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β24 in pure class A

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Re: β24 in pure class A

Postby NZST205 » June 20th, 2014, 11:26 am

Thank you, my understanding of the variables is improving. Looks like it'll be a standard B24 then.
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Re: β24 in pure class A

Postby goldkenn » July 28th, 2014, 3:12 am

I have built the b24 in pure class A, I am using 225VA transformer per channel, not sure it is because I am driving 4 ohms speakers, the tansformers run hot, it is normal or I need bigger transformers?
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Re: β24 in pure class A

Postby amb » July 28th, 2014, 3:38 am

goldkenn wrote:I have built the b24 in pure class A, I am using 225VA transformer per channel, not sure it is because I am driving 4 ohms speakers, the tansformers run hot, it is normal or I need bigger transformers?

The transformer runs at full load the whole time in pure class A, so it's expected to get hot. 225VA per channel is enough.
How about posting some photos of your β24 (inside and out) for all to see?
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Re: β24 in pure class A

Postby goldkenn » July 28th, 2014, 9:32 pm

Now still burning in to make sure everything stable before putting into chassis, will take some photos later.

However, I am wondering, the amp/heatsink run reasonable hot, but not the transformer, too bad I don't have any 8 ohms speakers in hand, and no tools to check the actual temperature of the transformers, but since usually 4 ohms draw much current, that's why I am worring 225VA/per channel may not enough....
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Re: β24 in pure class A

Postby amb » July 29th, 2014, 12:04 am

A pure class A amp draws maximum current from the power supply constantly. The output transistors run hottest when the amp is idling, because the full current flows through them from the positive rail to the negative rail. When you turn up the volume and play music, the output transistors actually cool down a bit, because some of the current is now going into the speakers.

A 225VA transformer can output 225W theoretical power, even after factoring any losses in both the transformer and the amp, there is still plenty of headroom for a 40W amp. Transformer loss is turned into heat, and the more current draw there is, the hotter it gets, and a class A amp draws a lot of current constantly. I purposefully over-spec'ed the transformer to ensure that it will never be stressed, whether electrically or thermally.
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Re: β24 in pure class A

Postby first » July 29th, 2014, 3:31 pm

Hi:goldkenn

looking forward to post picture.

is it any chacne to listening your B24
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Re: β24 in pure class A

Postby goldkenn » July 29th, 2014, 11:36 pm

amb wrote:A pure class A amp draws maximum current from the power supply constantly. The output transistors run hottest when the amp is idling, because the full current flows through them from the positive rail to the negative rail. When you turn up the volume and play music, the output transistors actually cool down a bit, because some of the current is now going into the speakers.

A 225VA transformer can output 225W theoretical power, even after factoring any losses in both the transformer and the amp, there is still plenty of headroom for a 40W amp. Transformer loss is turned into heat, and the more current draw there is, the hotter it gets, and a class A amp draws a lot of current constantly. I purposefully over-spec'ed the transformer to ensure that it will never be stressed, whether electrically or thermally.



Fuly understand
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Re: β24 in pure class A

Postby goldkenn » July 29th, 2014, 11:37 pm

first wrote:Hi:goldkenn

looking forward to post picture.

is it any chacne to listening your B24


Maybe not, wife factor, sorry, let's see later
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Re: β24 in pure class A

Postby first » July 30th, 2014, 1:46 pm

Hi:goldkenn

Thanks, quick answer

looking forward B22 picture
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Re: β24 in pure class A

Postby MASantos » October 31st, 2017, 3:34 pm

Hello Ti,

I am considering a B24 next year. I would like to mix the class A/B and class A versions and have a high biased class A/B where the first 30-40 watts would be class A and then go up to 80-100 in A/B. This means larger heatsinking and PSU. I have a hifi2000 5U 400mm dissipante for my diy first watt class A amp and it dissipates about 100W per channel without a problem, so it might be a good choice for the amp.

I think I'll need something in the 24-26V to get the wanted AB power output for peaks right?

what other changes would I need to consider for such an endeavour?
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