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Old 30th August 2010, 09:53 AM   #561
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Hi. Yet another noob Gainclone DIYer here. Has anyone seen this power amp PSU circuit Power Supply for Power Amplifiers ? Seems to happily use two bridges from a centre tapped transformer.
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Old 30th August 2010, 11:06 AM   #562
AndrewT is offline AndrewT  Scotland
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it is not a dual bridge from a dual secondary.
It is a single bridge from a CT secondary in parallel with an identical single bridge from the same CT secondary. If you power two amplifiers from this you may find problems eliminating hum. I'm not sure you can eliminate the hum. I couldn't.

Someone show me how.
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Old 30th August 2010, 12:58 PM   #563
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Quote:
Originally Posted by AndrewT View Post
it is not a dual bridge from a dual secondary.
It is a single bridge from a CT secondary in parallel with an identical single bridge from the same CT secondary. If you power two amplifiers from this you may find problems eliminating hum. I'm not sure you can eliminate the hum. I couldn't.

Someone show me how.
What's the expected source of hum? As the author sells this PSU as a kit you'd think, if there was a problem, someone might have complained? The site is worth exploring - many good articles and circuits.

I was planning to use this as my PSU circuit, with some pi-filtering resistor ideas and a regulator circuit from Roman Black Roman Black's gainclone amp .

This is my schematic so far (I'm incautiously confident I won't have to retitle it 'instant pyrotechnic device' but not so sure, now, about having to call it 'very expensive 50Hz tone generator'): Click the image to open in full size.
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Old 31st August 2010, 08:46 AM   #564
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That 35-0-35 ac transformer is going to give you nearly 50V dc

What load speakers are you going to use? a 20V drop over your regulator is going to dissipate too much heat.

Here is a simpler regulated powersupply design:

PA100 DIY 2x LM3886 in parallel gainclone audio amplifier

You need +-28V dc for 4 Ohm loads. for maximum power into 8 ohms you need +-35Vdc
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Old 31st August 2010, 09:52 AM   #565
AndrewT is offline AndrewT  Scotland
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Forget the regulators and buy the correct transformer.

Or

keep the transformer and build an amp that suits +-50Vdc.
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Old 31st August 2010, 10:19 AM   #566
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Thanks for the feedback and suggestions.

8ohm speakers.

I just found a 30-0-30V 160VA toroid (ah, the happy glow of finding a vital, expensive part bought 10 years ago and forgotten about, hiding the the back of a cupboard - YES!) so I can dispense with the dual rectifier centre tapped design from Elliott Sound Products and go with a full twin secondary design. I already have have the LM317s and PNPs for the regulators and the LM317's control resistors in the circuit shown are already set up to provide 35V... so I may as well build it.
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Old 27th November 2010, 07:30 PM   #567
sardonx is offline sardonx  Canada
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Well one more person needing help here I got some bridged tda7293 boards off ebay that call for a power requirement of 30 to 35 volts Dc. TDA7293 parallel BTL mono power Amplifier borad 350W - eBay (item 120595963571 end time Dec-11-10 06:58:28 PST)

I have a dual secondary 2x20 volts ac 400VA plitron trafo. The picture shows how it's wired. When measuring the assembled supply with no load, from v+ to v- i'm getting a reading of 48 volts. But measuring from ground to v+ i'm getting around 30. This makes sense to me but the 48 volts does not... I'm wondering if i did something wrong or i fried the boards cuz when i had it hooked up and turned it on there was a buzzing sound and then complete silence. No smoke, no heat on the chips nothing.. did i do something wrong?
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Old 27th November 2010, 07:49 PM   #568
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some help on TDA7293 boards off Ebay
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Old 28th November 2010, 09:35 AM   #569
AndrewT is offline AndrewT  Scotland
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post567
what is the 5th (middle) ground wire going to?

It is not needed for a dual secondary transformer, it has no centre tap.

Could it be going to the Safety Earth?
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Old 30th November 2010, 04:28 PM   #570
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post567
what is the 5th (middle) ground wire going to?

It is not needed for a dual secondary transformer, it has no centre tap.

Could it be going to the Safety Earth?
One might also consider paralleling the dual secondaries transformer for just 20 VAC out put = 28.5 volts DC after connection to a single diode bridge ... OR ... connecting the dual secondary transformer outputs and passing that through a single diode bridge = giving one a true center tap between the series coils (as is "standard" practice).
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