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Old 19th March 2007, 06:00 PM   #11
pjpoes is offline pjpoes  United States
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can you give me more information on the Pi filter, I believe it would be a CRC, correct, however how do I determine the size and value of the choke. How large a capacitor is needed to handle the current, etc. I assume a larger capacitor should go after the choke in this situation? I am starting to wonder if it would be cheaper to try a capacitor multiplying cuircit as suggested on the ESP labs site, given how cheap transistors are, and how simple it could be. Anyone have any thoughts on the positive and negative of the plausible methods. I have also considered saving my money on such extravigances as chokes, and simply using better capacitors such as the Jensen 4 poles, but still question the difference they will make over a better power supply.
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Old 20th March 2007, 02:49 AM   #12
CBS240 is offline CBS240  United States
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Quote:
.....at 15A a 100 ohm resistor would be dropping 1500V which is impossible with 60V rails...
If I understand correctly, you are referring to a series resistor between the first cap and the second, to isolate the pulse currents of the transformer from the pulse currents of the amplifier, which are different. Since these currents are large, I would think something on the order of 0.1 Ohms, no?




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Old 21st March 2007, 09:45 AM   #13
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Hi pjpoes,

An old fashioned way of smoothing amplifier rails was to split the Cs insert a low value resistor selected to drop about 1V under quiescent conditions, then parallel with a power bridge to limit the voltage drop under load. As here.

Since then however, amplifiers have been designed for decent immunity to rail fluctuation and noise.

Cheers ........ Graham.
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Old 21st March 2007, 05:05 PM   #14
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Graham & pjpoes: That's a very neat trick ... diode forward voltage is quite predictable.

Silicon diodes = about 0.6 volts (typical of 1N4001)
... X 2 in series = 1.2 volts +/- 0.05 volts
... X 4 in series = 2.4 volts +/- 0.10 volts
... dependant on current.
Germanium diodes = about 0.2 volts, likewise as above.
Schottky diodes = about 0.4 volts, but these have upper limits on reverse voltage & current (breakdown).
"Fast recovery" diodes = about 0.4 to 0.5 volts, depending on ...

Anyway, this is often used to get solar cell voltage regulation under control = double or quad or more, parallel diodes = high current, low voltage drop, etc. Diode pop corn noise can be greatly reduced with an inductor in parallel with or in place of the low value resistance, creating an avalanche effect = sudden release of electrons across the diodes rather than a trickle at the transition on the current curve = "reverse spring loading" the diode threshold as it were ... I love the hydraulic model of electron flow ...
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Old 21st March 2007, 05:17 PM   #15
pooge is offline pooge  United States
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Quote:
Originally posted by Graham Maynard
Hi pjpoes,

An old fashioned way of smoothing amplifier rails was to split the Cs insert a low value resistor selected to drop about 1V under quiescent conditions, then parallel with a power bridge to limit the voltage drop under load. As here.

Since then however, amplifiers have been designed for decent immunity to rail fluctuation and noise.

Cheers ........ Graham.
Would this really be considered a bridge in a "bridge rectifier" sense? It appears to be two series strings in parallel to increase current capacity of diode strings.
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Old 21st March 2007, 07:59 PM   #16
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Hi pooge,

You can use two single diodes in series, but a 35A bridge is a very convenient way of ensuring low voltage drop under load.

For instance with R= 2R2, second C= 22mF and quiescent current= 400mA, a 100Hz psu ripple can be reduced by 20dB !!!

The only sacrifice being two diode volt drops under full power.

Cheers ......... Graham
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Old 21st March 2007, 08:50 PM   #17
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" ... with R= 2R2, second C= 22mF and quiescent current= 400mA, a 100Hz psu ripple can be reduced by 20dB !!! ..."

Throw an inductor in the mix and squish the ripple down few more db ...
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Old 22nd March 2007, 12:47 AM   #18
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Quote:
Originally posted by FastEddy Throw an inductor in the mix and squish the ripple down few more db
Now we are getting somewhere. Seriously, can someone draw up the ultimate combination?

"Squishing Ripple" sounds very good. I think I will call my next song or band after that statement. The first album would be called, " Down a Few More db"...damn that's magical!

Cheers,

Shawn.
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Old 22nd March 2007, 01:15 AM   #19
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"Squishing Ripple" ... could be a new soft drink ... or a new milder detergent.

See the image = http://www.diyaudio.com/forums/attac...amp=1174470303 ... That "Low R" resistor could just as easily be a wire wound resistor = it has a slight inductance. Otherwise you might wind your own resistor / inductor and put 'er there.
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Old 22nd March 2007, 01:31 AM   #20
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Quote:
Originally posted by FastEddy
[B... That "Low R" resistor could just as easily be a wire wound resistor = it has a slight inductance. Otherwise you might wind your own resistor / inductor and put 'er there. [/B]
Take out the R and insert L? Would this be a good combination with big fat caps on a medium/large (150~300Watt) BJT amplifier? It would be nice to draw this up on PSU Designer but I guess that is a "no go".

Shawn.

..."Ripple Squisher"
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