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Old 17th August 2012, 07:01 PM   #11
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Quote:
Originally Posted by AndrewT View Post
There is no significant power available from the -ve of a computer PSU.
It really is s single polarity supply PSU with a little -ve tacked on the side.
True, but as I work repairing SMPS last 2 decades, I know that replacing the -12 common anode diodes (1A e/a) with more robust 3A (It uses the same secondary winding as the +12 out), u can get up to 5 amp from -12V line, augmenting cap filtering and eventually re-winding the -12V winding in the mutually coupled common core choke. But at power level I use, none of the above mentioned mods are necessary, but capable.

Several times I rewind the trafo to get +24V 8 amps from a standard AT PSU. And at to date, they are working fine.
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Last edited by Osvaldo de Banfield; 17th August 2012 at 07:03 PM.
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Old 17th August 2012, 07:41 PM   #12
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so the bridging should give not less than 60watts rms with Distortion .01 percent..
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Old 17th August 2012, 07:42 PM   #13
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the price of 4 channel x 30watt chip costs 12 USD which is pretty high for what it offers but still cant ignore of driving with low single supply voltages....

LM1875 costs close to 2 dollars so overall I can get 4 x lm1875 clean power instead of going with TDA but the problem is the PSU which gets expensive overall...
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Old 18th August 2012, 05:42 AM   #14
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so what happens with if im driving the 10 inch subwoofer lets consider its drawing not less than 6amps peak Then will there be any problem with smps will it die? On the smps ratings it says that at +12v we can draw about 13amperes.. How much does the rest of the system draws. I can add not less than 10000uf for the psu cap at the TDA amp which might be sufficient ( I understand there wouldnt be any ripple ) but just not to load the smps for pow hungry amp. Can the SMPS sustain for this kind of load? Or shall I have more capacitance as buffer.
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Old 18th August 2012, 08:40 AM   #15
AndrewT is offline AndrewT  Scotland
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Can the smps drive a 10000uF load?
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Old 18th August 2012, 08:56 PM   #16
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no idea... so how to calculate this is out of my reach... but using computers spare power is a better choice if we want to save on the transformer and capacitors... Using one 10000uf should serve the job...

I have an idea lets consider if im getting a transformer 9v-0-9v 1 amp. But with bigger diodes can we have bank of capacitors coz... the trans costs about 10$ for 2 amps and for 4 amps its 20$ instead Im getting each 10000uf for 2$ can I have good 40amp rectification diodes and then use more capacitors after the 9-0-9v 1 amp trafo?
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Old 19th August 2012, 08:55 AM   #17
AndrewT is offline AndrewT  Scotland
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Instead of buying a tiny 18VA transformer buy a 160VA transformer for far less than 4 off 18VA.
The regulation of the 160VA will be far lower than the regulation of the 18VA.
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