According to Benchmark the amp in bridged mono the maximum unclipped output voltage is 45.5 Vrms (64.4V peak) into a 4 Ohm load.
I would expect it to be higher. If the rails are 60 volts then the peak volts should approach 120, say 100 Volts with losses, but the current won't support that as 25 amps are needed. BTW 18 amps is not an impressive amount of current for modern amp of that size. Should be more like 40 amps. The Mitsubishi Docking Amp of 1978 delivered 60 amps, I measured it! Something is a little off here and the more I here the more I wouldnt want to bridge this amplifier. I have nothing against bridging in general and have made bridged amps. The reason we bridge amplifiers is when WE DO NOT have a low impedance load. We bridge to get voltage not current. We bridge to get some juice into 8 ohms. When we have 4 ohms we dont bridge. Where are the italics around here? All caps is my best substitute. :) |
georgehifi, my question was in the form of yes/no.
Are you speculating, or do you have actual experience with the amp in different configurations? I repeat, If you have a technical background and understand what happens when you bridge an amp, you wouldn’t be asking this question. Cheers George
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That 18 amp number was a mistake if you read further down it was clarified to be 29 amps. I am not an expert just going by what I read on benchmarks site and various reviews. Benchmark used the amp at a 2017 show to drive a pair of 4 Ohm PCM monitors in bridged mode. Reviewers have used it to drive 8 Ohm, 6 Ohm and 4 Ohm speakers in bridged mode apparently with good results. Actually I agree with you and George I don't really see why 1 amp in stereo would'nt be enough with the OP's efficent speakers that have powered subs so this amp is just driving the mids and highs I assume. But he seems to want 2 amps to try in bridged mode and from everything I have read on this amp it can do it. |
djones51
George I don’t really see why 1 amp in stereo wouldn’t be enough with the OP’s efficient speakers Been there, done that. https://forum.audiogon.com/posts/1647982and here https://forum.audiogon.com/posts/1647933
But he seems to want 2 amps to try in bridged mode and from everything I have read on this amp it can do it.
Not really into 2ohm which is what the amps will think their driving (bridged) and then there's the disadvantages with bridging that I and many on the net outline. If there was no disadvantages then we'd all be using and selling bridged amps. Cheers George |
George I agree with you that with efficient low impedance speakers the OP may likely be better off with a single AHB2. However it’s worth noting that unlike most power amps, the Benchmark AHB2 does not have increasing distortion into lower impedance loads. The bridged AHB2’s distortion is just as low as in stereo mode - the THX AAA circuit takes care of that - the quoted THD+N spec is the same for stereo/mono "at full rated output into any rated load". This has been corroborated by independent measurements. Note that Benchmark only provides power ratings for nominal 8 and 6 ohm loads in bridged mono. In my case the bridged AHB2 amps do sound better than a single AHB2, but my ATC speakers are very different from the OP. The ATC’s are inefficient with high power handling (ATC recommends 75-300W) and have a nominal 8ohm rating with a minimum of 5.6ohms - pretty much the ideal application for the bridged AHB2. Using the amps in mono mode also allows for much shorter speaker cables, which may also have contributed to my positive impressions vs a single stereo AHB2. Having said the above, Benchmark have demoed with bridged AHB2’s on several occasions with nominal 4ohm rated speakers. So clearly they don’t see any issue. Here is a recent positive impression: https://parttimeaudiophile.com/2018/05/21/axpona-2018-benchmark-stays-smooth-with-martin-logan/ |
In my case the bridged AHB2 amps do sound better than a single AHB2, but my ATC speakers are very different from the OP. Yes because your speakers need the extra watts, the OP’s don’t, and that’s what the discussion is all about. I would lay money on it, that if your speakers didn’t need those extra watts, you’d be saying one stereo sounds better that two bridged, regardless of the cost saving. Roger Modjeski (Ramtubes) a few posts back has also tried to say similar. Cheers George |
I would lay money on it, that if your speakers didn’t need those extra watts, you’d be saying one stereo sounds better that two bridged, regardless of the cost saving.
Perhaps. But you did say that "distortion goes up" with bridged amps - however this is not the case with the AHB2 in bridged mono, nor into lower impedances in stereo mode for that matter. So in that respect it is a bit different to most conventional power amps. |
You believe what you want, and I'll believe what I know for the OP's speakers, and that's what this thread is all about.
In general Bridged Amps
Pros=
More watts.
Cons=
Worse damping factor
Higher output impedance (has relevance to damping factor)
Lower stability (especially into low impedance's)
Current ability is reduced
(especially into low impedance's)
Higher distortion.
