[flyte3333]

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

Hi , yes I’ve read the manual but “very low impedances” doesn’t tell me how low.

My question to @jsiau is can HPA4 drive a ruler flat 10 ohms headphone with no increase in distortions?

 

[townes]

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?

Just to make this clear: I did not compare the V281 with the HPA4 side by side. I sold the V281, then there was a gap of ca. 10 days, then I received the HPA4. Nevertheless, I had the V281 for several years, and the HPA4 seems sonically to be on the same level (at least). For the lower frequencies: surely not weaker and otherwise (transparency) even a bit better.
Otherwise (preamp quality and user interface/handling) I clearly prefer the HPA4, but this I wrote already in my previous post.

I am sure that the HD800S shines significantly more with each of the three amps (GSX Mk2, V281 and HPA4) than with the Hugo 2 built-in amp. Though I never heard a Hugo 2, I have at least some limited experience with the Mojo:
Mojo with a MrSpeakers Ether was not convincing at all. Mojo with HD800S: it cannot drive the HD800S (of course it can somehow, but it sounds awful).

 

[Tobes]

Hi , yes I’ve read the manual but “very low impedances” doesn’t tell me how low.

My question to @jsiau is can HPA4 drive a ruler flat 10 ohms headphone with no increase in distortions?

I think the answer to this is obvious.
Purely reisistive loads are easy to drive and the HPA4 has plenty of current reserves to ensure high power into low resistances.
Note a pure resistive load won't present any variance in phase angle.
The THX tech will ensure distortion remains at the same vanishingly low level.
From the manual:

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.

 

[flyte3333]

I think the answer to this is obvious.
Purely reisistive loads are easy to drive and the HPA4 has plenty of current reserves to ensure high power into low resistances.
Note a pure resistive load won't present any variance in phase angle.
The THX tech will ensure distortion remains at the same vanishingly low level.
From the manual:

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.

Thanks. I know the manual mentions 16 ohms. But I’m asking @jsiau about 10 ohms

 

[Tobes]

Thanks. I know the manual mentions 16 ohms. But I’m asking @jsiau about 10 ohms

I presume you are talking about the nominally 13ohm Aeon headphones?
Mr Speakers quotes their sensitivity at: 92dB/mW Closed, 94dB Open
@M Siau has already stated: "at 13 ohms the HPA4 can produce between 7 and 7.5 W with a current of up to 0.75 A" - which is 7000-7500 times the power required for the above SPL's.

What are you planning to do, launch the drivers into space?

 

[flyte3333]

I presume you are talking about the nominally 13ohm Aeon headphones?
Mr Speakers quotes their sensitivity at: 92dB/mW Closed, 94dB Open
@M Siau has already stated: "at 13 ohms the HPA4 can produce between 7 and 7.5 W with a current of up to 0.75 A" - which is 7000-7500 times the power required for the above SPL's.

What are you planning to do, launch the drivers into space?

Hi. Thanks, I'm very much aware that the question about the ~13 ohm impedance AEONs and power output was already answered.

My question about 10 ohms (for IEMs) is not about power output... it's asking (out of general interest) about distortion levels when going down further in impedance...

Greatly appreciate your attempts to help, but appreciate if we can leave the technical expertise and technical clarifications to @jsiau

 

[M Siau]

Hi. Thanks, I'm very much aware that the question about the ~13 ohm impedance AEONs and power output was already answered.

My question about 10 ohms (for IEMs) is not about power output... it's asking (out of general interest) about distortion levels when going down further in impedance...

Greatly appreciate your attempts to help, but appreciate if we can leave the technical expertise and technical clarifications to @jsiau

Sorry we have been busy here at Benchmark, we are getting ready for a few shows coming up RMAF, CanJam RMAF, AES and CAF! At all of these shows you will get a chance to hear the HPA4 with a variety of headphones and hear the distortion free listening on ALL headphones! The HPA4 has a lot of protection circuitry built into it and one of those is a distortion/clip detection, distortion apart from ruining the listening experience can be harmful to your ears and to headphones. The reason I'm saying distortion/clip is the HPA4 stays distortion free all the way though the volume range right up until it clips, and when the HPA4 detects a clip is about to occur the HPA4 mutes for 3 seconds, this is to protect the headphones and your ears. I have only experienced the HPA4 getting to this point once and that was during a show when a guy was listening to his headphones and I was standing about 3 feet away on a noisy show floor and I could hear what song he was listening to... needless to say he was listening at an extreme volume. Can the HPA4 drive your headphones distortion free? absolutely!

