Running Benchmark AHB2 in bridged mode and 4 Ohm Speaker
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?.
Anyone running Benchmark AHB2 in bridged mode with low impedance speakers?.
The Stereophile graph referenced above is done at 2.83V which is equivalent to 1W/8ohms and 2W/4ohms. Obviously, whether bridged or in stereo mode it won't be effected by any insinuated current limitation. What will effect the simulated speaker load is higher output impedance - which is doubled with the bridged amp - but because its already usefully low this won't make a substantial (read audible) difference. It certainly won't turn the bridged AHB2 into a tone control - which is a ridiculous exaggeration - especially in comparison to any tube amp or many other SS amps for that matter.
I would bet looking at the wattage's I posted before, the "wavy black line" in the graph above, would be far more wavy with the bridged than the non bridged. But were’re never ever going to see that with the same test equipment now.
It is also possible that 480W limitation comes from power dissipation of the output or power supply (29A max current seems adequate) and is not relevant, unless one listens to continuous sine waves. Music has very low average power while peaks might still reach close to 800W.
Benchmark clearly states in it’s specs: Not bridged 100w into 8ohms 190w into 4ohms =Clearly very close to doubling it’s watts, good current
Bridged: 380w into 8ohm 480w into 4ohms =Nowhere near doubling it’s watts, current diminishing.
Clearly the "not bridged" AHB2 is pushing current better because it’s closer to doubling the wattage into 4ohm, and therefore keeping the amp FR flat into varying speakers loads and not sounding like a tone control. Like the bridged would, regardless of how many more watts it has up it’s sleeve.
How much power the amp can actually put out will vary. My point was just that bridging increases the watts an amp can deliver to a speaker and increasing watts means increasing current.
There's a bit of anti-bridging hysteria on this thread. I've run bridged, vertical bi-amp and regular and the idea that bridging is necessarily bad is silly. Current certainly doesn't go down in bridged mode. Watts are volts times amps and volts = amps times impedance. An amp that can put 100 watts into 10 ohms, say, means that it is putting 3.33 amps at 33.3 volts into the speaker. If you bridge it and get 200 watts into the same load the current has gone up. In this case the formula for current is the square root of the watts divided by ten. The current for 200 watts is the square root of 20. For 400 watts it's the square root of 40, etc.
Keep in mind, too, that the amp is only driving one speaker so it's not working as hard for the same volume. There is certainly the potential for problems with low impedance loads but I've never experienced it. I'm running two amps bridged mono into 4 ohm speakers now, have been doing it for 6 years and have never had a problem. I like the option of being able to buy a second identical amp if the first one is a little underpowered.
Lordcloud is not making a claim (an assertion without evidence). He is sharing the experience of using the AHB2 in Mono mode.
George, let's suggest someone bought two parasound bridgeable amps, and they said they sound better in Mono mode than biamping. Would you suggest that Parasound bridgeable amps are a sales gimmick to sell more amps, and Parasound, "should never have released this amp in stereo form, they should be all bridged, as the Stereo version is in some way hobbled and should not be purchased."
I'm checking for consistency. Imo you are making claims far beyond that of biamping versus bridged operation, suggesting that the AHB2 has been poorly designed or intentionally hindered to sell more units. To date I don't think you have provided one shred of evidence to support such claims. Frankly, I think you are walking on very thin ice with such claims against Benchmark. :)
No answer to the above claim. All I can say to that is "if correct", that Benchmark should never have released this amp in stereo form, they should be all bridged, as the Stereo version is in some way hobbled and should not be purchased.
And there is no parameter that’s improved with bridging with this amp, except for and increase in wattage, and as Roger Mojeski said "it’s just a sale gimmick to sell more amps".
I have a pair of AHB2s. My speakers are 6 ohm nominal and not sure where they dip to (Tempo Electric EP-1).
However going form one amp to two, was relatively dramatic in my opinion, and I would recommend it. If you don't love it, send one back.
I didn't do it for the watts, as my speakers are 91 db sensitive and were designed with lowish power tubes in mind. I also listen very much in the near field, so again, not really looking for more watts. I was looking for the benefit of one amp not having to share a power supply, and more ease tot he sound. What I got was more realistic sound, larger sound, and an overall increase in sound quality
I am running a small tower that is 89dB and 4 Ohm, and two of AHB2 in Mono with Exogal Comet and Plus Power Supply take 90 of 100 setting sometimes at listening level. This is no issue for the Comet or the amps, but with less efficient speakers you might bump into a barrier with listening level and amp output.
