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Old 29th November 2012, 12:32 PM   #1981
AndrewT is offline AndrewT  Scotland
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2mF (2000uF) is generally enough for 1A of output from the smoothing capacitance and have acceptable ripple ahead of the circuit be it a regulator or an amplifier.
On that basis 500mA will require only 1mF of smoothing capacitance. 4700uF will reduce the ripple by about 4.7times lower than is normally deemed necessary.
10mF is simply silly for 500mA of load (into the regulator) current.
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Old 29th November 2012, 12:43 PM   #1982
Rush is offline Rush  United States
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Quote:
Originally Posted by AndrewT View Post
2mF (2000uF) is generally enough for 1A of output from the smoothing capacitance and have acceptable ripple ahead of the circuit be it a regulator or an amplifier.
On that basis 500mA will require only 1mF of smoothing capacitance. 4700uF will reduce the ripple by about 4.7times lower than is normally deemed necessary.
10mF is simply silly for 500mA of load (into the regulator) current.
I agree with Andrew 100%.
The silly part is what I do. I always go silly on the caps size and for that matter the transformer amp rating too! I only know when to stop adding caps and amps when I have no room left in the chassis or it has become too heavy for me to lift/work on.
I am convinced that an over sized power supply sounds better than a just right sized.

Rush
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Old 29th November 2012, 01:13 PM   #1983
qusp is offline qusp  Australia
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one thing is for sure, its noisier...
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Old 29th November 2012, 01:18 PM   #1984
AndrewT is offline AndrewT  Scotland
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What's noisier?
The output from the amplifier, or the output from the regulator, or the output from the smoothing? Or are you referring to something different?
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Old 29th November 2012, 01:38 PM   #1985
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Rush,
Just stick a simple Cmultiplier (with good quality cap) and make all that ripple go away - I, too, like to add things until no more "improvement" is either heard, or imagined!

A shunt reg is already excessive in many cases, so why stop at "unreasonable"
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Old 29th November 2012, 02:16 PM   #1986
qusp is offline qusp  Australia
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using a transformer and caps that are far larger than needed for a particular load, as mentioned above by Rush
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Old 29th November 2012, 02:35 PM   #1987
AndrewT is offline AndrewT  Scotland
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Is this because it is noisier to use adequate transformer and smoothing?
How much noisier?
At what frequencies?
Where in the system are you measuring this extra noise? at the PSU output, or at the regulator output, or at the amplifier output?
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Old 30th November 2012, 12:15 AM   #1988
qusp is offline qusp  Australia
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think Andrew, or does your arguing instinct override everything? transformers, they make noise and interference, its proportional to their size.... if you have infinite space, no problem.

Last edited by qusp; 30th November 2012 at 12:19 AM.
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Old 30th November 2012, 01:57 AM   #1989
Rush is offline Rush  United States
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think Andrew, or does your arguing instinct override everything? transformers, they make noise and interference, its proportional to their size.... if you have infinite space, no problem.
You are dreaming up problems that don't exist in my world.
In a pre-amp I always remote the transformer in a separate box and it doesn't need to be in another room, just a couple of feet away.
No noise, no interference, and much lower impedance!
I don't think Andrew was arguing this time, you made a statement that none of us could tell what you meant by.

Rush
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Old 30th November 2012, 03:00 AM   #1990
qusp is offline qusp  Australia
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well maybe so and yes in your application not a problem, but the problem still exists, it still creates more noise, the caps will create more current/voltage noise when charging etc if they are also oversized. its a pretty common recommendation to NOT oversize the transformer too much for low noise circuits for this reason. It can be overcome sure.

the impedance of the transformer is hardly going to be the dominant impedance in a preamp is it?

that being said I do understand the motivation/compulsion
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