What's the optimal transformer for a UCD700? Assume that the UCD700 power supply will be used and that the amplifiers will be built as monoblocks - since that's what I, and at least a couple of others plan to build. 🙂 Actually, I don't think the specs would be very different for someone looking to build their own power supply or build a stereo amp with one UCD700 power supply.
Looking at the UCD700 power supply manual on Hypex's website, we find that we need:
2 - 63V secondary windings
2 - 13V secondary windings
1 - 16V secondary winding
Figure on dual 120V primary windings.
Since we're looking for the optimal, we want to make sure the transformer is adequately sized for the worst case scenario, so my thoughts are that the following current capabilities would be appropriate:
On each 63V secondary 9.5A
On each 13V secondary 1A
On the 16V secondar 1A
Multiplying it out to get the VA, we get 1197 + 26 + 16 = 1239VA. Figuring about a 3% loss from primary to secondary, we end up with a 1277VA transformer.
A static shield between the windings also seems like a good idea if not too costly.
Hopefully this is a good starting point for discussion.
Edit: Corrected voltage error.
Looking at the UCD700 power supply manual on Hypex's website, we find that we need:
2 - 63V secondary windings
2 - 13V secondary windings
1 - 16V secondary winding
Figure on dual 120V primary windings.
Since we're looking for the optimal, we want to make sure the transformer is adequately sized for the worst case scenario, so my thoughts are that the following current capabilities would be appropriate:
On each 63V secondary 9.5A
On each 13V secondary 1A
On the 16V secondar 1A
Multiplying it out to get the VA, we get 1197 + 26 + 16 = 1239VA. Figuring about a 3% loss from primary to secondary, we end up with a 1277VA transformer.
A static shield between the windings also seems like a good idea if not too costly.
Hopefully this is a good starting point for discussion.
Edit: Corrected voltage error.
Some additional thoughts/questions
Looking at the UCD700 supply manual, it recommends 63V secondaries and shows 65V as the absolute maximum. This doesn't seem to leave much room for any sort of overvoltage situation, 4 percent, or less than 5V at the 120V nominal mains. It even warns "! Correct operation at these limits is not guaranteed. Operation beyond these limits may result in irreversible damage.", when referring to the max voltage figures. Is this just Hypex being cautious, or is this warning only applicable for continuous operation and not for a momentary spike in the voltage, or is 63V maybe pushing things a bit too much?
The 16V with a max of 18V, and the 13V with a max of 15V should be ok in almost any reasonable scenario with more than 10% available for over voltage conditions.
Looking at the UCD700 supply manual, it recommends 63V secondaries and shows 65V as the absolute maximum. This doesn't seem to leave much room for any sort of overvoltage situation, 4 percent, or less than 5V at the 120V nominal mains. It even warns "! Correct operation at these limits is not guaranteed. Operation beyond these limits may result in irreversible damage.", when referring to the max voltage figures. Is this just Hypex being cautious, or is this warning only applicable for continuous operation and not for a momentary spike in the voltage, or is 63V maybe pushing things a bit too much?
The 16V with a max of 18V, and the 13V with a max of 15V should be ok in almost any reasonable scenario with more than 10% available for over voltage conditions.
seems to me like you are calculating the 63V output for two modules on a single transformer?
I'm building true monoblocks with one toroid each channel. For that, I figure a 625VA to maybe 750VA output should suffice, although if the price is right, I'd go bigger.
And on the 13 V secondaries: make sure those are 13V when used in series (13-0-13, rather than 13-0 13-0, since otherwise you have 26-0-26). I was going to get a separate 6.3-0 6.3-0 transformers and connect that one in series to get to 12.6-0-12.6 at half the amp rating of the 6.3 spec.
I think the key here is to keep the cost of the custom job down and focus on what's hard to obtain - the 63V rating. I found really affordable transformers that can handle the 16V and dual 12V inputs. When you get quotes, I think you should also ask for a plain dual 63V output unit with just those two secondaries. $30 will buy you the other two small transformers from Mouser or Digikey. The other thing to keep in mind is that transformers with 60V secondaries are quite easy to come by and very affordable. $70 buys an Avel 800VA, $97 a 750VA Plitron that has that rating. Sure, you'd lose a few watts from peak output, but how much is it worth to you to get to the true 700 watts?
