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Old 2nd September 2010, 11:42 PM   #1
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Default Dual PSU layout - how does this look?

Hello everybody.

I'm a long time hobbyist but I've only just got into amps and their PSUs (built a couple of 10/15w battery powered so far). I've been doing a fair amount of research into the transformer/rectifier/smoothing setup and have designed a wiring plan for the PSU I need for my amp, based on many hours browsing and a dual supply circuit diagram I found courtesy of ESP here... Power Supply for Power Amplifiers

I'm no artist but I think the attached diagram serves its purpose! My main concern was the transformer-bridge rectifier wiring but after reading up I think I've got it...! Each AMP module requires 55v @ at least 225 VA.

If anybody has a spare 5 minutes I'd appreciate your thoughts...

Thanks!

John.
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File Type: png PSU wiring diagram.png (94.4 KB, 1255 views)
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Old 3rd September 2010, 02:19 AM   #2
star882 is offline star882  United States
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A similar trick is used in some "multiple rail" ATX power supplies.
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Old 3rd September 2010, 11:44 AM   #3
AndrewT is offline AndrewT  Scotland
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First:
Move the two fuses.
One goes in the mains primary circuit.
One more goes in the secondary circuit AFTER the main smoothing caps for every polarity. That's five fuses in total.
Use a close rated slow blow in the mains.
Use a fast rated in the supply lines to suit the current output of the amplifiers.

You show a parallel dual polarity supply from a single centre tapped transformer.
There is a thread running now that is discussing the noise at the amplifier outputs when two linked amplifiers are run from paralleled supplies from a single transformer. This set up is extremely difficult to get operating quietly.
4 secondary windings helps attenuate some of this noise as does two dual secondary transformers, but consider also using a single bridge rectifier on each secondary output and then combining these into dual polarity supplies.
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Old 3rd September 2010, 05:52 PM   #4
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Quote:
Originally Posted by AndrewT View Post
First:
Move the two fuses.

I was wondering about those, the idea was from G Randy Sloane's High Power Amp book to protect the transformer if there was a short circuit in the rectifier

One goes in the mains primary circuit.

Yup got one after the mains switch (just not illustrated)

One more goes in the secondary circuit AFTER the main smoothing caps
for every polarity.

I have 4k7 resistors after the caps to discharge them after the mains is switched off - should I fuse before or after these?

That's five fuses in total.

So one mains, 4 after the the caps - the amp modules are also fused so I actually have 7 in all!! Is that overkill or better to be on the safe side?

Use a close rated slow blow in the mains.

Done!

Use a fast rated in the supply lines to suit the current output of the amplifiers.

Ah, Mr Sloane advises delay fuses to 'be in line with the huge surge currents resulting from the initial charging of the reservoir capacitors'. I guess fast blow offer better protection....?

You show a parallel dual polarity supply from a single centre tapped transformer.
There is a thread running now that is discussing the noise at the amplifier outputs when two linked amplifiers are run from paralleled supplies from a single transformer. This set up is extremely difficult to get operating quietly.

Thanks, I will search out that thread and give it a good read...

4 secondary windings helps attenuate some of this noise as does two dual secondary transformers, but consider also using a single bridge rectifier on each secondary output and then combining these into dual polarity supplies.

OK so Vsec & 0v secondary outputs to rectifier AC inputs for both A & B?
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Old 3rd September 2010, 07:18 PM   #5
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Default Dual PSU updated...

Hi Andrew.

Many thanks for taking the time out to give me your advice. Working on this I've revised my layout...do you think this would work better?

Regards,

John.
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File Type: png PSU wiring diagram.png (97.9 KB, 1132 views)
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Old 4th September 2010, 09:48 AM   #6
AndrewT is offline AndrewT  Scotland
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dual rectifier from dual secondaries produces two single polarity supplies.
Join the two single polarity supplies in series and you get one dual polarity supply.
The junction is conventionally taken as Zero Volts and this also becomes the tapping point to run to Safety Earth and another run to the Main Audio Star Ground.
You don't need 4 capacitors, 2 are sufficient. Expect +-58Vdc to +-60Vdc from your 40+40Vac transformer.
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Old 6th September 2010, 05:37 PM   #7
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Hi Andrew.

