| RHosch |
I've been doing some searching and haven't found any thorough explanations of how to properly match a transformer to a Class D amp. I'll admit up front... I'm quite confused on this one.
I've studied Slone's writings on sizing a transformer, and his calculations all seem to be topology invariant... unless he is making the unstated assumption that the amp is always Class B. It seems natural to think that the efficiency of the amplifier itself will have an impact on the required size of the transformer, but no such efficiency coefficient is to be found in his calculation.
So I did some less "scientific" research, and took a look at hundreds of posts here, elsewhere, and looked at commercial Class D offerings to see what transformer sizes were being used for various amplifier output ratings. It looks like it's all over the board. I see some here using 1kVA or 1.5kVA trafos for 400W outputs. I see in some commercial products what looks like 500VA~800VA trafos for 1000W+ output. Using Slone's method, 1000W looks like it would need some 1.5kVA, but I'm not sure if that applies only to Class B or to all topologies.
Could someone point me in the right direction? I'm sure the information is already on the Web somewhere, probably in multiple places, but my Googling skills seem to be lacking lately. |
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| classd4sure |
Hi,
Slone's methods are for a no compromise class B topology, hence all the added losses, if you used that method for class d you'd have extreme overkill.
You can still use it as a reference though but keep in mind the differences in topology.
Assuming class d amps are ~90% efficient (close enough), if you want 100W at the load, then 100W+10%, the only voltage drop of worth is that of the rectifier diodes, so you can take that into account when working backwards to get your secondary requirement. Double that VA rating for a 2 channel amp off one transformer.
The OEM penny pinch method is to use ~70% of the calculated requirement based on the fact that music signals are not pure sine waves and therefore dont' demand the same kind of power.
Then you have everybody else who swears bigger is best.
The determining factor might be that using a higher VA rating might get you a transformer that has a tighter load regulation factor.
Hope that helps ya. |
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| RHosch |
| Yeah... that does help. Thanks. |
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| djk |
I just spent the evening at the B&O ICE Power site.
They claim 79% efficent into 4 ohms and 82% at 8 ohms.
Those are believable numbers, others I have seen are not.
First timers' always forget the power factor for cap input supplies. A 1KVA transformer will only drive about 700W into caps around 10,000µF or so, bigger caps only make the power factor worse (no, you can't 'make up' for a weenie transformer with big caps).
Duty cycle on rap bass and some lead guitar may be as bad as 50%, but driving a 45* load will make up for this. A wash.
100W + 100W at 8R would give X2 at 4R. Divide by 0.8 for efficency and you need 500W in. Divide by a 0.7 power factor and you need a 700VA transformer for your 100W stereo amp that will be 4 ohm stable into a real loudspeaker (a 45* load).
Less is less.
You can figure your design around a 25% duty cycle, I have done this before. But the bigger transformer sounds better.
I also burned up a 25% duty cycle transformer when bench testing an amplifier into clipping using FM radio as the source material (of course no one you ever met has driven an amplifier into clipping, right?).
Don't try and save too much money on the transformer, in the long run it doesn't pay. |
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| Yves Smolders |
DJK,
Your post is very contradictory to the discussion in the UcD power supply thread.
According to calculations there, 1000VA/2*40V with 33.000uF per rail should be enough to drive UcD400's up to 3 ohms (>550W/channel?)
Do you believe these calculations wrong? What would you recommend?
There's also the "hard limit" - UcD400 V2 pumps 20A max.
Would love to hear your comments. |
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| UrSv |
Want to have and need to have are two different things.
Don't forget that duty cycle as we are not talking about powers running full power 100% of the time which will "never" happen. Also a transformer rated at 500 VA is rated 500 VA continuous with a certain temperature rise. It will happily provide 750 VA during shorter intervals and since it is not continous it will do this without getting warm.
The general rule IMHO, is thus to take as much as you want to pay for. Lars at LC Audio had very good results using 80 VA (or possibly 50 VA) with his 200 W ZAPpulse. I myself would be very happy with 500 VA for a stereo UcD400 driving 8 Ohm speaker. |
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| djk |
You obvously don't understand things like 'duty cycle', and 'power factor'.
"Don't forget that duty cycle as we are not talking about powers running full power 100% of the time which will "never" happen."
As the service manager in a hi-fi shop I found that many customers drove their amplifiers into clipping on a regular basis, if not all the time. What is the duty cycle of a square wave?
