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Old 22nd June 2018, 09:24 PM   #11
FriedMule is offline FriedMule  Denmark
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Quote:
Originally Posted by KatieandDad View Post
That is overkill. Main reservoirs as big as you want, parallel them with 100uF and then bypass with 1uF.
Would that be enough to 4 ohm speaker speakers?

How do you calculate how much you need?
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Old 23rd June 2018, 07:20 AM   #12
FriedMule is offline FriedMule  Denmark
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Default What do the third rectifier do?

There are two rectifier near the transformer and those do I know what are doing but what does the third rectifier do?
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Old 23rd June 2018, 07:42 AM   #13
MarcelvdG is online now MarcelvdG  Netherlands
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When the output stage draws a lot of current (high volume into low-impedance load), the voltage across the 22000 uF capacitors will have a considerable ripple on it. Using separate rectifiers and electrolytic capacitors for the earlier stages reduces the amount of ripple that they see on their supplies.
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Old 23rd June 2018, 07:47 AM   #14
FauxFrench is offline FauxFrench  France
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The first two rectifiers (closest to the transformers) generate voltages from each transformer and stack the voltages. These voltages are used for the output stage (high current/power).
The third rectifier rectifies the voltages from the two transformers together to be used for the low power (and low current) part of the amplifier.
The idea is to avoid supply line noise from high currents in the (power) output stage to be propagated to the sensitive low power circuits.

If you take for instance a TDA7293 amplifier chip, it has got both high power and low power supply terminals with the same purpose of avoiding noise on the low power part from the high power output circuit.
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Old 23rd June 2018, 08:38 AM   #15
FriedMule is offline FriedMule  Denmark
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Okay thanks for your great answers!

What would you select of component(s) for that rectifier?
I am going for a max limit of 15A just because most of the other components are max 15A
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Old 23rd June 2018, 08:44 AM   #16
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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The third bridge could be a W04 http://uk.farnell.com/multicomp/w04/...ase/dp/2127554) or four 1N4002 (http://uk.farnell.com/w/search/prl/r...earchlookahead) as less than 1Amp is required.
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Old 23rd June 2018, 08:46 AM   #17
DF96 is offline DF96  England
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1A would probably be fine. No need to over-engineer. Big rectifiers have big capacitance so may let more noise through.
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Old 23rd June 2018, 08:50 AM   #18
FriedMule is offline FriedMule  Denmark
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Many thanks!

Last questions:-)

1) Does the type influence the sound?
2) The input and output what are they labeled? (We/Wy) if that, what is what? :-)
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Old 23rd June 2018, 08:52 AM   #19
DF96 is offline DF96  England
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The most important thing about a reservoir cap is not its brand, but its capacitance. Then comes ESR and ripple current rating. Then price/size.

To work out capacitance, first decide how much ripple you can tolerate and max supply current. Then calculate how much voltage the cap will drop during 10/8.33ms. If you want to be cautious you can double this value.

Bypassing is of little value, and might do harm if you are unlucky. Better to put decoupling where it is needed.
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Old 23rd June 2018, 09:02 AM   #20
FriedMule is offline FriedMule  Denmark
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Thanks!

But how do I decide how much ripple I can live with?
My max supply current are 14A

And how do I calculate all this?

Sorre are a total noob!!
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