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Class A vs Class AB |
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Analog Kid
Senior Member Joined: 07 Mar 2008 Location: Germany Status: Offline Points: 209 |
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Posted: 13 Nov 2009 at 8:05pm |
That made me think: if you can get rid of the "transistor sound" from a solid-state power amplifier by making it operate in class A mode, then class A valve power amplifiers must sound extra valvey. Edited by Analog Kid - 14 Nov 2009 at 12:54am |
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rhmbus
New Member Joined: 20 Apr 2008 Location: east london Status: Offline Points: 16 |
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Marantz did one a couple of years ago ,
ray
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many an old tune
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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Ever seen a 100W light bulb?
Yes, I know you have, but do you realise it disipates 100 watts without a heatsink? So do big valves. Because Eddison was trying to develop the light bulb when he accidentally discovered the valve! Therefore with big valves you can easily turn the wick up (the bias current that makes them conduct harder and become "class A" biased) Not so easy with a sliver of silicon stuck to a little metal tab (a transistor: Bipolar or FET) It needs a giant lump of finned aluminium to keep it "cool" Therefore, if you're going to that much trouble, you're not going to waste it by having a switch that puts it into A/B, where a much smaller heatsink would have done. |
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Analog Kid
Senior Member Joined: 07 Mar 2008 Location: Germany Status: Offline Points: 209 |
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This question still remains, so I will try again: is it not possible to design a HiFi power amplifier, either valve or solid-state, that can be switched between Class A and Class AB at the flick of a switch? Never seen this in a HiFi amplifier before, but in guitar amplifiers it is a quite common feature.
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Graham Slee
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I guess they'll all have to do that eventually... ...then I'll get ALL their sales! (who dares wins) |
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That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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Analog Kid
Senior Member Joined: 07 Mar 2008 Location: Germany Status: Offline Points: 209 |
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Maybe the best way to get rid of the "transistor sound" is to replace the transistors with valves.
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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Forcing Hi-Fi amps to get hot by moving the bias into class A quarters can help get rid of the "transistor sound", but I think sometimes it is a crutch.
The transistor sound is usually because of instability - messing about with increased bandwidth can take a design to the edge of high frequency instability - and that should also answer why things sound bright. What made matters worse was the RoHS - many components lost much of their warm character with the removal of alleged hazardous substances. From my point of view, rather than pushing bandwidth (taking pole splitting techniques to extremes), with RoHS it's about bringing bandwidth down very slightly to buy a bigger stability margin. In my opinion this gives better results than class A bias. |
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That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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