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Old 4th September 2012, 09:57 AM   #1
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Default A-Class 30W

Hi this is my new power amp!! OK let's take a look at the components that i chose!!

1.Resistance : Holco H4&H4P

2.Filter capacitor: RIFA 22000uF/63V 150'C X4

3.Capacitor: NO input capacitor

4.Transistors: 2SC5200 2SA1943 MJE340/350 MJE15030/31

5.RCA input : Cardas Plated Rhodium

6.Input Signal Cable : +Cardas 6N 0.6mm -Mundorf 0.5mm silver/gold


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I set the bias at 1A during the summer it's working temperature is 49C with no air conditioner and i am will set the bias up to 1.5A during the winter!!

Last edited by perfectbell2; 4th September 2012 at 12:20 PM.
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Old 4th September 2012, 05:57 PM   #2
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Default Class A?

'Nice components and build but really, it cannot be claimed as a class A design, despite not posting any schematic to support your claim, since even push-pull class A designs will require a minimum constant bias current of 1.8A to qualify it.

Yes, that would make an uncomfortably hot amplifier but your heatsinks at least look capable of dissipating the ~85W per channel necessary. One amp bias will give you only ~17W in class A, though this could be increased slightly with a CFP design output stage.
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Old 4th September 2012, 06:23 PM   #3
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I have looked and looked again at this short thread i see no questions . Just a proud diyer showing of his latest amplifier.
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Old 4th September 2012, 06:26 PM   #4
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A pretty heat generator for those cold evenings.
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Old 4th September 2012, 06:39 PM   #5
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Quote:
Originally Posted by Ian Finch View Post
'Nice components and build but really, it cannot be claimed as a class A design, despite not posting any schematic to support your claim, since even push-pull class A designs will require a minimum constant bias current of 1.8A to qualify it.

Yes, that would make an uncomfortably hot amplifier but your heatsinks at least look capable of dissipating the ~85W per channel necessary. One amp bias will give you only ~17W in class A, though this could be increased slightly with a CFP design output stage.
not a class A design? well, not 30W class A with bias turned down to 1A. but still a class A design. and there is 1.36A to get 30W class A @8ohms. not 1.8A.
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Old 5th September 2012, 12:55 AM   #6
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I like it.

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Old 5th September 2012, 01:17 AM   #7
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Very nice clean amplifier... It does have class
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Old 5th September 2012, 03:05 AM   #8
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Thanks Guys!!! About the bias,I set it at 1A but actually i think it is working under 1.4A because the place where i put my amp does not have a good air convection so i think it is working 30W!!

PS:In my condition 1A bias is +V 1A -V 1A it means that per channel is absorbing 2A。My design is working push-pull class A so does it mean that my bias is 2A or not??
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Old 5th September 2012, 09:56 AM   #9
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Measuring 1A current in both rails is the same current, as the path is common. The bias current will be 1A rail current minus the small current required for the input and voltage amplifier stages. To measure the output stage bias current only, assuming you have 2 complementary pairs of output transistors, you can calculate from the voltage measured across either emitter resistor in both pairs and sum them.

Example: You have 0R22 emitter resistors and voltage measures 220 mV across a resistor connected to either pair. Current = 0.22V/0.22R = 1A. Summing both pair currents = 2A bias.

You mention poor ventilation - does that increase the bias to 1.4A total?

I commented that 1A would not be sufficient for genuine 30W in class A because real loudspeaker impedance, over the audio spectrum, is much less than 8R. This means the amplifier will be switching from class A to AB on signal peaks whenever the power rises above ~17W RMS. It is abitrary where to draw a line to say which is a genuine power rating or not, though I believe a 6R rating for a nominal 8R speaker is a reasonable compromise. The point being that resistive load ratings do not relate to practical class A operation. If, for example, you have 4R speakers, you would need to double the bias current for the same power rating as 8R speakers and so on.
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Old 5th September 2012, 10:21 AM   #10
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Thanks for helping me to understand about the bias in class A。I am sure that the bias is at around 1.4A when it is working due to my poor ventilation altough I set the bias at 1A

PS:I make a mistake about the title I wrote A-Class but what i actually mean is CLASS-A
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