OTL Asylum

RE: Someone Please Explain.

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In Reply to: RE: Someone Please Explain. posted by Larry I on June 05, 2008 at 15:23:29

Well.....This gets complicated quick. Without seeing a schematic i would take a guess that this works a lot like a pro audio Class H amplifier. Carver was one of the first to use such trick.

It essentially works like this. there is a small amp connected to two power supply rails that sit in the middle of two big mosfets connected to two more power supply rails. lets say the first rails connected to the little amp are +/- 10V and the mosfets are connected to two rails that are +/- 20 volts. The little amp is what actually drives the speaker load.

there are two voltage comparators that monitor the output swing of the little amp and compares it to the power supply rails. If that voltage swing gets close enough to the rails. it starts to kick in the mosfets. The mosfets essentially pull the little amp up past the 10V rails, all the way up to the 20V rails for a full 30V swing in each direction!

Why? because the little amp doesn't have to sit there between the big rails and dissipate all that heat. the little amp can be quite small because the amount of power it actually has to dissipate is very small, even when swinging at full power!

Its actually quite an ingenious design. But not what i would call high fidelity.

I am betting. that this amp works something like that. the tube section is the little amp essentially and it gets swung around by a couple of big mosfets in a class H type system.

Thats my guess anyway. check out QSC's website for some interesting reading on Class H amplifiers!

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