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xrk971 28th December 2018 12:45 AM

You can adjust voltage drop as low as 1.3v and I run mine at 2v. Note that drop has to be greater than levels of ripple you at trying suppress. So my voltage after cap Mx is about 22v.

samoloko 28th December 2018 07:01 AM

thx for reply

so It looks that you are better using It with few mF before cap multiplier Input

what Is ripple before and after cap multiplier for 1.27 A load and 2 V voltage drop (you have 24 V at Input)

can I use Mark Johnson cap multiplier feeding first watt amp rails at 24 Vdc / 4 Amp
what would be optimal spec for transformer secondaries 19 Vac or 20 Vac

xrk971 28th December 2018 10:18 PM

Size a C and bridge to get the ripple to a level below the dropout voltage. Let’s give it a factor of 2 margin so 1v ripple at 1.3amps. Know that the cap Mx will reduce ripple by up to -50dB. So the smaller you can get it before you go to the cap Mx, the better. You can run simulations to perfectly size it for your case, but use what you have and see how it works. For example, a 10mF cap before the cap Mx is a lot smaller than typical 4x33mF caps normally specified per rail. And even then, the ripple after the cap Mx is about 1mV vs maybe 100mV with a bunch of large caps in CRC alone.

jwjarch 25th January 2019 06:03 PM

I have a small batch PCB's for the smaller CapMx on the way from JLCPCB. Thanks for posting those gerbers Prasi! I'm planning to use these as future preamp supplies for a number of different preamps I want to try out. So ordering parts now. Is the value of R1/R5 critical? X, I noticed you used 10k. Is this basically a bleeder for the main caps? So 3k would be a minimum value?

prasi 25th January 2019 06:31 PM

if in bleeder position, value is not critical as long as dissipation is taken into account for safety. more clarity on "smaller cap-mx" would be useful, as i posted many designs in this thread.
use ohms law and calculate dissipation by V(squared)/R.

jwjarch 25th January 2019 07:10 PM

Hi Prasi. Referring to the CapMx that you posted gerbers for on post #626.

prasi 26th January 2019 01:27 AM

Hi jwjarch,
Ok. the Mark Johnson cap mx.
Yes, the bleeder can be any value as long as dissipation through it is taken into account.

lower value = quick bleed and high dissipation
higher value = long time to discharge the caps and lesser dissipation

play around with different values in excel for the voltage you plan to use.


jwjarch 27th January 2019 11:50 PM

Thanks Prasi. I will choose wisely. ;)

BRN 10th February 2019 08:25 PM

I'm running the CapMx in my FW M2c and wanted to know if I should adjust the voltage with no load or with a load?

xrk971 11th February 2019 02:17 PM

With load as that will change the output of the transformer significantly. The cap multiplier adjusts a delta from the nominal input voltage under load.

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