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Old 29th April 2012, 01:19 PM   #1
Jay is offline Jay  Indonesia
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Default Please suggest a high rail voltage (160V) amplifier

This is about building a good amplifier where transformer is utilizing the commonly available step-down transformer (230V to 120V) that can be found in many devices (including old television). Most of them have a high VA rating and the biggest I have is a 2000VA toroid. For EI transformers, unwinding the secondary is of course out of question, hence this thread.

I want the best quality amp I can build. Preferably suitable for home use but if not possible then for PA use. The output device is of course a mosfet. Currently I'm using IRFP460. But I plan to use high power mosfets in ISOTOP case as I have plenty of them. I couldn't find Spice model for the ISOTOP mosfets but I planed to model the mosfet using paralleled mosfet with equal Yfs per Ciss (I hope that possible).

I have only tried one topology with output coupling capacitor, and I wonder what others might suggest regarding topology, or even better if there is a working design already available. My next candidate (for the topology) is the Legend Quasor by Boraomega (Dr Jagodic). Then the hybrid tube-mosfet based on John Broskie (but I'm worrying the high output impedance so not in the top list). I was also considering cascoded bipolar output ala SAE PA amplifiers but not a priority as I don't have many bipolar devices.

Please suggest a topology that you think will work best with this kind of rail voltage (150Vdc-160Vdc). Thanks.
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Old 29th April 2012, 01:28 PM   #2
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How much do you want to spend ?

It might be more cost effective to sell transformer or trade it in for a lower rail voltage.
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Old 29th April 2012, 01:58 PM   #3
Jay is offline Jay  Indonesia
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I have plenty of parts. I usually don't buy parts for a project. I have hundreds of transformers, including these step-down ones.

I think not many have interest in buying step-down transformer, especially for a high price

Why do you think it would be costly? I have plenty of big heatsinks also.
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Old 29th April 2012, 02:03 PM   #4
Pano is offline Pano  United States
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Are these typical step down transformers used between the mains and a device?
If so, they are likely autoformers, not true and isolation transformers and thus would NOT offer isolation from the mains. Don't use that.
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Old 29th April 2012, 02:08 PM   #5
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I would start with building a low power amplifier like 50-100 watts per channel into 4 ohms, plenty of schyematics to choose from on this forum.

Suitable rail voltages for these would be 2x35-45 volts DC.

Building a reliable amplifier in the kilowatt range is extremely hard due to the high rail voltages, it is also very expensive, one mistake and you can loose hundreds of dollars in output devices alone.
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Old 29th April 2012, 02:10 PM   #6
Jay is offline Jay  Indonesia
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No they are not autoformers. Autoformers are not common here. I have only one autoformer. But many equipments work with 120V secondary. Common one is a washing machine.
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Old 29th April 2012, 02:19 PM   #7
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by Tekko View Post
I would start with building a low power amplifier like 50-100 watts per channel into 4 ohms, plenty of schyematics to choose from on this forum. Suitable rail voltages for these would be 2x35-45 volts DC.
If you mean the ones with "normal" rail voltage, I have built most of the best ones.

Quote:
Originally Posted by Tekko View Post
Building a reliable amplifier in the kilowatt range is extremely hard due to the high rail voltages, it is also very expensive, one mistake and you can loose hundreds of dollars in output devices alone.
Hundreds of dollar?? I hope not due to electric shock BTW, I'm trying to utilize transformers with 120V secondaries, not to build KW amps. Non-switching class-B is possible.
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Old 29th April 2012, 02:20 PM   #8
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There was a Maplin 1KW MOS-FET design that I've got somewhere that used +/-95V rails.

Keep looking for it as I can't find it here at the moment.

Using a single 160V rail is going to give you big problems. Any single failure will detonate some very expesive components.
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Old 29th April 2012, 02:27 PM   #9
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Here's one.

It does use split rails again though.

http://www.elektropage.com/images/ci...r_Shematic.jpg
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Old 29th April 2012, 02:33 PM   #10
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by KatieandDad View Post
There was a Maplin 1KW MOS-FET design that I've got somewhere that used +/-95V rails.
+/-95V is very common. 160V is not,mostly due to transistor SOA I guess. The original Legend Quasor uses 95V, and I think somebody has built it with very high voltage rail, but no schematic available.

I know this project is a bit crazy, that's why I posted it here, because I know there are many crazy people here
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