To clarify for those recently joining the discussion, my observations are based on an unusual room that is effectively large since the listening room has semi-porous walls within a 12Kcubic’ space, in a 30Kcubic’ building without many partitions. I also have modified the speakers for 3 separate inputs rather than a single pair. I listen at approx 90dB peaks.
Under those conditions the pair of bridged AHB-2s never clip.
I had hoped for a configuration with a bridged AHB-2 driving a woofer and another one (adjusted for matching gain) used in stereo mode with one channel driving the midrange and the other the tweeter. Alas, the upper amp clipped regularly in my conditions. But, in less demanding conditions that setup works quite well.
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yyzsantabarbara
My pleasure suggesting the MoFi caravanserai SACD.
Happy Listening! |
@jon_5912, It’s been 50 years since my middle school / high school physics classes, but I seem to remember:
current X voltage
_______________ = Watts
impedance
I’m rounding the 3.7’s as a 2 Ohm load.
Space is the ultimate luxury. I’m envious that you can have multiple quality systems. I agree that’s a great way to approach this hobby. |
@unsound,
90 dB at 2.83 V 1/m into 4 ohms means current = 2.83/4 = 0.7075. Watts = current x voltage = 0.7075 x 2.83 = 2 watts. 90db at 2 watts, 93 at 4, 96 at 8, 99 at 16, 102 at 32. Regardless, the older I get the more I'm convinced that the way to go is to have a couple of systems. My den (I guess you'd call it) has my Thiel system, and my family room has my rock 'em sock 'em robots system. I'm guessing this is actually cheaper than having a single system that tries to do everything. I've got around 27k in both systems combined but components going all the way back to 2003. Less than 2k/year, not an extravagant hobby by any means. |
In the case of my Revels the amps were very powerful, but I do understand your point about underpowered amps. |
^Most driver damage occurs when people try to play too loud with underpowered amps. |
When I spoke to Rob Gillum about the robustness of the COAX he said that it was something that should last a very long time. However, he observed that most of the damaged COAX drivers occurred because people thought a $13K speaker can play as loud as an amp was capable.
I blew out my old Revel Salon 1 tweeters a couple of times with my Bryston 600 watt mono blocks. I have learned my lesson of playing too loud.
What this means to me is that the 3.7's are my permanent take to the grave office speakers (not blasting it in the office). I will get something else for my living room. |
^With the right amp you can play these speakers pretty loud. Jim recommended up to 600 Watts per channel and used a Krell FPB 600 for them. |
This same AHB2 conversation was had in another A'gon thread in 2018 where John Siau participated. I don't think the folks responding to him realized he was the amp designer.
The vertical bi-amp will not work with the Thiel CS3.7 since it only has 1 set of speaker inputs.
As it stands:
1) The designer of the amp told me by email that the amp will be good with the speakers. He looked at the speaker specs.
2) The founder of the speaker company mentions that he has been testing 2 AHB2 for the last 2 years.
3) @unsound makes a great point about finding something else that does not shut down. I think there will another amp in the future to have in the stable.
At this point a second AHB2 is an easy buy for me. I love the sound of this amp. They are said to work with the 3.7's, issue is how well. One thing I have learned the last 2 weeks is that the CS3.7 is not a speaker to be played crazy loud. That is fine for my current application in my office. A little more grunt from the 2 amps will take me to an ideal spot. |
They are more like 2ohm, and at 60hz where the -phase angle meets the 4 ohm could represent even less EPDR load to the amp. https://www.stereophile.com/images/archivesart/1208T37fig1.jpg What the member who’s thinking of bridging should do if he must get another ABH2, instead of bridging it, which will be a step backwards with these CS3.7’s in all parameters except total wattage. He should vertical bi-amp the two ABH2 amps, that way the whole power supply energy is available to just one bass speaker of one channel instead of two. The amp/s remains stable and able to drive these nasty loads. https://www.av2day.com/wp-content/uploads/2014/05/biamp2.jpgCheers George |
Rory at Benchmark says that many customers have requested such an AHB-3. I tried my hand at it. John is adamant that the AHB-2 has enough power. Engineers can be that way.