As I stated in my review the amps do not pull off absolute power for any and all speakers with unlimited listening level. Know your speakers and know your preference. Now, having said that, I would guess that in 90% of the cases, perhaps more, this is not an issue.
What remains rock solid is the control, cleanness, tonal richness etc. from class AAA. It's simply a great design. BUT, you must work with cables to elicit the best result you are seeking.
The DAC3 is very good as a preamp. Tends toward lean and light, not a thick, warmish pre like tubed preamps. Again, cables make the difference in so many rigs. The Exogal Comet with AHB2 is a bit warmer, and the DAC3 a bit cooler, but both are superb with the amps.
I think you’d be hard pressed to find a better sounding amp period, much less for the money. I auditioned a number of amps through my dealer who had 20.1s in a show room with various amp configurations over the years including some uber expensive equipment such as Boulder 3050 Monoblocks. I read about the innovative design of the Bencmark amps and gave them a try. I don’t plan on ever letting them go. I now hear only the music recording rather than the equipment which I feel we audiophiles get caught up in more often then not. I have my 20.1 Maggie’s bi-amped with Benchmark amps and can get much louder than I can comfortably listen before I run into clipping. They both run in stereo mode . . . Geek101 I think you’d be impressed with the output of one amp and would try it before getting a second. That being said, it’s your system and John has said that two mono amps will work well. Please tell us what you think. It would be nice to hear your experience of driving the system with one stereo vs. dual mono Benchmark amps.
Legacy Wavelet and Aeris are an integrated system.
Meanwhile... Some ears at Stereophile are hearing the same attributes from the AHB2 as I have. Two honors each for the Benchmark DAC3 and AHB2. Kudos to Benchmark.
If I understand correctly Legacy Wavelet when used with Aeris at build time is configured to correct/adjust for the small errors among how different drivers work and also corrects for room also in the domain of time. I do like the idea of using dsp to correct these errors. I think from what I have heard in person it works well. No speaker can make the room go away!.
Buying passing Wavelet and the internal crossover is not an option, I think they add quite an amount of value.
As I said before in an another thread, if I could redo this it will be an all active speaker. The more expensive ATC look quite good to me. I want active crossovers and internal amplification. No need for this amp matching speaker merry go around.
@ramtubes The tube amps you guys make look quite good.
It bothers me there is no sub control. Makes me think you have to buy their pre.
I think the plate amp get a high level signal from the speaker terminals, and the xlr connection (room correction) may have something to do with this I found on line. And there’s a passive xover illumination lamp switch, so you can see it through the side grills??, how tacky. https://ibb.co/cKhCx0
https://hometheaterhifi.com/wp-content/uploads/2014/11/legacy-aeris-floorstanding-speaker-fig3-lg.jp... "The bass section is powered by 1,000 watts of included ICEpower® amplification and offers exceptional extension to 18Hz. The included 24-bit DSP room correction features balanced analog inputs and outputs for optimizing performance. The upper portion of the speaker cabinet is open air dipole for fast decay of mid-bass frequencies and airy spacious highs. The elegant design employs a 2.25” thick baffle with 2” side walls. LED Crossover Illumination within the upper portion of the cabinet reveals the intricately wired crossover design."
Ramtubes, could be my terminology is off, but if a loudspeaker has a built in power amp for the bass drivers and separate inputs for an external amp to drive the midrange/treble, then it requires bi-amping.
We really shouldnt have to be doing all this guessing. I wish the OP would tell us more about how this speaker is set up in his system.
I think he has the preamp/processor that goes with this speaker. If one looks at the back panel there is an XLR jack to drive the plate amp. There is one one pair of speaker terminals for the rest of the speaker so it cannot be biamped without going inside. What I do find curious is: If you do not have their preamp, which is featured on the website, then where are you supposed to get the signal to drive the XLR?
