800 VAC toriod for LM4780 Amplifier Kit from Daniel - diyAudio
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Old 27th December 2013, 09:26 PM   #1
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Default 800 VAC toriod for LM4780 Amplifier Kit from Daniel

Dear all,

I'm very new here and was thinking of building a gainclone amp for a long time.
Now I ordered the LM4780 amplifier kit from Daniel and looking for the extra components I need.

I found an Amplimo toriod transformer with an output of 24V but a VAC of 800! that I can buy cheap

I know this is much more then recommended but will this give problems using it?

Thanks for your attention.

Regards,

Joery
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Old 27th December 2013, 09:52 PM   #2
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The main issue you may face is that with an over-rated (VA wise) transformer your voltage will be higher than specified.

If the regulation of the transformer is speced at 10% then at no load the output voltage will be 10% higher than the rated voltage. The rated voltage is at full load.

Tony.
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Old 27th December 2013, 10:11 PM   #3
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Dear Tony,

Thank you for your reply.

So if I understand correct the max output voltage will be 10% higher with no load.
It will then be 24 + 2.4V is 26.4 volt.

Would this be a problem you think?
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Old 28th December 2013, 04:07 AM   #4
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If you cannot calculate the DC voltage after rectification, then I suggest you do more research before building the kit.
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Old 28th December 2013, 06:31 AM   #5
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Quote:
Originally Posted by Joerytech View Post
Dear Tony,

Thank you for your reply.

So if I understand correct the max output voltage will be 10% higher with no load.
It will then be 24 + 2.4V is 26.4 volt.

Would this be a problem you think?
Hi,

The max rating for voltage supply to the chip is about +-40V so you should be fine. Just make sure that your capacitors are all rated for 50V or 63V ideally.
The output your transformer should produce is 1.41 x Vac - 1V = 37V approx. You are in range. Look at article below.

Getting confused with LM4780 "parallel" and "bridged"



Rgds
Vinod
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Old 28th December 2013, 09:48 AM   #6
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Quote:
Originally Posted by vinodt1347 View Post
Hi,

The max rating for voltage supply to the chip is about +-40V so you should be fine. Just make sure that your capacitors are all rated for 50V or 63V ideally.
The output your transformer should produce is 1.41 x Vac - 1V = 37V approx. You are in range. Look at article below.

Getting confused with LM4780 "parallel" and "bridged"



Rgds
Vinod
Thanks for the info, specially the link gets me started.

I think I will wait for a little smaller transformer, I read that with 800VA actually a softstarter is needed and if its overkill anyway and will not improve the sound quality I better use a smaller one.

Greetz
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Old 28th December 2013, 10:28 AM   #7
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if you know how high your ac power lines go, we can tell you for sure...
i see no problem if you use that 800va traffo...
i like big big traffos in my amps if i can afford it and have space for it...
there will be lower voltage sag from no load to full load than when using a
lower rated traffo...just make sure you use a heatsink big enough...

24 volts is 35 volts rectified no load, it will drop when loaded...
these voltage are all withing the spec of the 4780....
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Old 28th December 2013, 11:05 AM   #8
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Quote:
Originally Posted by AJT View Post
if you know how high your ac power lines go, we can tell you for sure...
i see no problem if you use that traffo...
there will be lower voltage sag from no load to full load than when using a
lower rated traffo...just make sure you use a heatsink big enough...

24 volts is 35 volts rectified no load, it will drop when loaded...
these voltage are all withing the spec of the 4780....
Okay, My main power fuse is 16A and I just now see that the transformer must have a 6,3A Slow fuse so it might work then.

Only I must consider the weight of 6,7Kg (about 15 pound) It will become a serious bulky amplifier, hehe
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Old 29th December 2013, 10:02 AM   #9
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you also need to consider you may need a softstart for this transformer. and the 6.3A mainfuse will not protect much, unless it's a short.
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