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Old 10th January 2002, 08:59 PM   #1
JoeBob is offline JoeBob  Canada
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Default PSU Caps.

All the psu plans I've seen involve a bridge rectifier for each channel and caps on each rail after the rectifier. The other day I was ripping appart an old amp for a volume knob and maybe some caps when I only noticed two large caps by the psu (5 channel amp).

So I wondered, I can get very large caps for free or very cheap, but not large amounts of them. So if there's a way I can use 6 or so 25,000uF caps in my 5 channel LM3886 based amp I'm building it'd save me quite alot. So I wondered how my old amp I killed did it, did it have the caps before the rectifiers and a rectifier for each channel? Or did it use one rectifier for all channels with one cap on each rail?

I'd really like to know a way to do it with 6 25,000uF caps, but if the only ways will ruin sound quality, I guess I'll have to go the expensive route...
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Old 10th January 2002, 10:22 PM   #2
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"Or did it use one rectifier for all channels with one cap on each rail? "

Joebob,

That would be the easiest and most common way to do it .

william
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Old 10th January 2002, 10:30 PM   #3
Won is offline Won
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That is an awful lot of capacitance for an opamp-based amplifier, even a 5-channel one. Opamps have ridiculously good power supply rejection (that 47labs opamp thing got away with just 1000uF!) So I would just use a pair of those monsters in the PSU (probably bypassed with smaller, higher-quality capacitors), and pay more attention to how you bypass the opamps themselves.

Now, you have 100,000uF left over which you can use to build the PSU for a class-A amp or something else that can really benefit from it (e.g. Aleph).
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Old 10th January 2002, 10:42 PM   #4
JoeBob is offline JoeBob  Canada
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I see, so the LM3886 doesn't need too much capacitance... As for using the other caps to build a psu for a class-a amp, I just might do that, since I just got a whole bunch of military power transistors today for my fathers work, hell if they're good enough for multi-million dollar equipment, they've got to be good enough for me .
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Old 10th January 2002, 10:48 PM   #5
JoeBob is offline JoeBob  Canada
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Well, if I only go with around 50,000uF in total would I still need a soft-start circuit to power it up? I was planning on going with one but was originally thinking of between 100,000 and 250,000 uF in total. These will be fed from two 750VA toroids...

Also, if it'd still need a soft-start switch for 50,000uF, could I get by buying smaller caps and use less total uF to avoid the need of a soft-start switch? If using less then 50,000 sacrifices quality, I wouldn't mind building a soft-start switch, but I'd rather keep things as simple as possible (less to go wrong).
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