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Old 8th February 2004, 12:12 PM   #1
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Question Up-Grade My Car Amplifier

I have a car amplifier.... the volt that out from power supply is 33V+/- (66V) and i have 6600uF per side (33-0) 13200uF TOTAL.
if i put more 47000uF per side... what it will do ??

thanks!

tamir
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Old 8th February 2004, 01:55 PM   #2
Netlist is offline Netlist  Belgium
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Default Re: Up-Grade My Car Amplifier

Quote:
Originally posted by Dj BASS AMP
what it will do ??
Hi Dj
As far as I can think, not much.
You'll have a bigger inrush current, that is more current will flow at startup to load the caps, and maybe the Bass will improve a bit.

/Hugo
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Old 8th February 2004, 02:52 PM   #3
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Default Re: Re: Up-Grade My Car Amplifier

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Originally posted by Netlist

Hi Dj
As far as I can think, not much.
You'll have a bigger inrush current, that is more current will flow at startup to load the caps, and maybe the Bass will improve a bit.

/Hugo
OK Thanks! Hugo....
and what about a 1,000,000uF (4700uF 25V x213 caps) in the input power of the amp ??

Tamir.....
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Old 8th February 2004, 03:02 PM   #4
Netlist is offline Netlist  Belgium
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Default Re: Re: Re: Up-Grade My Car Amplifier

Quote:
Originally posted by Dj BASS AMP

..and what about a 1,000,000uF
This will be a nice buffer to start the engine when your battery fails.
No seriously, you should ask the car forum, but to me it seems useless. Build yourself a Pass amp with these caps

/Hugo
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Old 8th February 2004, 03:18 PM   #5
Eva is offline Eva  Spain
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You can compare the effect of the capacitors before and after the power supply by calculating the amount of energy they store

E = .5 * C * V^2

1 Farad charged to 12V will be storing 72 Joules

To get this energy stored at 66V youll need :

72 = .5 * C * 66^2

C = 72 / (.5*66^2) = 34,4mF

So, 68.000uF per supply rail will have equal or better effect than 1F at 12 V [actually better because peak current in the power supply will be greatly reduced and so voltage drop]

The effect of all this capacitance is to gently smooth the current drawn from 12V supply, reducing instantaneous voltage drops and losses in the power supply

Adding more capacitance would be a overkill, actually 2x 33.000uF should do a great job reducing voltage drops in 12V supply since current from the capacitors is drawn at 2*signal_freq and 33.000uF have 0.08 ohms plus ESR at 60Hz [30Hz signal], much lower impedance than the power supply itself

Most amplifiers have a gentle soft-start, slowly ramping the duty cycle of the power supply from 0% to maximum, so inrush current rarely is a problem [you may put a bigger soft-start capacitor or resistor in the control IC to get even slower soft-start]

NOTE : I'm assuming the usual car-audio amp whose channels draw current from opposite supplies when driven with same polarity signal, and the usual stereo or bridge configuration where signal is the same for both channels at LF [ie: power drawn at 2*F from each supply]
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Old 8th February 2004, 03:59 PM   #6
Netlist is offline Netlist  Belgium
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Thumbs up math’s and math’s, all over the place...

Quote:
Originally posted by Eva

E = .5 * C * V^2
Well Dj, there you got it from an expert.
Sometimes it's worthwhile to keep a thread on top

/Hugo
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Old 8th February 2004, 04:37 PM   #7
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Hi Eva Be carefully wiht the capacitors.
Your mathematical it´s right, but it not a real wordl.
I made one amplifier 50W Clase A with 470000uF for rail.
If you, calculate the filter in low frecuencyt and the amotiguation factor is brutal but is not the best factor when us listened the music, eva the music is not one real frecuency generartion , is a complex wave you have treat each as it is , and depend of the each capacitors not only the static response versus the frecuency.
For example I use Black Gate capactors of 1/100 versus anothe mark
and I sure that the Black Gate Capacitors was winer that other marks with the 100/1 more Capaicior.

Jesús

E = .5 * C * V^2

1 Farad charged to 12V will be storing 72 Joules

To get this energy stored at 66V youll need :

72 = .5 * C * 66^2

C = 72 / (.5*66^2) = 34,4mF
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Old 8th February 2004, 05:03 PM   #8
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Default Re: Re: Re: Up-Grade My Car Amplifier

Quote:
Originally posted by Dj BASS AMP


OK Thanks! Hugo....
and what about a 1,000,000uF (4700uF 25V x213 caps) in the input power of the amp ??

Tamir.....
No need to parallel two hundred "small" caps... there are 1 Farad caps commercially available for just for that purpose.

But the premise for using them is a bit different. The idea is that when a high power car amp hits 100 amp peaks, the voltage at the amp's terminals drops because of source resistance in the power system. With unregulated internal power supplies, the amp's power also drops during those peaks. Holding the input voltage steady with a huge cap can give the amp the juice it needs to handle those peaks.

Just 50 milliohms of source impedance (alternator, battery, wiring, fuses, connections etc) is a 5 volt drop at 100 amps. A 1 Farad cap on the other hand:

i = C dv/dt
1 Farad will lose 1 volt when supplying 100 amps for 10 millisec.

The usefulness of big caps in car audio systems is endlessly debated in the car audio foums. The consensus is you're much better off eliminating the source impedance by using a heavy duty alternator and bigger wires.
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Old 8th February 2004, 06:30 PM   #9
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so what will be batter?? 1F connect to the amp??
or 2x 33.000uF after the power supply of the amp??

thanks!
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Old 8th February 2004, 06:38 PM   #10
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Quote:
Originally posted by Dj BASS AMP
so what will be batter?? 1F connect to the amp??
or 2x 33.000uF after the power supply of the amp??

thanks!

better (or worse) in what regard?

you can always argue that 10000000F is better than 1F. but does it make a difference in real life? if not, why should we care?
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