If anyone is planning on attending any of the shows we will be at, especially CanJam RMAF, I encourage you bring your headphone and try the HPA4 out for yourself! Currently we will have 5 different headphones available on our table in the CanJam area.

 

[Tonybo]

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.

"The incoming RCA ground is connected to HPA4 chassis ground through a 30-Ohm resistor.

I was trying to establish if my unit is faulty. I have just gone looking for this resistance with my multimeter (between input rca shield and mains socket earth pin). It indicates infinite resistance. Seems like the 30ohm resistor has been missed, Is this possible (question for M or JSiau)?

 

[Tonybo]

Just bumping this because I would like to have a response to this question, as, I imagine, would other HPA4 owners, since this is likely to affect all units produced so far.

 

[jsiau]

I was trying to establish if my unit is faulty. I have just gone looking for this resistance with my multimeter (between input rca shield and mains socket earth pin). It indicates infinite resistance. Seems like the 30ohm resistor has been missed, Is this possible (question for M or JSiau)?

Based upon your measurements, it looks like the 30-Ohm resistors (located on the rear panel circuit board) are missing, open, or incorrectly populated. We have now confirmed that a few units were populated with 1M resistors in place of the 30-Ohm resistors. This was probably caused by a mid-run reel change in production. These units would still pass all of the performance tests, but could produce hum problems in unusual situations (usually involving low-quality power supplies in an upstream device). We are now measuring these resistors on every unit that goes out the door to make sure that they are populated correctly. Each L/R pair of inputs shares a 30-Ohm resistor. The RCA shield to chassis ground connection should read 30 Ohms. The resistance between the L and R shields on each input should be 0 Ohms. The resistance between the shields on inputs 3 and 4 should be 60 Ohms. If your unit measures differently, contact our service department and we will arrange to service your unit.

The 30-Ohm resistors provide ground-loop isolation between the HPA4 and upstream devices. The RCA inputs feed the balanced input stage on the HPA4. This structure provides many of the advantages of a fully-balanced interconnect, but it only works if the resistors are a low enough value to overcome the leakage currents produced by the upstream power supply. If the upstream power supply is working properly, the 30-Ohms ground termination is ideal.

 

[Tonybo]

Many thanks for the reply John. Mine is showing infinite resistance between the input shields and chassis ground and also therefore between shields of inputs 3 and 4, the L and R shields are connected in each case however. So, as you say a 30 ohm resistors problem. For your information the unit is s/n 18230068-0 and mfg date 7/10/18.

 

[Tobes]

FWIW, mine measures differently - but not as it should according to @jsiau.
I'm getting 500K ohms between any of the the SE input shields and the earth pin.
Between the respective SE L&R channel shields I measure 0 ohms.
Between SE shields of input 3&4 I measure 10K ohms.
My s/n is 18230148-0, mfg date 7/17/18.
https://www.dropbox.com/s/2o6pj6s5ahw3vcj/20180923_130249.jpg?dl=0
https://www.dropbox.com/s/6nv4lzlokbdmf7m/20180923_130211.jpg?dl=0
https://www.dropbox.com/s/rzitcdf07mygush/20180923_130315.jpg?dl=0

 

[Tsyer]

It would be easier if Benchmark told us which units based on serial numbers are affected. Not everyone is as knowledgeable as Tonybo is.
I am wondering if my unit has a problem or not.

 

[Tobes]

It would be easier if Benchmark told us which units based on serial numbers are affected. Not everyone is as knowledgeable as Tonybo is.
I am wondering if my unit has a problem or not.

They are most likely trying to work that out.
Even looking at the serial/dates between Tonybo's and my unit we're possibly talking about a week of production and 80 units.
The good news from my point of view is that my unit doesn't exhibit obvious hum with the SE components I've paired it with so far. Though to be honest 95% of my listening has been with the DAC3L to a balanced input of the HPA4, which of course sidesteps the issue.
@Tsyer have you encountered any hum issues with SE components?

 

[Tsyer]

I use Chord Qutest dac which only has rca to HPA4 rca input. No hum issues at all. However, my confidence in the unit is Low seeing the issues of others so far.