Determining Capacitor Specifications

[Logistics]

Okay, I want to determine things like leakage current for a given frequency since I need power caps for a cMoy, but I'm obviously not dealing with 100kHz in a headphone amp. I don't understand the little I=X CV thing. The multipliers for ripple current are simple enough, but I don't understand how the math is supposed to work for leakage current or ESR if they aren't listed. I don't understand the tan value. Help me, I'm dumb.

[starfury1]

Re: Determining Capacitor Specifications

Firstly haven't answered your questions directly
(I should remember how all this works but frankly I've forgotten)

With some spec sheets its not given as ESR but a combination of things and summed as one spec

Ok I found this later and is this whats prompted your questions?

Are you intending to run it from a mains type PSU?

Op-Amp Power Supply Quality Considerations

(I did this post partly the other night and for some reason couldn't get badcaps again so I saved it)


Is this the project you are talking about?

Original article Here cMoy

cMoy pocket headphone amp

Dans data review

From the original page

The power supply circuit (figure 3) converts the 9V battery into a ±4.5V dual supply. Although the OPA134 could run from a single supply, it (and other opamps) are designed for dual supplies, and a dual supply is required for direct-coupling the output. This virtual ground sits at 4.5V, but works because opamps only care about relative power supply voltages. At idle, the opamp output is still 0V (minus a millivolt or two of offset) without capacitor coupling. However, if the headphone amp will also double as a preamp, add a capacitor to the opamp output to block DC, if the input stage of the power amplifier is direct coupled.

Since the first supply shown is basically using 2 resistors to form voltage divider, So voltage is evenly divided across the caps to create + - supply rails with a virtual earth (ground) since its floating who cares


Since

It has fine PSRR (power supply rejection) numbers,

If you are using a battery or batteries

I would just use good quality caps. if you got some low esr hanging around
dont think they would hurt
The op-amps are not going to pull huge currents


Op Amp PDF Here

The caps I think would be better then pulling straight of the battery anyway for the dynamic nature of audio

if you want I will try to dig up some hopefully more easy to understand info on caps
I do have a few links posted here already in ESR threads etc.
(not that there all that easy to understand)

Some links here but note, don't seem to directly answer you questions
of course there more then what quoted and other links of some of these.

Capacitor Characteristics (audio related)

ESR - Equivalent Series Resistance
While inductance is not affected by the dielectric material, ESR is - it is dependent on the dissipation factor (DF) of the insulation material, as well as the resistance of the leads, plate material and plate terminations. Because DF varies with frequency in most common dielectrics, so too does ESR. However, ESR is rarely a problem in most audio circuits. It is important in passive crossovers used in high powered systems, or for other applications where capacitor current is high. ESR (like all resistance) creates heat when current is passed, so for high current circuits the ESR is often a limiting factor.

ESR is very difficult to measure with low value capacitors, because the capacitive reactance is usually a great deal higher than the ESR itself. In general, it is safe to ignore ESR in most electrolytic and film caps used in signal level applications (such as electronic crossovers, coupling capacitors and opamp bypass applications). ESR becomes very important in high current power supplies, switching regulators/supplies and Class-D amplifiers, many digital circuits and any other application that demands high instantaneous currents that are supplied by the capacitor.

Bypass Capacitors

PeteS has posted a link on this too somewhere in the forums

Capacitor ESR Ratings

Equivalent Capacitor Circuit

Equivalent series resistance (ESR): The square root of the difference between the impedance squared and the reactance squared. All the internal resistance [losses] of a component [both series and parallel] treated as a single resistance at one point, at a given frequency. ESR allow the device to be described as a simple series R-C circuit

don't ask me what they mean by the above but it sounded interesting ...haven't stopped to think about it yet!

ESR Wiki


Characteristics of Aluminum Electrolytic Capacitors

Leakage Current (DCL)

The dielectric of a capacitor has a very high resistance which prevents the flow of DC current. However, there are some areas in the dielectric which allow a small amount of current to pass, called leakage current. The areas allowing current flow are due to very small foil impurity sites which are not homogeneous, and the dielectric formed over these impurities does not create a strong bond. When the capacitor is exposed to high DC voltages or high temperatures, these bonds break down and the leakage current increases. Leakage current is also determined by the following factors:

1. Capacitance value
2. Applied voltage versus rated voltage
3. Previous history

The leakage current is proportional to the capacitance and decreases as the applied voltage is reduced. If the capacitor has been at elevated temperatures without voltage applied for an extended time, some degradation of the oxide dielectric may take place which will result in a higher leakage current. Usually this damage will be repaired when voltage is reapplied.

I guess you are going to find a lot of fact and fiction out there when it comes to Audio, So you will have to sort the wheat from the chaff

Anyway just my thoughts and some info,
those into audio may have more accurate info, opinions thought.

HTH Cheers

[Logistics]

Re: Determining Capacitor Specifications

KYAHAHAHA! I'm going to have to save this post. Too much good info! Actually, I was only concerned that a capacitor such as the ones pushed here or even Panny FM's, while good for what they are spec'd for (100kHz) may not be good for others. I imagine in the cMoy (yes the tangent tutorial is the one I'm doing) has no relation to anything 100kHz.

I noticed that using the multipliers, the FM's, at 120Hz, still have superior Ripple compared to other capacitors which are spec'd at 120Hz, but they don't provide something so easy for calculating the ESR. The suggested cap in the tutorial is the Panny NHG which in 220uF 25V form has along the lines of 230uA Ripple, but the Panny FM specs at 665uA at 120Hz so is far superior in that area, but dunno how to figure the ESR... should I just assume it is better also? LOL! IIRC it's also ideal to have low leakage current. I'm not keen on what leakage current is, other than to say it strays inside the circuit until it finds a path to ground... which doesn't exist if you're running on batteries. I thought it also resulted in more DC offset at the output of the amp, (if it doesn't find it's way to ground first) which is something you want the least off, especially if you want to get away with no capacitors at the output because supposedly anything higher than 20mV at the output can damage headphone drivers.

Anyway, that's not important in the cMoy because it doesn't use output caps anyway, but I could use to know about this for other projects. In any case, too many people have used too many cheap caps to build cMoy's so I probably should have just assumed that an FM or and MCZ/GC would bust a cap in many others caps to begin with, even at 120Hz. But then... the FM is cheaper than the NHG...??? BLEARGH, SO CONFUSING!