Cheers George
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I would expect it to be higher. If the rails are 60 volts then the peak volts should approach 120, say 100 Volts with losses, but the current won't support that as 25 amps are needed. The manual states: Output voltage: >80Vpp into any load Output current: 29A peak into 1 ohm, both channels driven BTW 18 amps is not an impressive amount of current for modern amp of that size. Should be more like 40 amps. I presume you mean current compared to power output not physical size? The AHB2 is very small and lightweight. IMO the power/current output - not to mention almost non-existent distortion, super high SNR, efficiency, cool running and (most importantly) resulting purity of sound - are very impressive. Other than bragging rights, I doubt 40A of current has any advantage in driving practical loudspeaker loads. |
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And of course all topologies of amps behave identically when bridged, and no amps are ever specifically designed to be bridged.
Is this sarcasm or what you believe? Can we at least get a little more real, we might just figure out something. |
I presume you mean current compared to power output not physical size?
The AHB2 is very small and lightweight. IMO the power/current output - not to mention almost non-existent distortion, super high SNR, efficiency, cool running and (most importantly) resulting purity of sound - are very impressive.
Other than bragging rights, I doubt 40A of current has any advantage in driving practical loudspeaker loads.
I meant of that size power wise, not physically. Now we have a report of 29 amps. This is like the stock market. Or are we just playing poker and raising? I will bet you that this amp bridged into a 4 ohm load played at 1/3 average power will probably overheat. Where is John Atkinson when we need him? :) 40 amps of current is needed to produce 40 volts peak (100 watts RMS) across a 1 ohm dip in impedance. If this impedance is reactive the amplifier will be really unhappy. ps. I did read the review by JA. It's worth a look but doesnt answer all the questions. It's clear to me what the OP should do. One amp or get busy and truly BiAmp. When are we going to get out of the sandbox? |
@tobes
With all due respect George, it's not a matter of believing what I want.
Implying higher distortion in bridged mode for the AHB2 is incorrect.
This has been independently verified.
Not sure why you keep insisting on this?
https://www.stereophile.com/content/benchmark-media-systems-ahb2-
power-amplifier-measurements
Thanks for this link. JA knows how to measure things. However he did not precondition the amp bridged at 4 ohms. No biggie here, but the OP is asking about bridging at 4 ohms which I am certain would get very hot. My answer to the OP remains the same. Do not bridge this amp into a load that dips below 4 ohms. For that load, the amp will provide more power if not bridged. That analysis does depend on getting some of the facts straight, such as 18 amps vs 29 amps. Guys if you really want to do something. Bypass the crossover in your speaker, crossover at line level with simple RC or active crossover, get two amps and let each see their driver DIRECTLY. Put a monster SS on the bottom and some nice tube or class A SS amp on the top. Generally less poweron top because most tweeters are padded down in the crossover. The crossover in a speaker is its weakest link. |
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@george
I imagine in the 4 ohm bridged mode the current limiting would become apparent. JA is often kind by omission. I think the amp would shut down with a 4 ohm bridged load. Thats like 2 ohms per channel as you well know.
I am just amazed at how well Benchmark marketing has pulled off selling 2x amplifiers.
Now that I am sucked into this I want to study their white papers for veracity. I understand there is some power supply wonderfullness going on. Feedforward is always amusing too. What a world we live in. |
I imagine in the 4 ohm bridged mode the current limiting would become apparent. JA is often kind by omission. I think the amp would shut down with a 4 ohm bridged load. Thats like 2 ohms per channel as you well know. Yes and before it shut down, the distortion would be higher than the 8ohm they did give. I am just amazed at how well Benchmark marketing has pulled off selling 2x amplifiers. Great marketing, all in the wording and the omission of certain measurement graphs. I understand there is some power supply wonderfullness going on.
Yes, like Krells Plateau biasing except done on the voltage rails instead, Quad 405 I think used something similar, and maybe Devialet Class-D amps do something similar also. " Output voltage is variable by a factor of 8 from +/- 10V to +/-80V and constantly changes to minimize overall thermal dissipation." Cheers George |
40 amps of current is needed to produce 40 volts peak (100 watts RMS) across a 1 ohm dip in impedance. If this impedance is reactive the amplifier will be really unhappy. I don't understand it. 40V across 1 ohm (or 40amps thru 1 ohm) would make 1600W. Note: Watts RMS means something different and has no relevance. Power, obtained by multiplying RMS current and RMS voltage is AVERAGE power (equal half of peak power for sinewave). It represents DC power that would produce the same amount of heat. RMS Power does not represent anything useful. AHB2 power supply is highly regulated SMPS capable of producing large currents. As for amp being less stable in bridged mode - AHB2 is designed to be stable since it does not have feedback in traditional sense. Of course in order to reduce distortion that low it has to have negative feedback, but this feedback in not recursive, meaning it is not zapped back to the front of the amp. Instead it drives another amp (error amplifier), with another set of power transistors, that at the very end corrects output signal. Also, low output impedance, doubled in bridged mode, might be important for driving complex loads, but it is already very low, about 0.03ohm @1kHz. For the purpose of damping the speaker membrane it does not matter, since most of the speaker resistive impedance is in series anyway, reducing highest obtainable effective DF to 1.5 |
I don't understand it. 40V across 1 ohm (or 40amps thru 1 ohm) would make 1600W. Kijanki, Thank you. I am glad someone is paying attention.. You are correct it would make 1600 watts. My bad. I appreciate your bringing up the speaker resistive issue which indeed lowers the effective damping factor. Please keep reminding people and good luck getting that point across. From what I read it appears people think damping somehow "controls" the speaker. We know the series resistance limits that control. If we put aside the term "damping" , because thats not what really matters, we need to inform people that an amplifier with high output impedance may cause a marked change in the frequency reponse of their speaker. Thats what really matters. I invite you to the task at hand. |
If we put aside the term "damping" , because thats not what really matters, we need to inform people that an amplifier with high output impedance may cause a marked change in the frequency reponse of their speaker. Thats what really matters.
