Benchmark AHB2 design

[PristineSound]

Also, keep in mind, for every 3dB SPL increase, you need to double the amplification power.

 

[Hear Here]

I want to reassure everyone here that you cannot tell any difference between a Hypex, Purifi and AHB2, level matched. I have both, the AHB2 and Hypex, there are no audible differences. In fact, with most competently designed amps, there is no difference.

I couldn’t agree less, I'm afraid!

Over the last 20 years or so, I've had numerous amps in my system and the only reason for them being there (or being rejected) is their sound quality when used with my high sensitivity speakers.

The two amps that have seriously disappointed (though not the "worst" sounding ones as I take expectations into account) were the Red Wine Signature 30 Mk II and the AHB2. The former was a 30 watt battery powered amp that was amply powerful enough for my 101 dB speakers, but the use of a Tripath Evaluation board was what really let it down, despite many favourable reviews at the time.

The Benchmark was another amp I had high expectations of as it was raved about by a fellow Avantgarde speaker owner (he had Trios, I had lowly Unos), but this was early on when no worthwhile reviews were available and the only dealer stocking it in the UK was 400 miles away. I bought it unseen and unheard. Nicely built, amply powerful enough, great features such as selectable gain and exceptionally good measurements. However, for me, measurements are secondary to the sound they deliver and the "excitement factor" they generate in the listener. This has to approach that of a live performance in a concert hall. Sadly, even after 3+ months of ownership, the Benchmark remained dull. There was a temptation to TURN DOWN the volume of music I'd normally like to TURN UP the volume of to get excited about. It was more like Muzak than music and this is not what I expect from speakers known for their excitement potential.

This unfortunate purchase led me to buy or borrow from dealers a wide range of ss amps of A, AB and D classes in an attempt to get the speakers sounding as I knew they were capable of. Other amps, such the GamuT D200 Mk III, NAD M32, Accuphase A36 and others delivered music way better than the AHB2, but of course others were worse including a Sugden Masterclass (to my surprise) and a Quad. In the end I went for the Purifi Eigentakt technology found in the NAD33. This does not use the cheap Eval board than so many Purifi amps feature, but a built-under-license board with enhancements to NAD's requirements.

There is no way anyone could claim that all amps (presumably within a given price range) sound the same – they just don’t, whatever their measurements may suggest. I liked the Benchmark in most respects, but not the way is delivered music. For me, this is the sole reason for choosing one amp (or more so one speaker) against another.

 

[jmdesignz2]

You are 100% correct. Not a lot of people know, but the AHB2 has a myriad of protection mechanisms - hence another reason why it is the best amp of all time.

From the AHB2 manual.
View attachment 479787

Though, I gather others here are talking about other amps that's being pushed to clipping. However, merely being underpower without pushing your amp to clipping will NOT damage any speakers.

Yes. IF an amp doesn’t have sufficient protection when it clips it can damage speakers. These are all well known facts

What’s interesting here is the AHB2 actually ALLOWS “occasional clipping” but when it senses whatever threshold it vaguely deems as “severe overdrive” it goes into a handicapped limp mode and must be restarted. To me that’s a bit dumb.

 

[jmdesignz2]

Addressing this at face value of the exact words used actually can be disputed:

“PristineSound said:
I want to reassure everyone here that you cannot tell any difference between a Hypex, Purifi and AHB2, level matched. I have both, the AHB2 and Hypex, there are no audible differences. In fact, with most competently designed amps, there is no difference.”

Yes one must be pedantic to argue against this. I understand the concept Mr pristine is trying to convey which I believe is better stated “competently designed amps at 2.8vrms output into a set resistance sound the same, poor or intentionally colored amps will sound different

HOWEVER. IF level matched one most certainly can tell a difference. Since he didn’t specify the level. I would pick the level at which the AHB2 experiences clipping and even “severe overdrive” whereas the more powerful amps would still sound normal

Ultimately most don’t listen to tone signals or frequency sweeps running through a set resistor value. THERE ARE speaker interactions and dynamics to contend with

 

[voodooless]

Also, keep in mind, for every 3dB SPL increase, you need to double the amplification power.

