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Old 7th March 2013, 10:29 AM   #21
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Join Date: Jul 2010
Location: Middle East someware!
Hi Boys, may I ask a newbie question?

When in china I can get a 300V/A 220 v primary /2 x 18 volt output secondary transformer, however my mains input where I live is 240v, so to get 2 x 18 volts output on the transformer, what input voltage input should I select? (Bearing in mind my input is 240v not 220 v) should I select a lower secondary to get 18 v out or vica versa? (or wont it matter?)

I am interested to ask since I was looking at some mondorf mlytic caps from hi fi collective (2 x 47,000 uF per channel) at a nice price (around 12 UKP each) but there only rated at 25volts DC (+20% extra on the spec) my PSU PCB only has room for 2 caps per channel hence the fetish for the 47,000 Uf caps--or -are there better cap recommendations ???

see link: http://www.hificollective.co.uk/components/mcap_mlytic_si.html

Am i sailing to close to the wind here, or is the on load voltage low enough to be safe within the cap max tollrence

Thanks boys--blowed if i know!

regards

Johnny
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Old 7th March 2013, 11:07 AM   #22
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I wouldn't risk using a 220V transformer at 240V, it might well overheat.

But to answer your question all you need to do is find the Np ; Ns ratio.

220 / 18 = 12.2

So at 240V you should get 240 / 12.2 = 19.7V.

To get 18V you would need to find a 18 x 220/240 = 16.5V transformer.
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Old 8th March 2013, 04:37 PM   #23
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Thanks Katieanddad, looks like i wont be getting a cheeop Chineest Tx, ill save and get the Amtek (or piltron if rich?)

Thank you for the easy to understand explenation sir

Any one idears on the Cap issused raised here?

cheers

Johny
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Old 8th March 2013, 04:43 PM   #24
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go for 35V caps. and use the 220V transformers. that is no problem.
and i would get another PSU Board, that can hold minimum 4 caps and can be used With CRC/CLC filter, bleader resistor and bypass caps.

Last edited by AudioSan; 8th March 2013 at 04:49 PM.
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Old 10th March 2013, 07:43 AM   #25
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Thanks Audiosan, I have the Paul Danuals PSU board with only 2 cap per PCB, wish i had the option of say 4 x 22,000 uf- that would be easyer- Mundorf look good but i think others have used Panasonics to good effect?

cheers
Johnny
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Old 10th March 2013, 08:26 AM   #26
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do you mean peter daniels?
those Boards are single rail. so you ned 2 of them. 1 for +rail and 1 for -rail. so then you have for 4 caps, bleader resistor, CRC/CLC and bypass caps. if you want seperate PSU for each ch, then you need 4 PSU Boards.
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Old 11th March 2013, 03:40 AM   #27
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Hi Again Audiosan,

Thanks for the reply to my inept questions, yes I read the circuit diagram again, now i understand!, think i got confused!! but as i am building monoblocks i do indeed require another set of PCBS.

But at least i can get a set of 4 (per channel) of 22,000 UF caps in with decent voltage ratings (35v) - it may be a good idea to reconsider and get 2 x DIY universal PCBS? for a monoblock configuration?
Any how thanks Audiosan-i now "get it"- keep em coming .

Best regards
Johnny

(PS- Paul Daniels was a Magician who worked for the BBC IN THE 1980S-- what was i thinking??)

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