Do you already have any idea where to go and ask for pricing ? I heard Plitron is expensive for low volume custom jobs.
Peter
I'm building true monoblocks with one toroid each channel. For that, I figure a 625VA to maybe 750VA output should suffice, although if the price is right, I'd go bigger.
And on the 13 V secondaries: make sure those are 13V when used in series (13-0-13, rather than 13-0 13-0, since otherwise you have 26-0-26). I was going to get a separate 6.3-0 6.3-0 transformers and connect that one in series to get to 12.6-0-12.6 at half the amp rating of the 6.3 spec.
I think the key here is to keep the cost of the custom job down and focus on what's hard to obtain - the 63V rating. I found really affordable transformers that can handle the 16V and dual 12V inputs. When you get quotes, I think you should also ask for a plain dual 63V output unit with just those two secondaries. $30 will buy you the other two small transformers from Mouser or Digikey. The other thing to keep in mind is that transformers with 60V secondaries are quite easy to come by and very affordable. $70 buys an Avel 800VA, $97 a 750VA Plitron that has that rating. Sure, you'd lose a few watts from peak output, but how much is it worth to you to get to the true 700 watts?
Do you already have any idea where to go and ask for pricing ? I heard Plitron is expensive for low volume custom jobs.
Peter
Re: Some additional thoughts/questions
note that your wall voltage isn't 115V either. I measure 121.5during the day, 124V at night at my place....
so maybe a 60V unit off the shelf isn't such a bad idea?
Peter
GregD said:
note that your wall voltage isn't 115V either. I measure 121.5during the day, 124V at night at my place....
so maybe a 60V unit off the shelf isn't such a bad idea?
Peter
Peak currents through a power supply transformer can well exceed nominal output ratings of an amplifier suggesting oversizing is advised to reduce peak distortion.
Guys,
I'd opt for staying on the safe side, 2x60-volts really is the limit if you factor in 5% tolerances on the mains. Furthermore the efficiency of the UcD700 is close to 90% and maximum output is 700-watts in 4-ohms at 1% THD. Realistically you'd not want to run it at that output, so a 750 or 800VA transformer is really all you need, while still being able to deliver 700-watts peak if needed and over 500-watts RMS. For the seperate voltages I'd opt to have custom windings made onto the transformer. Also keep in mind that in reality you'll never come close to pushing it over a mere hundred watt in a normal living room.
Best regards,
Sander Sassen
http://www.hardwareanalysis.com
I'd opt for staying on the safe side, 2x60-volts really is the limit if you factor in 5% tolerances on the mains. Furthermore the efficiency of the UcD700 is close to 90% and maximum output is 700-watts in 4-ohms at 1% THD. Realistically you'd not want to run it at that output, so a 750 or 800VA transformer is really all you need, while still being able to deliver 700-watts peak if needed and over 500-watts RMS. For the seperate voltages I'd opt to have custom windings made onto the transformer. Also keep in mind that in reality you'll never come close to pushing it over a mere hundred watt in a normal living room.
Best regards,
Sander Sassen
http://www.hardwareanalysis.com
pburke said:
I agree that my sizing is overkill; basically I worked backwards from the output fuse sizing on the power supply, 2 of them 6.3A at 90V. I wanted to make sure that the transformer wasn't the limiting factor on the max output of the power supply after considering the inevitable slight losses in the power supply. Also, when I've had custom transformers made before, the difference in cost between a 1000VA and a 1500VA for instance, was only $30 each. I guess the labor is almost the same; you're just paying for a little more materials.
pburke said:
Two 13-0 windings will work correctly, just connect the two "0" parts of the windings together and you end up with -13V and +13V with the "0" part being the ground. Pretty standard in my experience.
