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Old 29th August 2005, 06:08 AM   #1
Ipanema is offline Ipanema  Malaysia
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Default Transformer calculation for GC

Hi,

I went to the electronic shops yesterday to buy power transformer for my GC. I ask for two 150VA 24v-0-24v transformer for my monoblock LM3875 GC. The transformer in the shop is only rated in ampereres not in VA, so according to the shop owner 6.25A 24v-0-24v is 150VA, but my calculation indicates that 48*6.25A=300VA. Pls let me know which is correct? 6.25A is 150VA or 300VA?

What is the minimum VA for each monoblock? Is 150VA optimum?

OTOH, I'm building my monoblock with seperate chasis for PSU and amplifier. So do I really need toroidal transformer or I can just use EI transformer which is much cheaper in my place. I understand that EI transformer produces more stray EMI, but since I have seperate chasis to house my transformer, will it matter?

Can I use 3 pins XLR connector for connection between PSU and amplifier chasis? If not what is the most appropriate connector?


Thanks for your advise.


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Old 29th August 2005, 06:36 AM   #2
agent.5 is offline agent.5  United States
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300va. I think whether 300va is enough depends on whether your PSU is regulated or not. 300va should be good for 2 channels regulated.
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Old 29th August 2005, 06:51 AM   #3
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A good rule is equally manu VA as watts out. That's minimum. So 100-160 VA for stereo is "normal". More than 300 VA is overkill.

Remember that it takes 5-10 minutes for a transformer to get hot and you will hardly play sinus 100% as a real music signal.
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Old 29th August 2005, 06:54 AM   #4
Ipanema is offline Ipanema  Malaysia
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Hi agent.5,

Do you mean that 6.25A is 300VA?

Regards.
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Old 29th August 2005, 07:02 AM   #5
agent.5 is offline agent.5  United States
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Yes. you have a total of 48V. 48V * 6.25A = about 300VA
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Old 29th August 2005, 08:19 AM   #6
Ipanema is offline Ipanema  Malaysia
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Thanks agent.5.

OTOH, I'm building my monoblock with seperate chasis for PSU and amplifier. So do I really need toroidal transformer or I can just use EI transformer which is much cheaper in my place. I understand that EI transformer produces more stray EMI, but since I have seperate chasis to house my transformer, will it matter?

Can I use 3 pins XLR connector for connection between PSU and amplifier chasis? If not what is the most appropriate connector?

Regards.
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Old 29th August 2005, 09:09 AM   #7
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The XLR's i know are good for 6 amps/50Vac.
For the GC's i hacked together i used Hirschmann Stas/Stak, those do 16 amps/250Vac.
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Old 29th August 2005, 06:21 PM   #8
agent.5 is offline agent.5  United States
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Quote:
So do I really need toroidal transformer or I can just use EI transformer which is much cheaper in my place. I understand that EI transformer produces more stray EMI, but since I have seperate chasis to house my transformer, will it matter?

My guess is that it will make no difference as long as you have a good power supply. But I suggest that you seek a second opinion.
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Old 30th August 2005, 01:32 AM   #9
Ipanema is offline Ipanema  Malaysia
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Thanks.
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Old 4th April 2006, 04:42 PM   #10
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Quote:
Originally posted by jacco vermeulen
The XLR's i know are good for 6 amps/50Vac.
For the GC's i hacked together i used Hirschmann Stas/Stak, those do 16 amps/250Vac.

Isnt that a bit high on the voltage side of things for a GC? Generally the national chips dont like anything above 35VDC I thought. Do you run them in series?
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