Benchmarking the Benchmark... AHB2 Amplifier

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  • JonMarsh
    Mad Max Moderator
    • Aug 2000
    • 15259

    Benchmarking the Benchmark... AHB2 Amplifier

    You know, sometimes you know right away good things are happening. In this case, there is no mystery... I've seen the other reviews... I've seen John Atkinson's measurements on Stereophile...

    The Benchmark AHB2 is a nicely proportioned little amp that seeing just a picture of the front may not tip you off to how diminutive it is... but seeing how those XLR and SpeakOn connectors fill the rear panel, you realize this is pretty itty bitty for an analog power amplifier (to be fair, it does use a very sophisticated resonant switching power supply, though).

    20150726132016_BenchmarkAHB2AmpFrontWeb by Jon Hancock, on Flickr

    And I've listened to these for hours and hours since just before Thanksgiving, last November. But nonetheless, when I finished connecting one of these to the AP, set the gain control switch to the mid point (adjustable between true Pro levels, a compromise level, and consumer input level- I went for the middle ground) and fired it up, and default it's showing a moderate level output signal (7VRMS with 1VRMS input), reading out the levels and THD+N, with a default FFT window, and right away, you know there's something special here... something one might have not believed could exist commercially for under $10K or $20K, much less for $3K.



    FirstCheck_SmallWindow by Jon Hancock, on Flickr


    No, you didn't misread that; at 6 watts output power, the THD+N (Total Harmonic Distortion + Noise) is just 0.00042%. Just think about how quiet the front end on this has to be to reach that level of performance... and about how your preamp does or doesn't match up to that!

    So, is this a "First Watt" design? optimized just for low Power? Let's take a look. (Keep in mind I DIDN'T use the Pro level input setting, which requires even more front end drive, and improves the SN ratio further- this middle ground setting will work fine with most good stereo preamps, say, units comfortable driving up to 4 or 5VRMS out). So don't expect to see as low numbers as JA published. This is a little more real world... :W


    First, we'll look at the swept sine behavior starting from a level a bit below 100mW and proceeding up to the clip point, at 1kHz.

    THD+N Ratio vs Measured Level Benchmark AHB2 by Jon Hancock, on Flickr.

    It's possible with with more careful approach to lead dress and the test setup, I could have gotten better numbers than this, but let's leave that for the future for now.

    One of the things one ought to do to appreciate this amp is compare what it's THD+N figures look like at 100mW compared to may other "high end" amps out there- here, we're coming in at 0.003%, and I've seen many amps for 10X the money coming in at 0.02 to 0.07% at 100mW. For a speaker that's 90 dB efficient, 100mW is a conversational playback level.

    By 1W we're down to 0.001% THD+N, and 20W we've reached 0.0003%! Yes, three zeros in front of that 3!

    OK, that's impressive, but what about that bridged mono mode? Benchmark supports in directly with a separate SpeakOn output connector, and using the balanced inputs and stereo-mono switch. Move the SpeakOn output connector (you did get some of the Benchmark Speaker cables, didn't you?) flip a switch, and voila, a miniature bridged mono block amp.


    THD+N Ratio vs Measured Level Benchmark AHB2 Balanced Mono by Jon Hancock, on Flickr

    Now we're seeing a bit past 350W at the clipping point- because the two channels are being added in series, the noise floor is doubled, but we're still looking at less than 0.001% at 10W output.

    Let's widen the frequency range of investigation- but keep in in bridged mono. It's a very competitive $2995 mono block, given the overall performance.

    Next up some frequency sweeps at different power levels.

    First, at 50W RMS.

    THD+N Ratio 50W Bridged Mono by Jon Hancock, on Flickr

    Just under 0.0005% up to 5 kHz, rising smoothly to about 0.0015% at 20 kHz.

    Let's push it harder- 200W now.

    THD+N Ratio 200W Bridged Mono by Jon Hancock, on Flickr

    Now we're seeing the effect of the noise floor dropping further, with lower THD +N below 3 kHz, but perhaps at this higher output level and higher frequency range, the feedforward error correction can't quite work as well, and the distortion is rising to a peak level of 0.003% at 20 kHz. Tsk, tsk. :W

    I personally like FFT's more than summed distortion measurements like this- the latter show the large trends, the former the nitty gritty detail. Let's try some low and high frequency examples.


