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Old 8th September 2012, 11:42 PM   #11
fdlsys is offline fdlsys  South Africa
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Hi Bear, my apologies for the very late follow up. Many, many projects in the pipeline.
Back on the subject:
You are absolutely right about the Acoustat transformers/xover overlap and the way panels are driven (full range), but the impedance does drop to 3 ohm and that is at rated -2db point (30Hz for Model-3). Lower Fq has not been plotted but the curve looks like dropping off a cliff. Legends say that many "audiophile grade" amps smoked on Acoustats.
Anyway... I have 2 F5s completed and they sing beautifully.
Since it doesn't cost me anything to give it a try, I have taken the interfaces off the M-3s today and had a look - dead easy to split. So we'll know soon. One stereo amp per speaker - that's about as close to identical drive as one can get.
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Old 9th September 2012, 12:01 AM   #12
john65b is offline john65b  United States
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What great timing...I also was planning on "splitting" the crossover on my M3 (I now have two of them)

I think two bass panels off the bass tranny and a single panel off the HF tranny... Looks like you will beat me to it... Let me know what you find out...
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Old 9th September 2012, 02:23 AM   #13
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fdlsys, the reason that amps smoke is mostly that the load looks capacitive, causing a phase shift that if the amp is not very stable can cause instability. Of course amps without enough current capability will have trouble no matter what.

I am surprised that you found a dip that low in impedance, I do not recall it being so in the original curve published by acoustat, but I have not looked at that for a long long time, so I guess it is possible... but that low a Z *below* 30Hz. is not likely to have much of an effect for most situations, since most source material has zip, nil, down there, and what it has is mostly transitory and short in duration.

I am surprised the F5s play loud enough, but may they are ok in a small room... happy to hear that they work well... being class A they should be ok, fine.
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Old 9th September 2012, 10:14 AM   #14
tyu is offline tyu  United States
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The bias is low on most of the Acoustat 121...an are so close to the hv mixer the bias get pull down... the power you put in ...goodluck
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Old 9th September 2012, 02:22 PM   #15
fdlsys is offline fdlsys  South Africa
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@John65b: Agh, the plan was this weekend, but that plan has taken a dive due to reoccurring electrical and other problems following the monster hail storm we had last week. Fixing the problems and hopefully securing the house against similar disasters takes precedence.

@Bear: For my room ("L" shaped 32sqm, with speakers along the shorter 3.6m wall playing into the 6.5m long part of the "L") and my liking, even just one stereo F5 is enough. But F5 (at least the "standard model" with one pair of IRFP devices) does sound a bit fat & flabby on the Acoustats. Or maybe I'm just not used to the interaction between them and the M3s playing the significant amount of bass which they usually don't with the more conventional A/B class amps. Anyway, the experiment might just as well happen to lead nowhere, but I have to give it a try.

@Tyu: My interfaces are (still) the standard MK121-2A (220uF bipolar cap, 6ohm varistor). This will soon change to "C", depending on how long it takes for 47uF caps to cross the ocean. The rest is available here.
In the meantime, I have never been disappointed or in any way let down by the standard interfaces; not in the tonality (except for the usual - low-mids taking a small step towards the back of the soundstage) nor in the efficiency - as a matter of fact, Acoustats are almost "twice louder" (perceptional, judging by the volume knob position) than the SoundLab 2A with bias pushed quite high.
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Old 9th September 2012, 03:07 PM   #16
tyu is offline tyu  United States
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after living with all the mods for the 121...a,b,c what ever... the best sound out of the Acoustat panels...is with the No crossover 121a ...jim new this was the best ....as anyone would...the best crossover is no crossover...sound lab put a crossover in there interface...an look what even you have to say about the output...what like 3db diff in out put...you are right.... why would you then do the same with the acoustat 121 put a 47mf cap in the input...the a 220 junk cap is by-passet...but not the 47mf...
look i no this because i have done the works ....i am all for you doing the same....so dont think i am say not to go there....you wont no if you dont go...long live Acoustats....goodluck
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Old 9th September 2012, 08:52 PM   #17
fdlsys is offline fdlsys  South Africa
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I hear you Tyu and thanks for that. I actually read (most of?) your threads on no-X-over subject and I generally agree with the concept - trafos are the xover already.

However... there's this worrying possibility of overloading the HF trafo, both sonically and electrically. So: I'll try all the options myself; listen and check for heat at my usual listening levels, and make a call. Now that I've split the interface (only one so far) and plan to re-wire using lugs wherever possible for the convenience if easy changes, nothing will be difficult from here.
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Old 10th September 2012, 02:43 AM   #18
tyu is offline tyu  United States
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one thing i well say in my setup 50tube watts sounds great with big output.from 3ea.. 9"panels pr side.....i have 5-6 high frc. Acoustat tranfourms here only time i get any heat is when the bias is down...that on the base are high frc...tranfourmers....goodluck
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Old 10th September 2012, 08:56 AM   #19
fdlsys is offline fdlsys  South Africa
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Quote:
Originally Posted by tyu View Post
one thing i well say in my setup 50tube watts sounds great with big output.from 3ea.. 9"panels pr side.....i have 5-6 high frc. Acoustat tranfourms here only time i get any heat is when the bias is down...that on the base are high frc...tranfourmers....goodluck
Ugh... a bit lost in this I'm afraid - would you mind expanding the abbreviations and providing a bit more detail for me?
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Old 10th September 2012, 12:38 PM   #20
tyu is offline tyu  United States
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With the mods i have on my 121....my bias is off the HV mixer ....an bias can be set from 4-7k.....an yes i can drive 3ea 9"panels with a 50watt tube amp an get full output...
my room is 18'X25'X14'...best base i have ever got out of any ESl....the mods came from the guy with sound labs...thay came up with a way to setup the interface to get better output....i have setup my 121 this way....

As for the Acoustat high frc transfourmers only time i have over driven them with any amp ....without any crossover in front of the tranfourmer...was with low bias...bias is the key to all ESls....but you know this

goodluck
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