What's in those guts? 8ight's Amplifier Analysis! Part I

[Wicks]

Nice thread

Love that you started off with a PPI A600, One of my favorite amps ever.

I have one if you need any more detailed pics to go along with the theme above.

I have some contributions, if I may:

Contrary to popular belief, the aluminum electrolytic capacitors used in basically all amplifier architectures are not for energy storage.

They're for something called "decoupling" or filtering two different areas of circuitry.

Electronic devices are built with the assumption that the supporting electrical supply is stable.

There is no possibly way for those caps inside the amp to hold enough energy to actually power the amp if the supply current drops significantly which happens regularly when people try and use huge amps on stock electrical systems.

The only amp (that I know of) that can support itself with internal caps is the Fosgate T15K which has a MASSIVE amount of capacitance inside it.

A capacitor acts like a short circuit at high frequencies. When paralleled into a circuit, it helps to eliminate (short-out) higher frequency noise.

Also, the voltage across a capacitor can not instantaneously change, therefore its great for voltage stability (noise smoothing).

There are two main capacitor sections in an amp, before the power supply and after (Class D amps will have some in the output but that's another topic).

The "Before" caps:

These are physically the smaller of the two and are likely rated up to 25V. Its common to use a cap with double the voltage rating for reliability, when possible. They are directly connected to the power terminals on the amp and "decouple" the input of the power supply from any noise and whatnot in the vehicles 12V electrical system.

The "After" caps:

These are the larger of the caps and are typically placed in the middle of the circuit board. They are usually rated a certain percentage above the voltage of the power rails in the amp and will give you a rough idea of what voltage the amp's power supply is capable of.

If you understand how transformers work then that is what's going on in the amp's power supply.

The initial ~12V is pulsed into the input of the power supply transformer by the switching MOSFETs.

This pulsed or switched voltage is now a form of AC which the transformer can use to step up the voltage.

The transformer outputs this higher voltage "AC" signal which must be transformed back to DC for the output section of the amp to use it.

The higher voltage AC is fed into a pair (or more) of rectifying diodes which remove the unwanted polarity of the AC wave.

The rectified waves are then fed into the large capacitors which smooth the voltage into DC.

The amount of capacitance and number of caps used depends on the amount of ripple voltage that needs to be smoothed and the output current of the amp.

As you would expect, the larger the amp, the more capacitance is needed in the output of the power supply.

Good idea on the illustrations, always helps to visualize what's going on.

I have a few more additions which I'll throw out in a later post.

[HunterJohnson]

woohoo rate my amps next!

[8ight]

I know the function of capacitors in the amplifiers, my explanation may have made it sound like they are being used as one would try to use a larger capacitor in a 12v charging system. I will have to revise the original post with a brief explanation about ripple suppression, stiffening.

EDIT: I have used your explanation as a stand-in for my own as it is far more thorough, thank you for the contribution!

[8ight]

Writing part II today on the subject of class D amplifiers, this should be more interesting to most of those posting here. I have selected my reference amplifier for the writeup as well: the excellent Sundown Audio SAZ-1500v2. Stay tuned!

[purplesyrup]

great thread eight, can you do one on my eclipse 7232 amp? remember the one i took that chrome piece off off and we found a bunch of goodies in there?

its a class d

[meade916]

had to remove some of the pictures. Feel free to re-upload pics that do not contain a URL to another site written all over it.

thanks!

[8ight]

had to remove some of the pictures. Feel free to re-upload pics that do not contain a URL to another site written all over it.

thanks!

Sure! I will be re-writing this all with my own pictures eventually, I've got enough gut shots for the task luckily.

[Jonahscustoms]

Updates???

[BrainzAmilkshake]

Any chance the class D write up is still going to be posted?

[purplesyrup]

I have not seen eight on here for about a week it seems