Benchmark ABH2 Mono Block Configuration

[JFRMusic]

I’ve posted this inquiry in another forum as well with some interesting responses. So I’d welcome any experience from this forum as well

I've owned the Benchmark ABH2 Amp for a few years but am now considering one two alternative upgrade paths:
A New Amp or adding a second AHB2. If I purchase a new amp so far I like the Bryston 3BCubed which is a dual mono design with 200 watts into 8 ohms or possibly the 4BCubed at 300 watts. In either case this is more power than the single ABH2 at 100 watts into 8 ohms. However adding a second ABH2 increases the power per channel to 380 watts .
So much for raw power. What about overall sound quality? The Bryston 3BCubed got an excellent review on Absolute Sound as an amp that would require significantly more $$ to better. Another review I read easily preferred the Bryston 43Cubed (300 watts per channel) over the ABH2.
I'm in the process of completely upgrading my system after several years of the same components. I will shortly have:
An Aurender N20 Streamer into an MSB Discrete DAC with dual power supplies feeding the single ABH2 which drives my Harbeth C7es-XD speakers.
Everything will be new except the older ABH2. Hence the consideration of an amp upgrade.
Now Benchmark will tell you that adding a second ABH2 is only needed when the single amp clips. Other than that there is no sonic benefit to adding a second. I Ffnd that hard to believe. I would think having a second would offer improved soundstage, separation and possibly better performance from the speakers. So my question is:
Have any of you added a second ABH2 and if so what were the overall sonic benefits if any? Also any opinion or experience on the Brystons vs the Benchmark? Or any suggestions of a better upgrade path would be welcomed.
jfrmusic

 

[steve59]

I haven't used the Benchmark. One thing I've found is some speakers i've owned show little or no change with regard to source while some speakers can change dramatically to source. I can't afford to swing and miss, so I try what I think I want with what I have first. When I buy a new product and decide I don't like its sound I'll be told it's not broke in yet, so I borrow the floor demo for a weekend b4 deciding.

 

[DonH50]

I have little exposure to either amp. Benchmark has lower distortion and noise and draws less power on average so runs much cooler. It has pretty extensive monitoring for protection and clipping. Crosstalk is very low so I do not see a second amp increasing separation, nor understand how soundstage would be impacted unless the amp is clipping. The AHB2 (not ABH2) has very low distortion at low power levels where you likely listen most of the time. Note your speakers are 6-ohm nominal so you will get more than the 100-W 8-ohm spec of the Benchmark, and they are rated for 150 W program max power, so an AHB2 bridged pair or the Bryston could potentially overdrive the speaker.

It seems unlikely you would benefit from either amp, but it is hard to resist scratching the itch. If it were me, and I just had to get something, I would get a second AHB2 even though I have been a Bryston fan for many years.

 

[JFRMusic]

DonH50
I would be very interested in your experiences with Bryston specifically what makes you a fan.

 

[Kal Rubinson]

Now Benchmark will tell you that adding a second ABH2 is only needed when the single amp clips. Other than that there is no sonic benefit to adding a second. I Ffnd that hard to believe.

Why is that hard to believe?

I would think having a second would offer improved soundstage, separation and possibly better performance from the speakers.

Soundstage? Unlikely to better than a single stereo amp.
Separation? Only if the separation of the single amp channels is inadequate.
Better performance? Too nebulous to say.

Have any of you added a second ABH2 and if so what were the overall sonic benefits if any?

I've added a second and a third but my reasons were based on the ergonomics. There were ocassions when I used one in stereo config but I cannot recall anything notable, one way or the other.

 

[JFRMusic]

Kal

Thanks for your reply. Can you suggest an upgrade path from the Benchmark. So far it seems a difficult amp to better.

 

[Kal Rubinson]

Kal

Thanks for your reply. Can you suggest an upgrade path from the Benchmark. So far it seems a difficult amp to better.

The problem is in the term "better." There are many other excellent amplifiers and I will not deny those who choose other than the Benchmark. What, specifically, do you need to fix or improve or, alternatively, how does the current amp fall short?

 

[JFRMusic]

Kal
I feel the weakness of the Benchmark to me is a forwardness in the upper midrange and lower treble where I also sense a very slight grain. This may be attributed to the DAC3. I will find out once my Aurender and MSB DAC arrive. I plan to drive the Amp direct from the MSB.

 

[DonH50]

DonH50
I would be very interested in your experiences with Bryston specifically what makes you a fan.

I used one many years ago and have touched on them now and then since but not recently. They are very reliable, old-school amps (heavy and hot). Sonically they bested Crown that was all the rage for high power back then and also Phase Linear (the least-reliable amp I have ever owned). Bryston is just a solid amp design.

