Capacitance Factor

[wreckingball]

OK Folks, I am a new member to Audioholics, and am glad I joined.
First of all, thanks to Gene and other "strictly the facts" Commentators on this site. We all know that a lot of "snake oil" has been bantered around in the realm of audio, and audio equipment.
That being said, I have not found (and did many searches) of the role that capacitance plays in (power) amplifier designs...period.
Am I just not getting what role it plays, or am I missing something simple?
Any help would be appreciated
Best to you and yours, Steve

 

[Adam]

Welcome to the forum, Steve!

My answers would likely be overly simplistic and, well, wrong...so I'll wait along with you for one of the knowledgeable people here to give us the scoop. I mostly just wanted to welcome you and let you know that your post wasn't being ignored.

 

[jamie2112]

Hey there and welcome. I would read this it may give you a better idea of what capacitance is...http://sound.westhost.com/project15.htm

 

[Haoleb]

capacitance in power amplifiers designs, At least the capacitance that I would assume you are reffering to being power supply filter capacitance, pretty much goes like this...

This is reffering to a traditional Linear power supply... as found in nearly all amplifiers.

The power supply of the amplifier does just that, supplies the power. First it goes through a transformer which (usually) reduces the voltage from 120v to what the design needs, it then goes through diode rectifiers that will take the negative half of the sine wave and, in essence, flip it to make it positive. As seen in figure 3.

As you can see in the picture diagrams 1 and 2 are what it looks like before the rectifiers, And once rectified, Then the filter capacitors come in. They are what fills in the gaps between the "bumps" Capacitors are like a battery, in that they can store energy. The amount of energy is determined by their capacitance rating (and voltage rating) Capacitance is measured in Farads. A farad is a very large amount of energy so in home audio applications a usual spec you would see is say 15,000 microfarads, which is just a fraction of one farad. The difference between a capacitor and a battery however is that a capacitor dumps its entire amount of energy nearly instantly. The energy that is store in the capacitors is used to fill in the gaps in the sine wave to make (ideally) a completely flat DC voltage, pictured on the very bottom of the diagram. In a poorly designed power supply you would get something more like figure 4 with a certain amount of ripple. This is undesireable.

Not only do the capacitors fill in the gaps but they also add to the amount of current that the power supply can put out during musical peaks requring large amounts of power, more than can even be supplied by the wall outlet at any one time and because that extra reserve is there ready to be released in an instant. The bigger the power supply is the more power is going to be available. MOST power supplies i have seen, in my opinion are not sufficient enough to be called good but because of cost and size requirements many times sacrifices are made in the design.

Hopefully that gives you an idea of what it does without getting too technical.

 

[wreckingball]

Wealth of Information

First Off, I'd like to thank all of you for welcoming me, and for trying to understand my question (however simple it may be) and for knowing that there are those of us that seek truth on a slightly different "tack".
An observation that I am trying to "crack" is the role that caps play in amp design (output stage), more specifically, how they are used for replacing (or replicating)a tube designed amp. That being said, I understand why tube amp enthusiasts love the sound of their amps, but I do agree that their amps may not be entirely accurate across the audio spectrum
All that being said, I would like to know if the caps in a solid state amp design
are playing the role of "even order" generation ( which would be pleasing to the ear) and that using such devices would be beneficial WEHEWW!
Any Comments?
Steve

 

[Haoleb]

I personally have never heard any such concept of putting capacitors in the output stage to make it sound more tube like. Or to create distortion. I am not an amp designer so I am not fully familar with different circuit topologies but capacitors in the output stage is a new one on me, period.

In many preamp's they are used as a coupling capacitor which blocks any dc voltage from leaving the preamp and many people like to use esoteric capacitors for such purposes as they are in the signal path.

 

[3db]

I personally have never heard any such concept of putting capacitors in the output stage to make it sound more tube like. Or to create distortion. I am not an amp designer so I am not fully familar with different circuit topologies but capacitors in the output stage is a new one on me, period.

In many preamp's they are used as a coupling capacitor which blocks any dc voltage from leaving the preamp and many people like to use esoteric capacitors for such purposes as they are in the signal path.

Tube amps from what I've read are rich in even order harmonics which gives it that "warm" sound characteristic. But I think this is gnerated by the tube itself rather than the supporting reactive components. Capacitors in the output stage are mainly used to block DC from leaving the output terminals as Haoleb mentioned. As far as I know, ( I may be wrong here) I think its impossible to use the characteristcis of capaictance to generate harmonics.

 

[wreckingball]

My Bad

Guess I worded that all wrong. Many thanks Haoleb, jamie2112,and 3db. So caps act like a buffer or smoothing agent if you will, and also supply power for dynamic range? A few final questions... is it just a matter of "more is better" within reason, or does there come a point where this rippling effect (in essence) becomes inaudible? How does one know when there is enough say, in a typical class AB. A general rule of thumb? Or does that depend on designer/manufacturer, and a whole host of other factors?
Thanks once again, Steve

I Love tube amps!
...I play guitars through them :^}

 

[mtrycrafts]

Guess I worded that all wrong. Many thanks Haoleb, jamie2112,and 3db. So caps act like a buffer or smoothing agent if you will, and also supply power for dynamic range? A few final questions... is it just a matter of "more is better" within reason, or does there come a point where this rippling effect (in essence) becomes inaudible? How does one know when there is enough say, in a typical class AB. A general rule of thumb? Or does that depend on designer/manufacturer, and a whole host of other factors?
Thanks once again, Steve

I Love tube amps!
...I play guitars through them :^}

Caps in the filter bank offer power. Other places it has other functions.
More is better in the filter bank of a power amp, otherwise, the value depends on the application and design of that stage and its roll, what it needs to do, like bleed something to ground? In that case, more is not better, but has to be a specific design value.

As to tube sound, the output impedance has a lot to do with the amps frequency response into known speaker loads, the smaller the ratio, say 1 ohm amp out to an 8 ohm load, the amp will more closely follow the frequency response of the speaker and can certainly have that 'warm sound'. Say you increase it to 3 Ohms out, then you really have a warm sound. Carver did this with a switch on some amps of the past.

 

[Haoleb]

More is better is not really the best way to put it, Capacitors act like a short circuit when they charge up so if you have a very large bank of capacitors that are trying to charge up when you power the amp on you need a very large transformer, large fuses, and so on. It kind of depends on the designer to determine whats enough. In each of my monoblock amplifiers there is 120,000uf of filter capacitance which is quite a bit more than the majority of any amplifiers but you'll notice that the higher and stuff has a much more robust power supply than the mass market gear. for example, I think the amount of filter capacitance in my subwoofer amplifiers is pretty lacking. If they had more Im confident that the clipping light wouldnt flash on certain tracks when I am pushing them.