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Review and Measurements of Benchmark AHB2 Amp

walt99

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Hi Guys,

is there any way to connect the AHB2 in bridge mono mode ,without using the Speakon connector ?

The 2 "red" outputs marked as m+ and m- which is not clear to me.

thanks
Yes thats correct; • Use M+ and M- for the output in MONO mode.
 

Dgob

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Snce you have 2 AHB2, I would suggest you try to biamp the F208 too, instead of bridge mono.

Not saying which one is better, just test it out yourself which one you like more.

I myself like biamp more than bridge.
I have 3 AHB2 , for LCR.

To be honest, the design of the AHB2's and their User Manual strongly favour bridged mono using SpeakOn cables. I do not deliberately exaggerate in saying that this has produced a performance that is quite phenomenal.

However, I live in the umbra of my ignorance, and so how do you feel that these factors might relate to your biamp preference in this instance?

Also, if I were to adopt an external active cross-over, wouldn't it be suggesting that I can re-engineer the F208 cross-overs better than the good folks at Revel/Harman?
 
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Laserjock

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How much lower will the damping be to go from biamp > normal stereo > bridged mono using the Revel F208 as an example?
 

Hipster Doofus

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A newbie here so be kind…. Would it make any sense to run my gustard x16 into my Chinese clone tube preamp and then into the benchmark, the tube pre amp only has rca input ant output. Thanks, Some people say there is no pre amp like NO pre amp.
 

DonH56

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How much lower will the damping be to go from biamp > normal stereo > bridged mono using the Revel F208 as an example?

Damping factor is DF = Zload/Zamp so for bi-amping Zamp (amplifier output impedance) does not change from normal stereo. In bridged mode you are using both amp channels in series (out of phase) so effectively output impedance is doubled and thus damping factor is halved: DF = Zload/(2Zamp).

HTH - Don
 

DonH56

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A newbie here so be kind…. Would it make any sense to run my gustard x16 into my Chinese clone tube preamp and then into the benchmark, the tube pre amp only has rca input ant output. Thanks, Some people say there is no pre amp like NO pre amp.

Sure. If it is only a preamp, then you need an amp, and that won't hurt anything.
 

Laserjock

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Damping factor is DF = Zload/Zamp so for bi-amping Zamp (amplifier output impedance) does not change from normal stereo. In bridged mode you are using both amp channels in series (out of phase) so effectively output impedance is doubled and thus damping factor is halved: DF = Zload/(2Zamp).

HTH - Don
Ah, that’s what I was thinking but wasn’t sure about biamping being better than stereo.
Maybe that’s why biamping might be better if you don’t need the power that bridged gives ?
 

DonH56

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Ah, that’s what I was thinking but wasn’t sure about biamping being better than stereo.
Maybe that’s why biamping might be better if you don’t need the power that bridged gives ?

Maybe, but that's a rabbit hole I don't feel like heading down... It depends upon the speaker's impedance, amplifier's output impedance (both of which vary over frequency), and your perception as frequency response and other parameters change. There is also the (valid) argument that bi-amping (even "AVR passive") isolates the upper and lower drivers so they do not modulate each other through the wires and amplifier's output impedance, but again I remain skeptical. Some have done it and reported benefits in blind testing so I suppose it is possible. I am too cheap and lazy. :)

I have bi-amped my system in the past, using an active or passive crossover network before the power amps, but for the past few years have not felt it worth the effort. I am not a believer in "passive bi-amping" as implemented by an AVR; there are theoretical advantages, but in practice I suspect it is inaudible. By and large my choice the past few years (10 or 20, who counts anymore? ;) ) has been to get a single amplifier big enough to do the job and be done with it. We are long past the days when 10 or 20 W was typical and a 100-W amp a rare and expensive thing...
 
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Laserjock

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Maybe, but that's a rabbit hole I don't feel like heading down... It depends upon the speaker's impedance, amplifier's output impedance (both of which vary over frequency), and your perception as frequency response and other parameters change. There is also the (valid) argument that bi-amping (even "AVR passive") isolates the upper and lower drivers so they do not modulate each other through the wires and amplifier's output impedance, but again I remain skeptical. Some of done it and reported benefits in blind testing so I suppose it is possible. I am too cheap and lazy. :)

I have bi-amped my system in the past, using an active or passive crossover network before the power amps, but for the past few years have not felt it worth the effort. I am not a believer in "passive bi-amping" as implemented by an AVR; there are theoretical advantages, but in practice I suspect it is inaudible. By and large my choice the past few years (10 or 20, who counts anymore? ;) ) has been to get a single amplifier big enough to do the job and be done with it. We are long past the days when 10 or 20 W was typical and a 100-W amp a rare and expensive thing...
Very true, never tried it but was speaking of this particular amp for two member’s comments on the two options and possible reason for their differences.
 

