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Old 5th December 2013, 12:58 PM   #571
dazed2 is offline dazed2  Canada
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Thanks, thats not too bad for dissipation. For an application where I'm expecting a +/-50V rail and 6A continuous draw I would probably go with 100V parts. not the 55V Mosfet, just to be on the safe side.

Alright so I guess the next question is how would I calculate voltage drop?
eg, in traditional CRC power supplies, DC voltage after rectification is Vac x 1.414 = Vdc unloaded. In a class A amp it seems to be generally accepted that the multiplier goes down to about 1.3 loaded.
So in a situation of say a 40-0-40 secondary, we would get Vdc = 40*1.414 = 56.56V after rectification, or 52Vdc if the 1.3 multiplier is used.

In the case of CM filtering, how would I calculate the no-ripple voltage drop in the same situation? What would a 500mV voltage drop give me under load?

Last edited by dazed2; 5th December 2013 at 01:10 PM.
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Old 5th December 2013, 02:11 PM   #572
BigE is online now BigE  Canada
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irf3205 has a thermal coefficient of 62 degc/watt. Doesn't that mean a 3W dissipation requires a heatsink?
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Old 6th December 2013, 09:11 AM   #573
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I did not calculate it, I measured it . Experiments show that lower Rds can allow lower voltage drop for a no-ripple at the output. It is probably possible to calculate, but that is beyond my scope.

@BigE: It definitely needs a heatsink. But for 3W dissipation, it can be the aluminium cover/wall of the chassis, or they can be mounted on the main heatsink without creating thermal unbalance. Or you can use a separate one, PCB mounted, like PMI did. You just have more possibilities.
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Old 17th December 2013, 06:31 PM   #574
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Sorry for some basic questions this far in but I don't quite get how the multiplier supply's the capacitance for amp's designed to have capacitance of say, 40,000 uf per rail.
Would the idea be to try and fit the largest capacitors available that will fit the board to get the capacitance up to around the required amount?
e.g. For the main filter and reservoir cap use: 2 X 15000uF / 63VDC, MLytic® Audio Grade MLGO (Glue-On 2 Pin), 35mmD x 60mmH

and for the output cap use: 2 X 2200uf / 63VDC, MLytic® Audio Grade, MLGO (Glue-On 2Pin), 25mmD x 31mmH.

********

"The main filter and reservoir cap is intended to be 10,000uFd, 35-mm diameter, snap-in leads. The holes will also accept 12.5-mm spacing straight lead (checked already), at the expense of the snap in leads being a bit loose.

The output cap would depend on the application, and on what kind of rail caps are on the amplifier board. The board will accept a 4700uFd 25-mm diameter cap, or any standard smaller, 16-mm diameter elco."
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Old 17th December 2013, 10:26 PM   #575
Mr Evil is offline Mr Evil  United Kingdom
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Quote:
Originally Posted by marcus1 View Post
Sorry for some basic questions this far in but I don't quite get how the multiplier supply's the capacitance for amp's designed to have capacitance of say, 40,000 uf per rail...
If the amp needs 40 000uF to keep ripple low, then the capacitance multiplier will work great, because it filters ripple as if you had a humongous capacitor there. On the other hand, if the amp needs 40 000uF to provide dynamic headroom, then the capacitance multiplier won't do that, because it doesn't store energy like a real capacitor (but fitting large capacitors to it will help).
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Old 22nd February 2014, 07:45 AM   #576
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Quote:
Originally Posted by PMI View Post
On the front side, I plan to experiment with larger-value/lower voltage reservoir caps (before the cap multiplier filter), to get closer to an ideal combination for Class A amps. This will result in proportionally smaller ripple, smaller required Vdrop, and therefore less heat to get rid off.
Hello Pete, I've had a good read through the threads relating to this project to get myself up to speed and I'm wondering if you made any progress with this?

I'm planning a build of the Linsley Hood Class A amp and this Evil contraption is on my list of power supply options; rails will be circa 22-25V and quiescent current around 1.7A, output around 10W.

I guess you're talking about trying larger value C1/2 caps. Maybe worth taking them (and the diodes) off board for more flexibility?

Thanks

Ray
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Old 31st March 2014, 11:05 PM   #577
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does it make sense to follow this circuit with a 338 regulator? 2x +supply of cap multiplier> pedja's 338 regulator. would it even work? pros/cons?

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Old 1st April 2014, 05:31 AM   #578
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it depends what you want to use it for....this circuit's purpose is to cut the ripple while dropping a small amount of voltage in order to minimize the dissipation. The opposite of a voltage regulator, whose purpose is to hold on a fixed voltage at the exit no matter what it costs in dissipation terms, while cutting the ripple as well. So technically speaking it doesn't make much sense, in my opinion, of course.
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Old 14th April 2014, 03:44 PM   #579
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Hi guys...
I have difficulty to find the same parts as you use.
Can I only use N channel mosfet, may I use
IRF540 or IRF2807
BS170 & K246 as CCS...
(the target output is 40 to 45VDC for now)

I modified the schematic & I think it is OK to try...
need some thought

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John
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Old 14th April 2014, 05:20 PM   #580
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Hi John,

I think it should work fine. If my memory serves me well Mr Evil proposed BS170 and BS 250 as alternative for J-fets on the original schematic.
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