Balanced 240V AC mains supply, simply does it

[Barry]

The two (half) secondary winding voltages of 117.2 and 119.0V, being in antiphase will simply add to give you 238.2v

I assume you are worried about any common-mode noise only cancelling out to 1.5% (= (119 -117.2)/119). Is this the distortion to which you refer? Have to confess I don't understand the power supply arrangements for the two amps in your circuit

Apropos, your protection circuit operating within 1us. I do believe that such a circuit can be built, but feel that because it is so fast, it would be tripping all of the time. The RFI and noise will be of the order of 100kHz to 1MHz and I'm sure dropout and over-voltage spikes can be of this order.

Following this thread with interest.

[Reid Malenfant]

This is fascinating stuff!
Thanks Mark.

If only life was easy, a lot of people wouldn't be interested but thanks for the interest & the post! Take it from me that a lot will look & crawl under a rock & dismiss it all

The two (half) secondary winding voltages of 117.2 and 119.0V, being in antiphase will simply add to give you 238.2v

I assume you are worried about any common-mode noise only cancelling out to 1.5% (= (119 -117.2)/119). Is this the distortion to which you refer? Have to confess I don't understand the power supply arrangements for the two amps in your circuit

Apropos, your protection circuit operating within 1us. I do believe that such a circuit can be built, but feel that because it is so fast, it would be tripping all of the time. The RFI and noise will be of the order of 100kHz to 1MHz and I'm sure dropout and over-voltage spikes can be of this order.

Following this thread with interest.

Hi Barry. I'm worried about the lack of pure balance forcing a current to run through the earth.

The circuit diagram was incredibly basic. If you understand about electronics you might understand this so you know where i'm going. I'll use a fast op amp to generate a square wave driven from the mains so in phase. I'll then filter this with something like a 24Db octave filter at a lower frequency (say 20Hz), this will result in a low distortion sign wave. I need to set the output voltage of this sign wave, so rather than using a compressor i'll create a circuit that alters the power supply to the square wave generator & keeps the AC waveform at a constant voltage. Phase shifting isn't a problem & i'll most likely need this after the filter.

The output from this will be in phase with the AC input to the transformers & so all i need to do is compare the clean AC generated signal to the output from the transformers. The amps will correct anything up to a certain frequency & that depends on the transformers in all honesty. It's a simple feedback network & will need to be SOT (set on test). I see no reason why up to 500Hz or beyond can't be corrected so we get a pure AC waveform rather than the 5%+ distortion cobblers that we are used to having supplied to our equipment. I might need to use 500W+ to do this but it's the little things that add up to make the big picture

You know that late night stuff when nearly everything is switched off & the whole system seems to open up? Well that's what i want all the time

[Barry]

If only life was easy, a lot of people wouldn't be interested but thanks for the interest & the post! Take it from me that a lot will look & crawl under a rock & dismiss it all

Hi Barry. I'm worried about the lack of pure balance forcing a current to run through the earth. Why should it? Only if it was feeding another centre-tapped transformer earthed at the centre point, would any inbalance current flow. Just as it does in an un-balanced Wheastone bridge.

The circuit diagram was incredibly basic. If you understand about electronics you might understand this so you know where I'm going. I'll use a fast op amp to generate a square wave driven from the mains so in phase. I'll then filter this with something like a 24dB octave filter at a lower frequency (say 20Hz), this will result in a low distortion sine wave. I need to set the output voltage of this sine wave, so rather than using a compressor I'll create a circuit that alters the power supply to the square wave generator & keeps the AC waveform at a constant voltage. Phase shifting isn't a problem & I'll most likely need this after the filter.

The output from this will be in phase with the AC input to the transformers & so all I need to do is compare the clean AC generated signal to the output from the transformers. The amps will correct anything up to a certain frequency & that depends on the transformers in all honesty. It's a simple feedback network & will need to be SOT (set on test). I see no reason why up to 500Hz or beyond can't be corrected so we get a pure AC waveform rather than the 5%+ distortion cobblers that we are used to having supplied to our equipment. Can you please explain what you mean by distortion. Do you mean deviation from a pure 50Hz sine wave? I might need to use 500W+ to do this but it's the little things that add up to make the big picture

You know that late night stuff when nearly everything is switched off & the whole system seems to open up? Well that's what i want all the time

I can see what you are trying to do, and your circuit idea might work. However it does strike me that it's all starting to become very complicated. Why don't you build a crystal controlled oscillator to produce a clean 50Hz sine wave and use this as an input to a 500W power amplifier?

