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"This Harbeth User Group (HUG) is the Manufacturer's own managed forum dedicated to natural sound from microphone to ear, achievable by recognising and controlling the numerous confounding variables that exist along the audio chain. The Harbeth designer's objective is to make loudspeakers that contribute little of themselves to the music passing through them.

Identifying system components for their sonic neutrality should logically proceed from the interpretation and analysis of their technical, objective performance. Deviations from a flat frequency response at any point along the signal chain from microphone to ear is likely to give an audible sonic personality to the system at your ear; this includes the significant contribution of the listening room itself. To accurately reproduce the recorded sound as Harbeth speakers are designed to do, you would be best advised to select system components (sources, electronics, cables and so on) that do not color the sound before it reaches the speakers.

For example, the design of and interaction between the hifi amplifier and its speaker load can and will alter the sound balance of what you hear. This may or may not be what you wish to achieve, but any deviation from a flat response is a step away from a truly neutral system. HUG has extensively discussed amplifiers and the methods for seeking the most objectively neutral among a plethora of product choices.

HUG specialises in making complex technical matters simple to understand, getting at the repeatable facts in a post-truth environment where objectivity is increasingly ridiculed. With our heritage of natural sound and pragmatic design, HUG is not the best place to discuss non-Harbeth audio components selected, knowingly or not, to introduce a significantly personalised system sound. For that you should do your own research and above all, make the effort to visit an Authorised Dealer and listen to your music at your loudness on your loudspeakers through the various offerings there. There is really no on-line substitute for time invested in a dealer's showroom because 'tuning' your system to taste is such a highly personal matter. Our overall objective here is to empower readers to make the factually best procurement decisions in the interests of lifelike music at home.

Please consider carefully how much you should rely upon and be influenced by the subjective opinions of strangers. Their hearing acuity and taste will be different to yours, as will be their motives and budget, their listening distance, loudness and room treatment, not necessarily leading to appropriate equipment selection and listening satisfaction for you. Always keep in mind that without basic test equipment, subjective opinions will reign unchallenged. With test equipment, universal facts and truths are exposed.

If some of the science behind faithfully reproducing the sound intended by the composer, score, conductor and musicians over Harbeth speakers is your thing, this forum has been helping with that since 2006. If you just want to share your opinions and photos with others then the unrelated Harbeth Speakers Facebook page http://bit.ly/2FEgoAy may be for you. Either way, welcome to the world of Harbeth!"


Feb. 2018
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Clone Class D "digital" power amplifiers - can we really trust them....

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  • Clone Class D "digital" power amplifiers - can we really trust them....

    ... as high fidelity components?

    I have on my test bench a very typical, inexpensive, so-called 'digital' amplifier. It is not positively promoted as being of audiophile or even high-fidelity grade, but I understand that it uses similar components and technology to all 'digital' amplifiers although perhaps cost reduced.

    What is alarming is that when I connect an oscilloscope across the output terminals, even when there is no signal connected and the volume control is fully off, there is a strong signal at about 250kHz, ten times greater than the highest frequency reproducible from CD, and 10 to 20 times beyond the limit of normal human hearing. The frequency is so far beyond the audio band that it cannot be reproduced by a tweeter, and the argument is that it can be safely ignored.

    The problem is that the 'scope can't ignore it, and even when a normal audio sine wave signal - say, 1kHz - is connected to the amp, the amp's output is displayed as the ever present drone 250kHz super-audio whistle modulated by the 1kHz tone. It looks horrible on the 'scope screen, and if the test signal is a square wave, it shows alarming ringing behaviour - pictures to follow. Consequently, because the on-screen display is so confused, I am unable to make any meaningful measurements on basic frequency response, other than to observe that when a speaker load is connected, there is a huge boost in output to the speaker load around 30kHz, which is not far beyond the end of the audio band.

    I first encountered this super-audio whistling some years ago, and had assumed that improvements in filtering technology in the amplifier circuit would eliminate this. Indeed, I recall that I could not use an AM radio within some meters of the speaker leads which acted as RF radiating antenna. I will try this with this new module.

    I've written to the makers asking if there is some recommended external filter pre-loudspeaker (although that may make a mess of the speaker input drive conditions). Is anyone successfully using 'high-end' digital amps (is that an oxymoron?) and have they tried bringing an AM, medium wave radio near the speaker cables?
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  • #2
    Can anyone post here in a clone of the orig. thread? (was cloned, then closed, then opened)
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

    Comment


    • #3
      I know this thread is a bit old but since I've been using a Halcro Class D amp with my M30.1's for nearly 12 months I thought I'd share my findings.
      Halcro use their own modules and I'm not sure how they differ form other class D - but I can confirm (and measurements from Stereophile confirm) that the Halcro does produce significant ultra sonic noise in the 500khz region.
      I bought this amp S/H and unheard out of curiosity. I know it is contentious on this forum to remark on the sound of amplifiers, but I think this amp is the best sounding I have heard with my M30.1's.
      On paper the amp is a bit of a brute - rated at 200W/8ohms and 400W/4 ohms (but measuring even more) - however it sounds delightfully delicate and detailed with superb clarity.
      I can't hear any artefacts in it's sound - just beautiful music. In fact it beat out my class A/B amp, giving a more unvarnished clarity and realism, so I sold the latter.
      As for the ultra sonic noise - well I know it's there, but in my system I can't hear any negative consequence or modulation with the audio signal so I've found it to be a complete non-issue.