    First, 50Hz at 100W output in bridged mode. This is interesting because it can reveal both signal related harmonic distortion and power supply related noise, with harmonics related to the line frequency. Keeping in mind the output signal is at +30 db rA, 2nd harmonic is essentially none-existent, and 3rd harmonic at 150Hz is -135dB from the signal output level. There are some power line related spuriae; at 180Hz, 300Hz, 420Hz, etc, but generally not above -130 dB relative to the 100W output.

    FFT Spectrum 50Hz 100W AHB2 by Jon Hancock, on Flickr


    Considering the rise in high frequency distortion, an obvious avenue of investigation is two tone CCIF Intermodulation distortion, with 19 + 20 kHz. They're mixed at equal levels, and setup to reach a peak output of 40V, equivalent to the peak level for 100W RMS output. Needless to say, this would be very quick death to almost any tweeter, but it's a good stress test for HF distortion, both harmonic and intermodulation.

    Here is what the test signal looks like:


    Scope_AHB2_CCIF by Jon Hancock, on Flickr


    And this is an FFT of the results, plotted from DC to 40kHz. Ideally there would only be the two spikes reading out at 19kHz and 20kHz, but we can see a variety of side band components at 1 kHz intervals, both around the test signal, and at an image at the 2nd harmonic of the test signal. There are also difference tones present at 1 and 2 kHz.

    FFT Spectrum 19+20kHz 100W Pk AHB2 by Jon Hancock, on Flickr

    Let's keep in mind that most of these are below the -100dB point, which means they are 122.5db below the actual signal! The worst case components, at 18 and 21 kHz, are about -95 dB relative to the actual signal peaks. This calculates to a percentage basis of 0.0017%. This is a very low number compared with most power amplifiers.


    Of course, what really matters is what it sounds like- or if it sounds like nothing at all, just the proverbial piece of wire with gain. I haven't heard or measured anything else that comes as close to achieving this ideal, so if this characteristics is what you want in your system, give these an audition before spending money elsewhere.


    Positives
    • Very compact for the amount of output power, and not being Class D
    • Run very cool, not a high bias design
    • Transparent as all get-out, with tight articulate bass- but with no extra fat
    • Stunningly good measurements- state of the art
    • Available with choice of either black anodized or silver anodized front panels
    • SpeakOn and binding post output connectors
    • XLR input connectors



    Concerns
    • No unbalanced input connectors - you'll have to use cable adapters
    • Best performance does require a high performance preamp-
    • Most preamps can't match the S/N or THD performance of this amplifier
    • It would be strikingly unfortunate if your preamp is bigger and hotter than your power amp - this is completely plausible with this unit.
    • Not available in Rose Gold...
    • Where am I going to come up with the money for a pair of these after spending so much on test equipment this year? (this pair is on loan from their owner).
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  • ergo
    Senior Member
    • Mar 2005
    • 675

    #2
    Very impressive performance indeed.

    If you have not heard it yet check out
    BENCHMARK AHB2 POWER AMPLIFIER: HOME THEATER GEEKS 242
    full show on exactly this amp and history behind it.

    Comment

    • ergo
      Senior Member
      • Mar 2005
      • 675

      #3
      How does the load (resistor?) look like for measuring upto 300W. Quite some heat to get rid of... and I assume it's x2 for both channels.

      Comment

      • wkhanna
        Grumpy Old Super Moderator Emeritus
        • Jan 2006
        • 5673

        #4
        holly crap that is one quiet motor!
        in bridged mode to boot!

        another fine piece of testing/journalism, there, Jon.
        do i see someone's retirement profession here?
        _


        Bill

        Practicing Curmudgeon & Audio Snob
        ....just an "ON" switch, Please!