If a speaker has a built in power amp for the sub, no other amp is required there. It wants a line level signal. So there is no biamping in this case. One could s
Many speaker makers, Vandersteen and others provide two pair of inputs that can be biwired, biamped or simply strapped for one amp. That is when biamping is possible. Some choose different amps in that situation as the upper speaker often needs less power than the lower (regardless of the sub). So a big SS amp on the bottom and a nice tube amp on the top.
There are many of us who feel small amplifiers sound better. The sins that are committed in making a large amp will cause the lower power range to suffer. As an amplifier designer I happen to agree.
That is why the FTC stepped changed the rules in the 70's. Before distortion could be specified at full power where it is often lowest (in SS amps). At low levels there was often large amounts of crossover distortion. So they changed the rule to quote maximum distortion from 0.25 watts to full power. I would further reduce it to 0.000000025 watts to full power. We dont want distortion to climb at the bottom of the range.
It bothers me there is no sub control. Makes me think you have to buy their pre.
Ramtubes, could be my terminology is off, but if a loudspeaker has a built in power amp for the bass drivers and separate inputs for an external amp to drive the midrange/treble, then it requires bi-amping.
@geek101, just so you'll know (in case you don't), poster ramtubes is Roger Modjeski of Music Reference, designer and maker of tube electronics. Asking him for an amplifier recommendation puts him in an awkward position ;-) .
Suggest me few amps better than AHB2 at this price and I will consider them, I am only looking for a great amp that do justice to my speakers. I don’t have any past baggage or any biases.
I did, a pair of used John Curl Parasond Halo JC1’s in high bias class-A mode on your speakers will sound majestic. I heard them on Wilson Alexia’s and they were just a little behind the Gryphon Antillion Evo. And they come with 5 year warranty.
@ramtubes Agree with you that great specs on a single tone at some frequency or even frequency sweep tests does not really come close to complexity of music. But at this point that is all I have. Good point about complexity yes it is more complex but the amp has been out there for a bit. And people who have it never seem to complain why it failed or how it faulted. Still I see these (amplifiers) as simple things compared to stuff I am aware of. These days manufacturing and design has come a long way with computer simulation etc. Testing techniques etc have come a long way. I am more concerned with someone in their backyard building a complex amp more than anything else.
Agree with you that good specs might not translate to good sound. But I cannot go on some one saying some monster class A/B or class A sounded great and since it is big and consumes a lot of power I have to go for it.
I have a class A SET tube amp and I am going to compare with this amp along with class D (Hypex NC500) before making my mind up on few things. I am in the bucket of people who think all good amp sound the same.
At the end can an amp just amplify the source faithfully and get out of the way. Can it just get out of the way!!. This is what I am going for and I want it at lowest price possible.
Suggest me few amps better than AHB2 at this price and I will consider them, I am only looking for a great amp that do justice to my speakers. I don't have any past baggage or any biases.
geek101 OP227 posts11-16-2018 2:07pm@georgehifi With Legacy Aeris what you are suggesting is not possible.
Of course it is, the plate amp still drives the lower bass as is, the passive xover is split (easy job) so the original terminals do just the mid/highs and a second set of speaker terminals (that has to be put on) do the 10" mid/woofer. So your vertical AHB2, one channel drives the 10" mid/bass and the other channel drives the Tweeters and 8’’midrange, the plate amp still drives the 2 x 12’ low bass. And your other ABH2 does the other speaker.
@ramtubes, Impedance minimum for top section of Aeris is only 3.8 Ohm (this information is from the source). So it seems AHB2 is fine with that.
Which amplifier would you think can be a better option than Benchmark AHB2 given that I have gotten myself one amplifier for $2100?. What do you think in technical terms another amplifier can be better than Benchmark and at what price and size?. I am looking for 150 watts with no distortion per channel easy, which means no crossover distortion or anything else. Just because I have spent some money on a speaker does not mean I am going to weight that and buy an expensive amplifier. If I could find a $2k Legacy Aeris I would have purchased that instead. I want a great amplifier optimized for cost.
Please let me know I have been looking for a while. I just cannot audition 10 amplifiers to compare and select which sounds good in my room and with the speakers I have. I have to look at the specs, build quality, technical innovation and what generally people think. Anything that comes close to this in my opinion is Hypex NC500 based modules which again can be obtained for $2k approximately. I will consider if you can point me few of them.
