power supply decoupling frequency

[goodguys]

Hi And thanks for reading this thread.


Most people report that the addition of a small 0.1 - 1 uf capacitor across the output of a power supply brings out the treble a little, that the very high frequencies are affected.


What range of freqencies would a 40uf capacitor typically affect.

 

[chris719]

This is not true. If "most people" say that, they are clueless.

I'm not even sure how to put this, or what a good analogy is.

Your question doesn't really make any sense. If you have a device in which the frequency response changes with a 0.1uF cap on the rails it is probably defective.

You really need to learn the basic fundamentals before you can do anything but harm here.

 

[FauxFrench]

Allow me an analogy: How much faster will my car drive down-hill if I increase the pressure in the tires with 0.1 bar?

We have discussed the purpose of decoupling capacitors in another thread and how capacitance value and ESR influence the ability to keep the supply voltage stable at different frequencies. This is a qualitative but valid discussion.

40uF is too little capacitance to help on bass. Somewhere in the mid-range/treble is likely. But, it depends on so many other factors like the specifications of the 40uF, the further decoupling on the amplifier board, the initial decoupling at the power supply output, the wires connecting the PSU and amplifier, the regulating speed of the PSU, the PSRR of the amplifier etc....

 

[martin clark]

Placing 0.1uF of low esr cap across the output of a regulator is a good way to invite instability, which might sound like 'brighter treble'. Its a very common mistake.

And in any case, such decoupling belongs right at the load - not back at the regulator/psu.

chris719 has said it all.

 

[DF96]

Yes, if a small cap is to be added (and in many cases it will do precisely nothing at all) then it should be where the PSU connects to the audio circuit rather than at the output of the PSU.

 

[TonyTecson]

@goodguys, search for the postings of Eva....very enlightening....you will find the answers there as well as post #2...

 

[Vovk Z]

Question in start topic has only one parameter but we need about ten or twenty to calculate a real answer.
In general - I agree with #2.
Phisical design have (can have) more influence than value of elements.
And "decoupling" have to be near the load, not in power supply.

 

[steveu]

Small capacitors are often placed physically close and between the output transistor supply voltage and the speaker ground to reduce the super audible voltage transients due to the power supply wire inductance. It can be important to avoid stability problems. Placing them on the supply itself before the wiring, would be of little value, although small caps are often paralleled with larger caps because capacitors have a resonance frequency above which they are inductive. However if your amp is not overheating or mysteriously blowing tweeter, adding small caps to the power supply will make no difference you can hear. People hear what they expect and DIYA is full of such things. But we have to play along because once in a while there is something to it.

 

[DF96]

In most cases an inductive big capacitor still has low enough impedance to do the job on its own. Adding a small bypass capacitor can increase impedance by creating a parallel resonance.