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Old 14th January 2017, 01:50 AM   #1
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Default Adcom 555 a thought

Nelson designed this amp, very very nice amp for class a/b, I don't know much about the circuitry. My question is that amp sounded great for class a/b, could those type of "can" transistors be used for a class A amplifier? Sorry for the "can" comparison but I don't know the correct term for the transistor.
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Old 14th January 2017, 02:02 AM   #2
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Yes, but the output power would be lower because class A heat is less efficient than AB. More cooling is necessary to accommodate the greater heat dissipation.
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Old 14th January 2017, 02:10 AM   #3
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Originally Posted by Richidoo View Post
Yes, but the output power would be lower because class A heat is less efficient than AB. More cooling is necessary to accommodate the greater heat dissipation.
ok they would get to hot with no way of cooling them, would be interesting if it could be done, they have a very warm sound, why I thought of them as possibly being used for class A
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Old 14th January 2017, 02:21 AM   #4
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You'd need to design a new amp from scratch, using those output transistors with much larger heat sinks and much bigger power supply. It would make ~25% of the output power as the class B version with same number and type of transistors. ~75% of the power as heat.
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Old 14th January 2017, 02:24 AM   #5
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ah ok not really a realistic idea do to price and weight to get any kind of power out of it.
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Old 14th January 2017, 02:29 AM   #6
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The only reason to do it is of you love class A sound, or if you get chilly in the winter.

Likely the sound of the 555 that you love has more to do with the overall amp design than it does with just the output transistors. All the stages and parts contribute to the end result.
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Old 14th January 2017, 02:34 AM   #7
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Originally Posted by Richidoo View Post
The only reason to do it is of you love class A sound, or if you get chilly in the winter.

Likely the sound of the 555 that you love has more to do with the overall amp design than it does with just the output transistors. All the stages and parts contribute to the end result.
Do love class A sound no doubt finishing up my f5 turbo v2, might be doing mono blocks next, lol my house is cold so a couple of hot amps wouldn't hurt a thing besides my electric bill which is already monsterous.
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Old 14th January 2017, 03:37 AM   #8
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ah ok not really a realistic idea do to price and weight to get any kind of power out of it.
You could probably do it if you limited Class A power to 10 watts then the rest transitioning to Class AB
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Old 14th January 2017, 05:49 AM   #9
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The bipolar Adcoms like the 555 are not such great candidates for dialling up the bias, but the mosfet Nelson-designed amps (5200, 5300, 5400, 5500, 5800, 5802) are superb candidates for making more class A if you can get rid of the additional heat and keep the ps ripple low.
I have been running a 5200 w 20W of class A (0.8A) for a few years now, but I added a bigger cap bank and a fan w additional hs.
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Old 14th January 2017, 07:02 AM   #10
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The bipolar Adcoms like the 555 are not such great candidates for dialling up the bias,
I don't think he was referring to dialing up the bias of his existing amp, it seemed to me he was referring to the suitability of the transistors for a Class A design.
At least that is how I read what he is saying.
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