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Old 8th February 2008, 06:34 PM   #1
Budric is offline Budric  Canada
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Default Power supply suggestions needed

Hi,
I'm new to diyAudio and was looking to build a GainClone or some simple class A amp to play around with. The problem I have is how ridiculously expensive toroid transformers are for the power supply. They cost 100+$ for 120VA. Compare this to a PC power supply that is rated for 600W and costs 70$ for the whole thing already built and in a box. Of course 12 VDC output is the problem.

Are there any simple alternatives? Maybe someone knows where to buy an SMPS that does +-30VDC. Or perhaps a simple circuit that can double the voltage of a PC power supply (all the ones I've seen use switching, and are quite complicated).

Thanks for any help.
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Old 8th February 2008, 10:24 PM   #2
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Default Transformer mishegas

First off, the requirements for class A are way different.
Continuous amps means heat, and, as usually stated, a toroid should be way over-speced vis. VA so it is safe.
For class AB, I recommend Elliot Sound Products, at least what he has to say about PS matters.
You can get good deals at APEX, something like 21.5-21.5, or 28-28
You don't need massive power if you are separating out the (Bass IE. sub plate amp) and particularly when you are just starting out. the results will be superb for only 35 watt or so and safer for the 3875.

At ESP there is a class a (p3a) that is a good starting point. it can be modded back to 55w (using a strong 30-30 vac )when you find out how much of a can of worms class A really is.

Switchers are a waste of time. They are very tough to use if quality of sound is your primary goal, and they can upsel other electronics, too.
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Old 8th February 2008, 11:45 PM   #3
tINY is offline tINY  United States
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There is always the "scrounge it from a dead amp" approach.

If you are doing a class A design, you only need a single ended supply....

Or, if the scrounge isn't an option and the torroid is to spendy for you, look to a traditional power transformer.




-tINY

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Old 12th February 2008, 03:30 PM   #4
Budric is offline Budric  Canada
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Thanks for the suggestions.

I was wondering how much worse are the square big transformers compared to toroid. Do they add noise? If so what kind (low/high frequency). If you get a toroid transformer with the same rating but costs 2x as much how much better will it be? 2%, 5%, 100%? I don't have experience with them so I'm relying on some from the members of this board.
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Old 12th February 2008, 10:13 PM   #5
tINY is offline tINY  United States
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You are in good shape as a DIY'er.

The main difference between the Torroid and rectanngle cores is radiated field. So, if you can put the PS in a different steel chasis, you won't see any difference in the performance of your amp.




-tINY

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Old 16th February 2008, 10:28 AM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
the EI attenuates the HF garbage slightly better than the toroid.
EI has a slightly higher regulation.
Small EI is slightly cheaper.
EI can be slightly noisier (mechanical).
EI will leak more magnetic field.
EI is much heavier.
EI is more tolerant of mains DC.

Try to find a secondhand that exactly matches your requirements, or design the amp to match the available cheap transformer.
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Old 17th February 2008, 05:49 AM   #7
gootee is offline gootee  United States
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Default Re: Power supply suggestions needed

Quote:
Originally posted by Budric
Hi,
I'm new to diyAudio and was looking to build a GainClone or some simple class A amp to play around with. The problem I have is how ridiculously expensive toroid transformers are for the power supply. They cost 100+$ for 120VA. Compare this to a PC power supply that is rated for 600W and costs 70$ for the whole thing already built and in a box. Of course 12 VDC output is the problem.

Are there any simple alternatives? Maybe someone knows where to buy an SMPS that does +-30VDC. Or perhaps a simple circuit that can double the voltage of a PC power supply (all the ones I've seen use switching, and are quite complicated).

Thanks for any help.
Where are you shopping?!

My current mouser.com catalog shows Hammond 120VA toroidal dual-pri dual-sec transformers for $56.67 for qty 1, or $51.01 for qty 5. For $102.44 for qty 1 you get a similar 500 VA transformer. And 1000VA is only $141.68 for qty 1 (You could get 24Vrms @ 41.7 Amps, for that!).

And mouser.com is not even the cheapest source. There are places that sell the slightly-older discontinued equivalent Hammond models, but still new in the box, for probably less than half of those prices.

BY the way: Switch-mode power supplies CAN make quite-excellent audio equipment power supplies. Many here have used them, as do some high-end manufacturers. Some people claim that they make their systems sound much better, compared to linear supplies. Also, in some ways, they are even easier to use than linear supplies, since their switching noise is not in the audio band, and is thus easier to filter out without affecting any audio frequencies. Even the worst ones' switching noise can usually be easily taken down to the tens-of-microvolts level with about $5-worth of parts for a single LC lowpass filter plus a basic three-terminal adjustable regulator circuit (at least for an SMPS output with a 5-amp or so maximum current draw. For more current, you might have to add a power transistor to the regulator circuit. But the <$2 qty 1 (J.W. Miller) toroidal inductors [a little over an inch in diameter] for the LC filter are good up to over 10 Amps.) BTW, if you do try to use an SMPS, remember to allow about three volts extra per rail, for headroom for the post-regulator.
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