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Old 14th April 2004, 01:07 AM   #21
Bryan is offline Bryan  United States
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Vortex,

I dont think I understand your reply....?


Quote:
Don't use more capacitors after rectifying !
I'm unsure what you mean here?

Thanks,

Bryan
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Old 14th April 2004, 02:06 AM   #22
Bryan is offline Bryan  United States
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Default Another observation.

I've been poking around with my DMM. I've asked about this before, but I still think something may be off.

With respect to the power suply, I can measure over 100mVAC on the first filter cap, on the second filter cap I measure 8-14mVAC, and it bounces around between these values. After the VR tubes, I measure 3.4mVAC, which is also on the plate, and thus at the outputs.

I'm wondering if this is acceptable and normal. I'm not sure why the voltage is bouncing around on the second cap, and if the 3.4mV is what is causing the residual hum that I hear?

Thanks,

Bryan
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Old 14th April 2004, 03:28 AM   #23
Bryan is offline Bryan  United States
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Slight cange in values....

I checked the accuracy of my Fluke, and it seems that the reading with both probes connected in the mVAC reange is 3.4, so I think I've reached the limit of the meter.

I measured with my old-school leader millivoltmeter, and I get a reading between 1.8 and 2.4mVAC, which still bounces around. Still wondering if this is normal, and acceptable.

Sorry for any confusion....

Thanks,

Bryan
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Old 18th April 2004, 02:54 AM   #24
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Hi,

Quote:
I'm unsure what you mean here?
What Vortex means, I think, is that instead of using several smaller caps in series, you're better off using a single big one.

The reasoning being that the one with the smallest C value is going to be hit by the most current and may not survive in the long run....
There are tricks for this but you could use a single cap or select the caps for equal C and ESR provided you have a bagful and a capmeter.

The actual value you use in the schem is very high already and may hurt the diodes at switch on unless you put the choke inbetween as I suggested.
Make sure the choke can handle the current...

While I don't think it would be a problem in practice, at least in theory his suggestion is a valid one.

Cheers,
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Old 20th April 2004, 01:52 PM   #25
Mike C is offline Mike C  United Kingdom
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Default Is Voltage Regulation Necessary?

Given that you have a CCS load in the driven circuit, I wonder if
the voltage regulation is really achieving much?

The CCS (esp a good FET type) should give near infinite power supply
rejection ratio. The use of low DCR chokes and fairly high value
caps should give a very 'robust' PSU to start with, so I think
any sag under load will be minimal.

I'd be inclined to try removing the VR tubes and dropper resistor.
Compensate for the voltage rise by adding a small cap to ground
before choke 1, making it a cLCLC 'transitional' 2 pi filter; try
about 1uF and tune by trial and error to give the desired voltage.
Also add a significant bleed of say 20% of the load current.

Might be worth trying, as I feel it could sound very good!
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