        FinleyAudio

        Comment

        • JonMarsh
          Mad Max Moderator
          • Aug 2000
          • 15259

          #5
          Originally posted by ergo
          How does the load (resistor?) look like for measuring upto 300W. Quite some heat to get rid of... and I assume it's x2 for both channels.
          The AHB2 is 100W/ch at 8 ohms, 175W/ch at 4 ohms rated stereo; flip the switch and it's 350w mono at 8 ohms, ~450W at 6 ohms. Most of the testing was done in bridged mono. I still have my power loads from the 70's when I designed Pro audio gear, but this was actually a new load I built for testing class D mono blocks; 750W forever and 1500W shorter term power, and it uses a heat sink normally used for high power modules; I'll post a picture of it when I have a chance (at Starbucks down in Milpitas near our work office right now). The heat sink for that weighs about 20 lb. :W


          BTW, my quip about the preamp being bigger and hotter was not some random comment- my friend and colleague in Munich that owns these has been looking at and evaluating some pretty esoteric tube preamps lately- the one that will be there when I arrive in Munich the end of this week is from NAT Audio, and weighs in a 88 lb. The last one he's been looking at is an Ayon Spheris II.
          the AudioWorx
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          Resistance is not futile, it is Volts divided by Amperes...
          Just ask Mr. Ohm....

          Comment

          • JonMarsh
            Mad Max Moderator
            • Aug 2000
            • 15259

            #6
            Originally posted by wkhanna
            holly crap that is one quiet motor!
            in bridged mode to boot!

            another fine piece of testing/journalism, there, Jon.
            do i see someone's retirement profession here?
            Probably not, as I'm really just getting warmed up with the test equipment for working on some designs myself. Hush hush and all, that's why we have that private Class D forum... That's just getting started. Also have some ideas for a line preamp, though the investment to build something like that is considerable- there's only a few commercial products in that area that I like. The Taurus Pre is one of them.
            the AudioWorx
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            Resistance is not futile, it is Volts divided by Amperes...
            Just ask Mr. Ohm....

            Comment

            • JonMarsh
              Mad Max Moderator
              • Aug 2000
              • 15259

              #7
              Originally posted by ergo
              Very impressive performance indeed.

              If you have not heard it yet check out
              BENCHMARK AHB2 POWER AMPLIFIER: HOME THEATER GEEKS 242
              full show on exactly this amp and history behind it.
              Thanks for posting the link- somehow, I never came across that one!
              the AudioWorx
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              Resistance is not futile, it is Volts divided by Amperes...
              Just ask Mr. Ohm....

              Comment

              • wkhanna
                Grumpy Old Super Moderator Emeritus
                • Jan 2006
                • 5673

                #8
                Originally posted by JonMarsh
                Also have some ideas for a line preamp, though the investment to build something like that is considerable- there's only a few commercial products in that area that I like. The Taurus Pre is one of them.
                oh my!
                if only i could build a phono-pre of your design.....
                though, as you have said before, the older Ayre model was one of the best....
                _


                Bill

                Practicing Curmudgeon & Audio Snob
                ....just an "ON" switch, Please!

                FinleyAudio

                Comment

                • wkhanna
                  Grumpy Old Super Moderator Emeritus
                  • Jan 2006
                  • 5673

                  #9
                  got to check these out at last year's Capital Audofest.

                  LVK

                  best i have ever heard

                  Bill Hutchins is the Chief Designer of LKV Research
                  i attended a seminar he gave on the pros & cons of feedback circuits & spent more than two hours talking with him
                  this is his pre.....sorta looks like it might be a balanced topography....ya think?
                  i do not think he cares much for the compromises on feedback much, either




                  one of the top three system we heard all weekend




                  you can read more here and here if you wish
                  _


                  Bill

                  Practicing Curmudgeon & Audio Snob
                  ....just an "ON" switch, Please!

                  FinleyAudio

                  Comment

                  • JonMarsh
                    Mad Max Moderator
                    • Aug 2000
                    • 15259

                    #10
                    Originally posted by ergo
                    How does the load (resistor?) look like for measuring upto 300W. Quite some heat to get rid of... and I assume it's x2 for both channels.

                    Here's a picture of one of the load resistors...

                    IMG_Load by Jon Hancock, on Flickr


                    Don't know why this displays rotated here, as it looks normal on my Mac and on Flickr.

                    The binding posts and other connectors will give you an idea of scale.
                    the AudioWorx
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                    Resistance is not futile, it is Volts divided by Amperes...
                    Just ask Mr. Ohm....

                    Comment

                    • JonMarsh
                      Mad Max Moderator
                      • Aug 2000
                      • 15259

                      #11
                      Originally posted by wkhanna
                      got to check these out at last year's Capital Audofest.

