Juma's Easy-Peasy Capacitance Multiplier

[maouna]

This is great forum and has been very helpful. I just order some W204011ASH1
W61084ASN2_juma cap multi boards from PCBway! I am planing to modify one of the boards by adding a TL431 to add regulation and compensate for the difference in the Vgs of the mosfets.

I have one question about the original design. Do the diodes D1, D2, D4 and D5 eliminate the need for zener clamp between gate and source of the MOSFETs?

In case of a short circuit, C2 is going to discharge through the reference pin of TL431 and maybe destroy the IC

 

[Shawnstium]

So, leave C2 out?

 

[Shawnstium]

Actually that Zener I was asking about and the addition of resistor can provide simple over-current protection.

 

[lasercut]

A tweak worth trying is adding bypass cap to 220uf cap.
I had already added a selection of film caps from 1 uf down after the Mx.
It helped tame the ''fatness'' of adding what seemed like too many large electrolytics, keeping the full, smooth sound but tightening it up and adding some air. There was good synergy there.

increasing 220uf Mx cap to 1000uf seemed to have similar effect to the large lytics after the Mx, it was easier to solder a bypass cap the legs than desolder them again and surprisingly this also helped in the same way.
The Mx cap seems to influence sound nearly as much as the Mx output caps

also the Mx caps were silmics, which I believe are low ESR, A general purpose cap might benefit even more from a bypass cap here.

 

[Shawnstium]

hmmm, I briefly ran the cap Mx with my Pass F4 and the heatsink that the Mx MOSFETs mount on got to about 120F/49C. The current draw from the Mx is about 5 amps total. I have a feeling that the Mx isn't going to work in the F4...

 

[prasi]

Hello Shawn,
Is it the Juma Cap MX?
In that case try estimate the heat dissipated per mosfet by current through a given mosfet x 4.5V approx.
This will allow to estimate the heatsink size required.

Anyway there is BJT Cap MX by M. Johnson/ Gtose that has much lower voltage drop.

regards
Prasi

 

[Shawnstium]

Yes, it was the Juma cap Mx. The layout is awesome and I am disappointed the heat will be too much. I add zeners between the gate and source of the MOSFETs.

 

[danny_66]

Hi,
Are there gerbers for the BJT Cap MX by M. Johnson/Gtose without the rectifier bridge and input caps ?
so I can use a LT4320 based bridge and other caps ?

Regards,
Danny

 

[prasi]

here you go Danny. These are the ones xrk built.

Juma's Easy-Peasy Capacitance Multiplier

 

[danny_66]

Thx Prasi,
those are with a bridge and input caps, are there gerbers with only the CapMx circuit (right side of those PCBs) ?

 

[prasi]

The tabs marked BR1+/BR1- etc are the Faston tabs meant for connecting supply from the external chassis mount bridges.
So this ideal for using with THT ideal bridge PCBs😉

 

[danny_66]

OK, got it, thanks !

 

[xrk971]

Hi,
Are there gerbers for the BJT Cap MX by M. Johnson/Gtose without the rectifier bridge and input caps ?
so I can use a LT4320 based bridge and other caps ?

Regards,
Danny

I think what you want is the SLB. LT4320 bridge plus CRC plus CFP cap Mx for sub mVrms ripple under Class A load of 4A.

The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB

Here is data for the measured ripple under 4A load (yellow trace):

 

[Pauloalexb]

Hi Everyone.

I'm going to finish a Juma cap multiplier to put on a F5. Should it go after or before the existing CRC filter (few caps by now)?

Thanks.

 

[xrk971]

After the CRC. But CRC doesn’t have to be so big. Just 15,000uF // 0.1R // 15,000uF should be plenty.

 

[guitar91]

for mosfet cap mx; when not used zener diode between gate and source, mosfet don't breakdown? mosfets have 20 volt max gate-source voltage.
I'm confused and sorry for my poor english.

 

[guitar91]

For mosfet cap mx; when not used zener diode between gate and source, mosfet don't breakdown? Mosfets have 20 volt max gate-source voltage.
So I'm confused and sorry for my bad english.

 

[MMAdams]

Higher Vout / Iout

I would like to build a cap multiplier with 40-50 Vout and around 5 A. Is this suitable with some modifications?

Mark.

 

[lasercut]

yes just use IRFP240 and caps with sufficient voltage rating

 

[MMAdams]

yes just use IRFP240 and caps with sufficient voltage rating

Will I need to use a zener in place of the diode?