We wouldn’t be talking about this here if Thiel speakers had 4 ohm minimum impedances.
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but its anomalous behavior is limited to its stability into low impedences, BUT if it does become unstable, it tells you via indicators This may "save" the amp if the protection circuit is fast enough if it oscillates and there’s not too much storage capacitance, as you’d be crazy to put relays/fuses etc in the speaker outputs or power supplies. (another sound quality no no) I did say just one of the negatives was stability and low impedance drivabilty, there are many more. Cheers George |
I suppose it’s a good thing that this amp protects against overload, but I can’t help but think having extra power margins into lower impedances and the superior frequency linearity that come with it, wouldn’t be better. I’d rather an amp just keep delivering when called upon than shutting down, even if just briefly. As of now it seems as though there are better options available. Perhaps a beefier AHB3? |
George - I agree that all amps we know, either class A or AB, act worse in many ways when bridged. I recommend you investigate this particular amp, which does indeed act as you say, but its anomalous behavior is limited to its stability into low impedences, BUT if it does become unstable, it tells you via indicators, and protects itself. I had dismissed it for myself before I looked closer and now have used it for a couple of years. Check it out.
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When I get the AHB2 in mono
When you do this the "sound quality" not the loudness will deteriorate. As when any amp is bridged, the there are many negatives that happen, one is that will be here is the ability to drive low impedances and the stability into low impedances. Look at the impedance graph of the 3.7's, it's nasty. If you need more watt's get a bigger amp. https://www.stereophile.com/images/archivesart/1208T37fig1.jpgCheers George |
Yyz - yes. 3' cables are optimum if your configuration permits it.
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@tomthiel When I get the AHB2 in mono would it be useful for me to use two 3 foot speaker cables instead of the two 6 foot cables? |
@tomthiel Thanks for that explanation.
@jafant I am listening to the MoFi version of Santana's Caravanserai and I am amazed to how good it is. Maybe my second best SACD disc now after DSOTM.
There is no comparison with the SME version. The MoFi has bass that I can feel on my toes as I am stretch out listening. Not bass that bothers the ears but bass that should sound loud. The percussion is more powerful and you can feel it. You hear more of everything, and it is not a louder recording just a more vivid rendering.
Thanks for the heads up. I bought it on eBay. |
ampers - I’ll chime in here. The Benchmark AHB-2 has been my go-to amp for about 2 years now. It is unique in my experience for simple authenticity. Regarding their feed-forward, John Siau has written a white paper available on the BM website. In practice, the correction mechanisms are nearly invisible and inaudible. Under overload / clipping conditions (evidenced by the indicator lights), I can hear no artifacts of any kind. The error-correction compares the input signal with the projected output signal and introduces correction before the final power stage. When pushed ’too hard’ the output interrupts momentarily as though the offending peaks are erased, but with no audible distortion, mute indicators light up momentarily - and the music continues. I have purposely pushed the bridged amp into sub 2 ohm loads (two paralleled CS2.2s.) The over-current lights flicker on peaks and eventually the amp shuts down via overheating. No damage, no audible distortion, just safety shut-down waiting for manual restart in a few minutes.
Don’t try this at home. But my experience is that the AHB-2 is bulletproof for itself and its driven load.
In my large room, I run out of power in stereo mode and therefore use 1 bridged amp on each channel. Unlike class AB amps, the bridged distortion graphs match the stereo graphs. But output impedance is double (damping factor is half). Half-length cables makes up for much of the difference.
Considering the relative bargain price of the AHB-2, my dream configuration (seconded by John Siau) is 4 bridged AHB-2s -each channel getting a bridged amp for the woofer and another bridged amp for the combined midrange - tweeter. Power requirement is about equal, since the headroom required for clean midrange peaks about equals the current draw of the bass.
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My Lucian also doesn’t arrive till December 11 |
I’m picking up my AudioQuest 9 cables this weekend other than that nothing yet. May get more interconnects but as far as speaker cables go I have one for each speaker. The AudioQuest was terminated for the thiels. I chose the 9 for the natural warm timbre without detail smothering. |
thoft
Thank You for the update. Keep me posted as you massage the Luxman into your room/system. Any cabling updates?