                      LVK

                      best i have ever heard

                      Bill Hutchins is the Chief Designer of LKV Research
                      i attended a seminar he gave on the pros & cons of feedback circuits & spent more than two hours talking with him
                      this is his pre.....sorta looks like it might be a balanced topography....ya think?
                      i do not think he cares much for the compromises on feedback much, either




                      one of the top three system we heard all weekend




                      you can read more here and here if you wish
                      I applaud the use of relatively low and variable gain structure in the preamp, and using a switched network for volume control, though I do rather prefer the big Shallco switches for that task...



                      The circuit topologies and components are sound, similar to what I was doing in the 70's when I was building some custom phono preamps and line stages. I don't have any desire at this time to do phono stages again, but I'm still thinking about a line stage unit.

                      Yes, I like the fact he includes balanced inputs; I would likely only use balanced inputs, and suggest adapter cables when connecting to unbalanced components, as this gets the best signal definition at the source without any possibility of ground loops.

                      If he is doing a full active balanced input to output, as does Ayre, then, I'm going to go out on a limb and suggest that this is not the optimum situation, as it passes on common mode components and relies on the driven component to resolve noise issues, and do so after the possibility/inevitability of further gain miss matches and degradation of CMRR in active circuits.

                      Of course, I have another plan, it's not really particularly secret, but based on my time working on mixing console design decades ago. Bruno Petsys does something similar like that for Mola Mola. I would actually use line transformers, too, for the specific input receiver design I have in mind.

                      Like I say, have some ideas, at some point will test them out in real hardware, not just simulations, and build a single input preamp to listen and test them out. That's the only way to really find out if it works. No commercialization intent, just building stuff for myself and hopefully learning a little more.
                      the AudioWorx
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                      Resistance is not futile, it is Volts divided by Amperes...
                      Just ask Mr. Ohm....

                      Comment

                      • wkhanna
                        Grumpy Old Super Moderator Emeritus
                        • Jan 2006
                        • 5673

                        #12
                        i holly agree about the stepped attenuators.
                        especially with accurate & precisely matched resistors.
                        alas, the form factor is limiting otherwise one would be residing inside my highly modified Carver C-19 right now.

                        as it is, the OEM was replaced with far better quality Alps unit.
                        nice part is, i can set my C-19 for zero gain, so the pot normally resides at 70 to 90% attenuation, thus helping to limit the amount of distortion it is adding.


                        i flipped it \\ __ // //---\\


                        _


                        Bill

                        Practicing Curmudgeon & Audio Snob
                        ....just an "ON" switch, Please!

                        FinleyAudio

                        Comment

                        • JonMarsh
                          Mad Max Moderator
                          • Aug 2000
                          • 15259

                          #13
                          Originally posted by wkhanna
                          i holly agree about the stepped attenuators.
                          especially with accurate & precisely matched resistors.
                          alas, the form factor is limiting otherwise one would be residing inside my highly modified Carver C-19 right now.

                          as it is, the OEM was replaced with far better quality Alps unit.
                          nice part is, i can set my C-19 for zero gain, so the pot normally resides at 70 to 90% attenuation, thus helping to limit the amount of distortion it is adding.


                          i flipped it \\ __ // //---\\


                          easier to do with the picture than the real thing! :B
                          the AudioWorx
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                          Natalie P Supreme
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                          Resistance is not futile, it is Volts divided by Amperes...
                          Just ask Mr. Ohm....

                          Comment

                          • wkhanna
                            Grumpy Old Super Moderator Emeritus
                            • Jan 2006
                            • 5673

                            #14
                            they call me Mr. Easy....

                            ...among a multitude of other things.....
                            _


                            Bill

                            Practicing Curmudgeon & Audio Snob
                            ....just an "ON" switch, Please!

                            FinleyAudio

                            Comment

                            • JonMarsh
                              Mad Max Moderator
                              • Aug 2000
                              • 15259

                              #15
                              one of the few Portable PC with Windows 7 Professional & 4K output you can still get

                              One more tool added to the arsenal...

                              IMG_2550 by Jon Hancock, on Flickr

                              It's been a busy quarter... going to be a busy year.
                              the AudioWorx
                              Natalie P
                              M8ta
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                              Modula Xtreme
                              Isiris
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                              SMJ
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                              Calliope
                              Ardent D

                              In Development...
                              Isiris Mk II updates- in final test stage!
                              Obi-Wan
                              Saint-Saëns Symphonique/AKA SMJ-40
                              Modula PWB
                              Calliope CC Supreme
                              Natalie P Ultra
                              Natalie P Supreme
                              Janus BP1 Sub


                              Resistance is not futile, it is Volts divided by Amperes...
                              Just ask Mr. Ohm....

