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Old 19th November 2006, 12:22 AM   #1
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Default Need transformer size recomendation

I am building an active speaker and I am going to use 4 UcD 400 AD modules for each side. I was originally going to use smaller amps on the top end, but it would seem that it's cheaper to only have to build one bid power supply rather then several smaller ones. One of the amps will driver woofers in a 4 ohm load, the next the mids, and the last 2 will be tweeters in a dipole config. Since only woofer and maybe the midrange will be using alot of power, can I reduce the transformer size? I was thinking 500VA per 4ch amp. Should I go bigger? Thanks! Right now I have a pair of 200W monoblocks that each have a 500VA transformer, I figured that it's the same load just cut up and delivered to seperate amps. I know each amp wastes energy, but I wasn't sure how much. I will be using 2 10,00 uF panasonic 63v caps per amplifier.
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Old 19th November 2006, 08:33 PM   #2
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" ... I will be using 2 10,00 uF panasonic 63v caps per amplifier. ..."

There is your practical limit setting: 63VDC rated caps probably should not be driven past 45 to 50 VDC for reliability.

So, a 30 - 0 - 30 VAC secondary winding (to prudently accomodate the capacitors' limits) and your 500 VA amplifier requirement are not mutually exclusive = 60 VDC times 8+ amps ... for a cool running 115 VAC primary, passing 500 VA plus some for inefficienties is about 5 amps = above 600 VA rating for the transformer .... BUT running 4 of the '400 amplifiers from a single transformer would indicate a rating four times that = 2400+ VA !! = can be done, but not "cheaper" ... several 600 VA transfromers would probably be more cost effective than one 2400 VA transformer. (Higher rated caps = higher secondary voltages = lower power rating on the transformer(s).)

(Can't quite figure out exactly why you want that much power to be disipated in a single 2- 3- or 4-way box ...??)

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Old 19th November 2006, 08:50 PM   #3
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The four modules, will they drive full range speakers or separate ranges?
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Old 19th November 2006, 10:36 PM   #4
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Default I don't think you guys read the posting.

I want one power supply to drive 4 modules, each handleing a different range. According to Hypex a 500VA transformer is enough for 2 modules. I don't know where your getting 4 600VA transformers. Even I know that's crazy. All I want to know is: if only one module is really having to push out any power (i.e. the woofer module) and the other three mid and 2 tweeters aren't really seeing any use. can I still use the same 500VA transformer for all 4 amps rather then say 800 - 1000VA as would be appropriate if they were all driven full range?
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Old 20th November 2006, 12:05 AM   #5
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" ... I want one power supply to drive 4 modules, each handleing a different range. ..."

But each amp has the same power rating = 400 watts into 4 oms = four times four hundred = 1600 watts, minimum required VA of your single transformer, and that assumes no errors like clipping of all four amps .... suggesting if you want the transformer to runn cool, then you will need at least a 2000 VA rating ... and the secondaries should not exceed you 63 volt (absolute maximum) rated caps = 30 - 0 - 30 VAC. If I were doing it, I would use an overrated transformer (2400 VA) to cover all those bases and other possible consequencies ... OR ... several transformers instead of one = lower costs.

The problem as I see it is that, no matter what speaker loads you may have, the amps can, and probably will, at some point draw a whole bunch of their rated power output.

Got fuses?

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Old 20th November 2006, 01:10 AM   #6
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Default ummm no,

I see how you figured it, but in reality there will be a fuse that prevents too much current from being drawn through the transformer, and overheating it. The very idea that a tweeter would ever suck down more then a few watts is preposterous. Even at excruciating volumes, it wouldn't be pulling more then a few watts. Same for the midrange.
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Old 20th November 2006, 01:23 AM   #7
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Why not use three modules per speaker to save some cost? 1 for the woofer, 1 for the mid, 1 for the dipole tweeters. Then build two supplies per speaker. 1 with a larger transformer for the woofer and 1 with a smaller transformer for the mid and tweeter modules. As you said, most of the power will be required for the woofer so it would be most advanatageous to give that module it's own supply. This also helps to avoid interaction between the low and the mid/hi frequencies.

In the end how overkill you want to go depends on how much money you have to spend.
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Old 20th November 2006, 01:44 AM   #8
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Default cheaper

I will be using a special multichannel power supply board to cut costs. It costs me about 100 plus caps, if I use 2 HG power supplies then it's going to cost me almost 350 per power supply
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