Happy Listening! |
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@thoft, sounds like a nice piece for a different application. |
@yyzsantabarbara,
There are different types of distortions. Clipping is the consequence of some distortions.
The Benchmark is somewhat unique, I was wondering just how it’s feedforward mechanism works when confronted with low impedances? Does it reduce power when sensing overload, does it shut down, does it provide some sort of dynamic headroom, does it self correct the distortion ala DSP, or something else?
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@jon_5912, Before I forget, let's remember that those calculations were for a 1 meter distance, not the 3 meter recommended distance. Even allowing for the greater efficiency of doubling the channels, and the typical room gain, in practice we can expect much greater power demands in typical use. |
@yyzsantabarbara,@yyzsantabarbara, “A shame these things cost money.”
Haha😄 |
@unsound Your comment ties in the what John Siau emailed me today. When ss amps clip, it’s sudden and ugly. With ss amps t’s best to keep far distance from the clipping point. John’s last comment in the conversation. Yes, it will work well in your application. The feed-forward error correction keeps the amplifier distortion-free when driving low impedances. Or maybe distortion and clipping are not the same thing? Regarding searching for new speakers. I am very happy with the CS3.7’s I am enjoying the heck out of them now. I am just trying to squeeze every bit of performance, especially in a challenging room. What I have now is great, let me try for excellent which the CS3.7 is capable of. I do want the 2 COAX’s to measure the same though. Need to fix that. I am going to one day build out a living room system. That will be using different gear and the speakers will likely will be the KEF Blade or Yamaha NS5000. Along with the CS3.7 the other 2 are my fav speakers. A shame these things cost money. |
@jon_5912, I think you mean 64 Watts for 102 dB. And one would need 256 Watts for 108dB. Now one would not ordinarily play Thiel’s that loud, but should it happen you wouldn’t have to worry. Ultimate volume levels are a Thiel weakness. For me the Thiel virtues outweighs the compromises, and the speakers that can play that loud are too compromised elsewhere for me. Though not the last word in accuracy, I’ve used a phone app to track my listening volumes in my roughly >3800’cubed room for a few weeks. The average sound pressure was about 85 dB, but there were peaks a few times each day of well over 100 dB.
It’s not the ultimate power of the Krell’s that impresses me the most, but rather the ease in which it handles low impedance loads. There’s nary a strain, and it’s reflected in the sound. BTW, with my >4 Ohm Thiel’s I use a less powerful amp that’s not a Krell. |
@yyzsantabarbara, I’m a firm believer in working backwards: budget, room, speakers, amplification, etc.. But I offer this with sincerity: perhaps your affection (which might be well deserved) for the Benchmark might lead you to more compatible speakers? |
The simple reason I like the Benchmark gear is because with this gear I experience the illusion that I am in the studio or audience during the performance. I think it is their SNR that makes this magic happen for me.
That is also the reason I like the KEF Blades so much. Those speakers bring the performance into my room better than anything I have ever heard. The Thiel CS3.7 are also pretty good in that regard too.
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Let me add that theses impedance loads are typically best served by ss amps. Unlike tube amps, ss amps don’t clip gracefully. When ss amps clip, it’s sudden and ugly. With ss amps t’s best to keep far distance from the clipping point. Fortunately ss Watts are typically much less expensive than tube Watts. Making it much more affordable to avoid it altogether and have the safety of that extra power margin. |
The luxman is fully restored and completely rebuilt with a new transformer boards and etc. it is basically new. I have confidence that “failure prone parts” and “potential noise introductions” are well resolved and don’t even exist. |
Even so, it's 32 watts for 102 db. I appreciate the benefits of extra power but the Krell FPB300 puts 600w/ch into 4 ohms.
