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Old 9th March 2005, 05:41 AM   #1
taloyd is offline taloyd  United States
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Default transformer for UCD400

hello,

I'm working on two mono UC400's to be used via XLR cables (my system is fully balanced from the source) right next to the actual speaker.

What transformer should I use? I've read so many conflicting reports... I need to go with two seperate transformers, as the amps are going to be about 20 ft from each other. I generally order from Parts Express, so Avel Lindberg is the manufacturer.

For my purposes, would two 330VA 40V + 40V transformers be appropriate? Is 40V the voltage I want on the secondaries, or 45V? Is 330VA enough, or should I get 500? I think that considering that it's going to be biamplified >190Hz, the power demands are not going to be too intense.

Let me know which is best:

330VA 40V+40V (Avel part #Y236753)
330VA 45V+45V (Avel part #Y236754)
500VA 40V+40V (Avel part #Y236804)
500VA 45V+45V (Avel part #Y236807)

Part #'s from:

http://avellindberg.com/transformers...ange_specs.htm

thank you,

-tal allweil
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Old 9th March 2005, 09:38 AM   #2
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You may have problems with the 45 at unloaded/idle conditions + 10% mains overvoltage tripping the protection circuit.

43 would be nice, but if those are your only choices I'd opt for the 40, bit less power but not an amount you'll really miss, and as a bonus it won't be tripping the protection circuitry constantly.

330VA is lots, 500VA is much more on the overkill side, that would be good for two UCD400's, but it may get you better regulation which may be nice (rails will sag less under load).

So the final choice is yours, I think you'd be OK with the 40V/330VA model.

Regards
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Old 9th March 2005, 09:52 AM   #3
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I agree.

I did some calculations of my own and I believe 800VA for 2 modules is more than enough to handle all but the most extreme situations.

Nothing really scientific, just looked at the max. current that the modules could draw at continuous power, and then checked how much VA I need. I did throw in an additional 10% here and there.

Right now I'm looking at 800VA, 2 "block" bridge rectifiers, and 22.000uF caps per rail. (Should actually be 25.000uF to meet Bruno's conservative calculations at 4 ohms load, where the rails never can drop voltage more than 10% during the transformer idle times)

I looked at a single 1kVA first, so your 500VA/40V solution should be really good :-)

What I can't figure out is fysical caps sizes. In my Yamaha I found 28.000uF caps at 70V or something, they are about 10cm by 4cm diameter.

I've seen Philips caps 63v, 22.000uF and they look like half litre beer cans??
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Old 9th March 2005, 09:56 AM   #4
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Hi Yves,

It would be interesting to know how the two compared with ripple current, I would hope the bigger cap had the better rating.
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Old 9th March 2005, 04:54 PM   #5
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@classD,

I'm just an amateur, I have no way to do a test of ripple current. I just don't understand what is different between these caps, but i'm sure it should be audible.

I'm getting them friday for 30/piece, I hope that price is right.

Now just find a 800VA transformer in Belgium...

Oh, and I though Philips didn't make caps anymore? This guy just ordered 2 especially for me?

Oh well, I'll see friday.

Y
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Old 9th March 2005, 05:02 PM   #6
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Hi Yves,

It should say in the data sheet, no point measuring.

Philips doesn't, it's part of BCC? Which part of Vishay..... etc


Should be decent caps.
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Old 9th March 2005, 07:16 PM   #7
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Ordered mu UcD400's yesterday. Wil be using 2 300VA 42V transformers from Amplimo.
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Old 9th March 2005, 07:37 PM   #8
VT67 is offline VT67  Belgium
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Ives

Bij RS:
2x 0-40V/800VA stock no. 224-1590 @ 88,01 ex BTW
2x 0-45V/800VA stock no. 223-8364 @ 90,64 ex BTW

Cheers
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Old 9th March 2005, 09:51 PM   #9
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i also ordered transx from partsexpress, i got the 800VA 40V sec. because of the small difference in price, i think it's just $5 more than the lower VA. But be warned of the huge diameter (6.2")

for the filtering i'm going to use 4 x 6800uF 80V caps per rail ordered from www.newark.com ($~7 each)

onixuser
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Old 14th March 2005, 10:26 AM   #10
Bgt is offline Bgt  Netherlands
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Yves, look for the lowest ESR values. Anything at about 10mohm should be nice at 50hz and 20kc. The blue BCC's are nice caps.

http://www.acoustica.org.uk/t/naim/components.html
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