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In Reply to: RE: Benchmark AHB2 amplifier posted by coli on July 02, 2015 at 07:54:40
... is painful to read. Linked below for those curious.
I stopped at this:
The differences between 16-bit and 24-bit recordings are inaudible when the power amplifier can only deliver 16-bit noise performance.
Why? Because anyone, who has ever listened to CD vs. Hi-Rez with a "normal" amplifier through "normal" speakers, together providing even less than 96 dB of dynamic range, knows that it's an utter BS.
Follow Ups:
I am interested in your subjective experience but wonder how you reached your conclusion?
I see that you are not talking about specially prepared files but commercially available recordings i.e. CDs and (here I am presuming) hi-rez downloads or streams.In virtually all cases that means not only comparing a 16 bit v. 24 bit version but also simultaneoulsy comparing different sampling rates, one being 44.1 kHz the other being anything from 96kHz to 192 kHz. So it is then not possible to isolate the effect of different bit depths from the sampling rates. Of course I may be wong and you may have located 24 bit/44.1 kHz or 16 bit/96-192 kHz versions of the same recordings but I have never come across such bit depth/sampling rate combinations. That is aside from the Apple USB release of the Beatles stereo albums (24/44.1) but then there is no alternaive hi-rez version to compare. Please advise but you do state CD and not another format.
Life gets very complex when making meaningful subjective format comparisons as even if the files in question are directly comparable in theory it may well be that the processors used to replay them effectively favour one or the other due to their internal logic.This may become dominant in the comparison. There is a good article on this overlooked fact by Paul Miller in Hi Fi News recently.
There are two red flags with the design from my perspective:
"HIGH DAMPING FACTOR"
AKA, we use boatloads of negative feedback.
"In contrast, the AHB2 uses a tightly regulated resonant switching power supply"
Let's introduce EMI/RFI to the neighborhood.
d
Edits: 07/02/15 07/02/15 07/02/15 07/02/15 07/06/15
but that is only because it would be so non-linear as to be utterly unlistenable without it. Compared though to an amp that has been optimized to maximum linearity WITHOUT negative feedback I am quite sure the Benchmark won't "measure" up.
This amp does use negative feedback and feed forward and it sounds good because of it.
The individual who reviewed the amp above doesn't share your opinion.
while SMPS produce noise in the 200khz---> 1mhz and above range and can be filtered out with simple filters
The designers of the best sounding gear don't share this opinion either.
d
Edits: 07/06/15
try convincing the reviewer above who observed:
"With the Benchmark it was little better than loud background music. "
Good luck!
From their web page:
Traditional class-AB designs attempt to control distortion through the use of feedback. Unfortunately, these feedback systems have a limited ability to reduce the abrupt transients that are caused by output device crossover transitions. Feedback networks attempt to correct errors after they occur. In contrast, feed-forward networks can prevent errors from occurring.
The THX-AAA Technology™ includes an ultra-clean low-power error-correction amplifier that runs in parallel with the high-power main amplifier. The correction amplifier keeps the main amplifier virtually distortion free while the main output devices transition between push and pull states. Like a class-A amplifier, the AHB2 shows no signs of crossover distortion. The feed-forward system virtually eliminates the errors that would have been produced by the output devices in the main amplifier.
Now, how this approach is different from traditional negative feedback with regards to affecting sound quality - that's anyone's guess.
Bob Cordell wrote a book that details Error Correction pretty well. Also some papers by Dr. Malcomb Hawksford. Easy to find, but not in the HiFi glossy rags.
Agree Brad , also zero feedback amplifiers with degeneration, interesting ...
Negative feedback in large quantities doesn't mean bad sound.
Properly designed switch mode power supplies do not radiate copious quantities of rfi.
Just ask any of the many satisfied Hypex customers...
try it! you know you want to!
we disagree on all your points.
Lots of corrective feedback=sterile sound
Just ask any of the many satisfied Hypex customers...
That would certainly not be me.
Nt
try it! you know you want to!
So sayeth the Switching Amp Apologist.
