How easy is it to replace a transformer in a linear power supply? - diyAudio
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Old 28th May 2010, 07:43 AM   #1
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Default How easy is it to replace a transformer in a linear power supply?

Hi everyone, I have a 13.8V 4A linear power supply, its a samlex rps1204. I want to replace the steel plate transformer it has with a toroidal transformer.

There's no info anywhere on the transformer. The transformer has two cables for the AC input and 3 output cables that go to the small circuit board.

How easy would it be to replace it? Ive seen several 12v toroidal transformers on ebay and partsexpress would any of these be an ok drop in replacement?

I have experience working on house wiring, I know how to use a multi-meter, and I can solder. thanks
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Old 28th May 2010, 09:07 AM   #2
Spiny is offline Spiny  United Kingdom
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As there are three wires this is probably wired to two diodes as a Bi-Phase circuit. Measure the AC voltage of the current transformer, this will give the transformer required at a guess 15 - 0 - 15 @ 60VA. Then its a size and mounting problem.

Be careful when measuring the voltage as the case will be open and the live mains probably exposed

The question has to be asked why? This appears from the voltage to be a car battery replacement unit for driving car audio. Correct me if I'm wrong

If the PSU is working a toroid wont make any difference in my opinion.
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Old 28th May 2010, 10:22 AM   #3
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Ok I measured the the three outputs; when I measure 1 and 2 it gives me 18.80V when I measure 2 and 3 it gives me 18.80V, and when I measure 1 and 3 it gives me 37.62V.

From what Ive been reading it seem it might offer some sonic improvement such as lower noise , I think it will also be good practice since I would like to replace the transformer on my tube dac with a toriodal one eventually.

Im not sure what its used for, I bought it for my t-amp, heres is a link of it. I can also take pics of the inside of it if needed.

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Old 28th May 2010, 06:08 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
there is some, many would say much and measured, anecdotal evidence that a square frame transformer attenuates HF artefacts more than a toroidal does.

PS.
what was the mains' voltage when you took those measurements?
What was the load when you took those measurements?
What is your normal mains voltage where you intend using this transformer?
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Last edited by AndrewT; 28th May 2010 at 06:10 PM.
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Old 28th May 2010, 11:29 PM   #5
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The AC in my house was 120vac when I took the measurements
No load was connected to it.
120vac will be the normal mains voltage
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Old 29th May 2010, 12:34 AM   #6
infinia is offline infinia  United States
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Waste of time and money! Even if you get a better hunk-o-iron it will mostly be a step backward since HF isolation will now suffer! LF performance is mostly the Vreg circuit.
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Old 29th May 2010, 09:47 AM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by SilverStrings View Post
The AC in my house was 120vac when I took the measurements
No load was connected to it.
120vac will be the normal mains voltage
you probably have a 120:15Vac transformer. Regulation is ~25% about typical for a small EI.
Infinia agrees with the majority. Don't go to toroid unless you have good evidence to show why/how the toroid improves on the square frame.
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Old 2nd June 2010, 12:23 AM   #8
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There was an article I read about how toroidal transformers provide much better sound than other transformers, they said this was due to their efficiency and lower magnetic flux, I have a gauss meter which measures
ac magnetic fields at 50/60hz and indeed the the transformer emits a strong magentic field which extends about 5-6ft. Most high-end gear and pro gear use them, and many DIY'ers seem to use them for their builds

here is another article I read
Sound Lab Technology: Toroidal audio transformers for superior resolution

Samlex finally got back to me here is the info they gave me on the transformer.

Power: 200VA
Primary : 120 VAC, 60 HZ
Center tapped Secondary (No load): 37.5 V ( 18.8 V from one leg to the center tap)
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Old 2nd June 2010, 01:05 AM   #9
Eva is offline Eva  Spain
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Another vote for waste of time and money
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Old 2nd June 2010, 01:32 AM   #10
infinia is offline infinia  United States
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SilverStrings the article you linked above is about audio output transformers it's not for power supplies with solid state regulators. You don't want tighter coupling for a PS except at 60Hz. That's why using toroid's for a PS feeds more mains HF garbage through past the regulator. FWIW Standard split bobbin IE core XFMRs are excellent line conditioners with a few more filter components.
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