Power Supply -50V gnd +50V - Page 2

RipX · 27th February 2013, 09:27 PM

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

JMFahey · 27th February 2013, 10:37 PM

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:

from around 20 cm wide, at least 10 cm high.
Or better.

RipX · 28th February 2013, 10:20 AM

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

JMFahey · 28th February 2013, 12:53 PM

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.

RipX · 28th February 2013, 06:05 PM

Tu parles français ?

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,

JMFahey · 28th February 2013, 06:35 PM

Bien sûr !!

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.

RipX · 28th February 2013, 07:09 PM

Ok thanks ! So a 2*36V 300 to 400 VA for cheaper ... hard in France

JMFahey · 28th February 2013, 09:06 PM

Probably, but check Italy .
Or Eastern Europe such as Poland/Czechoslovakia/Yugoslavia .
I use the old names to avoid long lists

RipX · 1st March 2013, 09:13 AM

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

JMFahey · 1st March 2013, 10:22 AM

Excellent.

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27th February 2013, 09:27 PM	#11
RipX diyAudio Member Join Date: Feb 2013 Location: Nord (59)	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

27th February 2013, 10:37 PM	#12
JMFahey diyAudio Member Join Date: Mar 2009 Location: Buenos Aires - Argentina	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: from around 20 cm wide, at least 10 cm high. Or better.

28th February 2013, 10:20 AM	#13
RipX diyAudio Member Join Date: Feb 2013 Location: Nord (59)	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

28th February 2013, 12:53 PM	#14
JMFahey diyAudio Member Join Date: Mar 2009 Location: Buenos Aires - Argentina	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.

28th February 2013, 06:05 PM	#15
RipX diyAudio Member Join Date: Feb 2013 Location: Nord (59)	Tu parles français ? 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,

28th February 2013, 06:35 PM	#16
JMFahey diyAudio Member Join Date: Mar 2009 Location: Buenos Aires - Argentina	Bien sûr !! 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.

28th February 2013, 07:09 PM	#17
RipX diyAudio Member Join Date: Feb 2013 Location: Nord (59)	Ok thanks ! So a 2*36V 300 to 400 VA for cheaper ... hard in France

28th February 2013, 09:06 PM	#18
JMFahey diyAudio Member Join Date: Mar 2009 Location: Buenos Aires - Argentina	Probably, but check Italy . Or Eastern Europe such as Poland/Czechoslovakia/Yugoslavia . I use the old names to avoid long lists

1st March 2013, 09:13 AM	#19
RipX diyAudio Member Join Date: Feb 2013 Location: Nord (59)	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

1st March 2013, 10:22 AM	#20
JMFahey diyAudio Member Join Date: Mar 2009 Location: Buenos Aires - Argentina	Excellent.