We have very different points of reference as to how live unamplified music sounds.
You are welcome to your choice of high feedback amp. Take all of them - please! :)
No Dog in any of the above Races (I use Firstwatt )
But the attitude typed is clearly of the:
"Not What Granpa used" school.
Digi Amps Can/do sound Incredible as Do SMPS's.
When competently built ;)
Barking up the wrong tree in a dying forest IMO.
Real life.... Marches on... like it or not, My friend
The notion of using high levels of corrective feedback (because the design is inherently nonlinear) to *fix* errors already committed is not an approach I have found to be particularly successful for reproducing a natural musical experience.
To each his own.
Do you know whether it is less than the Benchmark, or are you just guessing?
my older version uses 15 db which is anything but "high".
The current type III version uses zero global.
I was looking around trying to find more info about how the Benchmark uses feedback vs. feed forward, and whether it is local or global, but the writeups are somewhat conflicting. One thing they are consistent about is that the Benchmark has a low power correction amp circuit which is summed with the main amplifier circuit. What's not clear is how much distortion reduction is achieved via feed forward, how much is achieved via negative feedback loop, and whether the feedback loop is global.
One thing we can look at is output impedance, i.e. damping factor. Bascom King's measurements of the Benchmark show a damping factor of 300 in the bass which falls with frequency down to 30 at 20 KHz. That is a little bit on the low side of average for a 100W Class A/B amplifier, which suggests that it doesn't use a lot of negative feedback.
For a tube amp that is high
That vintage of VTL amps used less feedback.
"Other design parameters include the use of approximately 6dB of feedback...
more reasonable...pity they feel they need it at all but maybe the amp is simply too complex to work properly without some.
that the current type III version (I linked to Stereophile review in earlier post) does not use any global feedback.
Simple designs don't require lots of correction.
Most designers use nested , the GF scare is just that ......
There is some local feedback employed and is user controllable.
Scare? Only if you care about sound quality.
You're welcome to all the global feedback you want. :)
Sure especially if distortion and clipping becomes your kind of sound quality, if it's sounds good To you I guess it doesn't matter , the Topology that is, not everyone want fast and real (SS) some like tooby soft and cosseting , every topology can deliver , choose your poison ...
Now hurry up before the Rotel guy with the stub ears shows up ..... :)Regards
Edits: 07/08/15
You have been decieved into believing that what SS delivers is real...it is not due to the problems that are inherent in most SS (particularly AB high feedback) designs.
I don't like the sound of distortion at all, in fact I am almost ceratinly more allergic to it than you. I choose componets that are inherently more linear and therefore produce predominantly low order harmonics in a pattern the ear/brain recognizes as natural. See the articles I posted above. You will see also that tube amps can generate voltage far in excess of their static ratings...especially SETs.
I am turned off by SS amps because of the kind of unnatural distortion they produce...it doesn't matter if it is low in level what matters is the kind. The distortions in digital reproduction are also unnatural, which is why such low levels of distortion and jitter are still audible in these products and good analog superior despite the obvious problems it also has. See Cheever and Geddes papers. For amps this has been known at one level or another for at least 60 years. For digital, people woke up to the issues in the last 15 years or so.
Fitting quote from John Marks:
"Every February 2nd I emerge from my burrow and caution audiophiles that the deep-seated need to have a logical explanation for everything is first and formost a deep-seated and largely un-met EMOTIONAL need, which is why "Objectivists" often can be relied upon to carry their search for an answer to irrational extremes....
If it sounds good, it is good."
try it! you know you want to!
With this kind of "experience", he feels the urge to participate in discussions, and express his valuable opinion on various topics, particularly tubes vs. SS?
This kind of sound aberration is possible, no doubt, but there are pre-requisites to be met, namely - the person who put that system together has to be at least SEMI-retarded.
What a humorless joke.
Or silly stupid worried about capacitor voltage ......
