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Old 8th August 2006, 04:33 AM   #1
oblerum is offline oblerum  Norway
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Default How to reduse voltage from PSU??

Hi!

I am building an Aleph 5 clone, and used PCB-KK pcb's.
Anyone with a god tip how too reduse 42,6V to 33-35V.
(500VA toroids)

I have 6X10000uF (each canal), and I have 42,6V before load is conected. When I connected an 8,4ohm load I mesure 37,1V.
That is a little to high for an Aleph 5 clone.

I planed to 0,235R in series with the + and - just after the bridge, is this a good solution to get the voltage down?
What is the negative with this solution?



O.B Lerum
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Old 8th August 2006, 09:17 AM   #2
araven is offline araven  United Kingdom
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Hi,

I'll start this one off, but i'll need alot of correcting as i'm still a bit of a newbie.
Firstly if you put a resistor in series after the bridge and before your filter caps, you have to remember that you are creating an RC filter low pass filter as well. with a 0.235r and a 10000uF filter cap alone you have a low pass filter operating at a frequency of 68hz, this is not good.
Secondly, the power supply should have as close to 0 resistance as possible, to improve the damping characteristics of the PSU, your large array 10000uF in parallel really help to keep overall impedance of the PSU down, it would be a shame to add 0.235ohms there.
You could either change you design to a fully regulated one, or use more wasteful bridges, and/or diodes to reduce the voltage, although this is a wasteful act.

Alex
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Old 8th August 2006, 10:41 AM   #3
sreten is offline sreten  United Kingdom
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Hi,

Search on CRC filters, common in valve amplifier supplies.

Adding R immediately after the bridge will not work
well as it limits the charging current to the capacitors.

also take a look at this :

http://sound.westhost.com/project15.htm

A Simple Capacitance Multiplier Power Supply For Class-A Amplifiers

/sreten.
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Old 8th August 2006, 10:41 AM   #4
Jennice is offline Jennice  Denmark
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I think this issue has already been addressed by others and commented by Mr. Pass. Since it's a class A design, current consumption is fairly stable, which gives alternatives.

Try searching for keywords on this subject, and posts by Nelson Pass.

Jennice
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Old 10th August 2006, 07:04 AM   #5
oblerum is offline oblerum  Norway
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Thanks

I think I'll use an CRC or an CLC.

I got myself the PSU-designer so I'ii take some new calculatins.
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