Yes add that to the other cons, the amp starts to behave like a tone control. (ie: not flat from 20hz to 20khz) Cheers George |
They are very similar yes? what do you think will happen if another measurement was done at 4ohm in the bridged mode????? It will be far worse than the non bridged into 4ohms or 8ohms, that’s why they didn’t give the graph even though they probably did measure it. George, this is speculative at best. The AHB2 has very comprehensive protection. I suspect the bridged AHB2 will maintain its ultra low distortion into low impedances until protection kicks in. If you recall I said this in my initial response above: George I agree with you that with efficient low impedance speakers the OP may likely be better off with a single AHB2. What I took exception to was your incorrect blanket assumption that bridging the AHB2 would result in higher distortion. This is NOT true for the specified 6 and 8 ohm loads. Despite what is specified, Benchmark demos at shows with 4ohm nominal speakers (see link above). Do you think they would do this if the sound quality was compromised? I am just amazed at how well Benchmark marketing has pulled off selling 2x amplifiers. Why are you amazed Roger? Some of us own low efficiency 8 ohm nominal speakers - for which the bridged mono AHB2’s are perfect. Honestly, Benchmark appears to be one of the least marketing oriented companies around. They don’t push BS, they comprehensively measure everything they make and are very much about accuracy and low coloration - not boutique sound tailoring. |
If we put aside the term "damping" , because thats not what really matters, we need to inform people that an amplifier with high output impedance may cause a marked change in the frequency reponse of their speaker. Thats what really matters. Yes add that to the other cons, the amp starts to behave like a tone control.
(ie: not flat from 20hz to 20khz) Oh my gosh, another straw man argument. This may be an issue with some amplifiers. The AHB2 has sufficiently low output impedance that this is not a problem. |
No matter what sort of spin you want to put on it
tobes the fact is that this thread is about the OP and his speakers, and bridged AHB2's are not the way to go into his speakers 4ohm load.
"Bridging good for more watts, but everything else takes a hit."
Cheers George |
@tobes
Why are you amazed Roger?
Some of us own low efficiency 8 ohm nominal speakers - for which the bridged mono AHB2’s are perfect.
Honestly, Benchmark appears to be one of the least marketing oriented companies around. They don’t push BS, they comprehensively measure everything they make and are very much about accuracy and low coloration - not boutique sound tailoring.
I do fine with 35 watts so I am curious what is your listening level and speaker efficiency? Have you measured the peak voltage at your speaker? If not we can estimate it fairly accurately with just your efficiency and SPL at 1 meter. Can you do this for us please? Since you brought up "extensive protection" what happens when this amplifier drives a 10 uF capacitor, typical of many ESLs. What is straw man about informing people that damping not damping but actually a variation in frequency response due to impedance variation that occurrs with high output impedance? I read JA's report. The Benchmark is about as perfect an amplifier as one can imagine. Yet we still dont know its current capability and some other things. This is an issue to a varying degree with many amplifiers, yours excepted, of course. I find the "strawman" accusation most inapproptiate to this thread. We are trying to figure out something here. Does anyone have a schematic for me to peruse? |
Ok, Im really getting into this amp now. Have a look at this white paper, its good, and the amplifier construction, ugh. https://benchmarkmedia.com/blogs/application_notes/14680625-the-ahb2-a-radical-approach-to-audio-pow...I fix rare amps like the Reference Line that one of my customers just loves. It is hard to work on. I like to think I can fix anything but I would not even bother to open up this Benchmark after seeing these photos. A blown up cap is no problem, but if the power supplies shut down or the amp circuits there is no chance in Hell to fix this at the component level at any reasonable cost. Unless these prove unusually relaible I would not want to own one past the warranty. Once the boards become unavailable you will have a nice boat anchor. Has anyone any experence with having one of these repaired? Its all surface mount, perhaps board swapping is the only way. Im sure the factory doesnt mind fixing them because they have the boards to swap around. But try to find even a smart tech who would like to take this on. |
