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Old 14th May 2012, 10:37 AM   #11
qusp is offline qusp  Australia
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exactly, more effort than is required to just use a clean DC supply to start with
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Old 15th May 2012, 02:35 PM   #12
1c4ru5 is offline 1c4ru5  United States
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It isn't necessarily about effort, although I do understand what you mean. I have found a suitable wallwart, but would still like to pursue the challenge of cleaning up the molex supply. Ideally I want a filter that doesnt allow anything between say...15Hz and 22kHz, right? And to figure out which capacitors and inductors I need to use, I need to first build the amp and measure the resistance across it with my headphones plugged in, correct?

I will likely create an over-complicated triple one-at a-time power supply monstrosity (molex, batteries, wallwart) on a breadboard before soldering it down to the protoboard the amp sits on.
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Old 25th September 2012, 12:21 AM   #13
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Not sure if this is the place to pose my question, but didn't want to start a new thread for a very simple question, so here goes . . .
I have a car radio connected to a computer power supply. Nothing fancy, but it works for me. The problem is that whenever I turn it off, I lose all the stations that are put into memory. I asked elsewhere on this site and was assured that a wall wart plug connected to the yellow wire on back of radio would save the memory pre-sets, if I left it plugged in when turning off the power supply.
Okay, so I found a 2-prong wal wart plug from an old answering machine rated at 12V - 500mA.
PROBLEM: How do I know which wire is positive and which wire is negative? I have a digital multimeter, but don't want to blow it/myself up! Can I plug it into the wall and test each wire safely? Thanks ahead for any replies.
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Old 25th September 2012, 01:14 AM   #14
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Yes,plug it into the wall and measure the wires with your meter set to the 20V scale (or similar). Touch the probes to the wires,and you should see a reading on your meter. (It will likely be higher than 12V,because there is no load)
For example,lets say that the meter says "15.50V" Then you know that the wire with the red probe on it is positive. If the meter reads "-15.50V" then the probes are backwards,and the wire with the black probe on it is positive.
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Old 25th September 2012, 01:55 AM   #15
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THANK YOU Digital Junkie!
I kind of figured that would work, but not being 100% sure about some things can get you in hot water - or FRIED!
Thanks again,
The Woodworker
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Old 25th September 2012, 05:02 PM   #16
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in all honesty the cmoy is very tame an tolerent of noise vs say a 12au7 circuit

the issue with heavy filtering is the voltage drop but since the cmoy can work with 9 volts or less you could filter the 12 volt supply quite easily. I've even ran it noise free off a 3.7 volt battery and a dc charge pump

I'd just try putting this across the 12v power and see if that works If your hard wiring it you can ignore the led 3.3k resistor an diode
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Last edited by doulos24; 25th September 2012 at 05:19 PM.
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Old 15th September 2013, 12:46 AM   #17
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PI filters are effective; cap, series choke, cap

You might find more on the ham radio bbs on using a computer power supply.
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Old 15th September 2013, 05:29 AM   #18
dangus is offline dangus  Canada
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I'd try an RC or LC filter followed by a linear regulator. 8 or 9 volts should be plenty for a headphone amplifier. If not, use an MC34063 to step the voltage up first, or to invert it if you want a bipolar supply.

I'm pretty sure it's not that hard to make quiet power from a computer supply. Sound cards have been doing it for years. It just seems to be the monkeys that implement motherboard sound that do it badly. And whoever designed the Gemini iKey, and the audio recording portion of the Nomad Jukebox, and the Zoom digital recorders (note the lack of published S/N specs).
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