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Old 27th February 2013, 09:27 PM   #11
RipX is offline RipX  France
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So, if my calculs are goods

8 ohms = 100W = 5A = 360VA
4 ohms = 200W = 10A = 720 VA
2 ohms = 400W = 20A = 1440 VA
1 ohms = 800W = 40A = 2880 VA
...

It's ok ?
Thanks
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Old 27th February 2013, 10:37 PM   #12
JMFahey is offline JMFahey  Argentina
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1) As a very loose calculation, you need *at least* 50% more VA than the RMS power and preferably 100% more so for 2x100W amplifier you'll need at least a 300VA transformer (and that would be for home use) to 400VA.
If you go higher, it does not hurt
Load each channel with a normal 8 ohms speaker (or cabinet) and you'll be fine.
Don't bridge it, or load with 4 ohms, etc., just work well within its specs, not worth getting close to the limits.
Anyway you already have a very powerful amplifier.

2) the heatsink shown in the project page is *very* small, guaranteed to burn your amplidier.
At most it's suitable for a single 50/60W chipamp or less.
You'll need something like:
Click the image to open in full size.
from around 20 cm wide, at least 10 cm high.
Or better.
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Old 28th February 2013, 10:20 AM   #13
RipX is offline RipX  France
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1) Ok, why I can't load into 4 or 2 ohms ? The amplifier going to be dead ?
And, the transformer is it necessarily a torroidal ? I have find on ebay a led transformer : 30$, 36V with several output (3*"36V+", 3*"Gnd" and 3*"36V-") for 9.7A

2) thanks for this advise
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Old 28th February 2013, 12:53 PM   #14
JMFahey is offline JMFahey  Argentina
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1) Yes. You will burn it.
1.5) post the EBay link.
As you write it, it's wrong.
Plus I don't believe you can buy a 72Vx9.7A=700VA transformer for $30.
So you must have read something wrong.
2) Il n'ya pas de quoi.
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Old 28th February 2013, 06:05 PM   #15
RipX is offline RipX  France
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Tu parles franēais ?

Here is the "transformer"

36V DC 9 7A 350W Regulated Switching Power Supply | eBay

So ... I don't know if is good or not !

Best regards,
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Old 28th February 2013, 06:35 PM   #16
JMFahey is offline JMFahey  Argentina
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Bien sūr !!

Back to electronics: this is not a transformer but a 36V DC regulated switching power supply.
*Maybe* two of these can supply a power amp which needs those rails , but it's useless for you.
*Plus* it's in China, you have to pay extra for shipment but even worse, any Tax or Customs Duty is extra.
Try to get a transformer locally or at least within the E.U., transformers are heavy and pay a lot.
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Old 28th February 2013, 07:09 PM   #17
RipX is offline RipX  France
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Ok thanks ! So a 2*36V 300 to 400 VA for cheaper ... hard in France
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Old 28th February 2013, 09:06 PM   #18
JMFahey is offline JMFahey  Argentina
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Probably, but check Italy .
Or Eastern Europe such as Poland/Czechoslovakia/Yugoslavia .
I use the old names to avoid long lists
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Old 1st March 2013, 09:13 AM   #19
RipX is offline RipX  France
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Finnaly I have find (within 15km from my home) a used toroidal transformer 2*35V 300VA with invoice and warranty for 30€ ...

I think is it the best price, no ?

Thanks
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Old 1st March 2013, 10:22 AM   #20
JMFahey is offline JMFahey  Argentina
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Excellent.
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