This is John Siau, VP and Director of Engineering for Benchmark Media Systems. I would like to clear up some erroneous information in this thread. The AHB2 is a unique design, so some of the usual assumptions do not apply. 1) The peak output current of the AHB2 is 29 A not 18 A. Many of the posts above are based upon the 18 A number which is incorrect. 2) The SNR of the AHB2 improves by 3 dB in Mono Mode (bridged mono). The signal is 6 dB higher but the noise is only 3 dB higher, producing a 3 dB improvement in SNR when running bridged mono. The low-level noise produced by the two channels of the amplifier is uncorrelated white noise and this is why the noise only increases by 3 dB when using the two outputs differentially. 3) The THD is virtually identical when comparing stereo mode to bridged mono mode. This is achieved through the use of the feed-forward error correction. Every other power amplifier will show a substantial increase in distortion when bridged. 4) All references to "Mono Mode" or "Bridged Mono" on our website or in the AHB2 manual refer to the bridged mono mode of the amplifier. 5) The THD produced by the AHB2 does not increase as the impedance decreases. The THD into 2 Ohms, 4 Ohms, 8 Ohms and no load are virtually identical. Again this is a unique characteristic that is achieved through the use of feed-forward error correction. 6) The AHB2 is not just stable into low-impedance loads, it stays clean when driving low impedances. The THD does not change with loading. 7) We do not specify the output power at 1% THD because, unlike other amplifiers, the THD does not gradually rise as the output level increases. The amplifier maintains 0.0003% THD+N, into any rated load, until the clip point is reached. 8) The rated "continuous average output power" of the AHB2 is not specified below 3 Ohms stereo or 6 Ohms mono because of the FTC regulations (16 CFR Part 432) that require continuous operation at 1/3 rated power for one hour. This is a long-term thermal limitation when playing sinusoidal test signals and has little significance when playing music. It should not be taken as indication that lower impedances cannot be driven cleanly. 9) The AHB2 has a high damping factor and this allows excellent performance in bridged mono. The damping factor is 350 into 8 Ohms stereo and 175 into 8 Ohms bridged mono. The AHB2 will deliver THD+N < 0.0003% at full output voltage into various loads is shown in the following table:
< 0.0003 % THD+N at the following output voltages and load impedances, 20 Hz to 20 kHz - 29.03 dBV, 31.25 dBu, 28.28 Vrms into 8 Ohms, both channels driven
- 28.92 dBV, 31.14 dBu, 27.93 Vrms into 6 Ohms, both channels driven
- 28.81 dBV, 31.03 dBu, 27.57 Vrms into 4 Ohms, both channels driven
- 28.57 dBV, 30.79 dBu, 26.83 Vrms into 3 Ohms, both channels driven
- 27.14 dBV, 29.36 dBu, 22.76 Vrms into 2 Ohms, both channels driven
- 35.05 dBV, 37.27 dBu, 56.57 Vrms into 16 Ohms, bridged mono
- 34.83 dBV, 37.05 dBu, 55.14 Vrms into 8 Ohms, bridged mono
- 34.59 dBV, 36.81 dBu, 53.67 Vrms into 6 Ohms, bridged mono
- 33.16 dBV, 35.38 dBu, 45.52 Vrms into 4 Ohms, bridged mono
Bottom line, the AHB2 is well suited for bridged mono operation into 4-Ohm nominal impedances and the performance is virtually identical to stereo mode except that the power is nearly 4 X higher. Dips in the speaker impedance curve are not a problem and the AHB2 drives these cleanly. The SNR actually improves by 3 dB when running bridged mono, and the THD is virtually unchanged. We almost always demonstrate the AHB2 in bridged mono mode at trade shows and have done so with many different hi-fi and pro loudspeakers. In most cases, these demonstrations have used speakers with a 4-Ohm nominal input impedance. The following link will take you to a series of application notes that discuss the performance of the AHB2 in more detail. They include a plot of THD vs output level under various load conditions: https://benchmarkmedia.com/blogs/application_notes/tagged/ahb2 |
Thanks, great response gearbuilder |
Benchmark have been making ground breaking products for years. They are an embarrassment to most of the old school industry. Out performing incumbent market leaders technically (measurements) by considerable amounts at reasonable cost.
This is healthy and exciting for us as hi-fi customers. Of course reliability is always a concern especially with radical new designs. Time will tell if these new products like the AHB2 and the HPA4 perform as reliably as their DACs.
Of course measurement based design targets measured performance and therefore only address a portion of the market. Flavoured designs like tube amps etc. will always have their important place and many audiophiles will continue to opt for flavour over pure tech specs.
That said. You could consider the AHB2 as a transparent way to drive speakers (if you like the sound of your speakers) and then look to a tube preamplifier to add some sweetness or sizzle to taste.