Cab,If memory serves me correctly Geddes papers on amplifiers were disproved, correct me if not. I dont get your unnatural sound from SS mantra, a drum set for eg sounds real thru SS, blurred and slow thru Toobs, simple recordings of single instruments sound better on toobs, toobs have an effect to the recording,listen thru headphones or do you own recordings , there is an artificial ambiance from the toobs, some like this others not, there is no superior topology or NFB magic number, its all about application.
I wonder how you would fare in an unsighted test, same as Disbeliever, it would be worth it to have the two of you in the same room doing such..
ROFL...
Edits: 07/10/15
Evidence please of their being disproved? I don't know what tubes you have heard but drums sound anything but slowed and blurred through good tubes and you hear much more of the volume of the instrument as well as the sound texture of the skin of the drum with tubes...with SS it is often little better than an undifferentiated thud and in better cases the leading edges but little body.
there is an artificial ambiance from the toobs,
I disagree...there is an unnatural truncation of sound decays with SS amps that have (added) negative feedback. This destroys natural ambience that is on the recordings. Crowhurst noted this be demonstrating that a signal modulated noise floor would arise that would mask low level signals when feedback is applied.
Or perhaps you unsighted for that matter.
This is absolute nonsense, if drums sound best via SS, so do single instruments both stereo & especially mch. well designed SS amps do not produce unnatural distortion, tube amps probably do.
Edits: 07/11/15 07/11/15
Read the paper by Boyk and Sussmann...transistors are distinctly less linear than tubes and in Class AB they make a lot of crap. They make plenty of unnatural distortion...
You need to hear the Rotel Cab .............
Of course I do...
Spending more than the Rotel 1552 MK2 costs is a waste of money unless you require more than 120 wpc. OTH the input sensitivity is 1.5 volts and I prefer an amplifier with more gain say input sensitivity of.75 volt to I volt,my own amp is 1 volt. The bigger 200 wpc Rotel has a for me unacceptable input sensitivity of 2 volts.
Edits: 07/12/15 07/12/15
Why? Do you honestly believe that the Rotel is the pinnacle of sound quality? Do you think that all amps sound the same?
I should get 3 and tri-amp my system ........ :)
I do not know which amp is the pinnacle of SQ does it exist ? , depending on speakers IMO there is no point in buying a more expensive amp than the Rotel 1552 MK2 provided the input sensitivity is compatible with your pre. The 200 wpc model is not as far as I am concerned and I sold it on . I definately do not think all SS amps sound the same. some like the Class D I have auditioned are unlistenable. Whilst some antique valve amps are listenable they are full of problems, Cost, Heat, Housing, deterioation etc. etc.
Edits: 07/13/15 07/13/15 07/13/15
I am turned off by all antique valve amps because of the euphonic coloration they produce, plus heat ,deterioation etc.etc.
Edits: 07/09/15
Morri, has recommended some really good toobs , you should give them a try,
:)
I would not touch hot antique tubes with a barge pole
Your comments are not worthy of discussion.
Cab ,
You do realize degeneration is feedback, interesting proposition in your zero feedback amplifiers and why does it matter , it's all about the sound , correct ?
Regards
Morri , Too much ? Is this why you don't like the VTL house sound ...?
You are putting words into my mouth, A. Wayne. I never said I dislike the VTL "house sound" as you put it. I just like other designs better but the models I have heard were not bad sounding just not amazing sounding.
Lol , OK Cab ,
I must have gotten our previous 2000 conversations on this mixed up , I thought we had agreed the VTL house sound was off your list , when we disagreed about you taking Lamm off the very same List .
It's a tuff list , when Lamm and VTL can't make it ......................., :)Regards
Edits: 07/07/15 07/07/15
I agree, but so far I have only taken the Lamm hybrids off the list...I rather like the all tube models.
And I would even say, expanding, including in the price bracket where Benchmark resides ($3K). No need nor reason to settle for product from a company with strong track record of chasing lowest THD numbers possible, and producing bad sounding gear in the process.
who enjoy them too...
try it! you know you want to!
.
I see that good ol' Benchmark doesn't disappoint - its music-making abilities are just as good as those of early generation DAC-1, which I sent back, with a sigh of relief, mere 2 weeks into evaluating.
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