General rule of thumb is fine but at the end I am constrained by my experience and capacity to audition amps and I like to re-verify past ideas. Technology changes and things change. If someone says X amp sounds good then I have no context, I will go read the specs, read the forums and reviews and move on.
Thanks for your questions.Right now you have an amplifier and speaker that are working for you. It would be wise to find out some things about how you listen.
Do you have and SPL meter, the RadioShack one is quite good? The cellphone aps accuracy is unknown but better than guessing, Guessing never works.
Do you have a meter that can read AC or Peak volts? An old analog meter would work also. We need to find your power level unless you already know it.
The sensitivity appears to be 95 dB. Is this at 2 or 2.8 volts? Try to find out, makes a 2 to 1 difference in power,
No one needs an amplifier with specs this good. If the distortion was a four timer higher you would not hear it. I hope the amp has good sound but I would not own it due its complexity. Distortion measurements are done steady state, music may not enjoy those same specs. They worked hard to get distortion this low yet I am unimpressed at how they did it. Look inside that amp and then a Bryston or something traditional. Look at a Hafler, or TransNova, perhaps even a tube amp. This amp has too many parts and the failure rate if chip capacitors is alarming. I pulled a noisy one out of a Mic pre. Last thing I would have expected.
What happens in Electronics is someone gets on a tear to make an amp that excells in some area. If they do this by creating some thing very complex they can make a monster.
Read the Atkinson review. His test equipment is the best and latest test gear yet he can hardly measure the distortion. No one needs this low distortion. How will you know how long it will stay that way?
The coments in this thread about the small increase in distortion was like children arguing over pennies. Same for the damping factor as I have pointed out.
Bottom line, go get a real amplifier. (My shields are UP) :)
Is this amplifier made completely in China, or boards or parts from China? I cant imagine a surface-mount board that large being populated in USA.
With someone who knows, looking at the access via the back plate amp, it wouldn’t be hard to split the passive xover and add a second pair of speaker terminals for the bass driver. Then you can purchase the 2nd AHB2 and can vertical by-amp for the best sound, as I said in my first post.
@ramtubes, Impedance minimum for top section of Aeris is only 3.8 Ohm (this information is from the source). So it seems AHB2 is fine with that.
Which amplifier would you think can be a better option than Benchmark AHB2 given that I have gotten myself one amplifier for $2100?. What do you think in technical terms another amplifier can be better than Benchmark and at what price and size?. I am looking for 150 watts with no distortion per channel easy, which means no crossover distortion or anything else. Just because I have spent some money on a speaker does not mean I am going to weight that and buy an expensive amplifier. If I could find a $2k Legacy Aeris I would have purchased that instead. I want a great amplifier optimized for cost.
Please let me know I have been looking for a while. I just cannot audition 10 amplifiers to compare and select which sounds good in my room and with the speakers I have. I have to look at the specs, build quality, technical innovation and what generally people think. Anything that comes close to this in my opinion is Hypex NC500 based modules which again can be obtained for $2k approximately. I will consider if you can point me few of them.
General rule of thumb is fine but at the end I am constrained by my experience and capacity to audition amps and I like to re-verify past ideas. Technology changes and things change. If someone says X amp sounds good then I have no context, I will go read the specs, read the forums and reviews and move on.
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.
I looked at the manual and I dont see any requirement for bi-amping. I dont know of any speaker that "requires" bi amping though I am all for it if there is an active crossover before the power amps.
This is a $21,000 speaker, Why use the Benchmarks on that? There are better choices and bridging the Benchmarks is not a good idea given the low impedance
Speaker impedance always varies with frequency. Speaker impedance may be much lower than the rated "nominal" impedance at certain frequencies. The over-current fault detection circuits prevent potential damage that can be caused by driving very high signal levels into very low impedances. In STEREO mode, at full output, the current limit can be reached if the load impedance dips below about 1.3 Ohms. In MONO mode, at full output, the current limit can be reached if the load impedance dips below about 2.6 Ohms.
clio09 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.
twoleftears 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?
My first post to the OP geek101 at the beginning of page one.
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.
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.
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?
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.
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.shtml
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!
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.
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.
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.
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" :)
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).
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.
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!
@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.
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."
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.jpg
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