Today I would get an AHB2, however, based on reviews, measurements, and opinions of those I respect (including Kal). Plus my back is less able to handle the weight of the big Bryston (or any other) amps. The AHB2 has small size, low weight and heat, lower distortion, and a modern circuit design, all of which appeal to me.

I find it hard to believe the Benchmark exhibits grain unless it is clipping as indicated by the display LEDs. The problem with listening for weakness is that you will always find it, but nailing down the exact cause is almost impossible (source, electronics, speakers, ear/brain system...)

 

[JFRMusic]

Kal

I forgot one other item. I feel that while the soundstage depth is good it’s always between and behind the speakers so not much 3D expansion beyond the speakers. This has been the case with my previous ATC speakers and the Harbeths I now have.

 

[Kal Rubinson]

Kal
I feel the weakness of the Benchmark to me is a forwardness in the upper midrange and lower treble where I also sense a very slight grain. This may be attributed to the DAC3. I will find out once my Aurender and MSB DAC arrive. I plan to drive the Amp direct from the MSB.

Kal

I forgot one other item. I feel that while the soundstage depth is good it’s always between and behind the speakers so not much 3D expansion beyond the speakers. This has been the case with my previous ATC speakers and the Harbeths I now have.

The problem with listening for weakness is that you will always find it, but nailing down the exact cause is almost impossible (source, electronics, speakers, ear/brain system...)

That's one thing. The other thing is that "a forwardness in the upper midrange and lower treble" is a universal assessment nor is it supported by measurements of the amp. Personal preference may be the issue and that cannot be discounted nor should it.

 

[audiobomber]

I am not a fan of bridging amplifiers, which results in cutting both the impedance and damping factor in half. Sure, it will play louder, but looser.

Loudness or voltage clipping is rarely the main problem in audiophile systems. Most are more likely to suffer from current clipping, which means insufficient current to supply the loudness or transient demand. Current capability is the reason a 25W Pass amp sounds more muscular than a 200W mass-market receiver.

I have a friend with a pair of Bryston 3B-ST power amps, driving B&W 802 speakers. The speaker specs say 90dB spl (2.83V 1m), 8 ohms (minimum 3.4 ohms). The retailer set her system up with one amp per channel, bridged, which resulted in a minimum impedance of 1.7 ohms. That is a brutal load for any amp. I thought it sounded awful, so I rewired for vertical bi-amp mode, one amp channel driving the woofers on one speaker, the other channel driving the mid and tweeter. The difference was night and day better.

If you feel the need, my advice is to forget bridging and either add another Benchmark for vertical bi-amping, or else choose a different amp altogether.

 

[DonH50]

I am not a fan of bridging amplifiers, which results in cutting both the impedance and damping factor in half. Sure, it will play louder, but looser.

Loudness or voltage clipping is rarely the main problem in audiophile systems. Most are more likely to suffer from current clipping, which means insufficient current to supply the loudness or transient demand. Current capability is the reason a 25W Pass amp sounds more muscular than a 200W mass-market receiver.

I have a friend with a pair of Bryston 3B-ST power amps, driving B&W 802 speakers. The speaker specs say 90dB spl (2.83V 1m), 8 ohms (minimum 3.4 ohms). The retailer set her system up with one amp per channel, bridged, which resulted in a minimum impedance of 1.7 ohms. That is a brutal load for any amp. I thought it sounded awful, so I rewired for vertical bi-amp mode, one amp channel driving the woofers on one speaker, the other channel driving the mid and tweeter. The difference was night and day better.

If you feel the need, my advice is to forget bridging and either add another Benchmark for vertical bi-amping, or else choose a different amp altogether.

Bridging doubles the output impedance, not halves it, but yes damping factor is halved. DF = Zload/Zamp and Zamp is doubled.

For short peaks most clipping is voltage-based IME.

 

[MarkusBarkus]

...a data-point for the thread: I have two experienced audio friends that each have the Benchmark amps. They brought them together and evaluated the dual model in each respective system. Both gents preferred the single-amp in their respective systems/rooms. Speakers, cabling, power, etc. were different between those systems.

 

[Hear Here]

I’ve posted this inquiry in another forum as well with some interesting responses. So I’d welcome any experience from this forum as well

I've replied to you posting on "another forum" so won't repeat here.

Only to add that changing speakers will make a massive difference to the rendition of music, whereas changing amp makes a much smaller, more subtle difference, This means that if you are not changing your speakers, you should audition a range of amps within your budget range to establish which sounds best to you.

Don't be over-influenced by others' suggestions (even my own!), because they are not using the same speakers that you have. Also, in my view, take little note of quoted or reviewer-generated measurements. Modern amps are all pretty accurate and it's the unmeasurable "character" of the amp that has to gel with the character of your particular speakers. When you get this right, your music listening experience will be at its maximum enjoyment factor.