pburke said:
The optimal is never cheap. 😀
That said, I do like to get the best bang for my buck. I also took a look at small transformers on Mouser and Digikey for the 12V and 15V. I wanted small encapsulated toroids to minimize any stray magnetic fields, and at least 20VA to have a decent amount of voltage regulation. The ones I found were around $20 to $40 each. Figuring 2 transformers per amp times the midrange price of $30 each equals $120 for the transformers. I'm pretty sure that the extra windings on the main transformer will cost much less than this, and have the added advantage of significantly less complication in the amp. Also, per the UCD700 supply manual, the recommended voltages are 13V and 16V to allow for losses in the regulators, and I didn't notice any standard transformers in these voltages, although I didn't look too hard. 😉
I had 2 transformers made for my UCD400s last year in a 1500VA size with dual 40V secondaries, potted center and with a magnetic shield on the circumference. I have to look it up, but if I remember correctly, they were about $150 each plus shipping. There are a number of toroid transformer manufacturers here in the U.S. that will make custom toroids to order; I plan on sending the specs out for quote to a few of them once I have the requirements finalized.
Re: Re: Some additional thoughts/questions
The voltages that I measure at home are similar to yours, which prompted my post #2 in this thread. Hopefully Jan-Peter will chime in about this, or I'll email him directly if he doesn't.
pburke said:
The voltages that I measure at home are similar to yours, which prompted my post #2 in this thread. Hopefully Jan-Peter will chime in about this, or I'll email him directly if he doesn't.
pburke said:
I actually tried a pair of Avel 625VA transformers on my UCD400 amps, hoping that I'd be able to make the amps phsically smaller since the 1500VA tranformers are almost 8" in diameter and 3.25" high. It wasn't a dramatic difference, but the amps didn't sound as effortless and the noise floor didn't seem to be quite as low as with the larger transformers. The difference in sound was worth the added bulk to me, but I'm willing to make a substantial effort to get the last few % of sound quality possible.
Greg, I mentioned this in another thread and thought I would reiterate here for prospective tranformer hunters. Topaz makes a line of isolation transformers that could be wired two in parallel to give the required output voltage. The Topaz model is double shielded and has 0.005pF for 140dB of common mode noise attenuation. The transformers come in ratings of 250VA to 10kVA. I think a smaller model goes for about $300. I use the 5kVA model to feed my TV/secondary stereo (including a class d amp). Its reduces noise quite nicely in this system.
The manufacturer is MGE UPS, by the way, and the model goes by the name Topaz 100 Ultra Isolator.
serengetiplains said:
Yes, I saw your post, and it's worth thinking about. The one negative that came to mind was the likely sizing of the wire used on the transformer. Since it's designed for 120V on the secondary, I would expect that the wiring would be sized accordingly, i.e. a 1000VA with 2 120V secondaries would be designed to handle a nominal 4.5A of current per secondary. Whereas, a custom built 1000VA transformer with 2 60V secondaries would be wired to accomodate 9A of current per secondary. Of course, how often would the amp really push the transformer that hard; but it does imply that you should roughly double the size of an isolation transformer to have the same current capability as a transformer designed for the actual output voltage.
GregD said:
I am not worried about the extra cost for more windings. I am worried about the custom charge - it'll really depend on the vendor where you get the quote. Some may charge a little more, but there are vendors that will be multiple times the price of an off the shelf unit.
And as for never pushing more than a 100 watts - that nor really depends on your speakers. Mine are quite power hungry (i.e. inefficient), which is why I plan to biamp with 4 UCD700s.
Peter
GregD said:
so what vendor do you have in mind for the custom job?
And two 800VA are too small? We're talking 1600VA for the pair of 700s and that's 400VA more than Hypex recommends for the pair -- unless I am misreading their comments about the 1200VA unit they recommend. Clearly, if they mean a 1200VA per module, yes, then we need bigger iron.
Peter
GregD said:
well, that sounds reasonable - given Plitron sells the good stuff off the shelf for about $450 at that rating...
Have 'em make me four 1200s then, what the heck! Throw in the windings for the rest of the setup. I have a few weeks before I can start building so there's no real hurry on my end.
Peter
I'm going to order some custom units for mono blocks. I plan on doing mono-blocks so 800VA with dual 60V windings and the other small secondaries also. I like to account for 10% line swings so even with that we get 93V rails which is just under the maximum 95V listed in the data sheet.
I'll get them potted with the electrostatic shield between windings. It only cost a few dollars more.