"Lars at LC Audio had very good results using 80 VA (or possibly 50 VA) with his 200 W ZAPpulse. "
Sure, driving 2W out at a duty cycle of 4%, so what?
If we are going to brag about doing stupid things...I know someone that mounted a 10HP lawnmower engine in his pickup truck. It got in excess of 100MPG and would go maybe 60MPH on flat, level ground with no wind.
I have about a ton of Yamaha, Sony, and Denon transformers that have the thermal fuse out in the primary, why I'm saving them I'm no longer sure.
Feel free to ignore my comments based on 30 years of experience in the hi-fi business.
To finish the story about the 25% duty cycle transformer that burned up during testing, I also provided a 50% duty cycle transformer I recommended they use in production, and a 100% duty cycle transformer just to show what a difference in sound it made.
While they cheated and used the 100% rated model at the trade show, to their credit they rejected the 25% model and sold the amplifier with the 50% model.
You guys are welcome to do what you want.
(are you all bean counters, or are some of you DIY hobby types?) |
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| Yves Smolders |
DJK,
We are only asking you your opinion, and when confronted by other people's opinion you call them bean counters... I believe that is unasked for. It's a discussion and I want to see opinions from different people, also yours. Just enlight us with your 30 years of knowledge and present us with your recommended setup.
So again, I'd love to have your opinion for PS and transformer for this setup:
I want to be able to run 3 ohms on 2 UcD400's, fully loaded. Feel free to enter a duty cycle that you feel is "difficult".
Thanks. |
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| classd4sure |
Hi,
Take a deep breath. Just because you were disagreed with is no reason to take it as a personal assault which you seem to have done.
As to the question of who understands things like duty cycle...
| quote: | | Duty cycle on rap bass and some lead guitar may be as bad as 50%, but driving a 45* load will make up for this. A wash. |
You do realize that a 50% duty cycle =0W output? What the hell is a 45* load anyway, and what the hell is a 25, 50 or 100% duty cycle transformer?
| quote: | | Sure, driving 2W out at a duty cycle of 4%, so what? |
You do realize a 4% duty cycle = near clipping? While a 25% duty cycle = about half power?
This isn't an attack really, I'm just a bit confused by your lingo, maybe you can help me out.
I had previously decided on an 800VA transformer for a stereo UCD400 driving 4 ohm loads, 1000VA would of course be nicer, hardly a necessity though. I think even an 800VA would handle a pure sine wave test with reasonable heating, for maybe an hour or so, not 24.
Thanks |
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| Yves Smolders |
ClassDforsure,
That would already exceed any real-life test I believe... except maybe continuous max-power near-clipping bass for multiple hours, like in discotheques.
If a sine wave at full output can be handled at 3 ohms for an hour, there is *no way* I'd ever run into problems with my speakers.
Yves |
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| classd4sure |
| quote: | Originally posted by Yves Smolders
ClassDforsure,
That would already exceed any real-life test I believe... except maybe continuous max-power near-clipping bass for multiple hours, like in discotheques.
If a sine wave at full output can be handled at 3 ohms for an hour, there is *no way* I'd ever run into problems with my speakers.
Yves |
Yep, that was my train of thought when I decided on 800VA.
Considering OEM's under-rate their transformers by 30% based on the statistics of audio verses a full sine wave.
I did ignore the non ideal effiency though, but if Jan-Peter say's his module is >90% I take his word for it. The other factor I took into account was that while I do like to crank it up at times it is never for very long, my speakers are just too efficient to require it.
I should state this was an example of me trying to pinch what pennies I could without making too huge a compromise. Ideally I'd have gone for a 1000VA. |
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| richie00boy |
The sizing of a transformer is noting at all to do with class of amplifier (neglecting class-a with large quiescent current requirement). The fact that a class-d amp may be 90% efficient is simply talking about the heat losses in the amplfier.
The sole factors are voltage required to drive your desired power into your desired load, and duty cycle. If you assume worst case of 100% duty cycle (50% on, 50% off, i.e. sinewave) then a good approximation for an amp with little or no quiescent curent is transformer VA is 2x speaker power. At the end of the day, it's all about the acceptable temperature rise of the transformer. |
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| UrSv |
djk,
I do understand these things quite well and I have also read the information given by people I trust quite a lot. These people are people like Bruno who designed the UcD module, Nelson Pass and Lars from LC Audio as well as many others.