Langston Holland

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How much lower will the damping be to go from biamp > normal stereo > bridged mono

Damping factor will be cut in half when bridged, but it doesn't matter.
Would it make any sense to run my gustard x16 into my Chinese clone tube preamp and then into the benchmark

Depends on your goal. If you want the least distortion and noise, connect the balanced output of your DAC directly to the AHB2 and use the lowest gain setting on the amp that still allows you to achieve the maximum loudness you want.

When using the AHB2 with an unbalanced source, you should short pins 1 and 3 on the amp's balanced input. That is also the default behavior of RCA to XLR male adapters and adapter cables.
 

misterdog

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Some people say there is no pre amp like NO pre amp.

Hence the Topping pre 90.

If you like all the distortion produced by the Chinese pre then there is no gain from having the AHB2 IMO.

But hey we all have opinions, so try Gustard/XLR >AHB2 and Gustard RCA>CPA>AHB2 and let us know which you think sounds better.
 

DSJR

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Damping factor will be cut in half when bridged, but it doesn't matter.
I know it as Damping factor as drilled into me by Crown amps in the mid 70's, but I suspect the question ought to be if by going bridged, what's the output impedance then (I did work it out from the Stereophile measurements and apart from a potential half a dB change over 10khz which many of us oldies can barely hear these days? the rest of the range isn't an issue at all really).
 

DonH56

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I know it as Damping factor as drilled into me by Crown amps in the mid 70's, but I suspect the question ought to be if by going bridged, what's the output impedance then (I did work it out from the Stereophile measurements and apart from a potential half a dB change over 10khz which many of us oldies can barely hear these days? the rest of the range isn't an issue at all really).
Output impedance doubles when bridged as you now have two amps in series with the speaker terminals. Damping factor = Zspeaker/Zamp.
 

pma

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Can you hear this ?

No if there is not extensive modulation of FR. However, as any of the bridged amp halves sees half of the load impedance, current limitation may occur and this is extremely audible.
 

DonH56

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PGAMiami

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I’m using 4 ABH2s, all in bridged mono mode in a biamped system. They sound fabulous and replaced my beloved Constellation Centaur mono amps that cost much much more. Over the years I’ve had many amplifiers. These ABH2s combine the best attributes of them all. The timbre, musicality and smoothness rivals the Pass amps. Transients and transparency is on par with the various Spectral. Bass and dynamics exceeds what I obtained with vintage Levinson , MXB and Cello. And practically is right there with the Belcanto digital amps. Add to that, customer service is outstanding. Only areas where these hyper expensive audiophile amps exceeded the ABH2 were cosmetics and bragging rights.
 

PGAMiami

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Regarding damping factors and current limiting, the output impedance on the ABH2 is low enough that doubling it by bridging the amps should make little or no difference in sound quality into almost any speaker. There is more than enough current capacity. Also these amps have a regulated power supply, which is rare even in the most expensive audiophile products. This will also stiffen the current output. In bridged mode the voltage swing is double, which the quadruples the power, up to the current limits of the regulated power supply and protection circuits. The amps also will let you know if they are clipping with the LED indicators. If they are not, then they are performing within spec for ultra low noise and distortion. Engineering is the science of compromise, meaning you typically cannot optimize all parameters simultaneously, so one must decide what trade offs yield the largest overall improvements. In my case that was clearly to bridge, doubling the output voltage, as the amps have ample current capability to hold those voltages at even the maximum volume levels I would ever want from my speakers.
 

PGAMiami

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Another way to look at this is every amplifier within have a maximum voltage that it can swing and a maximum current that it can supply. The bridge vs vertical biamp decision is then about which ones of these limits make the bigger difference in the sound quality of your sound system. In my case I’m bridging and biamping, with 4 amps and with an active crossover. It does sound fabulous.
 
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