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Review and Measurements of Benchmark HPA4 Headphone Amp/Pre

JohnYang1997

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Why it it higher than the other review I saw?
Using the same condition as the other review, it should be 136dB. Idk why it's lower on his. 141dB is tested with unbalanced in.
 

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.
 

ShiZo

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Is channel frequency not being 1.00000 hz exactly a problem?
 

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.
 

Takanaka

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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.
 

Sal1950

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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% is achieved by designing 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, the crosstalk is almost entirely composed of 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.
 
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tomchr

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

Tom
 

MC_RME

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Kaiede

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I am using a Pronto remote. The LA4 mute, volume up/down, and input up/down are the codes used for the DAC3. Try using that device. As I have mentioned before, the direct input commands do not work unless used with a companion DAC2/DAC3. Benchmark,, Benchmark, Bueller... :p

So it looks like Harmony has the DAC2 HGC in the database, so the IR codes are there.

The bigger issue is that Logitech tags devices for inputs a particular way in their device database, for the automation side of things. Fortunately, it is possible to tell Harmony how the inputs of a device are handled. Unfortunately, it's not well documented on how you make the configuration button appear for a device so you can do that. I'd probably have to reach out to Logitech support to figure out what the secret sauce is.

I know your post is a bit old, but the LA4 is a preamp I'm looking at, and I use a Harmony, so I had the same question. I did a bit more digging and just wanted to share with others what my findings are.
 

RichB

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So it looks like Harmony has the DAC2 HGC in the database, so the IR codes are there.

The bigger issue is that Logitech tags devices for inputs a particular way in their device database, for the automation side of things. Fortunately, it is possible to tell Harmony how the inputs of a device are handled. Unfortunately, it's not well documented on how you make the configuration button appear for a device so you can do that. I'd probably have to reach out to Logitech support to figure out what the secret sauce is.

I know your post is a bit old, but the LA4 is a preamp I'm looking at, and I use a Harmony, so I had the same question. I did a bit more digging and just wanted to share with others what my findings are.

I had the remote and used the Pronto remote to learn them. The direct input do not work without the DAC 2/3 connected. I'd hoped that Benchmark support direct input by now.

- Rich
 

dougi

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At least Stax came with their own amp. Still expensive. You could buy them individually. At the upper end Stax offered the SRA12S which included a fairly full function preamplifier--the HPA4 of its day. $500.00 ($2100.00 in today's dinero--phones extra).

View attachment 55785

Then there was the Jecklin Float (imported by Mark Levinson). At three hundred dollars ($1500.00 in today's funny money) it gave you that authentic Zombies of the Stratosphere sci-fi experience (girl an option at extra cost).

View attachment 55786

View attachment 55787
Ooh! I had the dynamic driver version of the Jecklin Float in the late 80s/90s. Very comfy but not much bass. All the foam padding eventually degraded.
 

Kaiede

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I had the remote and used the Pronto remote to learn them. The direct input do not work without the DAC 2/3 connected. I'd hoped that Benchmark support direct input by now.

- Rich

Doesn’t the direct input only work for the DAC’s inputs though?

Harmony can cycle inputs, as it will remember what input was previously selected. But it needs to be told the order of the inputs.
 

tgray

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So how does one integrate this unit (or the LA4) with/without the rest of the Benchmark lineup (amp and DAC), into a 2.1 or 2.2 setup WITH room correction/DSP? What are the options here? The HPA4/LA4 is very impressive and gives a lot of nice functionality, but it doesn't provide any accommodation for bass management other than some parallel outputs. It would be great if the volume could control 3 or 4 independent channels instead of just 2.

Alternately, one could do all the DSP (minus crossovers) in the digital domain upstream of the HPA4/LA4, but then how do you handle input from multiple digital sources, never mind analog, and have DSP apply to all? I'd love to see a DAC with digital effects loop I/O, post input selection and pre DA converter.
 

RichB

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So how does one integrate this unit (or the LA4) with/without the rest of the Benchmark lineup (amp and DAC), into a 2.1 or 2.2 setup WITH room correction/DSP? What are the options here? The HPA4/LA4 is very impressive and gives a lot of nice functionality, but it doesn't provide any accommodation for bass management other than some parallel outputs. It would be great if the volume could control 3 or 4 independent channels instead of just 2.

Alternately, one could do all the DSP (minus crossovers) in the digital domain upstream of the HPA4/LA4, but then how do you handle input from multiple digital sources, never mind analog, and have DSP apply to all? I'd love to see a DAC with digital effects loop I/O, post input selection and pre DA converter.

I have the LA4 connected to the RMC-1 for HT and directly to the Oppo UDP-205. It can drive the AHB2s in low gain mode, which is technically better, but I am not sure if that is audible. I can achieve 106 dB in my room before clipping bi-amping the Salon2s which is plenty for me and my family.

After working with Benchmark tech support, I can get the LA4 to switch between XLR inputs reliably with my programmable remote. I cannot fathom why Benchmark does not provide discrete code to select inputs without attaching a Benchmark DAC. Clearly, they could. It is frustrating.

The MiniDSP SHD can be also be used as the preamp with crossovers, bass management, 4 DACs, PEQ, and Dirac. I have one and it works well but there are couple of nits. It is Roon Ready but not yet certified. That should be forthcoming. It does not have a trigger but the newer units (with NEO3) processors power off the USB Input that allow that to be used for a trigger. That requires cobbling together a USB to trigger cable and an amp that powers on with 5 volts.

- Rich
 

DACs_Lover

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This is astonishing. Never heard of a preamp actually improving your system. I might have to buy one of these.
Wait. Do you work for Benchmark? I feel like that should be disclosed.
Mr.Siau works for Benchmark. And inserting a Benchmark between DAC3/AHB2 improves the sound clearly. I use this three units combo for 2 years. It's very very transparent.
 
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