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Discussion Starter · #1 ·
So currently running off an old PSU (source will later be invertable from PSU to deepcycle leisure camping battery which could also be charged using the PSU - later plans to make this fully mobile/portable for camping)

i know very little about this stuff ..you guys are the experts i hope lol

AMP is 2channel with 100w 8ohm per channel. so im thinking my 4ohm 200w speaker nad my 4ohm 200w sub will blow the amp quickly if volume is too hifg? i notice it heats up once i put the volume too high so im thinking it will eventually blow after low volume/mild use anyway (prolonging blowing the amp)

here is a diagram.. basically what do i need to fix this, change speakers?.. change the amp? and do i need a crossover if so which type? passive? how to i wire the passive crossover to the speakers from the amp also.??
 

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It looks OK to me.

Your analysis of using the 8ohm rated amplifier with 4ohm rated speakers is reasonable.

I suppose it is a car amplifier (hence the 12v input)

Using it at lowered volume would be a good idea to increase its longevity.

100w limit at 8 ohms = 28.2v output at 3.535amps

Safe (or at least rated for that)

28.2v output being loaded by 4 ohms = 7.07 amps and 200w

Unsafe.

Using the "safe" current limit of 3.535 amps output:

3.53 amps into 4ohm = 14.14v amplifier output and 50w dissipated in the load, per channel

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Plug in numbers here - http://www.rapidtables.com/calc/electric/watt-volt-amp-calculator.htm
 

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Discussion Starter · #4 ·
It looks OK to me.

Your analysis of using the 8ohm rated amplifier with 4ohm rated speakers is reasonable.

I suppose it is a car amplifier (hence the 12v input)

Using it at lowered volume would be a good idea to increase its longevity.

100w limit at 8 ohms = 28.2v output at 3.535amps

Safe (or at least rated for that)

28.2v output being loaded by 4 ohms = 7.07 amps and 200w

Unsafe.

Using the "safe" current limit of 3.535 amps output:

3.53 amps into 4ohm = 14.14v amplifier output and 50w dissipated in the load, per channel

--

Plug in numbers here - LINK REMOVED DUE TO BEING A NOOB WITH 2 POSTS ONLY
Thank you buddy so much for your input.. my old man has been doing wededing bandwork/sound guy and has spent his whole life it for years around speakerts and amps and pa systems etc... but i went ahgead without his help and after making this he was the one he suggested said the amp wont last as he said 2 x 4ohm speakers on 8ohm amp is pushing the amp to 2ohms and it will blow eventually.... i can see why too.. but.. also about crossovers, the amp should be able to direct the treble signal to the small speaker (for high freq) and divert or channel the bass control from the bass knob to adjust the bass output on the big sub, as it is now both are being fed from the amp, the little speaker is bouncing (too much bass) how do i cross this over?

once again thank you..
 

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Discussion Starter · #6 ·
Ive read up on crossovers and know what i need, without the sub I wouldn't need one as the 4ohm speakers are dual cone coaxial
So if i wire another identical 4ohm speaker in series to the first one from channel 1 then this would bring the load to 8ohms for that channel, i also have an 8ohm sub speaker which i can replace the current 4ohm sub with, so would i be correct to assume the overall load for each channel matches them amp impedance of 8ohms per channel?


according to this image...
 

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Discussion Starter · #8 · (Edited)
Only want to crossover for the sub, the small speakers are coaxial dual cone with internal crossovers so no need to worry about filtering them. But I will need to crossover from the amp to sub so i can divert more of the bass to it ( hey thats whats its for eh) lol

So added a 12v calcium battery 10hours use so far and still green, its deep cycle :)

Now ...with reagrds to my PSU/invertible charger for the battery.. I'm sure i need resistors/capacitors for this to be able to be interchange from battery to mains without disconnecting wires, in case of a power surge while the battery charging the battery (and connected to the amp

So here is my new diagram...please advice me if i need any of the components at the bottom of image and correct me please if i have put them in wrong place
thank you so much
 

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I don't know what you are asking.

I'd put a female connector at the battery to plug/unplug the amp, or the PSU.

Or:

Put two female plugs at the battery, and run the amp, or the charger, or both, assuming the amp works ok just using the PSU.
 

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Discussion Starter · #11 ·
I don't know what you are asking.

I'd put a female connector at the battery to plug/unplug the amp, or the PSU.

Or:

Put two female plugs at the battery, and run the amp, or the charger, or both, assuming the amp works ok just using the PSU.
Thanks for replying

The amp runs off both the battery and the PSU fine. The PSU can be used as a battery charger also (Ive read online). So what I want to do is connect both the PSU+ and PSU- to the Battery + and - terminals so the power source can be inter changable

Flat battery = plug into mains and turn on PSU switch to charge the battery without disconnecting any of the amps + or - wires from the PSU/Battery + and -.

Prob not a good idea to power the amp on and charge at the same time i know this, but should I have some type of capaciotr between the PSU and the battery to make it a fully functional charger or can I charge it by connecting the PSU+ and - the battery + and -?

Can the PSU prevent a surge? If so then it wont ruin the battery and the amp connected to it. Otherwise Ill need a switch between the battery and amp to turn off while charging,,,
am i making sense?

thanks
 

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I'm assuming it is a car type amplifier due to it being powered by a nominal 12v.

Car batteries charge (at least mine does) at 14.75 volts or so. So the amplifier can take that voltage without a sweat.

You don't have to turn off the amplifier in the car while you are driving around and the car battery is charging.

The Computer PSU probably puts out 12v, so you may never really get a full charge on the battery.

There is unlikely to be a 'surge' from the PSU, as that could be bad for the PC circuits it used to be connected to.


Put a meter on it and see.
 

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Discussion Starter · #14 ·
I learned a few things from that. Thanks, The PSU - I can't remember the brand but it was removed from an old PC so agreeable upon no possible surge happening after all and also as it was an old PC I can confirm the only output voltages are are 5v and 12v. Not sure if PSUs are capable of outputting 14v+ maybe new/modern PSUs can. So I do already have a battery charger which I'll use to charge the battery (I could put a breaker/switch which can break the circuit for when the battery is charging at 14v+ just to be sure but then you kinda hit the nail on the head as a car battery does be charged as you drive around and you do not have to power off the amp so I'm sure it could charge). Thanks buddy
 
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