I'm not bragging about doing stupid things at all. I'm being realistic which is a totally different thing.
Sure some people drive their amps into clipping on a regular basis. Even I do sometimes.
I read classd4sure (but let him speak for himself) as he doesn't quite understand what you are talking about and quite frankly, at least to me, most of your post does not really make sense at all.
Thanks for the offer of letting me ignore your experience of 30 years in the business. I certainly will and I will also continue posting my views on things. Not to be less grand than you I also offer you the same and you can happily ignore my 30 years of experience without upsetting me the least. |
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| Yves Smolders |
I'm settling for 1000VA for stereo UcD400 as well... should do just nicely without ever breaking a sweat.
I even think a 3rd channel wouldn't be a problem on 1000VA. (my center is an easier load though, 120W/8ohms max, dips to 5 ohms)
By the way, is the input gain identical on the 180 and 400 model UcD's?
Now i'm looking for a nice case to put it all in. |
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| UrSv |
| quote: | Originally posted by richie00boy
The sizing of a transformer is noting at all to do with class of amplifier. The fact that a class-d amp may be 90% efficient is simply talking about the heat losses in the amplfier.
The sole factors are voltage required to drive your desired power into your desired load, and duty cycle. If you assume worst case of 100% duty cycle (50% on, 50% off, i.e. sinewave) then a good approximation is transformer VA is 2x speaker power. At the end of the day, it's all about the acceptable temperature rise of the transformer. |
Not quite true. Class A is a totally different thing since high currents are drawn from the power supply even at idle. In the case of SE amps the efficiency os very low and the favourite example here is SoZ which draws 1200 W continuously for a power output of 50 W. No "twice the rated power" is going to be enough there. |
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| classd4sure |
| quote: | Originally posted by richie00boy
The sizing of a transformer is noting at all to do with class of amplifier. The fact that a class-d amp may be 90% efficient is simply talking about the heat losses in the amplfier.
The sole factors are voltage required to drive your desired power into your desired load, and duty cycle. If you assume worst case of 100% duty cycle (50% on, 50% off, i.e. sinewave) then a good approximation is transformer VA is 2x speaker power. At the end of the day, it's all about the acceptable temperature rise of the transformer. |
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. |
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| UrSv |
| quote: | Originally posted by Yves Smolders
I'm settling for 1000VA for stereo UcD400 as well... should do just nicely without ever breaking a sweat.
I even think a 3rd channel wouldn't be a problem on 1000VA. (my center is an easier load though, 120W/8ohms max, dips to 5 ohms)
By the way, is the input gain identical on the 180 and 400 model UcD's?
Now i'm looking for a nice case to put it all in. |
1000 VA for 2-3 modules is perfectly fine.
Yes, the gain is 26 dB for both modules. |
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| UrSv |
| quote: | Originally posted by classd4sure
--snip--
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. |
"Twice the rated power" is rule of thumb used by some DIY:ers to estimate the transformer rating wanted (not needed). Please remember that there are twice (or very close at least) as many thumbs out there as there are DIY:ers so there are many rules and this is just one. Please also remember that an amplifier rated at 100 W into 8 Ohms would then call for some 200 VA of transformer (assuming we are talking Class B, AB or D/T/G/H et al). Fine, but what happens if we start using the amp at 4 Ohms? Does our amplifier then stop playing? Not at all, but more power is drawn from the power supply. To put some perspective into this I would recommend looking at consumer amplifiers, excluding the most expensive high-end and above segment, and to count the number of amplifiers that have a transformer rated at twice the total rated power in 4 Ohms. There are most likely very few...
And thanks for wanting to read my posts. |
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| richie00boy |
| quote: | Originally posted by UrSv
Not quite true. Class A is a totally different thing since high currents are drawn from the power supply even at idle. In the case of SE amps the efficiency os very low and the favourite example here is SoZ which draws 1200 W continuously for a power output of 50 W. No "twice the rated power" is going to be enough there. |
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 :) |
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| classd4sure |
Yeah, that'd be a great rule of thumb based on 8ohm speakers I think, would still be able to drive 4ohms easily. I calculate based on 4 ohms though since that is what I'm concerned with.
I believe transformer underrating is one of at least a few reasons why most (of the cheaper) consumer amps don't have a power rating that doubles when halving the load. They've already underrated it as much as they can based on 8 ohms and maybe are only willing to sacrifice an extra few watts before transformer heating does become a concern.
