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Amplifiers - Amplifiers for IRS Beta
With the INFINITY IRS Beta, you must avoid the tubes amplifiers: they are not powerful enough, whatever they are (AudioResearch, etc...). They cannot deliver enough current (A).

In addition, this system also requires excellent transistor amplifiers. Here are the brands able to drive the IRS Beta:

1.MARK LEVINSON. Actually, the ML-432 for the bass section and a pair of ML-434, with a ML-326S do a perfect job !
Alternately, the older 334 / 335 / 336 are also good.

2-.The THRESHOLD (the old ones, meaning the ones designed by Nelson PASS) or the PASS LABORATORIES. Both are truely excellent amplifiers. For those of you who remember the big IRS V (2.32meter tall) had their bass section very often powered by the THRESHOLD SA/12e. So the THRESHOLD or PASS are superbly adapted to drive the IRS. This is something to know if you are lucky enough to find a 2nd hand THRESHOLD SA/6e monoblocks (almost impossible to find in Europe) or SA-1 optical bias.

2.bis The brand JADIS and in fact the JA500 in class A/B developped for this kind of loudspeakers with it's own power supply (a monster).

3-.KRELL. These amplifiers are simply impossible to destroy...I have tested the old KMA-160, KSA-200B, and whatever the volume is, the amplifier can deal with it... The sound is generous, the high frequencies of the IRS seem to fulfill the room... The sound is very rich, but is it natural ? not sure, this is the reason why it is ranked at the 3rd place.

4-.JEFF ROWLAND. We are talking only about the excellent old models, not about the current production which is, in our opinion, far to reach the musicality of its predecessors... We are talking about the models 5, 7, 8 or 9 (difficult to find).

You must absolutely avoid: Accuphase, Mac Intosh, Classé Audio, Gryphon.

Edit by Nounours:
I feel free to add this comment as I am sure that Florent thinks like myself.
INFINITY has made its brand image in the 80's with products like the INFINITY IRS Beta: these products were the "state of the art" at this period, they were designed by very serious engineers, with a lot of time spent in optimization and tunning, in order to provide the best possible musical reproduction.
INFINITY has been bought by HARMAN (they manufacture the Harman Kardon amplifiers for ex), a very rich group that also bought MARK LEVINSON. But they have never kept intact the audiophile approach of these companies. Have a look at the current INFINITY product line on their website, and you will immediately understand the difference with the IRS Beta philosophy ! It has nothing to do with nostalgia, but this makes me very sad....

Article written by Florent ("provence13" on the Forum).

Creation date : 03/02/2007 @ 21:56
Last update : 11/01/2016 @ 20:52
Category : Amplifiers
Page read 1063 times

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Reactions to this article

Reaction #7 

by MLAS 08/03/2018 @ 11:42

Hi Florent:
Your statement:
"Là aussi ça marche d'enfer. Une info : vous connaissez les IRS V, celles qui mesurent 2,32 m de haut ? : leur grave était très souvent amplifié par des Threshold SA/12e."
is incorrect.
The IRS V had his own dedicated 1.5 kW amplifier inside the basstower.
Arnie Nudell never used any solidstate amplifier on this system and for the mid/high towers he used Conrad Johnson Premier Fives (as on the mid/high sections of the RS-19(b)) or Audio-Research M300.
If your looking for amplifiers that can deliver loads of current to tough loads Threshold should be avoided by definition. I've had Threshold S/300, SA/3, S/1000 series II, SA/1 and SA/1 optical bias with fullrange Acoustats and with my Infinity QLS and the only amps that could deliver enough power to get both loudspeakers sounding real loud where my Krells KMA-200 (Mk2) and Jeff Rowland Model 7.

Greetings Robert

Reaction #6 

by jean130369 15/03/2011 @ 10:53


et bien maintenant un troisième dnas le (57) moselle wink


Jean Roveri

Reaction #5 

by provence 01/03/2011 @ 17:11

Nous avons fait des essais poussés avec les Infinity IRS Beta et le meilleur combo fut : Krell KSA200 + AR250MKII mais après de longues écoutes  nous sommes passés aux TACT numérique !
En France je n'en connais que deux, l'un dans l'Oise (60) et l'autre en région PACA.(13).

Reaction #4 

by jeanroveri 28/02/2011 @ 22:14


je suis un peu surpris en lisant cet article.

Je suis l'heureux possesseur d'un système infinity IRS Beta que je drive avec 4 ARC 300 et tout ce que je peux vous dire c'est qu'ils sont loin d'être ashmatiques, jamais plus du 1/4 de la puissance pour un volume de son largement au-dessus des 100db. J'en avais entendu beaucoup à ce sujet et je viens de faire l'experience avec le test de 4 x 9008 de chez MBL ( pure ampli à transistor et dont la reputation n'est plus à faire ) la différence est vraiment minime, infime et les aigus sont plus christallins.

Donc pour moi mes ARC sont super et je ne changerai pas.

Par contre je serais curieux de savoir combien de systeme IRS Beta existe en france ?


Jean Roveri

Reaction #3 

by don 31/03/2010 @ 08:20

Hello I operate my Infinity IRS Beta in the medium high clay/tone with Threshold SA 1 and in the bass the Threshold S 500. As preliminary stage I decided for the audio Research LS 15. CD player is a Wadia with ext. Transducer. The plant I feel as very perfect, the S500 make its job at the bass very good. The SA 1 is for my ears with best which I so far heard. I am very happy which I a SA 1 find could.
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