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Old 30th August 2006, 12:16 AM   #1
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Default need good supply design

I need a good power supply design that can handle two symasm4's and is possibly switchable power output. it needs to be low-hum and I am also wanting to run my 3-amp CB radio off of it. It doesn't necessarily need to be my exact specifications- it just needs to be versatile enough to fit my needs. I am trying to set up a somewhat hi-fi audio amp in my house with as little money as possible so I would prefer it to be low-cost, but good. If you know of another design that is good but not necessarily low-cost feel free to post, though. any replies are greatly appreciated!
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Old 30th August 2006, 06:17 AM   #2
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Default Capacitance multipler for low hum

One of the cheap solution could be to use capacitance multiplier circuit using a series pass darlington made from two transistors.

Gajanan Phadte
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Old 30th August 2006, 07:40 AM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
you specify Low Hum, why?
Do you know that either of the amps you intend to hang on the output have a bad PSRR?

A standard rectifier/smoothing capacitor PSU is hum free for most well designed amps.

Incorrect grounding can and often does cause hum.

PS. cap multiplier certainly reduces output ripple, at a slight cost of slightly reduced output voltage.
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Old 30th August 2006, 10:16 PM   #4
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Hmm. I still want a good design though. If I can manage to build one, I wouldn't just trash it with everything else when my amp blew out, I would use it for other things too. I was wondering about the 4QD supply here:
http://www.4qdtec.com/psu1.html
Any modifications? Know of a better one? I'm serious about this. Thanks for any response!
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Old 31st August 2006, 12:00 AM   #5
Tweeker is offline Tweeker  United States
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What voltage(s) and current(s) do you need exactly?
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Old 31st August 2006, 12:53 AM   #6
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for the symasm's I need four 36V outputs and I guess I need 200W in power. For my CB I need 13.8V and 3A output.
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Old 31st August 2006, 02:26 AM   #7
paulb is offline paulb  Canada
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That would almost certainly be two different power supplies.
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Old 31st August 2006, 07:19 AM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
36Vdc is quite low for a power amp. It will need a dual secondary 25Vac transformer. Centre tapped 25-0-25 will do just as well, unless Symasim say otherwise. A four secondary each @ 25Vac would be ideal but they tend to be expensive.

The 13.8V sounds like it might need to be regulated. Therefore your loaded input voltage will need to be about 16Vdc to 17Vdc requiring a 13Vac transformer. 12Vac might just do, but it leaves just 1.5Vdc through the regulator. That will drop out on low mains input voltage. 12Vac would need to be an LDO high current type.

VA rating would be 2*3*13=80VA due to the capacitor loading after the rectifier.
You could use a 15Vac 100VA transformer but that would increase the dissipation in the regulator and would require an enormous heatsink or blown.
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Old 31st August 2006, 11:07 PM   #9
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I was working on another circuit one day and it somehow evolved into a power supply idea... The only problem I see with this supply is the voltage at Q1's base being around 117V! Any ideas as to how I can lower this? Here it is:
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Old 31st August 2006, 11:11 PM   #10
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D5 charges C1, wich upon full charge triggers Q2 which triggers Q1 and regulates current in accord with the fluctuations. C2 regulates voltage. I think connecting a 2K resistor between + and Q1's base might help the freakishly overdone voltage... Any suggestions?
C1 can be increased for better current stability and the same for voltage with C2.
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