One interesting question does come to light by all this mess, and that is increasing transformer size to counter act a poor power factor. Would that be as aimless as I think it is? It might lead one to believe we can get away with using 200 000uF in a supply providing we had a 20 000VA transformer. PF correction would be the obvious option.
Thanks |
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| UrSv |
| 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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| classd4sure |
| 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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| richie00boy |
| 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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| richie00boy |
| 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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| classd4sure |
| 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 :D |
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| richie00boy |
| 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 :D |
Unfortunately that calculation is meaningless as you have neither magical PSU nor amp from Star Trek :D |
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| Yves Smolders |
| quote: | | 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! :D |
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| 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 :bigeyes:
Dave |
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| classd4sure |
| 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 :bigeyes:
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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| classd4sure |
| quote: | Originally posted by richie00boy
Unfortunately that calculation is meaningless as you have neither magical PSU nor amp from Star Trek :D |
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.
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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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| richie00boy |
I thought from my post of #23 in this thread you would have got it into your head that I am not simply doubling power arbitrarily. It's not to take account 'in case of' lower loads or anything like that -- it is simply the minimum requirement to drive your desired power into your desired load and no lower, with sinewaves, without burning up.
If you read that post again you will see why the transformer has to have an AC voltage that is 0.707 x DC plus a bit, that I trust is simple and obvious. The reason that DC current is multiplied by 1.61 is that is the current capacity required from the AC side when pulling through a bridge rectifier is increased by this factor. This is simple, fundamental bridge rectifier theory!
Thank you :) |
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| classd4sure |
| quote: | Originally posted by richie00boy
I thought from my post of #23 in this thread you would have got it into your head that I am not simply doubling power arbitrarily. It's not to take account 'in case of' lower loads or anything like that -- it is simply the minimum requirement to drive your desired power into your desired load and no lower, with sinewaves, without burning up.
If you read that post again you will see why the transformer has to have an AC voltage that is 0.707 x DC plus a bit, that I trust is simple and obvious. The reason that DC current is multiplied by 1.61 is that is the current capacity required from the AC side when pulling through a bridge rectifier is increased by this factor. This is simple, fundamental bridge rectifier theory!
Thank you :) |
I didn't ask you why you used 45V, if you read my post again, you'll see that simply and obviously. I would say 45V is likely on the high side though, conducting mosfets won't even drop 1 volt.
I'll also point out this is an incorrect way of calculating rails for a UCD which has voltage protection, and for which good design requires one to account for a 10% mains overvoltage condition, as well as the transformer's regulation factor.
Post #23 isn't arbitrary, but a mindless doubling is. You can absorb that much can't you? Maybe if you can't, try comming down from your high horse, it could help.
If it is simple fundamental bridge rectifier theory you're using then you should know it's 1.8. Not a single rectifier version uses 1.61.
You're apparently incapable of an intelligent exchange, perhaps your blood sugar is low? You seem cranky. Go have a biscuit.
Thank you. |
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| richie00boy |
Oh come on, let's not let this flare up again :)
| quote: | Originally posted by classd4sure
I didn't ask you why you used 45V, if you read my post again, you'll see that simply and obviously. I would say 45V is likely on the high side though, conducting mosfets won't even drop 1 volt. |
Conducting MOSFETs will drop a little and unless they have a gate driver that can rise above the +ve rail they will drop more than a volt or two. I'm guessing that the UcD will have sufficiently sophisticated drive circuitry to overcome this and thus the bulk of the losses will be through the rectifier diodes. So for a 400W UcD you are looking at a required AC voltage of about 45V. I think we are reasonably in agreement with that.
| quote: | Originally posted by classd4sure
I'll also point out this is an incorrect way of calculating rails for a UCD which has voltage protection, and for which good design requires one to account for a 10% mains overvoltage condition, as well as the transformer's regulation factor. |
I agree that for a good design we should take line and transformer regulation into account. However, if we do this it puts up the AC voltage requirement (and hence VA) even more to maintain that 400W output at worst case. And I cannot see what relevance any overvoltage protection an amp may have has in this part of the calculations.