                              Comment

                              • wkhanna
                                Grumpy Old Super Moderator Emeritus
                                • Jan 2006
                                • 5673

                                #16
                                I see a workshop expansion soon in some one's future
                                _


                                Bill

                                Practicing Curmudgeon & Audio Snob
                                ....just an "ON" switch, Please!

                                FinleyAudio

                                Comment

                                • JonMarsh
                                  Mad Max Moderator
                                  • Aug 2000
                                  • 15259

                                  #17
                                  My man cave is like working in a submarine, and unfortunately I don't think the walls are going to be expanded any time soon! :B

                                  I'm actually planning on taking this one in to work, and bringing home the 4 channel one I bought last year.
                                  the AudioWorx
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                                  In Development...
                                  Isiris Mk II updates- in final test stage!
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                                  Modula PWB
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                                  Natalie P Ultra
                                  Natalie P Supreme
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                                  Resistance is not futile, it is Volts divided by Amperes...
                                  Just ask Mr. Ohm....

                                  Comment

                                  • ergo
                                    Senior Member
                                    • Mar 2005
                                    • 675

                                    #18
                                    Hi Jon,

                                    The "load" does look very much what I expected - big and heavy. Nice one.

                                    On preamp topics - have you seen this Bruno Putzeys article. In end there is a pre-amp circuit that for me looks interesting enough, so that I'm participating in diyaudio group buy to get one built. It's not a full discreet one but it is balanced throughout. So interesting and promising in that sense.


                                    One guy ammended it also with stepped (relays) pot replacement

                                    Comment

                                    • wkhanna
                                      Grumpy Old Super Moderator Emeritus
                                      • Jan 2006
                                      • 5673

                                      #19
                                      nice, ergo!

                                      are you guys getting PC boards made?
                                      _


                                      Bill

                                      Practicing Curmudgeon & Audio Snob
                                      ....just an "ON" switch, Please!

                                      FinleyAudio

                                      Comment

                                      • JonMarsh
                                        Mad Max Moderator
                                        • Aug 2000
                                        • 15259

                                        #20
                                        Originally posted by ergo
                                        Hi Jon,

                                        The "load" does look very much what I expected - big and heavy. Nice one.

                                        On preamp topics - have you seen this Bruno Putzeys article. In end there is a pre-amp circuit that for me looks interesting enough, so that I'm participating in diyaudio group buy to get one built. It's not a full discreet one but it is balanced throughout. So interesting and promising in that sense.


                                        One guy ammended it also with stepped (relays) pot replacement
                                        http://linearaudio.net/sites/lineara...tmeter%203.pdf
                                        Thanks for the PDF links. I am familiar with the Mola Mola preamp block diagram, as well as being familiar with the utility of those circuits. As what AURALiC accomplishes shows, it could be valuable for the so called high end audio guys to pay more attention to what people have done for mixing console systems in the past- there the challenges are significant and taken seriously, including in a cost/performance sense.



                                        Bruno comes from a very pragmatic but well educated and thoughtful viewpoint that cuts through a lot of the BS in high end audio, to achieve real results. All one has to do is go through the hardware reviews on Stereophile magazine to see what silliness and self delusion get's assembled as "high end" home stereo equipment. Well, maybe the sheet metal looks nice in most cases...

                                        The G word article summarizes a lot of good stuff for preamp design, and I'm in violent agreement with the second article, about managing the gain system, and actually limiting it to sensible values. This is an area not well addressed in power amps either- we'd all be much better off running line level circuits at pro signal levels, and power amp gain reduced to 10 or 12 dB. You only have to look at the THD+N curves of most preamps and power amps and ponder how to best arrange that to get a high results at the output. High gain power amps are frankly only workable if they're very low noise and use impedance transformation at the input (I.E., transformer) to step down a higher level signal and better match the noise characteristics.