I am now somewhat confused...is everything I've learned so far wrong? My transformer has two identical secondary outputs rated at 40v/250VA each, as per the data sheet from Nuvotem (the actual output as measured with my DMM is 46v AC).

I salvaged a chassis from a defunct DVD player and used it to setup a (safe) mock-up of the first stage of the above diagram. Having connected one secondary output to the bridge rectifier (black/red) as expected I obtained a DC voltage at the rectifier outputs (42 volts). Connecting the other secondary (orange/yellow) I again obtained a DC voltage of 42 volts.

Does it not stand, therefore, that as and when I purchase an additional bridge rectifier and connect them as above, I will have two 42v DC outputs, both of which I can then route through my capacitors/resistors to the DC rails of the amp modules?

Kind regards,

John.
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Old 6th September 2010, 08:52 PM   #8
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After further searching the forum including this thread,

Dual rail supply, no centre tap

there appear to be several options regarding this kind of supply…please see below for diagrams...

Option 1:

Each secondary feeds a separate bridge rectifier, creating two DC outputs which in turn feed each amp module via smoothing…

Option 2:

The NEUTRAL of secondary A and the LIVE of secondary B are combined to produce a centre tap (as per the above thread), which is then grounded. The LIVE of secondary A and the NEUTRAL of secondary B are then split to feed two rectifiers which then create 2 DC outputs to feed the amps as above…

Option 3;

The NEUTRAL of secondary A and the LIVE of secondary B are combined to produce a centre tap. The LIVE A and NEUTRAL B feed one rectifier to create 1 DC output which is then split PRE-smoothing to feed the amp modules…

Option 4

The NEUTRAL of secondary A and the LIVE of secondary B are combined to produce a centre tap. The LIVE A and NEUTRAL B feed one rectifier to create 1 DC output, which is split POST-smoothing…

Option 5

As per Andrew’s comments above – Andrew I think this is what you’re getting at (well partially)?

The NEUTRAL of secondary A and the LIVE of secondary B are combined to produce a centre tap. The LIVE of secondary A and the NEUTRAL of secondary B are then split to feed two rectifiers. The outputs from the rectifiers are combined in series to produce 1 DC output, which is then split pre-smoothing…

Personally I see option 1 as the most logical, although this excludes the center tap. I'm continuing my research to ascertain...

1) the importance of the transformer being center tapped...
2) whether grounding one of the secondaries affects the transformer output in any way...
3) whether it's best to split the supply pre or post smoothing or whether this makes no difference...

Any further advice (and/or diagram!) would be appreciated!
Attached Images
File Type: png PSU wiring option 1.png (97.1 KB, 967 views)
File Type: png PSU wiring option 2.png (98.2 KB, 888 views)
File Type: png PSU wiring option 3.png (94.0 KB, 845 views)
File Type: png PSU wiring option 4.png (82.8 KB, 237 views)
File Type: png PSU wiring option 5.png (98.2 KB, 285 views)
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Old 7th September 2010, 09:29 AM   #9
AndrewT is offline AndrewT  Scotland
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pic5 does not work.
Pics2, 3 & 4 are some of the centre tapped options.
Pic1 is one of a series of dual secondary options.

I have never managed to get a two channel amp using pic3 to be completely silent.
I have had a little more success with pic2, but two channel is not completely silent, in the many ways I have tried to ground it.
I have tried literally hundreds of combinations of ground wires to zero volt reference.
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Last edited by AndrewT; 7th September 2010 at 09:33 AM.
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Old 7th September 2010, 10:08 AM   #10
mdm102 is offline mdm102  Russian Federation
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Hello Andrew,

Could you say your experience about this topology: http://www.tnt-audio.com/jpg/psu3.jpg
Interesting, how it compared to pic #4. Is there any difference in the noise floor between them?

Thank you!

Max
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