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Old 6th July 2001, 04:53 AM   #1
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I just completed a two channel Leach Amplifier but I can't get the power supply to work. There are three output leads on my transformer; two rated at 44 volts and one rated at 0 volts. They can either be connected in series for 44 volts at 9 amps or in parallel for 88 volts at 4.5 amps. I attempted to wire the leads in parallel by connecting the 0 volt lead to central ground and the other two leads to the ac connectors on the bridge rectifier. I don't think any current is drawn when the amp is on, but I have verified that the power plug, socket and switch all work.

Thank you.
Peter
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Old 6th July 2001, 05:14 AM   #2
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Peter,
The Leach, I believe, uses a standard power supply arrangement where the center tap of the transformer (0V) is connected to ground. The other two leads will go to the rectifier, yielding + and - DC which should go to separate banks of caps.
Always observe proper polarity on electrolytic caps.
The negative terminal of the cap on the positive rail will go to ground. The positive terminal will receive positive charge from the rectifier.
The positive terminal of the cap on the negative rail will go to ground. The negative terminal will receive negative charge from the rectifier.

Grey
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Old 6th July 2001, 05:16 AM   #3
grataku is offline grataku  United States
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Ok,
are you doing exactly what it says here?

http://users.ece.gatech.edu/~mleach/lowtim/pwrsply.html

From your email I think you may be confused about series and parallel.

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Old 6th July 2001, 04:07 PM   #4
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Yes, my caps are attached correctly, but perhaps they could be broken. I have no way to test them. Also, could it be that they are too large? Right now I have 42,000 micro farads/rail. I checked the wiring diagram and everything is attached correctly. I did have my series/parallel explanation wrong. Sorry, it was a late night. I want the transformer leads in series. By your explanations, it seems that I have the transformer wired correctly, but what else could it be? Thank you for your help.

Peter
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Old 6th July 2001, 04:24 PM   #5
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Default Testing Caps

You can get a go/no-go reading from an analog multimeter.

Take the caps out of the circuit. Set you meter to a high ohms read, like kohms. Then attach the positive lead to the positive side of the cap, then the same for the negative.

If the cap is ok, the meter w/ jump to less resistance and work its way higher resistance. If it is a small cap, this will happen quickly. It is more obvious w/ large power supply caps.

If it is broken, you'll get infinite resistance.

Best practice would be to discharge the cap w/ a 5 to 10 watt 1k ohm resistor, just to be safe.

If you are using a bridge rectifier, make sure you have the AC end of the transformer going into the correct leads of the bridge. Some bridges are marked w/ ~ ~ for the AC input and then, + - for the DC output to the circuit.

Good luck,

Vince
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Old 6th July 2001, 07:45 PM   #6
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Ok, I found my problem and I feel like an idiot but I'll post my solution for those who are having a similar problem or are just in need of a good laugh. When I attached the transformer leads to the power cord I forgot to sand off the second layer of insulation. Anyway, thanks for all of the prompt help.

Peter
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