                                        In a world that I ran, normal line level preamps would be expected to output 8 to 10VRMS minimum, as the standard working value, and the amp gain structure would look like an AHB2. Back in the 70's, when designing Pro audio gear, I wrestled with that even then, and ended using a front end design that borrowed from my custom built phono preamps, using monolithic matched differential pair JFETs (NPD5565 from National Semiconductor) in parallel (to further drive down the noise figure and increase the drain current available for slowing compensation capacitors- so this amp had front equivalent input noise like a high grade phono preamp, but a large signal slew rate of 100V/usec. Of course, it took more than JFETs at the front to do that. :W

                                        Geez, this is terrible, I sound like some codger or curmudgeon talking about how things were different or better when I was a kid... But they weren't, in most cases; one of the most popular amps back then was the Crown DC300!

                                        Thanks again for posting the link- it confirms some aspects of what I've had in mind for doing a basic preamp with switched gain, but I have a few more tricks left in the drawer compared with what Bruno published, just as I'm sure he does.... :B
                                        the AudioWorx
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                                        Resistance is not futile, it is Volts divided by Amperes...
                                        Just ask Mr. Ohm....

                                        Comment

                                        • JonMarsh
                                          Mad Max Moderator
                                          • Aug 2000
                                          • 15259

                                          #21
                                          One of the best things about Bruno's article is that I can just send it to anyone who wonders why I've only been using balanced gear at home for ages, (since about 2000) and I won't have to go into any long explanation about it...

                                          Another thing nice about the Linear Audio site, besides the interesting articles, is they do host some good downloads for free, including Bob Cordell's review of Gilles Brocard book about LTSPICE IV Simulator- it's a great book, I've had it a while, and it's worth every penny of the $50 price (published by Wurth Electronik, but then I use magnetics components from them, too). LTspice is a very good simulator, and available for free- it's better than a number of commercial simulators that cost thousands of dollars (such as the one our FAE manager foisted off on the FAE team... ) but that's another story. Anyone that has interest in circuit simulation should have a copy of it, I have GOOD expensive commercial simulators, but I still like/prefer LTspice for many things, including my Class D amplifier work, and some kinds of power supply simulation. It's a no brainer. But this is the book to have, hands down.
                                          the AudioWorx
                                          Natalie P
                                          M8ta
                                          Modula Neo DCC
                                          Modula MT XE
                                          Modula Xtreme
                                          Isiris
                                          Wavecor Ardent

                                          SMJ
                                          Minerva Monitor
                                          Calliope
                                          Ardent D

                                          In Development...
                                          Isiris Mk II updates- in final test stage!
                                          Obi-Wan
                                          Saint-Saëns Symphonique/AKA SMJ-40
                                          Modula PWB
                                          Calliope CC Supreme
                                          Natalie P Ultra
                                          Natalie P Supreme
                                          Janus BP1 Sub


                                          Resistance is not futile, it is Volts divided by Amperes...
                                          Just ask Mr. Ohm....

                                          Comment

                                          • ergo
                                            Senior Member
                                            • Mar 2005
                                            • 675

                                            #22
                                            Bill,
                                            The group buy unfortunately closed a few days ago
                                            I open this thread to propose the 6 inputs board for the Bruno Putzeys preamplifier and understand if there is sufficient interest to start a GB. I designed this board for my own Bruno preampli. I need more than 2 inputs and I want also a rotary switch in the front panel with a LED indicating...


                                            I ordered 2 assembled (SMD stuff assembled) boards. I will use one for sure and don't quite know about second one yet.

                                            I do have a bare PCB that came with the Linearaudio Vol 5 book. I just do not have time to get all parts and assemble it, so I decided to try if I can make it happen with almost ready boards. If you have a big urge I might be willing to part with the original PCB once I get the new ones.

                                            Jon - yeah Linearaudio is a good source. I have supported Jan Didden by buying all of the books in series this far. As well as the LTSpice one and Jan's amplifier design DVD etc. He's personal website is by the way here

                                            Comment

                                            • JonMarsh
                                              Mad Max Moderator
                                              • Aug 2000
                                              • 15259

                                              #23
                                              Thanks for his web site link. Though I try to keep up with the cool stuff in Europe, it's a big place and a big job! :W
                                              the AudioWorx
                                              Natalie P
                                              M8ta
                                              Modula Neo DCC
                                              Modula MT XE
                                              Modula Xtreme
                                              Isiris
                                              Wavecor Ardent

                                              SMJ
                                              Minerva Monitor
                                              Calliope
                                              Ardent D

                                              In Development...
                                              Isiris Mk II updates- in final test stage!
                                              Obi-Wan
                                              Saint-Saëns Symphonique/AKA SMJ-40
                                              Modula PWB
                                              Calliope CC Supreme
                                              Natalie P Ultra
                                              Natalie P Supreme
                                              Janus BP1 Sub


                                              Resistance is not futile, it is Volts divided by Amperes...
                                              Just ask Mr. Ohm....