      Comment


      • #4
        Originally posted by tobes View Post
        I know this thread is a bit old but since I've been using a Halcro Class D amp with my M30.1's for nearly 12 months I thought I'd share my findings.
        Halcro use their own modules and I'm not sure how they differ form other class D - but I can confirm (and measurements from Stereophile confirm) that the Halcro does produce significant ultra sonic noise in the 500khz region.
        I bought this amp S/H and unheard out of curiosity. I know it is contentious on this forum to remark on the sound of amplifiers, but I think this amp is the best sounding I have heard with my M30.1's.
        On paper the amp is a bit of a brute - rated at 200W/8ohms and 400W/4 ohms (but measuring even more) - however it sounds delightfully delicate and detailed with superb clarity.
        I can't hear any artefacts in it's sound - just beautiful music. In fact it beat out my class A/B amp, giving a more unvarnished clarity and realism, so I sold the latter.
        As for the ultra sonic noise - well I know it's there, but in my system I can't hear any negative consequence or modulation with the audio signal so I've found it to be a complete non-issue.
        Is the Halcro more powerful than your previous A/B amp? Perhaps the extra power ensures less distortion?
        Getting to know my C7ES3

        Comment


        • #5
          Originally posted by acroyear View Post

          Is the Halcro more powerful than your previous A/B amp? Perhaps the extra power ensures less distortion?
          While the Halcro is more powerful than my previous Odyssey class A/B amp (which was rated at 110W/8ohms) I have a hard time believing this would be responsible for the increased clarity given the conservative levels at which I normally listen. Subjectively the Halcro seemed to produce music from a 'blacker' background i.e. having a lower noise floor and perhaps consequently better low level detail. Apart from this the music just has less of a 'thumbprint' on it - by that I mean different music and sources sounded more individual with less pervasive 'sameness' so the sound. Despite this cleanliness and clarity the Halcro has a wonderfully smooth character - I seriously doubt anyone listening to it would guess it's class D topology. A I noted above, there is no hint of noise or grit in the highs as a consequence of the class D ultra sonic noise. Quite the opposite in fact as the high frequencies - in fact the entire frequency range - has a refreshing naturalness and purity.
          The icing on the cake is that despite being a large powerful amplifier the class D Halcro is extremely efficient and produces almost no heat and has no self noise (transformer hum etc).

          Comment


          • #6
            Originally posted by tobes View Post

            While the Halcro is more powerful than my previous Odyssey class A/B amp (which was rated at 110W/8ohms) I have a hard time believing this would be responsible for the increased clarity given the conservative levels at which I normally listen. Subjectively the Halcro seemed to produce music from a 'blacker' background i.e. having a lower noise floor and perhaps consequently better low level detail. Apart from this the music just has less of a 'thumbprint' on it - by that I mean different music and sources sounded more individual with less pervasive 'sameness' so the sound. Despite this cleanliness and clarity the Halcro has a wonderfully smooth character - I seriously doubt anyone listening to it would guess it's class D topology. A I noted above, there is no hint of noise or grit in the highs as a consequence of the class D ultra sonic noise. Quite the opposite in fact as the high frequencies - in fact the entire frequency range - has a refreshing naturalness and purity.
            The icing on the cake is that despite being a large powerful amplifier the class D Halcro is extremely efficient and produces almost no heat and has no self noise (transformer hum etc).
            Tobes. I agree 110W vs. 200W isn't really significant and you were no doubt using the A/B amp within its power limit. The lack of heat and noise are positive traits and the type of thing I check for when I examine an amplifier. I do wonder if the ultrasonic noise actually translates (harmonics for eg.) into anything anybody can actually hear. Currently I use a cheap pro class D power amplifier in to the C7's and find no specific issues sonically that I can pick out.
            Getting to know my C7ES3

            Comment


            • #7
              I am seriously thinking to try pure digital Lyngdorf TDAI-2170 amp with my SHL5+. It is not a class D amp, where signal is typically modulated in analogue domain, but a pure digital amplifier using pulse-width modulation technology which directly converts PCM to PWM signal to drive the speakers. You can call it power DAC. It's therefore best to use Lyngdorf's digital inputs and this way keep the signal in digital form up to output transistors, without conversion into analogue happening at any stage.

              What are the positives of using Lyngdorf? For me first of all digital room correction system built into the amplifier. You get a microphone and a tripod with the amp. All necessary measuring software is built into the amp, so you don't need to use a PC. I've heard that measurement of the room takes just a few minutes and can give very good results, especially when room acoustics are poor.

              Power seems sufficient to drive Harbeths (measured 98W into 8Ohm, 190W into 4Ohms), amp is very functional, well made and nice looking. It's also not very expensive considering its multiple features. I remember TacT Millennium by Peter Lyngdorf, some 15 or more years ago, using similar but older technology, was much more expensive.

              What are the negatives? I'm not sure about frequency response. It's measured to start rising at above 10kHz into 8Ohms and rolling off at the same frequency into 4Ohms. It's obviously caused by the passive low pass filters that need to be implemented in the output stage of this amplifier type.

              What do you think about employing this amp to drive Harbeths? Do you see any other negatives that I didn't think about?

              http://audio.com.pl/images/0/4/2/440...compl_fot1.jpg
              Attached Files

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