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-   -   how much class A power can be expected with a Pair of 2sc5200 1943 pair at +/-52V (http://www.diyaudio.com/forums/solid-state/226081-how-much-class-power-can-expected-pair-2sc5200-1943-pair-52v.html)

rhythmsandy 20th December 2012 02:24 AM

how much class A power can be expected with a Pair of 2sc5200 1943 pair at +/-52V
 
I would like to bias LM4702 into class A with Bias current of 500mA or may be 1A but will have very large heatsinks measuring 300mm x 200mm and fins will be about 50mm length.

I would like to know that the supply voltage be if its driven in class A.

the idea is to put a switch where we can switch the amp in Class A and Class AB

but the question is when the amp is delivering about 100W in 8 ohm with 2sc5200 1943 pair then how much it can deliver in class A 20W?

tinitus 20th December 2012 06:58 AM

why drive this amp in classA ?
do you think this amp will sound better with higher bias ?
(bias adjusting a classAB amp is not like 'the more the merrier')

knutn 20th December 2012 07:08 AM

Quote:

Originally Posted by rhythmsandy (Post 3292157)
I would like to bias LM4702 into class A with Bias current of 500mA or may be 1A but will have very large heatsinks measuring 300mm x 200mm and fins will be about 50mm length.

I would like to know that the supply voltage be if its driven in class A.

the idea is to put a switch where we can switch the amp in Class A and Class AB

but the question is when the amp is delivering about 100W in 8 ohm with 2sc5200 1943 pair then how much it can deliver in class A 20W?

The important thing here is the bias current. With a bias of 500mA, Class A power into 8 ohms is 4 Watts, increasing to 16 Watts with 1 A bias.

jan.didden 20th December 2012 07:44 AM

Absolutely right Knuth!
The definition of class A is that the output devices are not turning off during the signal cycle.
With 500mA bias, max output peak current in class A is 1A, which is 0.7A RMS (1A * sqrt of 2). Power in 8 ohms is then 0.7^2 * 8 = 4W.
The supply voltage is irrelevant as long as it is high enough for the required class A output level.
1A peak in 8 ohms is 8V, so this 4W class- A can be delivered with a supply voltage just above +/-8V...

jan

bobodioulasso 20th December 2012 09:12 AM

Without forgetting that disipation is proportional to V supply.

BachAudioDK 20th December 2012 10:34 AM

100W in 8 ohm requires a bit more than +/- 40V rails.

If your heatsinks are big enough, then a rough guess is that it should be possible to have a bias current between 1 - 2 amp.
2 amps of bias current with no input signal, gives a power dissipation of 80 watt in the NPN and 80 watt i the PNP transistor with +/- 40V rails.

There might be some problems with derating at high Tcase temps:
http://www.st.com/internet/com/TECHN...CD00249630.pdf


I assume that you only use one 2SC5200 and one 2SA1943 in your pushpull output stage correct ?

jan.didden 20th December 2012 11:14 AM

2A bias gives 4A peak in class A which is 2.8A RMS which is 2.8^2 * 8 = 62W in 8 ohms in class A....

jan

jan.didden 20th December 2012 11:15 AM

Quote:

Originally Posted by bobodioulasso (Post 3292424)
Without forgetting that disipation is proportional to V supply.

Indeed.

knutn 20th December 2012 12:56 PM

So even if you are using large heatsinks (0.3 K/W), the heatsink temperature would become nearly 80 degrees for a mono 100 W Class A amplifier...

bobodioulasso 20th December 2012 01:23 PM

Anyway, Lme chip doesn't need to run class A for nice sounding .
It will bring nothing but heat.


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