier, which I did. Once done, volume could be adjusted smoothly.

The volume pot of my DAC3-HGC is quite nice. The knob is metal, with a grain, offering both a tactile and firm feel, with a slight resistance. The only downside, from an ergonomic standpoint, is you have to use a button in order to cycle through the inputs. But given everything on the front panel, and the unit's overall form factor, individual buttons for the multiple input functions would probably not be possible. Finally, the off/on button would be easier to recognize if it was red.
 

John_Siau

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The volume pot of my DAC3-HGC is quite nice. The knob is metal, with a grain, offering both a tactile and firm feel, with a slight resistance. The only downside, from an ergonomic standpoint, is you have to use a button in order to cycle through the inputs. But given everything on the front panel, and the unit's overall form factor, individual buttons for the multiple input functions would probably not be possible. Finally, the off/on button would be easier to recognize if it was red.
Like all potentiometers, the pot in the DAC3 has some L/R imbalance at low volumes when passing an analog input. We have a L/R trimmer in the DAC3 that trims out the L/R imbalance in the upper half of the volume range, but below that point, the L/R imbalance will begin to increase.

With a digital input, the DAC3 volume control is a 32-bit digital control with 0.5 dB steps. The digital volume is controlled by sensing the position of the rotary pot. The digital volume control has near-perfect L/R balance and near-perfect 0.5 dB steps. The only limitation is that the digital volume control reduces the signal level without reducing the output noise of the DAC. Excessive use of the digital volume control will reduce the effective SNR of the DAC. If the DAC3 is connected to a consumer-grade XLR input on a power amplifier, the passive -10 dB pads should be engaged at the output of the DAC3.

In contrast, the HPA4 and LA4 preserve the SNR of the input signal over a wide range of volume settings. This is achieved without the L/R imbalance problems of a rotary pot. The HPA4 and LA4 have a L/R balance that tracks to better than +/- 0.2 dB over the entire 142.5 dB control range. And it does this in 0.5 dB steps. Needless to say, this requires very high precision resistors. Many are 0.01%.

All potentiometers also add some distortion. In the DAC3, the pot is not in the signal path when playing a digital input. When playing analog inputs on the DAC3, the pot is in the signal path but we keep that to a minimum by putting the pot inside a feedback loop while configuring the circuit such that there is no wiper current. Placing the pot inside a feedback loop also allows us to use linear-taper pots instead of log-taper pots. The linear pots can have better L/R tracking, and a lower total end-to-end resistance. Lower resistances contribute less thermal noise to the system (Johnson Noise). Nevertheless, the DAC3 pot does not come close to rivaling the lower noise and distortion of the relay-controlled volume in the HPA4 and LA4.

Here is the icing on the cake:
Relay attenuators and gain controls normally cause clicks and pops in the audio while they are being adjusted. In contrast, the relay closures in the HPA4/LA4 are precisely timed into a make-before-break sequence that prevents pops and clicks. This system is so effective that we were able to include a soft fade and unfade when the -20 dB dim is toggled.
 

buttlep

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This is exactly what the HPA4/LA4 is intended to do. It can provide transparent gain reduction to interface professional DACs to Consumer power amplifiers. It can also provide transparent gain to allow consumer DACs to drive professional power amplifiers such as the Benchmark AHB2 power amplifier. The LA4 line amplifier can provide up to 15 dB gain and up to 127.5 dB of gain reduction in precise 0.5 dB steps (286 steps in total). Of these 286 steps, some are reserved for the balance control, so the user has direct access to 256 levels ranging from -112.5 dB to +15 dB in 0.5 dB steps. This is absolutely the state of the art in relay-controlled analog volume.

In short, the HPA4/LA4 line amplifier optimizes the interface between any combination of professional and consumer gear without adding any audible noise or distortion.

John, many thanks for this response. I wasn’t expecting it from the designer.
 

anmpr1

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When other brands talk non sense about audiophile quality Benchmark team talks about measurements, its design, how the gears work together.

I've said it before, but the value in Benchmark gear is unarguable. It's not 'inexpensive' but it's certainly not 'expensive' within the context of the high-end. Examine the documentation that comes with their products. That alone is enough to tell you they are serious people. Not only serious, but the folks at the factory are helpful, and pleasant, and they will answer questions forthright.
 

MalinYamato

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Why do you recommend this when there are much cheaper amps such as a Singxer or Zen CAN --- is this worth the money to drive my Audeze LCD-5?
 

sprellemannen

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I have used benchmark gears for almost a decade. Super happy and will continue to be a good customer.

When other brands talk non sense about audiophile quality Benchmark team talks about measurements, its design, how the gears work together.
I share your enthusiasm for Benchmark gear. I have been a Benchmark-gear owner for 12 years.
Benchmark.jpg
 

Sal1950

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is this worth the money to drive my Audeze LCD-5?
If your simply going to use it as a headphone amp, the value is debatable and a buyers decision.
If you extend to use it as a preamp to head a SOTA 2ch system, it can't be beat.
 

MattHooper

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I still really like my Benchmark LA4.

But...ugh!...the lack of direct input selection, forcing scrolling for different input, drives me nuts!

This is especially the case where I've recently been using the LA4 to try to compare it to the performance of my CJ tube preamp.
The LA4 is fantastic in flexibility insofar as I can route my CJ tube pre-amp through an LA4 input and fix that input to unity gain, thereby controlling the volume with the CJ amp when I'm on that input. Matching the sound levels I can switch between the signal going directly from the LA4 to my amps vs also going through my CJ tube preamp. But the lack of direct input selection means I always have to scroll inputs, and I very quickly forget which input I'm on. My kingdom for direct inputs!
 

RichB

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I still really like my Benchmark LA4.

But...ugh!...the lack of direct input selection, forcing scrolling for different input, drives me nuts!

This is especially the case where I've recently been using the LA4 to try to compare it to the performance of my CJ tube preamp.
The LA4 is fantastic in flexibility insofar as I can route my CJ tube pre-amp through an LA4 input and fix that input to unity gain, thereby controlling the volume with the CJ amp when I'm on that input. Matching the sound levels I can switch between the signal going directly from the LA4 to my amps vs also going through my CJ tube preamp. But the lack of direct input selection means I always have to scroll inputs, and I very quickly forget which input I'm on. My kingdom for direct inputs!
@John_Siau, @Kal Rubinson and I are not the only ones looking for direct input selection. ;)
All that is needed is another menus choice that accepts the existing remote input selections to work without a companion Benchmark DAC.

This adds value of the LA4 and HPA4 product offering...

- Rich
 

laidick

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@John_Siau, @Kal Rubinson and I are not the only ones looking for direct input selection. ;)
All that is needed is another menus choice that accepts the existing remote input selections to work without a companion Benchmark DAC.

This adds value of the LA4 and HPA4 product offering...

- Rich
I am also waiting for this feature for almost 2 yrs now.
 
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