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Old 17th January 2008, 01:16 AM   #1
TheMG is offline TheMG  Canada
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Default Powering 2 UCD400s

Hello,

I am going to be building an amp using two UCD400 modules from Hypex.

I haven't really done much in terms of amplifiers so far besides some fairly low-powered stuff, so when it comes to picking the right transformer, I'm absolutely clueless.

Say I wanted enough juice to power these modules under the absolute most power-hungry conditions (music of course, won't be feeding any pure sinewaves but very heavy bass is definitely going to happen), what transformer should I pick?

I see the one sold by Hypex which is 500VA and 42VAC (TR501A), now I don't know all that much about VA, but isn't that roughly equal to 500W? Doesn't seem like enough although they claim it is sufficient to power two UCD400s. The spec sheet doesn't even state the current ratings for that transformer.

Now, I probably won't be getting the one from Hypex, shipping on such a heavy item overseas is going to be killer! So I'm probably going to get something from Digikey.

Am I worrying too much or should I just bite the bullet and purchase the trany from Hypex and trust it's going to be powerful enough and that hopefully the shipping charges won't put me overbudget on this project?
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Old 17th January 2008, 02:03 AM   #2
john65b is offline john65b  United States
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I have used a 500VA 40V dual secondaries with no problems. The UCD400 datasheet may not state required transformer VA, but the TR501 is 500VA and states it is good to power two UCD400 Modules. I would not go any lower than 500VA on a pair of UCD400. Higher VA is always fine but why bother?

The Hypex power supply module I have no experience with - I just buy two heavy duty 25A rectifiers and two caps at least 10,000uF 63V. I also like to put a 10k 5W bleeder resistors across rails. I have also bypassed main caps with 20uF polypropylene cap and hear no appreciable difference...

I have a UCD with two 56,000uF caps - cant really hear a difference between that and two 10,000uF caps...except it take 45 seconds for the 56,000uF caps to drain when amp is shut down...
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Old 17th January 2008, 02:47 AM   #3
TheMG is offline TheMG  Canada
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Thanks for the response.

I just found a 700VA 39V transformer for $62 not including shipping. Much cheaper than the Hypex one. Probably a little overkill but at that price, can't complain.

Actually it's probably a good thing since this will give me a little headroom to add another module should I want to later on (for a subwoofer output for example).

I'll definitely need to build my own rectifier circuit and soft-start circuit (don't want to be tripping them breakers) for this beast, but that's no problem, and probably cheaper too.

From what I just read, VA = P when the current is in-phase with the voltage, so a 700VA trany would be good for 700W if the load is in phase.
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Old 17th January 2008, 02:52 AM   #4
BWRX is offline BWRX  United States
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If you want the full 400W then you'll need about 500VA per module.
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Old 17th January 2008, 04:16 AM   #5
john65b is offline john65b  United States
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Whoops, I just realized that the UCD400AD I have is a 700VA Antek 39V dual secondary off ebay, not a 500VA as mentioned earlier...

Maybe the same one you are looking at?

ebay link

And the soft start I use - works perfectly...

ebay link
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Old 17th January 2008, 01:00 PM   #6
BWRX is offline BWRX  United States
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Quote:
Originally posted by TheMG
From what I just read, VA = P when the current is in-phase with the voltage, so a 700VA trany would be good for 700W if the load is in phase.
Quote:
Originally posted by BWRX
If you want the full 400W then you'll need about 500VA per module.
To clarify, if you want the full 400W continuous output power you will need about 500VA per module. Under normal listening conditions you can get away with much less, hence the reason Hypex says 500VA is fine for a pair of modules.

CI Audio's UcD400 based amps use a 300VA transformer per module as does SSassen's UcD400 based amp.
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