Review and Measurements of Benchmark AHB2 Amp

[gfinlays]

I have a single AHB2 powering my KEF Reference 3 and it sounds wonderful. But I’ve started wondering, with the incredible Class D amp coming out lately, 4 and 5 way speakers don’t need to be in the purview of 100K+ USD territory anymore.

No need for ultra expensive crossovers. And yes, I have a friend who has definitely been cable-snagged and outlet fooled

Indeed, with affordable Class D Amps performing the way they do, a fully active 4 or 5 way speaker is now a relatively affordable proposition.

After my experiment, I had someone tell me that the noise doesn't carry through the DAC, but rather it somehow, in true audiophool testiculating (waving your arms around and talking bollocks) fashion "degrades" the D/A conversion and the only way to remove it is to employ fibre optic isolation via a FMC powered by a LPS. Oh, and I should only use shielded ethernet cables because he clearly heard sonic improvements with shielded cables in his system

 

[mcdonalk]

The efficacy of using the AHB2 in mono mode driving a speaker with a 4ohm impedance was not clear to me from this review. The review briefly discussed this configuration and the low distortion associated with it, and continued to note that the speaker protection switched in and shut the output off. I am interested in using two AHB2's in bridged mode, driving a pair of 4ohm (minimum) speakers. I queried Benchmark about why they do not list specifications for bridged operation into a 4ohm load, and they replied to the effect that they do not list output specifications unless the output has been preconditioned, if memory serves me correctly, at 1/3 output for 1 hour. Under these conditions, the protection mode would be asserted, which seems to be supported by the review here. Benchmark further assured me that this pre-condition did not represent actual conditions when playing music, so I should be fine. In any case, my speakers will be protected. In fact, Benchmark said, the AHB2 can perform reliably at lower impedances than 4 ohms. So, my question is, can two of these in mono mode drive 4ohm speakers witih a sensitivity of 87 dB/1W/1m minimum?

 

[gfinlays]

From Benchmarks specifications for the AHB2:

33.16 dBV, 35.38 dBu, 45.52 Vrms into 4 Ohms, bridged mono

Use dBV to calculate the peak SPL from your speaker/amplifier combination. Use the following formula: Amplifier output voltage in dBV + speaker sensitivity at 2.83V - 9 dB. Example: (29.03 dBV at 8 Ohms) + (90 dB SPL @ 2.83V 1m) - 9 dB = 110 dB SPL at 1 meter

In your case, 33.16 + 87 dB (assuming the (a) @1W is actually @ 2.83 Vrms, otherwise it's (b) 90 dB @ 2.83 Vrms) -9 dB = (a) 111.16 dB SPL @ 1 metre or (b) 114.16 dB SPL @ 1 metre.

85 dB (A weighted) is the level at which hearing protection is mandatory in the workplace here in the UK. Dual mono AHB2s into your speakers are more than capable of permanently damaging your hearing, unless you're sitting ~16 m away from them. And that's also assuming your speakers can handle ~500 Wrms.

 

[cheapsoundguy]

I just added a silver Benchmark AHB2 to my system.

The system now consists of an SMSL M400 DAC (AK4499), directly into the AHB2, which powers a pair of B&W 702 S2 speakers. I also have a MiniDSP SHD that I plan to use for DIRAC room correction (I've gone back and forth on using this).

The AHB2 replaces a pair of Outlaw 2200 monobloc amps. The Outlaws caused idle hiss in the speakers regardless of DAC used.

Objectively, the hiss from the B&W 702 tweeters is immediately gone with the AHB2 in the system. At idle, the hiss was audible from about 3 feet away from the speakers.

My subjective impression (sighted) is that detail retrieval is about the same between the AHB2 and the Outlaw 2200s, but I feel that there is a richer timbre to the music and it feels like the treble is also less sharp/crunchy. This last bit is very important to me as I was considering selling the B&W 702 speakers due to a bit of a fatiguing high-end.

I plan to do a level-matched/blinded A/B test using some Little Bear boxes that I have. Will update once I've done that.

Overall, I plan on keeping the AHB and demoting the Outlaw amps to my garage setup. (I do have an attachment to them -- they have traveled with me during 6-7 apartment/house moves over the years. I just checked, I've had the Outlaws for one month longer than I've been with my wife!).

 

[cheapsoundguy]

Question: Does the AHB2 do pure class A until the first watt or few watts? Does anyone know where the A/B power kicks in? Or am I not understanding how that works?

 

[Geert]

Question: Does the AHB2 do pure class A until the first watt or few watts? Does anyone know where the A/B power kicks in? Or am I not understanding how that works?

No Class-A operating range in the AHB2, but that's not what matters. What's important is the low distortion at low levels, which is on par with (or better than) good class-A amps.

 

[cheapsoundguy]

So this is interesting. On some (but not all) recordings, I can hear a slight hiss during quiet passages of music (with my ear about 1 ft away from the tweeter). When it hit mute the hiss goes away.

Does this mean that the music itself has a bit of pink noise in the recording/mastering?

