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Easing the load on OTLs

I have a pair of Einstein Final Cut OTLs. While they look big and beefy and put out an honest 50 clean watts, like most OTLs, they do not like low impedences or being driven hard.

When playing records, I would often notice that the mid-woofers on my current 2 ways and the bass speakers on my previous 3 ways would pump madly in and out on some records, indicating flaws in the cutting process. This behavior has to stress the amp forcing it to try and reproduce that noise and of course, it must smear the sound.

On another forum, I read about this problem with a proposed solution of a rumble filter, an item that was common on preamps in days gone by. A stand alone model is offered by KAB (no affiliation). As it was only $189, I ordered it for a try.

When I had installed the unit between the phono-pre and pre-amp I then cued up my worst offending record which is one of my favorites, Allison Krause So Long So Wrong. This is supposedly an audiophile record. I should have exchanged it long ago but did not realize it was a problem. At any rate, all is now quiet with my mid woofers and my sub. The amp is certainly happier and the staging does sound more accurate with longer decays.

Of course, this idea would work with any amp, but I thought since I am using OTL, you all would get to hear about it. The usual disclaimer apply.
Tom Collins


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Topic - Easing the load on OTLs - collinslaw@fuse.net 07:35:46 09/17/15 (3)

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