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RipX 25th February 2013 07:13 PM

Power Supply -50V gnd +50V

I'm a newbie in DIY Audio but I have a little experience in electronics :D I want to build a first cheap system just for fun & tests. I have seen this article which look good ! :) I want to order some different parts but I have a problem with the power supply !

The amp is very cheap, but PSU is expensive :eek: And I have some questions !

On the datasheet there is a 2*35V transformer but the output voltage is 50V : is-it normally ? :o
I want to order a 2*35V transformer (what is the VA stock ? I have seen 5A, so 350/400 VA is good or not ?) but is VERY expensive ...

Can you help me please ? Thanks :rolleyes:

PS : I'am french, sorry for my amazing bad english :D

MarianB 25th February 2013 07:34 PM

35Vac makes to almost 50Vcc so yes that is ok. ( well it actually makes about 47-47,5Vcc cus of the voltage drop on the bridge rectifyer ). So make the power transformer 2X35Vac @5 or 6A depending on what you are able to find, the latter ofcourse would be better.

RipX 25th February 2013 08:01 PM

Thanks for your attention :)

I have read an article for the output voltage and I have understand :D
Do you know a shop for the cheaper 2*35V transformer please ? I want not the best quality, just a little first device ;)

MarianB 25th February 2013 08:13 PM

Well as u can see we are from different countryes, so no, i have no ideea about the shops from your country ;)

Anyway, i doubt u will find a cheap and new of the shelf power transformer, maybe used ones...

RipX 25th February 2013 08:56 PM

Ok thanks for the advise ! I can order in some different contry, if shipping costs are not expensive and if paypal is available :)

xbdt 27th February 2013 12:20 PM

35V * srqrt(2) - 2x0,6 = 48,3V, perfectly normal.
I'm in Belgium and will check if I have a suitable transformer for you. I suppose you want a toroidal?

RipX 27th February 2013 04:15 PM

Thanks ! I want the cheaper ;)

And, in the post, I have new questions !

"And When connected to the bridge adapter with output altitude of about 400 watts is incredible." What is this ? The output power is 2*100W or not ?

"This our circuit use dual voltage positive – negative 50 volt and current is 5 Amp, we so use power supply as this figure which." Can you explain to me the details of the calculation of the capacity of the transformer VA ? I think I have not totaly understand ...

Please help me :)

Williams Audio 27th February 2013 09:29 PM

100w out put=vČ/r; r=8 ohm; v=28.28 vrms
100w=iČ*r; i=3.53 amp rms;
in order to convert these numbers to vdc of one rail of the power supply have to add the loss of the output stage and bridge rectifiers, efficiency of the power transformer and multiply by √2.
((28.28+5+1.4)/0.96)* √2=51.86 vdc
This will a sure you the voltage swing for 100w output.
The current will be: 3.53* √2=5 amp dc.
I hope I did a little for your calculus.
Best regards,

RipX 27th February 2013 09:39 PM

Hi, thanks for your advise !
I search the VA capacity of my transformer, so 5A = x VA, x = ?

On internet I have seen 2*35V 100VA to 500VA transformer, for price 30 to 150 € ... ;)

Best regards

Williams Audio 27th February 2013 10:03 PM

now do it so:
51 vdc/√2=36 v ac, taken in this case the max loss and full load for a 8 ohm
36*2*5=360 va
If you want ability of driving higher loads like 4 or 2 ohms, you will increase the current and the power va, that will increase linear.
Best regards,

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