| quote: | Originally posted by classd4sure
Post #23 isn't arbitrary, but a mindless doubling is. You can absorb that much can't you? Maybe if you can't, try comming down from your high horse, it could help. |
But my whole point was that it appeared to me that I was being accused of mindlessly doubling the speaker power to arrive at the transformer VA. Maybe I was wrong :)
| quote: | Originally posted by classd4sure
If it is simple fundamental bridge rectifier theory you're using then you should know it's 1.8. Not a single rectifier version uses 1.61. |
This is the best bit :D 1.8 is more than 1.61, which makes the VA add up to even more. That 800VA transformer of yours is now looking rather weedy to drive your 2x 400W amp. This is irrelevant anyway as (and I await your apology :D ) once you have read a basics text book or searched the net you will see that it is in fact multiply by 1.61 or divide by 0.62 (same result). Remember we are talking about full-wave, bridge rectified AC.
| quote: | Originally posted by classd4sure
You're apparently incapable of an intelligent exchange, perhaps your blood sugar is low? You seem cranky. Go have a biscuit.
Thank you. |
My exchange has been intelligent, I'm the one showing all my working and providing formulas, rather than, umm...
Sound of jammy dodgers packet being opened :cool: |
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| classd4sure |
| quote: | | Oh come on, let's not let this flare up again |
Sorry, I've an admittedly weak tolerance for concentrated condescension, like poison it can only be taken in small doses.
Anyway I'm really not here, or trying, to argue, just to learn and help where I can. I do appreciate that your recent post has a much better tone, and so I respond accordingly.
| quote: | | I agree that for a good design we should take line and transformer regulation into account. However, if we do this it puts up the AC voltage requirement (and hence VA) even more to maintain that 400W output at worst case. And I cannot see what relevance any overvoltage protection an amp may have has in this part of the calculations. |
Here I fail to understand, you know, thick head and all. The UCD has protection that shuts it down at a certain voltage, used to be 63 volts, now it's higher and a non issue, but this math was done before that, so what the hey. Let's assume a regulation factor of 5%, along with the 10% mains over voltage. We have to allow for a 15% overshoot worst case, without tripping the protection. So realistically we wound up with less voltage, because 56.6 * 1.15 = 65.09 and the amp has cut out 2 volts ago. So then to maintain VA, we'd want more current, but it will never get used because we can't fight ohms law. In reality, what we have isn't exactly a 400W amp. This has been fixed though so it's no longer a problem. That's the relevance to the over voltage protection as I see it. In truth it is no longer relevant with the higher protection level.
| quote: | | But my whole point was that it appeared to me that I was being accused of mindlessly doubling the speaker power to arrive at the transformer VA. Maybe I was wrong |
No not at all. I simply wanted to know more about it, which is why I asked originally. I fail to see why you couldn't have explained it without being so condescending. You had a decent answer which left me with another question, apparently you saw that as more accusations, I dont' work that way, I'm fairly straight forward.
| quote: | | This is the best bit I await your apology once you have read a basics text book or searched the net. Remember we are talking about full-wave, bridge rectified AC. |
I see more condescension and at this point, the smilie ain't smoothin it over.
http://www.atc-frost.com/products/design/va.htm
http://www.plitron.com/pages/technote.htm
have a scroll down to "Rectifier Circuits"
Apology denied. Besides I don't really care, I was just being combative at this point.
| quote: | | Sound of jammy dodgers packet being opened |
I'm glad that amused you, it was meant to.
All the same, it's time I took my leave.
Cheerio, ol chap. |
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| richie00boy |
I now see how you were concerned about the overvoltage protection of the UcD400. A very valid concern to those expecting to get 400W out of the amp. I wonder if they have increased the voltage on the amps as well, but's that's not for this thread :)
I must admit to never having seen the 1.8 factor in over 10 years of electronics, it's always been 1.61. However, those links you posted are valid sources. I can only assume that they are accounting for slightly higher peak currents and/or slightly longer conduction times for the rectifier diodes.
| quote: | Originally posted by classd4sure
Apology denied. Besides I don't really care, I was just being combative at this point. |
You were doing so well, winning me round, until you dropped that clanger :D
I think we've covered the bases on this topic anyhow, and anybody should be able to pick up the methodology, reasoning and formulas to design a PSU for a UcD or ZAPpulse amp easily enough from this thread :) |
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| destroyer X |
I can understand why you are discussing that matter so deep, and those things will are confused to me too, as i am completely crazy with things happening here, at my home.
I bougth a very good audio system (sorry, not rich) from Phillips, and its power consumption (written in the back panel) is 125 watts... so i expect to have something around 96 watts power...but as specifications are "manipulated"..... "tricky informs"....i will acept 60 watts of sound....and this is perfect in my mind.... very nice power....because those 45 years, i could realize that normal (not hard to move) speakers, goes to limit movement with 4 or 5 volts.....and the heavier ones need 10 to 15 volts...so.....30 watts is OK!....each channel, perfect!
