My experience with a Capacitance Multiplier

[rchua77]

Hi guys,

I have a little situation, hopefully you guys can help me out. I have a capacitance multiplier from Rod Elliots design. And I have 2 x 10,000uF capacitors with a 0.1ohm resistor connected between.

Should I place the 2 x capacitors before or after the multiplier in order to gain maximum benefit?

Regards
Chua

 

[Shoog]

Its easy to try both, but I found that the best result was got by placing the large capacitor bank after the Multipler.
I also found that I got a fuller bass by not using the resistor to earth.
Shoog

 

[Nelson Pass]

The Capacitance Multiplier had made the Zen behave more like a solid state amp as oposed to the choke filter which made it behave more like a Valve Amp.

The trick here is to bypass with output of the transistor with
lots and lots of capacitance, say 30,000 uF or more.

 

[rchua77]

Could someone explain the purpose of the different components in the capacitance multiplier to me? I seem to have trouble figuring it out.

Referring to the attached modified pic from ESP, how does one increase the ratio of the capacitance by modifying the values of which components?

By the way, i'm not too sure if I have wired out my circuit correctly for a supply rail of +63V and 0V.

As suggested by an earlier thread, I should connect my CRC network of 10,000uF, 0.1ohm, 10,000uF after the capacitance multiplier.

Regards and thanks to anyone who helps me clear up my confusion.

Chua

 

[Shoog]

My understanding is that the capacitor at the base of the transistor acts as a reference, but without any significant current passing over it, this allows it to smooth to a much greater extent than if all the current was passing over it. The Transistor then takes this relatively smooth reference current and uses it to control the flow of current through the transistor. Splitting the base capacitor into two and seperating them by a resistor improves the effect, though I left it out.

I would leave off the the 12K resistor from the base of the transistor to earth as it made it sound much harsher this way.

Mr. Pass I do not understand your explanation- could you clarify a bit more.

Shoog

 

[jcarr]

What is the largest capacitance value that anyone reading diyAudio has used at the output of a capacitance multiplier?

I'm thinking of using a single IRF140 for positive polarity and an IRF9240 MOSFET for negative polarity (with a bleeder resistor from gates to ground), at a standing current of about 1A.

thanks in advance, jonathan

 

[Zen Mod]

What is the largest capacitance value that anyone reading diyAudio has used at the output of a capacitance multiplier?

I'm thinking of using a single IRF140 for positive polarity and an IRF9240 MOSFET for negative polarity (with a bleeder resistor from gates to ground), at a standing current of about 1A.

thanks in advance, jonathan

teasing , or what ?

 

[jcarr]

Choky, wasn't it?

Certainly not teasing.

Earlier in the thread, Shoog stated that he had used 44,000uF after his capacitance multiplier, which used 2 pieces of MJ2955 (TO-3, 15A, 115W, 60V rating) to handle 5.2A standing current. OTOH, Rod Elliot suggests that the output capacitance not exceed 4700uF, because of excessive changing currents.

It would be useful to know what levels of charging currents can be expected as a function of capacitance value (perhaps modified by capacitor ESR or ESL), or equations to define the relationship.

Setting that aside, however, I am interested in knowing if other builder's experiences suggest that 44,000uF will work with a 30A device (15A parallel) and a 5.2A load (peak 7A), or whether someone happens to possess exceptionally large gonads.

If the above works consistently then I'd assume that 10,000uF after an IRFP140 (TO-247, 27A, 94W, 100V rating) to handle a 1A load should not be a problem (which is what I am planning to try).

cheers, jonathan

 

[Zen Mod]

Choky, wasn't it?

.....

who really knows ?

these days is hard to tell which I am of many of me

....

Certainly not teasing..........

it really depends more of upstream side of your "reg" - if you place some nice "softstarting" circ , either before cap multi or in it , you don't need to worry about excessive charging current ;

at least not initial one ; steady state charging (pulse ) current is easy to handle with either multiple pass devices , or with sole robust one .

anyway - 1A load is on wimpy side , so I can't see any reason for too much Carre

 

[jcarr]

Thank you, Choky. I'll probably make a layout with multiple smaller capacitors in parallel rather than one big cap, and test how the pass devices survive multiple turn-ons and turn-offs.