Review and Measurements of Benchmark AHB2 Amp

[pogo]

Might I ask why you want to know? Do you have a specific problem are you trying to solve or understand. Regards Andrew

Don't get me wrong, I love what Amir or others are doing. But there's more we can do, to understand why we hear what we're hearing.
A lower DF can add higher unwanted speaker deflections in the low frequency range (swing-out area) that do not correspond to the original input signal!
I miss such measurements in the reviews.

 

[RichB]

Don't get me wrong, I love what Amir or others are doing. But there's more we can do, to understand why we hear what we're hearing.
A lower DF can add higher unwanted speaker deflections in the low frequency range (swing-out area) that do not correspond to the original input signal!
I miss such measurements in the reviews.

It may be that lower DF results in the subjective impression of more bass.

- Rich

 

[Coach_Kaarlo]

Don't get me wrong, I love what Amir or others are doing. But there's more we can do, to understand why we hear what we're hearing.
A lower DF can add higher unwanted speaker deflections in the low frequency range (swing-out area) that do not correspond to the original input signal!
I miss such measurements in the reviews.

Not to mention that very little performance is measured in bridged mono, ironically where many AHB2 owners actually use the amplifier.

 

[Sal1950]

the AT522NC which varied by 2.72 to 2.86.

Poor power supply regulation in the AT ?

 

[Speedskater]

Actually, this matching proved a bit difficult. The AHB2 measured a steady 2.85 volts where the AT522NC which varied by 2.72 to 2.86.
This may be due to voltage variance from the power line but, even so, it is interesting.

While low AC line voltage may limit maximum power, line voltage should have no impact on lower level gain.

 

[HammerSandwich]

Could the Ncore's HF confuse the meter reading?

 

[pjug]

Could the Ncore's HF confuse the meter reading?

Interesting thought. You would think the switching characteristics would be consistent if the input does not change. But 5% variation does not seem right. Maybe worth an email to ATI to see if they can explain it?

 

[RichB]

Poor power supply regulation in the AT ?

This has a linear power supply, is there power regulation?
I did these measurements on power up and it seemed to ramp up.

I don't have the AT525NC at my current location so cannot test it again.

- Rich

 

[RichB]

While low AC line voltage may limit maximum power, line voltage should have no impact on lower level gain.

The A/B amp switch was used with the Fluke 87V sine-wave multi-meter connected to the speaker output.
The AT525NC varied from 2.72 to 2.86 volts and when quick-switching to the AHB2 it was stable at 2.85 volts.
It was very simple to switch between the amps.

- Rich

 

[restorer-john]

The A/B amp switch was used with the Fluke 87V sine-wave multi-meter connected to the speaker output.
The AT525NC varied from 2.72 to 2.86 volts

It's possible the Fluke 87V is additionally picking up HF switching noise from the Class D and causing aliasing in its front end A/D converter.

 

[pjug]

The A/B amp switch was used with the Fluke 87V sine-wave multi-meter connected to the speaker output.
The AT525NC varied from 2.72 to 2.86 volts and when quick-switching to the AHB2 it was stable at 2.85 volts.
It was very simple to switch between the amps.

- Rich

Do you have any Class D amplifier available to check? You might put together a low pass filter to put between the amplifier output and the voltmeter. Then see if the reduction in switching residuals makes a big difference in the Fluke measurement.

 

[RichB]

It's possible the Fluke 87V is additionally picking up HF switching noise from the Class D and causing aliasing in its front end A/D converter.

If you say so, but the readings were always stable with the AT525NC just drifting over time, usually minutes.

- Rich

 

[RichB]

Do you have any Class D amplifier available to check? You might put together a low pass filter to put between the amplifier output and the voltmeter. Then see if the reduction in switching residuals makes a big difference in the Fluke measurement.

I do not, but I want to try a Purify A/B to the AHB2 and was looking for a vendor because DIY is not my thing.

- Rich

 

[pjug]

I do not, but I want to try a Purify A/B to the AHB2 and was looking for a vendor because DIY is not my thing.

- Rich

FWIW I measured a little T amp I have at work with a B&K True RMS meter. I get 2.848V with and without a filter (close as I could get with the crappy Lepai volume control). With no input to the amp the meter reads less than 1mV (BUT it takes some time for the value to settle close to zero on the 20V scale, jumping between 0 and 1mV). So it doesn't respond to the switching frequency such that it would affect the level setting like you were doing. Of course it might be another story with the Fluke.

 

[RichB]

FWIW I measured a little T amp I have at work with a B&K True RMS meter. I get 2.848V with and without a filter (close as I could get with the crappy Lepai volume control). With no input to the amp the meter reads less than 1mV (BUT it takes some time for the value to settle close to zero on the 20V scale, jumping between 0 and 1mV). So it doesn't respond to the switching frequency such that it would affect the level setting like you were doing. Of course it might be another story with the Fluke.

Here is the meter:
Fluke 87-V Digital Multimeter - - Amazon.com

Since there is a slow drift, I think the AT525NC is the source of this behavior.

- Rich

 

[walt99]

Thought I would share this note I sent to Rory at Benchmark:

Rory,
I want to cancel my order for the second AHB2 and cables.

Reason: yesterday while the wife was fooling with the TV trying to get it to play through the AVR, I'm really not sure how, but the volume on the AVR got maxed out and when it finally switched over the speakers came on at a very high level and almost blew us over. Thankfully the AHB2 did it's job wonderfully and shut down almost immediately, I'm sure the protection saved my expensive speakers (Revel f328be) from a meltdown.

Had that been a pair of bridged AHB2's, I believe the current spike likely would have been to much for the speakers to handle.
So I think maybe more power is not always a good thing, in this case I'm glad I didn't have the 2nd AHB2 running in bridged mode.

I'm super grateful for the excellent protection circuits in the AHB2, they worked perfectly and saved my speakers yesterday!
When I purchased the AHB2 part of my rationale was for the protection it offered, well that decision paid off.

Thanks for making such a great product!

 

[Geert]

Exactly why I'll never by a power amplifier without a volume control. On professional amplifiers this is standard.

 

[Phorize]

Exactly why I'll never by a power amplifier without a volume control. On professional amplifiers this is standard.

Yep-a bit of incompetence on my part led to me unmuting my rme adi which in turn drove my purifi amp full tilt into a pair of 50 watt speakers. It’s easily done.

 

[digitalfrost]

I had something like this happen with my Sony TA-N77ES. Input sensitivity is specified as 1V. Amp can do 200W/8Ohm. I had it directly connected to the PC. The PC had a problem and the soundcard sent noise at full scale (2V) towards the output. Luckily I had the volume pots at -12dB, but it was still unbelievably loud. I tought my speakers would be blown, but somehow they survived.

 

[pjug]

Here is the meter:
Fluke 87-V Digital Multimeter - - Amazon.com

Since there is a slow drift, I think the AT525NC is the source of this behavior.

- Rich

I think this is probably true. But why? 5% drift seems like a problem. No reason that the Ncore should have this; even though it is Class D it is closed loop with feedback from the speaker connection so it should be stable. As previously mentioned by @Speedskater the line voltage shouldn't affect this.