The main problem are specifications...they informed us, power as their top maximum, short time....not even continuous seems to be.... specifications talk in 10 percent distortion....and that distortion is enormous...sounds terrible, it is not more sound, it turns noise!..... and when you go searching, you will find a very small power...i could see 12 watts to a 120 watts amplifier in some Philips Class D chip....and they are making those crazy things with us....mine, with 125 watts consumption, is rated to 200 + 200 watts (they did not tell us what kind of "watts" are those).
This is impossible....125 watts consumption producing more power than consumption....creating energy!
So i connected multimeters....in AC range...good to 60 hertz bass....those instruments can measure with less than 10 percent error, and having some continuous tone, we can avoid problems related to pointer weigth...i tried digital too..... could measure 7 volts over 4 ohms...and, increasing volume, could reach 20 volts, but distortion was a hell, as i use external hi level drive signal, and beeing square waves, measurements loose precision, as turns almost alike continuous.
So, for the good old days ...this amplifier can produce 12 watts each channel, clean watts.... can produce some square crazy wave of much more power.
But this is not what happens hearing....that crazy thing sounds alike 100 watts each channel.... and give a punch in bass enormous...and kicked all my amplifier's s without too much effort, not only in quality of watts produced, as in quantity of watts produced.
So...i cannot understand?....what is going on?
Can i respect those calculations you are discussing to have some idea of the power produced?
I am a hell confused.... those watts i cannot measure with multimeter!!!! HELP!!!
regards,
Carlos |
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| destroyer X |
This size makes me believe in much more than 400 watts.
regards,
Carlos |
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| destroyer X |
One more image.
Carlos |
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| destroyer X |
This way, things turns more real.
Carlos |
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| richie00boy |
Carlos,
Thank you for your contribution :) I assume you are using a 'known' same set of speakers for your tests, i.e. the same speakers for each amplifier?
The key thing about rating a transformer is the acceptable tempearture rise for a given power draw.
Your 'boom box' will likely be rated to give out high short term power, but cannot sustain this continuously without overheating the transformer, and the supply begins to collapse after not very long. In contrast, your 'hifi' amplifier will likely have a power supply that cannot match the same short term power as the 'boom box', but it can give out sustained power. |
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| destroyer X |
Thank you.
Carlos |
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| destroyer X |
And amplifier measured 100 watts peak each channel...so, this can be something alike 60 watts each channel....a little bit less related the consumption (125 watts).
Now it is clear that really is efficient...produce power without too much heat... and have incredible dinamics.
Very good.
Carlos |
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| richie00boy |
| You work fast, Carlos. Excellent job :) To finish off you could construct another power meter to monitor the incoming power and see how close to that 125 watts you really are :) |
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| destroyer X |
So, in the reality, you can reduce 20 percent the power measured, so, will reach the 80 percent normal efficiency.
Dinamics are wonderfull....distortion is reasonable with volume all the way up.
But have not AC ampere meter....maybe in the future, opening enclosure, i will check voltage and current both rails to calculate the consumption reflected in transformer primary.
Go ahead with supply, thank you and sorry to scape, just a little, the main thread subject.
Please...go to the track again.
regards,
Carlos |
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| Yves Smolders |
Another power supply design question:
For UcD400's, what cable should I be using from the bridge to the caps/caps to modules? Is 2.5mm enough? multiple strands or massive cable?
3 days, and still waiting for hypex to ship... i'm sooooo curious... maybe i'll start the power supply design this weekend.
:D |
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| richie00boy |
| 2.5mm^2 cable is fine even running a pair of modules off one PSU. It's what I use at those currents. Stranded is my preference as it's easier to work with. As long as you keep things short (less than 14cm) you shouldn't have any problems. |
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| richie00boy |
Just a note to people searching for transformer sizing as per the original thread title, whilst my calculations and methodology throughout this thread are valid, my assumption of the average current drawn by a class-d amp was not. Thanks to a couple of posts by Jaka Racman in the "UcD180 questions" thread, I understand that the average current is less than that which would be for a class-b amp, therefore the transformer does not need to be as large.
A reasonable rule of thumb is that the class-d amp draws 0.68x the current of the class-b amp/load. |
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