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As I said previously, better in Mono. :)
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None of what gearbuilder's copy/pasted post spiel from another thread/member. https://forum.audiogon.com/discussions/benchmark-ahb2-amplifier-what-to-expect Has anything to do with the OP's 4ohm speakers, and bridging this amp into them. Sure it's a great stereo amp. Really? Lets look at that. @gearbuilder said: 3) The THD is virtually identical when comparing stereo mode to bridged mono mode. This is achieved through the use of the feed-forward error correction. Every other power amplifier will show a substantial increase in distortion when bridged.
5) The THD produced by the AHB2 does not increase as the impedance decreases. The THD into 2 Ohms, 4 Ohms, 8 Ohms and no load are virtually identical. Again this is a unique characteristic that is achieved through the use of feed-forward error correction.
6) The AHB2 is not just stable into low-impedance loads, it stays clean when driving low impedances. The THD does not change with loading.
Bottom line, the AHB2 is well suited for bridged mono operation into 4-Ohm nominal impedances and the performance is virtually identical to stereo mode except that the power is nearly 4 X higher. Dips in the speaker impedance curve are not a problem and the AHB2 drives these cleanly.
We almost always demonstrate the AHB2 in bridged mono mode at trade shows and have done so with many different hi-fi and pro loudspeakers. In most cases, these demonstrations have used speakers with a 4-Ohm nominal input impedance. Could the OP get more than sufficient volume with a single AHB2? Most likely. But @geek101 asked this: Does running this amp in bridge mode mean each channel will see half the impedance i.e 2 Ohm each when connected to a 4 Ohm speaker. If so will this cause a problem when the speaker dips to 3 or 2 ohms?. The answer to the first part is 'yes' the amp will see half the impedance in bridged mode. The answer to the second part is "the AHB2 is well suited for bridged mono operation into 4-Ohm nominal impedances and the performance is virtually identical to stereo mode except that the power is nearly 4 X higher. Dips in the speaker impedance curve are not a problem and the AHB2 drives these cleanly.". What's the problem? |
I would like to thank John Siau a.k.a @gearbuilder for taking the time to provide detailed explanation and clarification. I appreciate the technical detail.
I have answers to my questions, apart from "damping factor" being halved I really do not see anything I am loosing by trying two AHB2 with each in bridged mono mode. My speakers can only dip to 3.8 Ohm minimum.
Sure two AHB2s may be overkill for my speakers but I will audition in both bridged and non-bridged mode now that I have all the information. Thanks to everyone. |
My speakers can only dip to 3.8 Ohm minimum.
That means the amp/s in bridged mode will see a load of 1.9ohms, not good for the bridged, but fine for a single stereo amp.
Sure two AHB2s may be overkill for my speakers
Yes as I told you before, with a single stereo you will not only get better sound, but be able to reach with your speakers in room at 3mts, 110db!!!! Enough to blow your eardrums out. Cheers George |
@georgehifi thanks. Consider this thread closed. |
tobes
Really?
Lets look at that. Show me where it states about and using the words "distortion being the same" in bridged mode into a 4ohm speaker, which means it’s seeing a 2ohm load? I doesn’t, and it’s a furphy! https://www.google.com.au/search?q=furphy&rlz=1C1CHZL_enAU820AU820&oq=furphy&aqs=chrome....But like Roger Modjeski "ramtubes" said, it’s a great spiel to be able to sell two amps with. Even though the user will go backwards in sound quality if he didn't need the extra watts. Cheers George |
@georgehifi said:Show me where it states about and using the words "distortion being the same" in bridged mode into a 4ohm speaker, which means it’s seeing a 2ohm load?
I doesn’t, and it’s a furphy! George, I don't know why I am responding to this, you clearly have trouble with reading comprehension.
@gearbuilder said:
The THD into 2 Ohms, 4 Ohms, 8 Ohms and no load are virtually identical. and for the 3rd time:
Bottom line, the AHB2 is well suited for bridged mono operation into 4-Ohm nominal impedances and the performance is virtually identical to stereo mode except that the power is nearly 4 X higher. Dips in the speaker impedance curve are not a problem and the AHB2 drives these cleanly. George, I don't intend to reply further to this thread. You only seem interested in carrying on with unsubstantiated argument.
Try to relax and enjoy the rest of your day - I'm kicking back listening to my bridged mono AHB2's :)
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I’m kicking back listening to my bridged mono AHB2’s :) And there it is, protecting ones self interest regardless of the facts for others. Yes you need bridged ones with your speakers (attached). But the OP does not, and he’ll get better sound with just 1x stereo one. ATC SM19 Lab Report " Average sensitivity (considering measurements in octave steps between 125Hz up to 16kHz) is close to 83dBSPL/2.83V/1m, a performance that undoubtedly classifies the SCM19 as a low-sensitivity loudspeaker," "SCM19’s impedance magnitude variation is quite small for frequencies above 100Hz and as an amplifier load is -for all purposes- constant. The minimum value of about 5.6 Ohm appears near 150Hz and allows us to conventionally consider the loudspeaker as an 8-Ohm load, although -typically speaking- a correct designation would be 6 Ohms. Below 100Hz, impedance magnitude significantly increases up to 50 Ohm, a behavior which could affect amplifiers with low damping factors. Also, phase behavior, ranging from +47° to -57° could be quite punishing for small amps." http://www.avmentor.net/reviews/lab/2016/atc_scm19/display/atc_scm19_impedance.jpgCheers George |
As usual, some of us try to help the OP and some of us go off on a tangent to defend their own stuff. Then everyone gets mad, I'm not mad though I am surprised at some of the responses. :(
I was surprised to see that the ATC 19 is actually 19 liters which is only 0.67 cu ft. I can't imagine why someone wants to connect this little guy to a 370 watt bridged amplifier. The speaker only goes down to 55 Hz. The resonance can be seen on the impedance graph.