Regards

[Reid Malenfant]

I can see what you are trying to do, and your circuit idea might work. However it does strike me that it's all starting to become very complicated. Why don't you build a crystal controlled oscillator to produce a clean 50Hz sine wave and use this as an input to a 500W power amplifier?

Regards

Quite easy that one AC mains isn't exactly 50Hz, it deviates all over the place frequency wise but over a 24 hour period it must have completed the exact amount of sign waves that it would have if it was at exactly 50Hz.

Taking that as a given i couldn't just get an accurate 50Hz oscillator because it would very shortly go out of phase with the incoming mains. The circuit needn't be complicated at all, a fast op amp to generate a + & - square wave which switches at zero crossing & a dual op amp to make a low pass filter (24Db per octave). One more op amp to control the DC voltage feeding the square wave generator, i decided this would be the best way of regulating the AC output to keep it constant rather than a compressor which would add distortion. A few other bits & pieces & we are off. 500 or so watts & it'd be up & running.

If i was to do the same thing with an accurate 50Hz signal i'd need to regenerate the whole 6.6KW as the only way of doing it like the PS Audio PPP is to keep it in time with the mains


Yes, when i say distortion i mean any deviation from a pure sign wave.

If what you say is correct & there isn't any earth current then there may well be no need what so ever to go to these lengths & balanced mains will probably be enough.

Cheers for your input Barry

[Reid Malenfant]

Well i have had a think, yet again

I decided i have a fairly easy way of getting them properly balanced to within a few hundred milli volts of each other. My secret weapon is a 60VA toroidal transformer that will have a new secondary wound on it. All i need is somewhere around 1.7V but at 29A which is within the 60VA rating.

Looks like i'll soon find out how many turns per volt i'll need & then i'll wind a load of 0.9mm enamelled copper wires in parallel to give me the correct current rating...

Back in a bit

[Ali Tait]

Interesting stuff Mark,just seen this thread.Have you tried the transformers as is and do you have any current flow to earth?

[Reid Malenfant]

Hi Ali, no i haven't but in reality i don't need to When Barry mentioned the Wheatstone bridge i had to cast my mind back a rather long way, he's correct, unless something is forcing an earth current to flow then there won't be one The only thing that could do that is (if all is in order) an earth fault in the equipment that is connected to it.

Hopefully just about to win on ebay a 25Amp 30ma RCD I decided to add the 60VA transformer just to get everything balanced as best as possible, it costs me nothing but a little time to wind the secondary i need but it'll get the thing balanced better which will result in better interference cancellation. As the whole idea is to cancel out interference & it costs just time then imo every little helps.

These transformers have what looks like 5.6% regulation (at 3.3KVA) so the addition of a few volts will help out here again. From what i'm getting mains wise i can expect 240V AC at no load & 226.6V with a 6.6KVA load. Frankly i seriously doubt i'll ever use that much power, let alone continuously So i should be good for 235V AC in normal use (maybe more) & maybe a tad less when pushing the envelope (trying to go deaf).

This is going to turn into a full project now. Maybe at a later date i might go mad & add power amps to generate 6.6KVA of mains with less than 0.5% of distortion, but right now the balanced mains is the aim

Bests to you fella..

[Ali Tait]

Ok,can you try it as is and tell us how it sounds?

[Reid Malenfant]

Yes, give me a day or so though, i'm not as fit or have the time like i used to.

Everything in the room at the moment is powered from the same point which is a spur from the fusebox, so i'll swap it over & have a good listen & let you know. A few days or so should see differences & i'll report them

[Barry]

Hi Mark,

I like the sound of the 60VA transformer. Can you sketch a circuit diagram for us so that we can see what you propose doing?

I don't think regulation is going to be much of problem; it's the mutual cancellation of common mode noise that is the more important benefit to be gained with a balanced mains supply.

Keep us informed.

Regards