Class AB car amp, switchmode power supply, what rails?? - diyAudio
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Old 8th December 2003, 12:20 PM   #1
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Default Class AB car amp, switchmode power supply, what rails??

my friend bought an old Clarion car amp for $10... I volunteered my services to work it out.... and so far, I have... I worked out what half a dozen wires in a single cable coming from the unit did and worked out how to power up the amplifier which would normaly be done by the headunit....

the amplifier says 50w + 50w on the front (so 50watts per channel) and it uses 25volt caps on the PS rails.... but, the trimpot used to adjust the feedback from these rails was shot (dirty, works now, but needs to be replaced) so, I have adjusted it, and am unsure what the voltages really should be... I currently have it set at +- 20 volts, but I believe the manufacturer would have run the caps as close to specs as possible.... If I increase the rails and they are too high for the powersupply, I will get increased heat, but no increase in power.

With +- 20 volts, the maths says you'd get 44 watts into 4 ohms (although it would be less than this)

with +-22 volts you get 54 watts, and +- 25volts results in 69 watts...

Currently am running the amp off a powersupply that really can't provide enough current anyway.... so I can't see how hard it can really go... I tried running it off a computer PS able to give 9 amps on teh 12 volt rail, or so they said... the amplifier running only one channel caused it to overload..

so... should I use something like +-24 volts, or stick to +-20??

its a pretty cheap, and great little amp either way... dang.. I wish I had money and had bought it...
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Old 8th December 2003, 01:24 PM   #2
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And here is the amp in question..

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EDIT!!!

The speaker terminals were added by me... very fortunate, I only had to drill one hole..

EDIT EDIT!!!

in the end there will hopefully not be a bunch of wires coming out the back..
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Old 8th December 2003, 02:05 PM   #3
sreten is offline sreten  United Kingdom
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Location: Brighton UK
25V is a standard capacitor voltage rating, the two nearest
being 16V and 35V.

The designed output voltage is much more likely to be
less than 25V, than be 25V, statistically speaking.

Playing it safe I'd regard +/- 22V as the maximum you should use.

/sreten.
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Old 8th December 2003, 02:19 PM   #4
ddog is offline ddog  Finland
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I would adjust it to +-22V and throw in 35V caps. So they wouldn't be so close to limit and will last longer.
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Old 8th December 2003, 02:26 PM   #5
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Quote:
Originally posted by ddog
I would adjust it to +-22V and throw in 35V caps. So they wouldn't be so close to limit and will last longer.

yeah.. I'm thinking +-22 volts would be best...

theres no way I'll be able to find suitable capacitors... expecially not higher voltage that will still fit..

the current capacitors are 3300uF 25 volt....

about 2.5cm in diameter and the same heigh....
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