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In the Forum: Audio Discussions
In the Thread: NAT Audio Magna -160 Watts of Single-Ended Class A
Post Subject: A powerful full-range SET? What a bogus idea!Posted by Romy the Cat on: 11/13/2007

Looking again at the NAT Audio Magna amp, the amps around the 833A, GU81, 50TH, 1000TH, GM100 and many other SETs that try to use powers transmuting tubes I feel that the entire endeavor of powerful SETs shoot itself in a leg.

If a person has too dead loudspeaker or a large listening room then a person might feel that need more power from him SET (it is not always correct). However, s it possible to get more single-ended full-range power out of SET without fundamentally compromising the performance of a SET? I am very much not expert on amplification topologies but my common sense suggests me that it is imposable and pursuing more power we unavoidably but voluntary screw up our SETs.

More power from transmuting tubes = higher voltage on plate. Higher voltage = less current. Less current = higher plate impedance. Higher plate impedance = more turns in the output transformer. With all excessive isolations and windings capacitance due to explainable needs to care high voltages, the  increase of power in any SET amp shoot against the HF extension and the quality of HF as high voltage (via increasing capacitance) dehydrates higher frequencies

Then there is a subject of transformer saturation at LF – it directly proportional to power – with more powers more and more inductance the transformer shell care. The NAT Audio Magna amp from my post above in order to pump full 160W power out of that 450TH tube (let presume that the drive it at 1000V that would make it to have ~ 7K plate impedance). This way it would need at least 250H inductance to go down to relatively low number of LF cut off (~30-40Hz). Can you imagine the size of 250H transformer able to care 160W? It is obviously not what the Audio Magna has under the hood. I would not mention what would happen with capacitance in oversized that transformer.

That all brings the subject of a necessity of powerful full -range SET. I personally feel that any powerful full -range SET is an aberration. SET should be up-to <10W and then if more power is necessary from then SET might be split to DSET. This would assure a topologic and implementation absents of any compromises.

People should not be under impression that more power can cure low sensitivity acoustic systems. Sure with more power lower sensitivity acoustic systems WILL perform much better but it will NOT be equal to higher sensitivity acoustic systems driven by a moderate power.

So, what high-power powerful full – range SETs prove? A celebration of wishful thinking over the sense of reality?  The Audio Magna has two operational modes: 40W and 160W. If the Audio Magna operates (electrically) well-enough at 40W then can you image how much compromised the sound of that amp is at 40W if the amps stages and magnetics were designed to care 160W?

Rgs, Romy the caT

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