If anyone is interested I'd be willing to offer them at a VERY discounted price so I can hit the minimum order of fifty units. I'll have to get a quote but I'm guessing they will cost around $60-$70 each after shipping and customs. They will take 6-7 weeks though because the only reasonable way of shipping them is via Ocean freight. Air cost a fortune.
I'll get them potted with the electrostatic shield between windings. It only cost a few dollars more.
If anyone is interested I'd be willing to offer them at a VERY discounted price so I can hit the minimum order of fifty units. I'll have to get a quote but I'm guessing they will cost around $60-$70 each after shipping and customs. They will take 6-7 weeks though because the only reasonable way of shipping them is via Ocean freight. Air cost a fortune.
Hi,
I ordered two transformers from Plitron, I wanted a mu-metal wrap and static shield, I highly recommend both additions they're only a few extra dollars each, highly affordable options, until they tell you it's an extra 50% "just for the extra paperwork" on the order, since none are stocked it becomes a custom job which supposedly required more paperwork, and that's per transformer.
If they had stock they supposedly won't charge that extra 50% (yeh right), and then tell you they don't keep any stock, which makes them all custom orders.
Having said that, they still won't give you any options like your choice of primary or whatever aux windings you want, having said "we don't do custom unless you want at least ten unites", and yet, I'm paying an extra 50% for two transformers because it's a custom job. Huh?
Still I figured they're close to home and was likely cheaper than to order cross border or overseas, but if you want to deal with Plitron you know what's in store for you.
Lead time was one month. There's no mechanical hum and it works great.... but I still feel like they ripped me right off!
BTW, I'd also enquired about their LONOISE technology which takes care of inrush for you etc. They wouldnt' even entertain me with a price, simply having said _EXPENSIVE_, and it doesn't sound like they even built a single one.
As per mains tolerance, someone said to allow for 5%, someone said 10%, it must be 10% because that's what mains are regulated to. On top of that you also have to allow for the transformer regulation, (5% for anything over 500VA).
So a total of 15% would be wise for worst case conditions and you won't have your amps going into protection mode all the time at the lower volumes you'll likely most use.
Has everyone considered their loads?
Regards,
Chris
I ordered two transformers from Plitron, I wanted a mu-metal wrap and static shield, I highly recommend both additions they're only a few extra dollars each, highly affordable options, until they tell you it's an extra 50% "just for the extra paperwork" on the order, since none are stocked it becomes a custom job which supposedly required more paperwork, and that's per transformer.
If they had stock they supposedly won't charge that extra 50% (yeh right), and then tell you they don't keep any stock, which makes them all custom orders.
Having said that, they still won't give you any options like your choice of primary or whatever aux windings you want, having said "we don't do custom unless you want at least ten unites", and yet, I'm paying an extra 50% for two transformers because it's a custom job. Huh?
Still I figured they're close to home and was likely cheaper than to order cross border or overseas, but if you want to deal with Plitron you know what's in store for you.
Lead time was one month. There's no mechanical hum and it works great.... but I still feel like they ripped me right off!
BTW, I'd also enquired about their LONOISE technology which takes care of inrush for you etc. They wouldnt' even entertain me with a price, simply having said _EXPENSIVE_, and it doesn't sound like they even built a single one.
As per mains tolerance, someone said to allow for 5%, someone said 10%, it must be 10% because that's what mains are regulated to. On top of that you also have to allow for the transformer regulation, (5% for anything over 500VA).
So a total of 15% would be wise for worst case conditions and you won't have your amps going into protection mode all the time at the lower volumes you'll likely most use.
Has everyone considered their loads?
Regards,
Chris
pburke said:
I have the information about the vendor filed away in some boxes, so it'll probably be sometime this weekend or maybe Monday by the time I dig it out. Also, I've seen a few others mentioned here on diyaudio.com upon occasion, I'm planning on doing a search later.
As far as the sizing goes, it's more of a case of want than need in my case. With the UCD400s I heard a small improvement with the custom 1500VA transformers versus the Avel 625VA. Of course, it's also possible that the custom transformers were just better made, and the difference wasn't due to the size increase. I don't know, but I haven't really heard of any negatives to the sound from oversizing a transformer, and the cost is relatively negligible.
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