Even better: if you want something to sound twice as loud, you need 10x the power (10dB)!

 

[rdenney]

Yes. IF an amp doesn’t have sufficient protection when it clips it can damage speakers. These are all well known facts

What’s interesting here is the AHB2 actually ALLOWS “occasional clipping” but when it senses whatever threshold it vaguely deems as “severe overdrive” it goes into a handicapped limp mode and must be restarted. To me that’s a bit dumb.

Actually it's not dumb at all. The peaks are going to look almost like a random variable. Finding the absolute peak in an entire recording and adjusting the loudness to avoid that little peak clipping would be pretty hard to do.

And if you play vinyl LPs--fuggedaboutit. One scratch will make a max-output click that will clip any amp if the music is at near its linear capability.

Clipping adds unwanted harmonic content--more high frequencies. Voice coils in tweeters can either handle it or not. But those high distortion peaks won't be any louder than the main signal (in terms of voltage that is insensitive to Fletcher-Munson--hearing is another matter), and any decent speaker should survive it just fine if it's kept within reason. Eventually, enough high-frequency content gets into the steady state that it can overload and overheat the tweeter voice coil, but that doesn't happen on short transients, clicks, and pops. (It can easily happen in just a few seconds playing a sustained top-octave signal like a sine wave at maximum power.) Most pros will look for the point at which the clipping indicators flash for very short periods occasionally--LED's are faster than voice coils. I rather doubt that at the listening levels associated with those occurrences anybody will be able to detect a few milliseconds of clipping, or at least be sure what they are hearing is the amp and not their ears.

But if even sustained harmonic distortion at lower frequencies cooked speakers routinely, no guitar amp these days would still be breathing.

So allowing occasional flashes of clipping but going into protection on sustained clipping sounds about right to me.

Rick "if it sounds bad, turn it down" Denney

 

[PristineSound]

There is no way anyone could claim that all amps (presumably within a given price range) sound the same – they just don’t, whatever their measurements may suggest. I liked the Benchmark in most respects, but not the way is delivered music. For me, this is the sole reason for choosing one amp (or more so one speaker) against another.

This silliness of a topic has been talked to death. I'll let others talk to this.

 

[PristineSound]

Since he didn’t specify the level. I would pick the level at which the AHB2 experiences clipping and even “severe overdrive” whereas the more powerful amps would still sound normal

Ah ha, you caught me! You got me, you got me good man. . .you got me real good.

 

[PristineSound]

Actually it's not dumb at all. The peaks are going to look almost like a random variable. Finding the absolute peak in an entire recording and adjusting the loudness to avoid that little peak clipping would be pretty hard to do.

And if you play vinyl LPs--fuggedaboutit. One scratch will make a max-output click that will clip any amp if the music is at near its linear capability.

Clipping adds unwanted harmonic content--more high frequencies. Voice coils in tweeters can either handle it or not. But those high distortion peaks won't be any louder than the main signal (in terms of voltage that is insensitive to Fletcher-Munson--hearing is another matter), and any decent speaker should survive it just fine if it's kept within reason. Eventually, enough high-frequency content gets into the steady state that it can overload and overheat the tweeter voice coil, but that doesn't happen on short transients, clicks, and pops. (It can easily happen in just a few seconds playing a sustained top-octave signal like a sine wave at maximum power.) Most pros will look for the point at which the clipping indicators flash for very short periods occasionally--LED's are faster than voice coils. I rather doubt that at the listening levels associated with those occurrences anybody will be able to detect a few milliseconds of clipping, or at least be sure what they are hearing is the amp and not their ears.

But if even sustained harmonic distortion at lower frequencies cooked speakers routinely, no guitar amp these days would still be breathing.

So allowing occasional flashes of clipping but going into protection on sustained clipping sounds about right to me.

Rick "if it sounds bad, turn it down" Denney

Well done, you said everything I would like to say but only more elegant.