10 replies to this topic

[Mr_Bob]

although external capacitors are generally considered to be useless (other than cosmetics)
Caps built into the circuit board of an amp are very important, especially for sub/midbass.
obviously the quality of these capacitors is important and their rated voltage, but is there some sort of formula to calculate wether or not an amplifier has sufficient internal capacitance?

i.e. if it's a 500WRMs monoblock (@4ohm) amplifier, what sort of capacitance should it have, obviously amps with higher capacitance will be better for lower frequencies, but how much is enough?
i'd like to be able to calculate how much "headroom" an amp has so i can compare it with others.

[ December 22, 2003, 09:51: Message edited by: Mr_Bob ]

[T-Bro]

ive never done a listening test with/without my external capacitor, but i do know that without it, i get headlight and instrumentation dimming which creates a cheap feeling - not good car power systems are terrible, they can use all the stiffening they can get i reckon.

[NUTTTR]

Well,
I guess in order to work out required levels of capacitance, you need to know the sort of draws/drops in rail voltage you would expect...
Also, this is dependant (usually) on supply voltage... So it would differ according to the different cars electricals. I know the audison has quite a fair bit of internal capacitance, but it still dims the lights one hell of a lot, but the output seems fairly constant, so i'd say capacitors are doing their job
My personal rule of thumb with modding that the wiring internally + capcitors internally should = the available space, with about 1cm air space and lotsa fans
Truely tho, the more internal capacitance the better chance you have of creating benefit... For example, the best way is to have a bank of caps per set of fets However, inside an amp, it's impractical to try and fit this
Aaron

[Bassaholic]

Obviously the perfect compromise line has to be drawn somewhere, but I do not have the experience to know where that is...

[NUTTTR]

Yes, there is a comprimise line, thats when musical peaks will draw more power than the capacitors can sustain... No one amp is the same, so it's different for all amps
aaron

[suparoo]

capacitors used in the amps power supply are for, smoothing out the ripple on the DC + line, with car audio. this is what gets me, they utilise switch mode power supplies, so once you have your DC line into the amp its turned into AC again anyway... this is why im not a beliver of Caps on your main power into the amp. the dimming on HU's etc is usualy caused by the large current drain on the battery drops its voltage, they can put out more current then you need with ratings of 550CCA and alike, and the capacitor on the main power in, stops this voltage dropping, which is more or less band-aiding the fact, the battery etc, could be replaced with an item better suited to the job.

[Bassaholic]

Even if you have a battery with plenty of capacity, you will still get voltage drop from the alternator voltage down to the battery voltage. But yes, since car audio amps use switch mode power supplies, the voltage drop isn't as much of an issue, sound wise. If you want the lights to stop dimming, hook a capacitor up to the lights.

[Nizzan]

would that seriously work?? a cap to the lights? i hate my headlight dimming, its looks cheap!

[suparoo]

a big enough cap would work yes,, whack a diode on before the cap, and your lights can fade off hah

[fr0st]

most of the caps used in an amp are after the switch mods power supply (SMPS). Any used before (ala the farad cap) are used to stiffen the alternator output and create a low impedence source of power as oposed to the battery which is signifigantly higher in impedence.
Internally the caps are used for a different reason. Most (if not all) of the noise generated by the alternator and god knows wat is transfered through the SMPS to the amp and then to the speaker. The cap is used along with an inductor to filter out this noise inside the amp. you probably won't see more than 10 000uF (micro farads) inside the amp before the SMPS.

[-DJ-]

Quote

Originally posted by supa-roo:
a big enough cap would work yes,, whack a diode on before the cap, and your lights can fade off hah

lol!

take a leaf out of krell's book.... just go crazy and overspec your supply so it can deliver 6x the power than the output stages will ever need. thats what i call headroom....