64/105, 128/108, 256/111, 512/114. I'm skeptical, do you buy Thiels because you like it loud? They're magnificent with unamplified music at reasonable volumes. I tend to doubt you can have the best of everything in one package. Wouldn't drivers that can play crazy loud need to be built differently than ones that are optimized for detail? |
@jon_5912, That’s not quite correct. They’re spec’d at:
90 dB at 2.83 V 1/m
not
90 dB at 1Watt 1/m
You need to drop the sensitivity by 3dB for each halving of impedance below 8 Ohms.
I don’t know what amp you are using to drive which speakers, but it’s not uncommon for an amp to halve it’s Class A output as it doubles it’s output with each halving of impedance. |
I think focusing on doubling is somewhat misguided. If an amp is stable and low distortion into 2 ohms it should be fine. How much power can it put into 2 ohms? An amp that can put 300w/ch into 2 ohms can put 150 into 4 ohms and 75 into 8. Whatever it can put into 2 ohms is what matters rather than doubling.
With the 3.7s it's hard for me to imagine they need a huge amp. They're 90db sensitive. (Stereophile measured 90.7.) 2 watts for 93db, 4 for 96, 8 for 99, 16 for 102, 32 for 105, 64 for 108, 128 for 111, 256 for 114. I'd be shocked if these can get anywhere close to 114db before exceeding their physical limits. The fairly inexpensive amps I have do the first 30 watts in class A. I'd bet that pretty much all of my listening is in class A. I worry about bottoming out the drivers a lot more than the amps. |
@thoft, the original Krell FPB's ("Full Power Balanced") are designed to work best through their balanced inputs, though if you wanted to direct connect to a high bit, high output DAC the RCA inputs might have an advantage to avoid bit stripping. The latter FPBC's and FPBCX's don't even have RCA inputs; only XLR and CAST.
As far as using an intergraded as a pre, well I suggest using the KISS approach. Your just introducing more potential noise and failure prone parts. |
@yyzsantabarbara , If an amp can't double down into lower impedances, at higher volume levels it can lead to frequency linearity issues. The Thiel's tend to have fairly steady impedance loads, so it might be less of an issue. FWIW, considering everything I'm not sure why you have such loyalty for the Benchmark. Something like the above mentioned Krell FPB 300 would be ideal. The FPB 300 has perhaps a bit of overkill power for your current room, but that's not a bad thing, especially if your considering moving your speakers to a larger room in the future. The FPB 300 is something of a sweet spot model in the line up, a nice step up from the smaller models, due to improved parts such as a bigger tranny. It's sensitivity also makes it a suitable model for direct connection for some of the newer high bit, high output DACS without having to worry about bit stripping, negating the need and expense of a line stage if you don't have analog sources to contend with. The issue with the Krells, perhaps due to their, though modulated, Class A output is that they seem to need recapping more frequently than some of the competition. That's not an inexpensive proposition unto itself and then there's the expense of shipping such heavy gear. Though I think you can conservatively expect 20 years between such servicing. |
Yea it is integrated and only has rca. I’m not too concerned about xlr connections. It’s a beefy unit. I’m getting it to replace the luxman l-450 that i was using as a pre amp even though it’s not meant to be used as one (doesn’t have pre out) |
In a previous post, I described the 2008 COAX terminal connection backwards (not important).
I just got off 2 email threads.
1) The Audio Engineer in Canada, Mitch Barnett, looked at the new graph I sent him and said we know for sure it is now the COAX drivers that have a problem.
2) John Siau from Benchmark looked over the specs of the Thiel CS3.7 and said the amp will work in mono. That is the mono amp will not damage the speaker. I should take the 30 day home trial and see if it actually improves the sound.
3) I will get in touch with Rob and pick his mind on what could be the cause of the COAX issue. |
@thoft Is that an intergated amp? Does it only have RCA outputs? |
I have decided I’m getting a luxman l-510x to be the pre amp for the krell fpb-300. One step closer... |
^i’m happy that you found the source of the problem so quickly. Perhaps sending both drivers to Rob so that they can be properly calibrated and matched might be prudent. |
@unsound Thanks for the feedback.