                                              Comment

                                              • hifidez
                                                Member
                                                • Feb 2007
                                                • 42

                                                #24
                                                Originally posted by JonMarsh
                                                You know, sometimes you know right away good things are happening. In this case, there is no mystery... I've seen the other reviews... I've seen John Atkinson's measurements on Stereophile...

                                                The Benchmark AHB2 is a nicely proportioned little amp that seeing just a picture of the front may not tip you off to how diminutive it is... but seeing how those XLR and SpeakOn connectors fill the rear panel, you realize this is pretty itty bitty for an analog power amplifier (to be fair, it does use a very sophisticated resonant switching power supply, though).

                                                20150726132016_BenchmarkAHB2AmpFrontWeb by Jon Hancock, on Flickr

                                                And I've listened to these for hours and hours since just before Thanksgiving, last November. But nonetheless, when I finished connecting one of these to the AP, set the gain control switch to the mid point (adjustable between true Pro levels, a compromise level, and consumer input level- I went for the middle ground) and fired it up, and default it's showing a moderate level output signal (7VRMS with 1VRMS input), reading out the levels and THD+N, with a default FFT window, and right away, you know there's something special here... something one might have not believed could exist commercially for under $10K or $20K, much less for $3K.

                                                [/LIST]
                                                I took delivery of my AHB2, along with the DAC2 HGC, last November and have been totally pleased with the pairing. Encouraging to see my choice measures so well. I have just the one AHB2 and it's coupled to the DAC2 with balanced interconnects. I have the gain of the AHB2 and the outplut level of the DAC2 set where Benchmark recommends. Sounds just fine. The single AHB2 is more than enough power for my realtively efficient Spendor D7 loudspeakers. I have seen the power amp's clipping indicators wink only the once. And that was because I was trying to do so. I couldn't ever play music at that volume. It's neither musical nor bearable at that level.
                                                Thanks for the post :-)

                                                Derek

                                                Comment

                                                • JonMarsh
                                                  Mad Max Moderator
                                                  • Aug 2000
                                                  • 15259

                                                  #25
                                                  You're welcome Derek.

                                                  I've brought this pair to Munich, and they do quite well driving a set of Egglston Works Savoy Signatures here; it's actually humorous to see the AHB2's sitting in front of some big Halcro's; even more humorous hearing how good they sound compared to the Halcro's, which are no slouches. Will post pictures after I get back- I'm in Munich until the end of the week.
                                                  the AudioWorx
                                                  Natalie P
                                                  M8ta
                                                  Modula Neo DCC
                                                  Modula MT XE
                                                  Modula Xtreme
                                                  Isiris
                                                  Wavecor Ardent

                                                  SMJ
                                                  Minerva Monitor
                                                  Calliope
                                                  Ardent D

                                                  In Development...
                                                  Isiris Mk II updates- in final test stage!
                                                  Obi-Wan
                                                  Saint-Saëns Symphonique/AKA SMJ-40
                                                  Modula PWB
                                                  Calliope CC Supreme
                                                  Natalie P Ultra
                                                  Natalie P Supreme
                                                  Janus BP1 Sub


                                                  Resistance is not futile, it is Volts divided by Amperes...
                                                  Just ask Mr. Ohm....

                                                  Comment

                                                  • ergo
                                                    Senior Member
                                                    • Mar 2005
                                                    • 675

                                                    #26
                                                    Those EgglestonWorks speaker have a curious design. Instead of minimizing the mid/tweeter spacing they seem to have deliberately extended it?

                                                    Comment

                                                    • hifidez
                                                      Member
                                                      • Feb 2007
                                                      • 42

                                                      #27
                                                      That'll teach me. I promise not to try and get this thread back on track again ;-)

                                                      Derek

                                                      Comment

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