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Old 30th June 2010, 08:01 PM   #1
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Default non-isolated power supply?

Hi guys,
i came across a 2.5 kw stereo amp (5 kw mono) schematic,and it uses 'high power non-isolated power supply'.Both channens uses the same windings (130 v rails).
How does this work?What is the efficiency and weight of the 'transformer' compared to the isolated power supply?
Regards.
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Old 30th June 2010, 09:17 PM   #2
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first of all i belive that for a number of reasons this is a subject that is not allowed to talk about in this forum

--- it is not safe to work with while constructing
--- it is not safe to work with while operating
--- there is mains leathal voltage all over the pcb of the amplifier
--- and most imprtant there is mains leathal voltage arround the speakers and speakers cables

i belive that this just a question of time before some moderator see this and lock the thread

there is a very high risk while constructing or operating this amplifier .... i would recomend that no one withouth the proper knowledge regarding safety and the danger involved is ever messing up with this amplifier


for the record ------------------------------------

--- you may forget this amplifier as a schematic .... any class AB amplifier that is rated above 300W is supposed to be a pro amplifier and this cannot be done without proper ltp, sophisticated vas stage , courent sources here and there, and most of all VI limiters or other protection methods .
As is this amplifier may operate more than properly but will stand absolutelly no abuse if pushed a bit hard

--- The all trick of this circuit is the transformer that is actually an autotransformer or in plain greek a couple of resistors conected to mains to a CT to create an artificial earth and there you go you have rails of 130+130 volts
*by this logic the size and weight of the trafo can be reduced to almost 25% of a conventional trafo ... A thing that can become handy in PA bussines where kilo/watt/cost is an important factor ( can you equalize that with the loss of a human life ???.... i prsesume not )
* then again you have mains all over the amplifier pcb , speakers and speaker cables

--- To preserve full saftey in the front end and isolation trafo is used to isolate mains and playing source that is in direct contact with human most of the times ...problem is that this trafo needs to be linear and with perfect bandwidth ( eventhough not really needed for most PA application ) while preserving other isolation high voltage creteria.... not easy to obtain

--- one other issue is that the specific power autotransformers have diferent behaviour regarding loads that can work both ways either as a benefit ot the amplifier or as a disadvantage


if we presume that all the mebers understand the risk of constructing and operating such an amplifier an adition will be that this could be an excellent idea for amplified speakers ...since you have no speaker cables that will reduce the safety problem by far down

i will not hide that such an idea was blowing my mind for very long time so i have made trafos to operate with one of my amplifiers the QLA ...keep in mind that a simple 100W trafo will happily power a 350W @8R amplifier

before opening a thread to post results of my work i will consult with moderators first

kind regards sakis
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Old 1st July 2010, 06:13 AM   #3
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Hi Sakis,
wow!Thanks for the info.I was not planning on constructing that,i was just curious of how a single traffo could drive such a big amp.
This is suitable for a powered sub.I am a bit more curious about your traffo design,since this is not allowed here,will you please mail me the details?The core size,wire size and turn ratios.Here is my address:sirtomsaw@gmail.com.
Thanks again for the info.
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Old 1st July 2010, 06:24 AM   #4
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Can you post a diagram of the PSU ?

If the amp is non isolated from the mains, how is the audio interface achieved ?
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Old 1st July 2010, 07:42 AM   #5
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read the all post re gamoto .... beyond the power tranformer ther is a front end isolation trafo 600/600 or so ...and here is the 5.000 W schematic

(schematic removed by moderators)
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Old 1st July 2010, 09:00 AM   #6
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Couldn't an optocoupler be used instead of the transformer?
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Old 1st July 2010, 09:25 AM   #7
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i dont know sorry
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Old 1st July 2010, 10:55 AM   #8
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Quote:
Originally Posted by Th3 uN1Qu3 View Post
Couldn't an optocoupler be used instead of the transformer?
It certainly could, but the trannys easier and cheaper.

So this is a "specialised" bit of kit... all parts of the amp and speaker must be totally out of reach of being touched.

And thanks for posting the circuit Sakis always interesting to see these kind of things.
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Old 1st July 2010, 11:16 AM   #9
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lets see how far we will go with that .... circuit and trafo is ready but now days we are way to busy to bother with new construction

we have a plan for a plastic enclosure that will feature 12" woofer +1.25 driver /passive xover and the above power supply all sealed very properly and ventilated for a power of about 300-350W at 8 R

then again it is very important to notice that the behaviour of such a trafo in a reactive load is by far diferent than any conventional trafo ... the transformer actually transfer all the power demands to the socket and that means that up to a point power is almost unlimited ... the question is what this almost means and what happens next ....


still extensive tests are to be made to get a complete picture ....

it might come us a surprize but it seems that ROTEL designed a thing like that in the past ....now days probably not allowed to put in the market

regards sakis
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Old 1st July 2010, 11:26 AM   #10
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The "transformer" is actually called an "autotransformer", often used in older TV's etc.

It's lethal for a DIY based forum... someone is going to try and copy this without any clue as to the implications or safety risks involved.
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