I have no doubt that the Benchmark performs as stated. I am surprised that there is such fuss about whether distortion at the 0.0002 level doubles or not. Or whether the very high damping factor is cut in half. Or whether the imperceptable noise is doubled or not. Most likely your preamp will create more noise than this amplifier.
Its a bit like Woody Allen said...
"Boy, the food at this place is really terrible." The other one says, "Yeah, I know; and such small portions."
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@ramtubes lol noted, it did cross my mind to get preamp and DAC from Benchmark but I am constrained by using Wavelet. My core concern was stability at or below 4 Ohm bridged. My questions are answered. I am in the process of getting a second amp. Thanks. |
My questions are answered. I am in the process of getting a second amp. Thanks.
Total $6K. Pity for that you could of got a pair of John Curl designed Halo JC1 monoblocks that would eat these bridged AHB2's for breakfast. They "unbridged" output
400W into 8 ohms, 800W into 4 ohms, 135 amps of peak current, and 25W of pure class-A power into 8 ohms. JUST SAYING! Cheers George |
ramtubes said: I was surprised to see that the ATC 19 is actually 19 liters which is only 0.67 cu ft. I can’t imagine why someone wants to connect this little guy to a 370 watt bridged amplifier. The speaker only goes down to 55 Hz. The resonance can be seen on the impedance graph. It’s a sealed cabinet design and bass rolls off slowly providing pleasing extension into the mid 40’s in room. Obviously 380W is not required (or used by me) but 150-200W is useful with the low sensitivity SCM19’s if one wishes to explore the considerable max spl of which they are capable (108dB). ATC recommends 75-300W, though to be fair a single AHB2 drives the SCM19’s very well. Since my equipment resides in a room corner I also wanted to exploit the placement flexibility of mono blocks which allows positioning behind the speakers and short speaker cables (which should also mitigate loss in damping factor from bridging - not that DF is an issue ;-) In regard to your other snipe at me, go back and read the first line of my first response in this thread. My subsequent posts were then attempts to correct (apparently deliberate) misinformation. Something you apparently have no problem with. |
Here is a plot of the no load and 6-Ohm load THD vs. output level for the AHB2. As stated above, the 6-Ohm bridged mono load is equivalent to 3-Ohm stereo loads on each output simultaneously. Note that the 6-Ohm and no-load curves are virtually identical. Also note that the THD is always better than -120 dB relative to full output and at lower power approaches -140 dB relative to full output. If you do the math, you can calculate the SPL produced by the distortion signal given your speaker sensitivity. In all cases, the calculation will show that the distortion will be reproduced at a level that is always below 0 dB SPL at 1 meter from the speakers. This means that the distortion signal could not be heard in isolation in a quiet room. For this reason we can say that the AHB2 produces no audible distortion at any output level below the clip point. In contrast, the JC1 (suggested by George) produces 0.15% THD at full output which is only 56 dB lower than the output signal. This means that the distortion produced by the JC1 will be reproduced at a level that is well above 0 dB SPL. The distortion produced by the JC1 should be audible. However, in George's defense, I should point out that he is correct in stating that 100 W is plenty of power (20 dB above 1 W) with reasonable speaker sensitivity in a small room. Add 20 dB to the speaker efficiency to calculate your peak SPL. But keep in mine that this is peak and not average. With music, your SPL meter will typically read about 12 dB lower than the peak SPL due to the "crest factor" of the music. Bridged mono increases the maximum achievable SPL by almost 6 dB. In some situations, this extra capability may be required. Unlike virtually all other amplifiers, there is no performance penalty when selecting the bridged mono mode on the AHB2, you just get a 6 dB increase in SPL (nearly 4 X power). Here is a link to the THD plot for the AHB2 |
@tobes It’s a sealed cabinet design and bass rolls off slowly providing pleasing extension into the mid 40’s in room.
Obviously 380W is not required (or used by me) but 150-200W is useful with the low sensitivity SCM19’s if one wishes to explore the considerable max spl of which they are capable (108dB). ATC recommends 75-300W, though to be fair a single AHB2 drives the SCM19’s very well.