 

[lordcloud]

I have two AHB2'S. Initially having one and then adding the second.

In my system, to my ears, adding the second amp made everything bigger, easier, and on a larger scale. Even though I have relatively sensitive speakers at 91db, and I listen very much in the nearfield.

I would say that two AHB2'S are a no brainer.

Henri

 

[MarkusBarkus]

...that's very interesting @lordcloud
Thank you for posting.

 

[audiobomber]

Bridging doubles the output impedance, not halves it, but yes damping factor is halved. DF = Zload/Zamp and Zamp is doubled.

The equation is correct, but your conclusion is not. Load increases as impedance decreases:
"For a given output voltage swing, the lower the impedance the higher the amplifier load. Bridging is used to allow an amplifier to drive low loads into higher power, because power is inversely proportional to impedance and proportional to the square of voltage, according to the equation

. This equation also shows that bridging quadruples the theoretical power in an amplifier, however this is true only for low enough loads."

Bridged and paralleled amplifiers - Wikipedia

en.wikipedia.org

For short peaks most clipping is voltage-based IME.

I disagree. Voltage clipping happens only at maximum voltage output, and is so ugly with a transistor amp, that you will quickly reach for the volume control to turn it down. Current clipping occurs even at low output levels, whenever current is not delivered quickly enough to fully power a transient swing. It does not cause gross distortion like voltage clipping. Current clipping causes loose bass, grit, and soundstage collapse. In other words, poor sound quality like you get with a crappy amp.

Speaking of distortion, I neglected to mention in post #12 that distortion increases with bridged amps. Bridging is great for professional sound reinforcement, not for audiophile use.

 

[DonH50]

The equation is correct, but your conclusion is not. Load increases as impedance decreases:
"For a given output voltage swing, the lower the impedance the higher the amplifier load. Bridging is used to allow an amplifier to drive low loads into higher power, because power is inversely proportional to impedance and proportional to the square of voltage, according to the equation

. This equation also shows that bridging quadruples the theoretical power in an amplifier, however this is true only for low enough loads."

Bridged and paralleled amplifiers - Wikipedia

en.wikipedia.org

Ah, I was looking at your comment from the wrong perspective. The actual (speaker) load impedance does not change; the impedance at the speaker terminals is the same whether the amp is bridged or not. I agree, the effective load seen by the amplifier does change, however, and is halved. I misinterpreted your statement, sorry, I was thinking of the actual load (speaker) and not the effective load seen by a bridged amplifier.

The Wiki explanation is a little misleading; reads like it was written by someone designing car amplifiers where low-impedance speakers and bridged amps are common to ease power supply design. Power is theoretically quadrupled no matter the load, but most amps (car or home) run into current or thermal limiting trying to deliver that much power constantly. IME (which again may not match yours) most bridged amps are rated for closer to twice than four times the power of their stereo (two-channel) configuration.

I disagree. Voltage clipping happens only at maximum voltage output, and is so ugly with a transistor amp, that you will quickly reach for the volume control to turn it down. Current clipping occurs even at low output levels, whenever current is not delivered quickly enough to fully power a transient swing. It does not cause gross distortion like voltage clipping. Current clipping causes loose bass, grit, and soundstage collapse. In other words, poor sound quality like you get with a crappy amp.

Not my experience, but experience differs. Your description sounds like current slew limiting, a problem of bandwidth.

Speaking of distortion, I neglected to mention in post #12 that distortion increases with bridged amps. Bridging is great for professional sound reinforcement, not for audiophile use.

Distortion ideally (theoretically again) decreases due to suppression of even-order harmonics in bridged mode. In practice other factors come into play, like matching of the two amplifier stages, and the impact of the effective load reduction. Channel imbalance between channels is sometimes such that low-order products are reduced but high-order terms increased, sort of the worst possible situation for listeners.

Bridging also theoretically improves common-mode noise rejection, but in practice noise rejection at the output of an amplifier is so high to begin with that it does not matter, and again the improvement (if any) is a function of how well the channels are matched.

One other thing to remember (and I know you know this) is that both output terminals of a bridged amplifier are "hot"; connecting either side to ground shorts the amplifier's output. I have seen that many times over the years, including by folk who should know better, e.g. a tech on a bench putting a 'scope or analyzer across the terminals without ground isolation. An audiophile example is a guy who bought an external power meter that had a common ground connection instead of isolating all the meter inputs; when he hooked it to his bridged amplifiers, the results were undesirable.

Bridging is a relatively easy way to provide greater power without needing to raise voltage rails or redesign the amplifier channels, but I certainly agree there are drawbacks. IIRC Bryston offers some (internally) bridged amp designs as monoblocks, as do others, and people seem to value them. Whatever.