 

[Doodski]

So this is interesting. On some (but not all) recordings, I can hear a slight hiss during quiet passages of music (with my ear about 1 ft away from the tweeter). When it hit mute the hiss goes away.

Does this mean that the music itself has a bit of pink noise in the recording/mastering?

The hiss could be caused by circuitry in place before the mute transistors or it could be in the source music too.

 

[cheapsoundguy]

The hiss could be caused by circuitry in place before the mute transistors or it could be in the source music too.

Sorry don't mean mute -- I mean if the music is put on pause, there is no hiss.

So it seems 99% certain that the hiss is from the source -- as in it's literally part of the recording.

 

[Doodski]

Sorry don't mean mute -- I mean if the music is put on pause, there is no hiss.

So it seems 99% certain that the hiss is from the source -- as in it's literally part of the recording.

Putting a unit into pause oftentimes engages the mute circuitry. So without more details we can only speculate.

 

[RichB]

Question: Does the AHB2 do pure class A until the first watt or few watts? Does anyone know where the A/B power kicks in? Or am I not understanding how that works?

No Class-A operating range in the AHB2, but that's not what matters. What's important is the low distortion at low levels, which is on par with (or better than) good class-A amps.

From the BenchMark website: https://benchmarkmedia.com/collections/all-products/products/benchmark-ahb2-power-amplifier

THE IMPORTANCE OF THE FIRST WATT
Dick Olsher once said that "the first Watt is the most important Watt". We agree! From the first Watt to the last Watt, the AHB2 shows no evidence of crossover distortion.

In contrast, all conventional class-AB amplifiers have crossover-distortion artifacts.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 before they occur.

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 actively drives the output 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.

- Rich

 

[cheapsoundguy]

Putting a unit into pause oftentimes engages the mute circuitry. So without more details we can only speculate.

Sorry I am not being clear. Putting the external DAC into pause is dead silent on the AHB2. The AHB2 has mute lights, these do not engage.

So I guess I am answering my own question -- the hiss is in the music, and when the music source is paused, the audio chain is completely silent.

This was NOT the case with my Outlaw amps, which had hiss when the external source was paused.

 

[restorer-john]

This is just Benchmark writing a yet another deceptive narrative to suit their marketing agenda:

"THE IMPORTANCE OF THE FIRST WATT
Dick Olsher once said that "the first Watt is the most important Watt". We agree! From the first Watt to the last Watt, the AHB2 shows no evidence of crossover distortion.

In contrast, all conventional class-AB amplifiers have crossover-distortion artifacts.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 before they occur."

The second paragraph is a disgrace.

 

[Doodski]

So I guess I am answering my own question -- the hiss is in the music, and when the music source is paused, the audio chain is completely silent.

It appears that is the way this gear is operating.

This was NOT the case with my Outlaw amps, which had hiss when the external source was paused.

Some amps are hissy. It's just the way it is. I had a SAE power amp that was a hisser and a Marantz receiver that was really horrible for hiss. I've handled tens of thousands of home and car audio amps/receivers and most hissed to some degree. It is a good day when one finds a silent amp.

 

[restorer-john]

It is a good day when one finds a silent amp.

The only silent amp is a dead amp, Doodski. That's why it was on your bench.

 

[xaxxon]

This is just Benchmark writing a yet another deceptive narrative to suit their marketing agenda:

"THE IMPORTANCE OF THE FIRST WATT
Dick Olsher once said that "the first Watt is the most important Watt". We agree! From the first Watt to the last Watt, the AHB2 shows no evidence of crossover distortion.

In contrast, all conventional class-AB amplifiers have crossover-distortion artifacts.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 before they occur."

The second paragraph is a disgrace.

Can you expound on your last sentence?

 

[AlexDD]

Would this amp pair up well with a RME ADI-2 DAC FS https://www.audiosciencereview.com/...version-2-dac-and-headphone-amp-review.13379/ or do I also need a pre-amp?

 

[gfinlays]

Sorry don't mean mute -- I mean if the music is put on pause, there is no hiss.

So it seems 99% certain that the hiss is from the source -- as in it's literally part of the recording.

The AHB2 has no hiss - I pulled a -120 dBFS 1kHz test tone into audibility with a DAC3/HPA4/dual mono AHB2s.The HPA4 was at +4dB.

 

[xaxxon]

Would this amp pair up well with a RME ADI-2 DAC FS https://www.audiosciencereview.com/...version-2-dac-and-headphone-amp-review.13379/ or do I also need a pre-amp?

that device you linked has a volume knob so you're good to go. Of course benchmark would say their preamp/headphone amp would be great to pair it with. (that's what I have for the fronts of my home theater system - hpa4 with an input from my AV processor as well as a standalone dac outputting to two ahb2 monoblocks.

 

[xaxxon]

The AHB2 has no hiss - I pulled a -120 dBFS 1kHz test tone into audibility with a DAC3/HPA4/dual mono AHB2s.The HPA4 was at +4dB.

Nice setup- I basically have the same thing except my dac3 is on my computer and I have an x-sabre 3 on my hpa4. Especially with the new firmware, x-sabre3 is a great source

And then I have 3 more ahb2's for my full range center and surrounds.