What value cap to bypass power supply cap?

Here’s some answers from some of our members

Short answer ...

05-03-05: Herman
Of course different designers have different opinions on this but a good place to start is to bypass with a value 1/100th of the big cap. You can bypass again with another cap 1/100th of the smaller and see if that does anything.

example, original electrolytic 4700 uF bypassed by a 47 uF film cap and a .47 uF film cap.

Long Answer ...

05-04-05: Sadownic
The values of bypassing caps are determined by the amount of ripple rejection desired and the frequency range. Any capacitor will have a self-resonant frequency calculated by
fr=1/2π√(LC)
Above the self-resonant frequency, the capacitor will start to look like an inductor and its impedance will increase. For optimum ripple rejection, you want the shunt impedance to be as low as possible. Impedance is calculated by

Xc=1/2πfC.

Where: f=frequency (Hz) C=capacitance (farads) L=inductance (Henrys).

As you can see from above, the self-resonant frequency will vary depending on the value of capacitor used and its inherent inductance. The physical construction, size and value of the capacitor will determine the amount of inductance. So in order to maintain maximum ripple rejection across a large frequency range you’ll need to add additional (smaller value) capacitors in parallel with large value caps. Find the spec sheets for the capacitors you plan on using to determine their inductance and self resonant frequency and then calculate the values you’ll need for the additional bypass values. It’s better to understand why things are done instead of using “rules of thumb”. I hope this helps.
Sadownic (Answers | This Thread)

Complete Thread

BY PASS POST
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Let's turn this up a notch ... as long as you have the hood up and soldering iron out .. you may want to construct a Snubber or Tank filter

SNUBBER Pdf

As your diodes convert AC to DC they switch on and off ... this cycling creates a ringing which can be tamed/toned down by placing a Snubber filter between the diodes and the PS caps ... read the PDF for field level box seats behind first base ... as again I’ve merely gotten you in the stadium

Here is an interesting read/point of view from one of my Sensei’s who likes to frequently poke me in the eye with a sharp stick to keep me in align

“Lets talk about FACTS. The AC powered audio devices in fact DON'T USE AC VOLTAGE AT ALL !!!
They are all DC devices and hence they need clean DC not AC. So creating "pure sine" is a most stupid, utterly heretic waste of time.
The AC, after entering our gear, becomes straight away brutally rectified into DC and that is the end of the road for the sine. Then the big electrolytic capacitors accumulate the electrons in a "bottle". These electrons become a source of energy for the active devices in our gear. They are being released slowly as a DC current.
THESE ELECTRONS HAVE NO MEMORY of their "childhood". They do neither remember nor care if they arrived in a form of perfect sine, cosine, square wave, or chaotic ripples. As long as they arrived, their sins are forgiven in the capacitor and they are purified. So in other words - the hi fi gear is indifferent to AC shape.

An absolutely another story is RFI. This frequency is millions times higher than the AC frequency. It behaves like radio-wave and it can penetrate the gear.

The problem is that the RFI can enter gear DESPITE the galvanic separation by transformer and despite filtering effect of capacitors in power supply. The RFI becomes the Trojan Horse of AC grid power system in our gear.

Getting rid of these is a bit tricky. But my advice is - that our intervention is focused on hundreds of kilohertz and not close to 50 Hz AC. So the intervention is very gentle, very low order, and nothing to do with our regular current feeding the gear.

The filtering is achieved by two opposite effects: parallel capacitive shorting and series inductive blocking.
The kindergarten explanation for non-engineers is that for high frequency - a capacitor presents a SHORT, and coil - presents a high resistance (impedance).
So a RFI noise rides by the AC cabling to our house very happy, like a Porsche on the autobahn. But when it arrives to the filter - the road becomes blocked by the coil. Oh shit thinks the noise, getting through is gonna be real tough. But then it notices an alternative route - an easy one - via a cap. It chooses the easy route and ends up in the ground. Dead. That's our noise trap. That applies of course to very dumb Porsches only. This method does not affect the AC performance because the cap is VERY small and the coil has a DC resistance of milli-ohms. Literally - of a foot of thick wire. So the impulse response of the AC source to the amplifier demand is not limited. We say that the supply is NOT CHOKED.

The audible effect depends on many many factors - the circuits in gear, the internal filters commonly built in, the ground quality and arrangement in the house, the type of devices playing together etc. It is IMPOSSIBLE to predict the degree of improvement, but strangely - the results are very consistent

END OF POKE IN THE EYE RANT

Lijanki .. OK I shall petition the federal government and the Treasury Department to put Almarg picture on the hundred dollar bill and your picture on the fifties ... the denomination value has nothing to do with your actual worth ... but only that the $100 are already occupied by Al’s picture

You are both the best at removing any self interest when giving a subjective opinion and Audiogon is lucky to have these two crown jewels in their in their collection

Keep up the good work

Dave

Dracule1 .. my post was a attempt at painting a picture with broad stokes ... and suggesting the number you were seeking was 1/100th or 1% as Kijanki stated

My post got you in the ball park but seated you in the third deck .. Kijanki's guidance has give you field level box seats 3 rows behind first base

6 years ago I upgraded the PS caps in my D500 Phase Linear .. I bumped the main caps from the factory stock 35k to 140K of Nichicon’s and bypassed with 1% Rels .. I also had a dual diode bridge installed and eliminated the stock factory attenuators by wiring the inputs directly to the outputs eliminate the old carbon pots and about 4 feet of wiring

The difference was far from night and day ... much more like dusk to dawn ... but the improvement was positive with no down sides .. tightening up the base and opening up the treble very nicely

I think the Rel’s helped extend and open up the treble and the Nichicon’s gave some boost to the bass

I have found greater gains in working with room acoustics .. power deliver and vibration control .. but have no complaints about the amp upgrade to this day .. that amp isn’t going anywhere nor are the double run of Ridge Street PIII speaker cables driving my NHT3.3’s

Dracule1 .. I’m sure you’ll agree with me that they should put Kijanki and Almarg’s picture on money for all their contributions and time donated to this forum

ATB Dave
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