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Old 18th March 2004, 07:30 PM   #1
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Question cap multiplier or not?

Hi there!

Really like this forum, lot´s of knowledge here!

Would like to ask u psu-gurus this:

Do u consider this circuit to be some kind of a cap multiplier?
(only showing the positive side of the psu)
That´s what I am wondering about...and if it wouldn´t be for the zener I would have been sure about it, but...??
Could u please enlighten me please?
And if it is a CM are there anything that can be improved there?

It´s a break out from a psu to a bass preamp.

thanx! /Peder
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Old 18th March 2004, 11:04 PM   #2
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No, it is a zener filtered power supply. This is better.
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Old 19th March 2004, 02:01 AM   #3
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I really often wonder what is the function of Cap multiplier. Is it to give cleaner supply to the CCT? Have tried this, it gives ultra clean sound (is it good or bad? Some people say it is sterile).

Mr. Curl, the example of Cap multiplier is in the Parasound HCA 1200 schematic, right?

Why do you consider this example cct is only zener regulated? Inspite of there is zener to ground, there is also cap to ground (both connected to base). The cap effect got tobe multiplied too?
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Old 19th March 2004, 02:22 AM   #4
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Quote:
Originally posted by lumanauw
I really often wonder what is the function of Cap multiplier. Is it to give cleaner supply to the CCT? Have tried this, it gives ultra clean sound (is it good or bad? Some people say it is sterile).

Mr. Curl, the example of Cap multiplier is in the Parasound HCA 1200 schematic, right?

Why do you consider this example cct is only zener regulated? Inspite of there is zener to ground, there is also cap to ground (both connected to base). The cap effect got tobe multiplied too?
You know... if you look at Rod Elliots page, his "cap multiplier" circuit looks just like this circuit, well with a protection diode.

I really wonder if either of these actually "multiply" the capacitance at all or just have a regulating effect like IF an equivelent sized capacitor XXX was there.

The truth is, if you take both circuits and flip the transistors into standard vertical alignment you'll see easily that they are EF buffers on fixed voltage source. What happens is that the main source of their filtering has to do with the diode voltage vs current. The base is being fed by a resistor which buffers it from the voltage ripple and instead converts this to current ripple. Diode voltages are quite resistant to current ripple being 1/sqrt(x) kind of nature. I think that's where the regulation is coming into play.

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Danny
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Old 19th March 2004, 04:25 AM   #5
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Zeners cannot be effectively directly bypassed by caps. Why is this? Zeners are good, IF you have enough extra voltage to throw away. The JC-1 power amp, for example, uses zeners and buffered caps in the driver power supply, because we have extra voltage. The 1200 had NO extra winding on the power supply, SO we had to use a multiplier. Also, it tracks the main power supply, so even with low line voltage, it still works.
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Old 19th March 2004, 07:42 AM   #6
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Adding the transistor shown in the diagram below makes it a zener pre-regulated capacitance multiplier.

Your schematic I would describe as a "reference follower" - in your case you have a reference voltage provided by the zener that is effectively low-pass filtered by the RC network. An emitter follower circuit is then used as a current amplifier to feed the following circuitry.

Does this help?
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Old 19th March 2004, 07:54 PM   #7
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Thanks a lot guy´s!

Your opinions is pretty much as I thought and now I´ve got it confirmed. Beautiful!

/Peder
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Old 20th March 2004, 10:55 PM   #8
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Annex has gone to the next level. However, you 'could' replace the zener follower with an IC regulator. This would give even better DC performance.
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Old 20th March 2004, 11:03 PM   #9
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Just want to ask u regarding ur first answer:
"No, it is a zener filtered power supply. This is better."
By that U mean that it´s a better regulator this way over all or do u mean that the "cap multiplier" is working better this way?.. no that couldn´t be it, right?

Thank u for answering my questions mr Curl!

/Peder
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Old 21st March 2004, 12:57 AM   #10
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The performance of each circuit, i.e. the cap. multiplier and the zener follower depend on components used.

I can't say which works best without some prior simulation/testing although both have different characteristics and can therefore prove to be better in a given situation.

I did state that original circuit you posted was not a capacitance multiplier although I did not actually tell you what it is. I simply told you how to make it a capacitance multiplier (albeit a slightly modified one) - the original circuit you posted is just a zener follower with the zener reference voltage filtered with a simple RC lowpass filter. A darlington pair is used so as to limit the effect of the current draw on the output voltage.
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