What amp could I build with 600VA 2x61V AC transformers? - diyAudio
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Old 18th May 2014, 08:47 PM   #1
Tinco is offline Tinco  Netherlands
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Default What amp could I build with 600VA 2x61V AC transformers?

Hey guys,

Hypex is over stocked on some transformers, and is selling them with a steep discount. Especially this one looks very interesting to me:

http://www.hypex.nl/docs/TR700_datasheet.pdf

It's 600VA, with dual 0-61V AC secondaries at 50 euro.

I am looking to do a nice high end amp for my next project and was thinking of either a Leach or the Honey Badger, but I'd usually pay double that price for half that VA, and transformers are the most expensive part usually.

Now 120VCT is a crazy amount, are there any amps that run on -/+85V DC that I could build?

I know the LM4780 does according to the datasheet, but I'm not sure if it's a good idea, and I've already built a chip amp and would like to try out something more complex.

Alternatively they also have 120VA transformers at 20 euro, also a good price, but they'd have to be parallel for any decent setup, and rectifier bridges aren't free either.

What would you guys do?
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Old 18th May 2014, 09:36 PM   #2
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61VAC > +/- 87VDC. That's a big, expensive amplifier whether Professional or DIY build. Unfortunately, It's more suited by VA rating for a monoblock application. I think.

Unless you really need to annoy your neighbours, you plan to power a party venue or your speakers are incredibly inefficient, this seems like the wrong way to plan a project. Start with the speakers you envisage driving and work back to amplifier size, then determine power supplies. It may just work out cheaper that way even with normal priced transformers.

In most domestic audio situations, you only need a small fraction of the power of say, a 300W/8R amplifier, which is what you may wind up with. Again, for sufficient current to run 4R loads (quite likely at that power level) a second monoblock would be necessary for stereo with those rail voltages. An even larger amplifier!

A parallel pair or a quality dual mono build of 2 x 60W/8R amplifiers with those 120VA transformers looks more attractive and whatever diode bridges you choose, their price will be a drop in the ocean of overall costs.
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Old 18th May 2014, 09:58 PM   #3
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You can build a linear CRC power supply with dual rectifiers. This will drop the rail voltages down a few volts due to losses. Then you can use a class-D IRS2092 based amp like the CxD500 from http://connexelectronic.com/:
Connexelectronic

Depending how many watts you will really need out of the amp, you could build a stereo amp from one 600VA transformer or stick with a monoblock. The linear supply rail voltages will just sag under high demand so as long as demands are brief or you do not need all the available power you can do a stereo amp that has high dynamic power to provide clean transients.

I am doing something similar using some 500VA 62-0-62V @115VAC transformers that I got for a song last year. I designed a combination regulated/cap-multiplier power supply to make sure I stay within voltage limits.
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Old 18th May 2014, 10:01 PM   #4
Tinco is offline Tinco  Netherlands
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Thanks Ian, you are right, building a straight up 87vdc amp would not be what I want at all.

I was hoping there was some cool way of working around it electrically. For example: After the rectifier circuit you end up with a 0 and a +87V side, and a 0 and -87V side.
What if there was some way to have a voltage divider, so that you'd end up with on one side 0, +43.5 and +87. And then on the other side 0, -43.5 and -87.

With those voltages you could run two channels at decent voltage and decent VA. Is there such a thing as a constant voltage divider? I guess it would need a variable z2 resistor that varied with the load, making everything really complex..

edit: @charlielaub thanks, running a class D amp is exactly what the transformer was designed for, so I should have guessed that was an option, but as far as I know class D amps are not really something that's easily done as a hobbyist right? in any case they're probably a bit above my current skill level

Last edited by Tinco; 18th May 2014 at 10:05 PM.
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Old 18th May 2014, 10:10 PM   #5
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Quote:
Originally Posted by Tinco View Post
edit: @charlielaub thanks, running a class D amp is exactly what the transformer was designed for, so I should have guessed that was an option, but as far as I know class D amps are not really something that's easily done as a hobbyist right? in any case they're probably a bit above my current skill level
You can do it!

True, if you had to design and build the circuit and do the layout for a class-D power amp board that would not be a trivial task (at least for me!). But when you buy the power amp module it is sold in a "ready to run" form and you are just connecting the wiring more or less. You are still building a cap filtered power supply just like you would for a class AB amp. The advantage of the class D amp is its higher efficiency, so less heat is given off. PSRR of class-D amps is sufficiently high that you can use a standard power supply without worry of hum from ripple on the rails.
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Old 18th May 2014, 10:13 PM   #6
Mikett is offline Mikett  Canada
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Old 18th May 2014, 10:56 PM   #7
Tinco is offline Tinco  Netherlands
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Wow.. that leach super amp seems to require exactly this transformer.. I wonder why Thanks Mikett!

Quote:
" One student who built it didn't have an audio system to use it with, so he connected power resistors to his amplifier and drove it from a function generator to heat his bedroom."
In his introduction he doesn't really explain who would want to build this and why, is it just a leach amp that can drive bigger/less sensitive speakers? Does it sound good? I'll google for some reviews.

edit: Heh after some searching I find this is the amp still4given had so much trouble with, now I'm a bit intimidated Also his initial reason to build it was also because he had a transformer that fit it, talk about coincidences :P

Last edited by Tinco; 18th May 2014 at 11:22 PM.
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Old 18th May 2014, 11:50 PM   #8
GChap is offline GChap  France
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Old 19th May 2014, 07:44 AM   #9
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Quote:
Originally Posted by Tinco View Post
Wow.. that leach super amp seems to require exactly this transformer.. I wonder why Thanks Mikett!



In his introduction he doesn't really explain who would want to build this and why, is it just a leach amp that can drive bigger/less sensitive speakers? Does it sound good? I'll google for some reviews.

edit: Heh after some searching I find this is the amp still4given had so much trouble with, now I'm a bit intimidated Also his initial reason to build it was also because he had a transformer that fit it, talk about coincidences :P
For the record, my troubles were due to great inexperience and first time etching home brew PCB. My biggest problems were dealing with solder bridges. It took a long time finding them. The amp actually sounds very good, but I would not really suggest it for a few reasons. One being the unavailability of PCBs. The other is the use of end of life parts. I would suggest the Slew master. There are a few different varieties but the design can be built to handle those voltages and there are PCBs available and all attainable parts. I am in the process of building one right now and am planning to scrap my Leach Super amp so I can use the PSU and chassis.

Blessings, Terry
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Old 19th May 2014, 08:37 AM   #10
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The Quad 606 can be operated at lower voltages and is a reasonably cheap DIY build.

Quad 909 Clone
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