Since my equipment resides in a room corner I also wanted to exploit the placement flexibility of mono blocks which allows positioning behind the speakers and short speaker cables (which should also mitigate loss in damping factor from bridging - not that DF is an issue ;-)
In regard to your other snipe at me, go back and read the first line of my first response in this thread. My subsequent posts were then attempts to correct (apparently deliberate) misinformation. Something you apparently have no problem with. Im not interested in getting into a fracus with anyone on here however you have stood fast and been a little in everyones face about your Bridged Benchmarks. You did not answer my questions about your listening level or power level. How do you know you need those watts? There is no evidence that "It’s a sealed cabinet design and bass rolls off slowly providing pleasing extension into the mid 40’s in room" Granted it is sealed, and thus rolls off at 12 dB/octave. Here are the specs. Drivers: HF ATC 25mm Neodymium soft dome, Mid/LF ATC 150mm SL Matched Response: ±0.5dB Frequency Response (-6dB): 54Hz-22kHz Dispersion: ±80° Coherent Horizontal, ±10° Coherent Vertical Sensitivity: 85dB @ 1W @ 1metre Max SPL: 108dB Recommended Power Amplifier: 75 to 300 Watts Nominal Impedance: 8 Ohm Crossover Frequency: 2.5kHz Connectors: Binding Posts/4mm Plugs, bi-wire Cabinet Dimensions (HxWxD): 438x265x300mm (grill adds 28mm to depth) Weight: 17.8kg If the speaker is already down 6dB at 54 Hz. (which agrees with the impedance curve) it is going to be down another 6 db or so at 40. The rolloff of sealed box speakers is 12 dB per octave in all cases. Its physics man. When bass is more than 6 dB down you are hearing more 2nd harmonic than the fudamental because our hearing slopes off rapidly down there. Im an information junkie, Ive been correcting things here the whole time while you keep fussing with George about whether this tiny distortion changes or not. No one is going to hear this low level of distortion! The entire discussion about this miniscule amount of distortion is a tempest in a teapot. THE OP JUST WANTED TO KNOW IF HIS IMPEDANCE DIP WAS GONNA BE A PROBLEM. Many of us advised him it would and further he might get more power with one amplifier in stereo and a lot safer. Besides the "strawman" snipe, you haven’t been very nice to George. He is in the industry.While he and I don’t agree on everything, we disagree on many things, yet our public conversation here has remained civil and I thank him for that. I am certain ATC makes a very fine speaker. I think their maximum recommended amplifier playing heavy music would but an end to the speaker. The powered version only has 35 watts on the tweeter, you have 350 watts which is an accident waiting to happen. Voice coils do melt and you have no protection against that at all. One full level HF or ultrasonic event and bye bye tweeters. If 29 amps of current ever goes through your woofer voice coils for more than fraction of a second ohms law will become quite apparent. With the amplifiers unbridged you have a 4 times greater margin of safety. And now a little story..... I like to brag sometimes too. I was engaged to fix a Bryston amplifier that had been back to the factory twice under warranty. It had already destroyed 2 x B&W woofers at $500 each (plus service calls). When it came back it blew up 2 more because the problem was intermittant. On my bench it did not show up either but I added external fuse holders and left a handfull of spares. There were no speaker fuses before. I said, lets not blowup any more expensive woofers, 2 amp fuses are cheap, the 20 cent ones will do the job and protect the woofers. Only DC would be doing this and you can play quite loud with 2 amps fuses. I asked his kids how loud dad played, they said not loud :) I told the customer to call me when he had blown up ALL the fuses. The day I returned to get the amp again the house was cold (Santa Barara cold is not very cold, like 60) The amp finally showed it was putting out 50 volts of DC. Now we had a problem that could be verified at last.. Because the Bryston was old and not easy to get to the part that was the problem we sent it back to Bryston in Canada with a full page letter telling the tech to simply cool the amp and he would finally see it act up where it had not before. It was in the last few months of its 20 year warranty and free is cheaper than me. He cooled the amp and ended up replacing the whole mother board. I will close with this. Elaine LaVasseur, besides being a fine artist, is co-founder of HI FI Club. Their company installs complete home systems and home theaters for wealthy Montecito filmstars and directors. They did both for Robert Zemeckis. She comes up with clever things to say and told the frustrated Bryston customer, who had now lost $2000 of woofers with no end in sight, "Having Roger come to fix your stereo is like having Picasso come to paint your house" :) https://santamariatimes.com/calendar/community/elaine-levasseur-collaborative-printmaking-and-home-s... |
In contrast, the JC1 (suggested by George) produces 0.15% THD at full output What fool, sorry no, idiot! would run these massive Halo JC1 powerhouses at full output. Here are the real figures into 4ohms. "Distortion was also acceptably low (fig.6), with the 1kHz difference component lying at -94dB (0.0015%). Note that these last two graphs were taken at 635W and 600W into 4 ohms!" Also +1 for Rogers last post, and I’m also signing off this stupid merry go round. Cheers George |
Good luck geek, let us know how they work out. |
@ramtubes said: Im not interested in getting into a fracus with anyone on here however you have stood fast and been a little in everyones face about your Bridged Benchmarks. You did not answer my questions about your listening level or power level. How do you know you need those watts? Roger, with a calm and unbiased mind go back and re-read my posts above. My only interest was in correcting misinformation, which I believe I did in a polite manner - at least up to the 'Straw man' comment, where I admit I lost patience with the obtuse replies. Sometimes it's hard to gauge the mood of a poster. You have completely mis-read me ;-) There is no evidence that "It’s a sealed cabinet design and bass rolls off slowly providing pleasing extension into the mid 40’s in room" Granted it is sealed, and thus rolls off at 12 dB/octave.
