Rabbit
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Post by Rabbit on Mar 30, 2013 9:32:08 GMT
I found out a while ago just how important the supply is in order to get good sound. Well here's an article about them which is in the process of being written at the moment. You can follow it as it's built up and may have a few words to say about it? diyaudioheaven.wordpress.com/tutorials/power-supplies/
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Post by puffin on Apr 5, 2013 19:00:21 GMT
I haven't read all of the article linked to, but I have made tons of power supplies. One of the things that I have found is fundamental to a good supply is to make suire that it does not sag under load. If say you want a regulated 5v or 12v load and use a 78** these are only good for up to 1A (and maybe less in reality) There are a number of good circuits available to boost the current available by adding an NPN to the input, to take the current up to 3A.
There is also the matter of ripple on the supply which can be dealt with by the addition of something like the JLH Ripple Eater.
What I would say os essential when building a power supply is to test it with a dummy load before using it in it's intended application.
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solderdude
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Post by solderdude on Apr 5, 2013 19:12:42 GMT
Strangely enough most power supplies are tested with 'static loads' such as dummy loads (big resistors). Most regulated power supplies have problems with handling dynamic loads. They should be tested with a varying load as well.
a way to do this is by making a current source (that can handle the power) and use a squarewave to switch the load on or off, or more realistic change the load by a number of percent.
Some regulated power supplies react fierce and thus the voltage also varies considerably. Sometimes there are tricks to make it behave better on transients.
Have fun with the oscilloscope a squarewave generator (could be a 555) and a few MOSFET's.
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Post by covenant on Apr 12, 2013 13:46:26 GMT
I fancy trying a linear power supply with a T-amp and have the parts. The toroidal transformer has twin secondaries and I cant remember how to wire it. One is red-Black and the other Yellow-Orange. Which ones get joined together?
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solderdude
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Post by solderdude on Apr 12, 2013 14:17:24 GMT
The easiest way is to connect the black to the yellow wire and measure across the 2 wires (red and orange) IF the voltage across the unconnected wires is double that of a single winding it is connected correctly. IF the voltage across the unconnected wires is almost 0V then connect the red wire to the yellow wire and remeasure to see if you get double the voltage in that case (it should)
do NOT connect red to black and/or yellow to orange :-)
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Post by covenant on Apr 12, 2013 18:18:32 GMT
The easiest way is to connect the black to the yellow wire and measure across the 2 wires (red and orange) IF the voltage across the unconnected wires is double that of a single winding it is connected correctly. IF the voltage across the unconnected wires is almost 0V then connect the red wire to the yellow wire and remeasure to see if you get double the voltage in that case (it should) do NOT connect red to black and/or yellow to orange :-) Many thanks but it looks like the transformer is fried. I am not getting anything showing on the meter. Oh well, back to the drawing board.
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solderdude
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Post by solderdude on Apr 12, 2013 19:04:01 GMT
Measure the windings in the Ohms setting of your meter.
the secondary should be max a few Ohms and the primary higher. You should read something there. If the primary is 'open circuit' there is a chance the thermal fuse is open (if it has one) It should be near the spot the wires enter the trafo.
Also a chance it is ready for the bin.
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Post by covenant on Apr 12, 2013 21:10:17 GMT
Ok, put the meter to the lowest ohm setting (200) and the display moves to 1. No difference on the primary. tried the secondary (black and orange) and it moves to 0.9. Can't see any thermal fuse.
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solderdude
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Post by solderdude on Apr 13, 2013 8:34:32 GMT
If the primary reads open circuit (or one of the 2 primary windings) and there is no visible fuse it can be binned.
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Post by covenant on Apr 13, 2013 8:41:18 GMT
Right, I will see what I can find on ebay!
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solderdude
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Post by solderdude on Apr 13, 2013 11:16:42 GMT
If you are going to look for a transformer search for R-Core transformers. (google: 'R-core transformer') these are more suited for hifi than toroids and the old fashioned E-core.
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Post by covenant on Apr 13, 2013 14:33:33 GMT
Will do. There are plenty on ebay mainly from China. Hope they are ok.
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Javier
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Post by Javier on Apr 13, 2013 17:20:21 GMT
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Post by covenant on Apr 14, 2013 13:01:27 GMT
Cheers Javier, I have a variable power supply and want to get about 14v to the T-amp. Should I go for one about 30v/a or would a lower value be acceptable?
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solderdude
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Post by solderdude on Apr 14, 2013 18:39:21 GMT
How much power is the amp rated ?
add max power of both channels... add 15% in losses. The calculated power above x 1.5 = minimum VA trafo The calculated power above x 3 = maximum VA trafo.
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