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Old 7th February 2005, 12:05 PM   #21
UrSv is offline UrSv  Sweden
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Quote:
Originally posted by richie00boy


I don't wish things to start getting ugly either, but I did add the caveat "neglecting class-a with large quiescent current requirement" in my first para, which you seem to have neglected
Yup, I notice now and obviously could have refrained from my post. Reading at the same time as posting is making me sloppy. Sorry.
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Old 7th February 2005, 12:06 PM   #22
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Quote:
Originally posted by richie00boy


I don't wish things to start getting ugly either, but I did add the caveat "neglecting class-a with large quiescent current requirement" in my first para, which you seem to have neglected

LOL too late I had you quoted!

This is a class d thread though, things still get confusing at times.
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Old 7th February 2005, 12:07 PM   #23
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Quote:
Originally posted by classd4sure


Power lost as heat in the amp is power that doesn't get to the speaker though. With class d I personally feel it negligible, this isn't the case with other classes though is it?

Why 2X speaker power? When I came up with 800VA for my case, I have two 400W 4Ohm speakers and was going to use one transformer to power them both. You just mean for stereo right? I think you're saying an 800VA would be a approximation in this case and hoping you're not saying i'd need a 1600VA, but it would be nice anyway, if for nothing else, perhaps as a means of theft prevention

UrSv, I personally will be looking forward to and reading your posts.

Damn it got ugly fast in here.
I don't want to get ugly either

2x speaker power is because of this (slightly simplified):

Find the peak voltage required to reach desired power in desired load. This will be the required rail voltage. V = 0.707 * this.

sqrt(800 * 4) = 56.6V
56.6 * 0.707 = 40V
42.2V with diode losses, call it 45V to account for some MOSFET losses as well.

Find the RMS current required to reach desired power in desired load. This will determine wire gauge (and core size, to a degree). I = 1.61 * this.

sqrt(400 / 4) = 10A
10 * 1.61 = 16.1A

Now, multiplying V * I will result in approx 2x the rated audio power.

45 * 16.1 = 724.5VA

Of course, this is for continual sinewaves. If you will be playing music that is not sinewaves and has a high peak to average ratio, then you can undersize the VA somewhat. However, with the trend for modern music to be more and more compressed, I prefer to use the sinewave rating and would not attempt to get 2x 400W of usable, reliable, power out of an 800VA transformer

EDIT: added calculations for UcD400 4 ohm load
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Old 7th February 2005, 12:18 PM   #24
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Quote:
Originally posted by classd4sure



LOL too late I had you quoted!

This is a class d thread though, things still get confusing at times.
Yes, I did add a little straight after posting for maximal unambiguity. At the time of writing I thought any sensible person would realise that class-a with like 4A quiescent current would have an impact on transformer VA, and this would be factored in
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Old 7th February 2005, 12:25 PM   #25
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Quote:
Originally posted by richie00boy


I don't want to get ugly either

2x speaker power is because of this (slightly simplified):

Find the peak voltage required to reach desired power in desired load. This will be the required rail voltage. V = 0.707 * this.

Find the RMS current required to reach desired power in desired load. This will determine wire gauge (and core size). I = 1.61 * this.

Now, multiplying V * I will result in approx 2x the rated audio power. Of course, this is for continual sinewaves. If you will be playing music that is not sinewaves and has a high peak to average ratio, then you can undersize the VA a little. However, with the trend for modern music to be more and more compressed, I prefer to use the sinewave rating.
I'd prefer to go with sine rating as well.

Here's an even more simplified version:

2* 400W RMS 4ohm speakers = 800W RMS required=800VA transformer... as VA rating is for continuous output, correct? That is, ignoring amplifier efficiency
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Old 7th February 2005, 12:32 PM   #26
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Quote:
Originally posted by classd4sure


I'd prefer to go with sine rating as well.

Here's an even more simplified version:

2* 400W RMS 4ohm speakers = 800W RMS required=800VA transformer... as VA rating is for continuous output, correct? That is, ignoring amplifier efficiency
Unfortunately that calculation is meaningless as you have neither magical PSU nor amp from Star Trek
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Old 7th February 2005, 01:09 PM   #27
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Unfortunately that calculation is meaningless as you have neither magical PSU nor amp from Star Trek
Well, in Star Trek there is no need for calculations anyway.

Just reroute the auxiliary power to Impulse engines, reverse the quantum flow into the main dish and you're all set. Don't forget to recalibrate the power matrix though.

It never should take longer than 50 minutes (length of episode)

Oh, in fact, this solution is omnipotential, it will work for *any* problem in the ST universe!
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Old 7th February 2005, 01:45 PM   #28
whams is offline whams  Australia
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Hi guys,

This is my first post but I have read all the threads regarding the hypex modules, lc audio modules and their associated power supplies with keen interest.

I feel the need to add my two cents here as you seem to have dismissed what 'djk' is saying...I think he has some smart things to say.

When sourcing transformers for my project...I had a couple of options. The cheap type standard trannies that any old electronics shop stocks or some very high quality custom made types.

The difference...largley 'duty cycle'...oh, and the cost of course. The standard ones are lucky to have a 50% duty cycle....which means under certain conditions and loads they will sag and have troubles. The custom ones I bought are 100% duty cycle....virtually full load all of the time. The difference in size is obvious. My custom type trannies are much LARGER then the standard ones (of the same VA rating btw) you can get from a regular electronics shop. The price of the customs was about 3x that of the standard too.

Re-read his posts....he has some good things to say, duty cycle is a factor worth thinking about

Dave
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Old 7th February 2005, 02:19 PM   #29
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Quote:
Originally posted by whams
Hi guys,

This is my first post but I have read all the threads regarding the hypex modules, lc audio modules and their associated power supplies with keen interest.

I feel the need to add my two cents here as you seem to have dismissed what 'djk' is saying...I think he has some smart things to say.

When sourcing transformers for my project...I had a couple of options. The cheap type standard trannies that any old electronics shop stocks or some very high quality custom made types.

The difference...largley 'duty cycle'...oh, and the cost of course. The standard ones are lucky to have a 50% duty cycle....which means under certain conditions and loads they will sag and have troubles. The custom ones I bought are 100% duty cycle....virtually full load all of the time. The difference in size is obvious. My custom type trannies are much LARGER then the standard ones (of the same VA rating btw) you can get from a regular electronics shop. The price of the customs was about 3x that of the standard too.

Re-read his posts....he has some good things to say, duty cycle is a factor worth thinking about

Dave

You're right, I had misunderstood the term duty cycle as he used it. PNOM = PLOAD (A / B), where a/b is 70% for audio. I automatically and wrongly associated it's use with the output stage duty cycle. I did ask for clarification, though I have no problem admitting I'm wrong.
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Old 7th February 2005, 03:43 PM   #30
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Quote:
Originally posted by richie00boy


Unfortunately that calculation is meaningless as you have neither magical PSU nor amp from Star Trek
That's obviously not how I originally came up with the number, it's about as much as a calculation as magically doubling required power is.

Quote:
Find the RMS current required to reach desired power in desired load. This will determine wire gauge (and core size, to a degree). I = 1.61 * this.
Since RMS Power is Vrms X Irms I trust the reason you're multiplying by 1.61 is possibly an attempt to correct what's an assumed rather poor power factor. Would power factor be so poor if caps were kept within reasonable limits?

Not having accounted for it, gets an answer much closer to 800VA, for two speakers that is, 43*20=860VA, more like what I used at the time.
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