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Old 4th October 2007, 03:32 PM   #1
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Default Power Supply for Chip Amp

I've been reading quite a bit about chip amps lately and am very interested in putting one together. My electrical know-how is pretty minimal, but I feel fairly confident about my ability to put together an amp kit from instructions. However, I'm not entirely comfortable working with wall voltage for the power supply. Is there a way to power one of these from a wall wart or other enclosed external adapter? In addition to my lack of technical expertise, I find this solution attractive because I want to keep the amp enclosure as small as possible.

If this isn't a viable solution, could anyone recommend simple step-by-step instructions or a good power supply kit?

Thank you kindly in advance.
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Old 4th October 2007, 05:38 PM   #2
Nuuk is offline Nuuk  United Kingdom
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It's always a bit of a risk encouraging anybody to 'play' with mains voltages but having said that, IF you are careful and sensible, it isn't a great problem to build a PSU!

Have a read of this and the other Gainclone pages and get a good idea of what is entailed before you make a decision one way or the other!
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Old 4th October 2007, 05:39 PM   #3
kaos is offline kaos  United States
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Ive seen some wall warts rated at 18 VAC at over 2 amps. If you half-wave rectify it you could get a split +/- 24 VDC supply, adequate for many chip amp applications. Just connect one lead to the gnd point and the other to the diodes.

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Old 5th October 2007, 06:41 AM   #4
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This might be a dumb question, but can you tell me what would be appropriate to use for a ground point in a wooden case?
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Old 5th October 2007, 08:00 AM   #5
Nuuk is offline Nuuk  United Kingdom
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This might be a dumb question, but can you tell me what would be appropriate to use for a ground point in a wooden case?
Assuming that you are putting the PSU and amp in the same case, you will (should) have your power and signal star grounds as usual in the amp section. If you then want to connect the power star ground to mains ground, that would be done using a 'lifter' consisting of a cap and resistor, and that could be connected to the ground terminal of your IEC input socket, or the earth wire of a captive mains lead.

Most people do not seem to connect the power star ground to mains earth when they use a non metallic case.
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Old 5th October 2007, 03:10 PM   #6
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If I do opt for an external enclosed PSU, would be a good choice?this be a good choice? The datasheet says that the TR36A18 will put out 18V at 2A.
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Old 5th October 2007, 04:00 PM   #7
kaos is offline kaos  United States
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One of those will only provide 18 VDC, barely enough for chip amp operation. The amp would need to be configured for single supply operation, which means an output coupling cap would be needed, unless you build a bridge amp. You could use two of the supplies for a +/- 18 VDC, closer to what youd want. The 2 amp output current limit may not work well on musical peaks with some speakers though, so youd probably need to put some large capacitors on the output similar to in the diagram that I posted. Probably better to take the plunge and build something. The wall wart I had in mind for the above diagram was Mouser P/N 507-XT1840, if you decide to go that way.
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Old 5th October 2007, 04:58 PM   #8
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Probably better to take the plunge and build something.
I am leaning in that direction. I'm torn between my enthusiasm at having discovered this forum and my desire not to overburden everyone with really basic questions. Toward that end, I've purchased an introductory electronics book and have been making frequent use of the archives. Thanks so much for all the help so far.
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Old 5th October 2007, 06:22 PM   #9
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Quote:
Originally posted by kaos
Ive seen some wall warts rated at 18 VAC at over 2 amps. If you half-wave rectify it you could get a split +/- 24 VDC supply, adequate for many chip amp applications. Just connect one lead to the gnd point and the other to the diodes.

Click the image to open in full size.

Um, am I missing something? How would you get +/- 24 VDC from 18 VAC with a basic half-wave rectifier? Wouldn't it be +/- 8.3 VDC max?
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Old 5th October 2007, 10:22 PM   #10
kaos is offline kaos  United States
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Its a basic voltage doubler. One side of the trans winding is connected to gnd, the other through the rectifiers to their associated capacitors. Each half cycle alternately charges the positive and negative rails respectively. 18 V x 1.414 yields a bit over 25V/rail. Subtract a diode drop and it's just over 24 volts/rail.
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