.................If the speaker is already down 6dB at 54 Hz. (which agrees with the impedance curve) it is going to be down another 6 db or so at 40.
I debated replying to this, since of been accused of excessive self interest - but I like to correct misinformation. Here is a quote from SCM19 lab report George referenced above: "Based on this figure, SCM19's bandwidth ranges between 40Hz and 23.2kHz (using the standard -6dB cut-off points) and between 52Hz and 21.6kHz for the standard -3dB cut-off points" If you're interested in reading the whole review, here is the link: http://www.avmentor.net/reviews/2016/atc_scm19_2.shtmlIm an information junkie, Ive been correcting things here the whole time while you keep fussing with George about whether this tiny distortion changes or not. No one is going to hear this low level of distortion! I agree that the AHB2's distortion is so low it matters little whether it doubles or not into low impedances (it doesn't at any rated load). However the inference by George - and this is important to the OP's question - is that the AHB2 will sound worse when bridged. This may be true with other amps but is NOT true with the AHB2. George goes on to infer stability issues which are also baseless. THE OP JUST WANTED TO KNOW IF HIS IMPEDANCE DIP WAS GONNA BE A PROBLEM. Many of us advised him it would and further he might get more power with one amplifier in stereo and a lot safer. What do you base this on? Experience with other completely different designs? Benchmark's John Siau says it won't be an issue - but what would he know right? FWIW - and I've repeated this many times - my first line in response to this thread was "George I agree with you that with efficient low impedance speakers the OP may likely be better off with a single AHB2". Besides the "strawman" snipe, you haven’t been very nice to George. He is in the industry.While he and I don’t agree on everything, we disagree on many things, yet our public conversation here has remained civil and I thank him for that. As I said above I lost my patience with the 'straw man' comment. Otherwise I've been polite and careful about what I wrote. Read my comments again without bias. I am certain ATC makes a very fine speaker. I think their maximum recommended amplifier playing heavy music would but an end to the speaker. The powered version only has 35 watts on the tweeter, you have 350 watts which is an accident waiting to happen. Voice coils do melt and you have no protection against that at all. One full level HF or ultrasonic event and bye bye tweeters. Not sure why you are taking me to task with this, it has nothing to do with the original thread. I don't think you know much about ATC and their drivers. The tweeter comment is obvious, but what's the relevance? Well designed, stable, high power amplifiers are only a risk if they are used injudiciously. |
All issues with AHB2 are settled! as far as I am concerned. Let us not continue this thread and discuss things not relevant to technical issues of AHB2.
I will report back if I try them in bridged mode and feel like it. Thanks everyone. |
@geek101
Thanks, its been fun. My well considered advice:
ONE AMP PER SPEAKER, BI WIRED, BI AMPED.
Bridged, no, no, no |
I’ll leave the technical discussion to the boffins. The point I was trying to make, as I said before, was that, by all accounts, Benchmark seems actively to promote the use of their amp in bridged form. Why else would they send pairs of them out to reviewers? Surely this indicates--perhaps against the electronic engineering evidence--that they have confidence in their product performing well in bridged form under most circumstances. BTW, am I right in noting that there has been little discussion here, until just now, of vertical or horizontal bi-amping, which are other possibilities, no? |
You are correct, other than the recommendation by Roger, we haven't really had any discussion on that. Vertical bi-amping is the way I roll these days and see no reason to go back, regardless of which pair of speakers I am using. I think using two Benchmark amps in that manner will yield very good results.
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The OP has Legacy Aeris loudspeakers (a design that requires bi-amping) which according to at least one Legacy dealer really likes high power amps. The OP wants to know if the Benchmarks in bridged/mono mode will have trouble driving the Aeris. The responses from people with actual experience using the Benchmark in mono configuration say that the amp should perform well. Other people with no experience with the amp beg to differ. The OP decides to go with the mono Benchmarks. The outcome really shouldn't come as a surprise being that Audiogon is primarily a subjectivist audio site. Experience trumps speculation, even when the speculation comes from informed sources.
I hope the OP will let us know of his experience with the bridged Benchmarks.
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