I was thinking that could be the case. What I did first was put my KEF LS50's back into my room and measure exactly as before. This measurement setup was done with the goal of removing the room as much as possible. The microphone was placed 3 feet directly in front of each speaker and my LEFT and RIGHT test tones were run from ROON. One tone per speaker and the analysis was done on my Windows laptop running REW
With the CS3.7 the Sound Pressure Level (SPL) graph on the REW software shows a lower level on the replaced COAX driver at 1K to 20K.
On my KEF LS50's the same test results in an almost 100% perfect match in the graph lines for each speaker. Beautiful to see that.
So the issue is not with my gear or the testing process. It is now isolated with the 2 COAX's.
The COAX that was originally wired out-of-phase was built in 2012 (there is a date sticker). The COAX on the other speaker also has a data sticker of 2008. It also has some electronic piece that is soldered onto the uncolored terminal (non-RED). A tiny label on the piece says something about 5% adjustment. I took some photos of this and got confirmation from the previous owner that Rob Gillum told him the 2012 COAX does not need this extra soldered piece.
I was not able to reach Rob today but I have a feeling I will have to get a second 2012 driver to make the SPL identical. As I said in my prior post, the sound is really good now. There is nothing I hear that tells me there is a problem. However, I am curious about going forward with DRC so I will replace the COAX if that will fix this issue. This has to be resolved before DRC can be done (at least with the Audio Engineer I am working with). |
@yyzsantabarbara, There are a multiple number of causes that might be responsible for this anomaly (including room). I’d suggest reversing components (speakers and cables) and channels from one channel to the other starting from the end (speakers) to the front of the chain.Then replacing components in the same manner. This might help you find the culprit. |
yyzsantabarbara
any journey worth taking will experience a rough patch or two. Enjoy the music!
Happy Listening! |
This journey I am talking with the CS3.7 is hitting rough patch after rough patch. It is not really bugging me though, a little interesting actually. Learning a ton of stuff about audio. My background is as an expert listener of music. :)
Today I did the REW software measurements of the 2 speakers. The new issue is that the Sound Pressure Level graph of my LEFT and RIGHT speaker are not identical. There is sufficient divergence between the L and R to indicate that something is wrong. This divergence occurs at 1K level. I got this feedback from the Audio Engineer who analyzed the data.
So I am going to learn how to interpret the REW software correctly and measure my KEF LS50s myself to eliminate the very new Benchmark gear as the culprit. I am almost 100% certain this less than 6 month old brand new Benchmark gear is flawless.
I have an idea what the issue is but will not speculate here until I speak with Rob Gillum tomorrow morning. If my hypothesis is correct it will cost me some funds to fix it.
I should note that both COAX drivers are in phase now and to my ears the system sounds great. However, I cannot move forward with the DRC until the SPL graphs are almost identical.
BTW - I was just playing The Boy’s Doin’ It - Hugh Masekela. That sounds so good on the CS3.7 |
@yyzsantabarbara Ok well if you are not considering integrated forget about Gryphon, the separates are too expensive for Thiel owners IMO.Only Diablo 120 or 300 is worth considering for CS 3.7s owners.
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@thieliste I appreciate your feedback. I will give it a try since it is so easy for me being local. I do not want an integrated since my system positioning is setup for separates. I wanted a cleared path from my speakers to my ears. I am very happy with what I have done to facilitate this in a small room. I will check out their dedicated amps instead.
I just did some quick looking at the Gryphon amps and they seem like competitors to the USA made CODA #16.
I am currently listening to Santana’s - The Woodstock Experience and while it sounds very good and I am bopping along. I would like more power to really feel that percussion.
@unsound you are correct about the 25% reduction at 2 Ohms. I asked them since you mentioned it before. I am not a big Class A guy. Whatever gets me to great sound will work, Class A, AB, D, etc.. |
@yyzsantabarbara I completely agree about Luxman being kind of too warmish and meaty.I 've heard the the M900-C900 combo several times and was never blowned away.Gryphon integrated are much more fun, it's very dynamic, transparent, fast, huge slam and still organic and never muddy.It will not cost you anything to just go for an audition and see if you like the house sound and compare to the gear you already know.
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