Speaker/Amp Ohms question

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Joined: Dec 20 2003
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What will happen if one hooks up 3.2 Ohm speakers to an amp expecting 8 Ohm speakers?

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Joined: Dec 20 2003
Posts: 455
If the amp is of medicore qua

If the amp is of medicore quality, it could blow the amp.

The lower the ohms, the higher the wattage the amp will drive.

Thats why is a bad thing to hook up car stereo speakers to a home stereo system unless is a good high quality amp that can withstand overdriving.

You drive a 100watt @ 8 ohm amp with a pair of 4 ohm speakers, the amp will then try pushing around 150-200 watts though and that isn't a good thing unless the amp can withstand it.

Its also why a lot of car stereo people will bridge the outputs on their amps, it gets them more power (bridging the 2 outputs of a stereo amp that puts out 100 watts at 4 ohms with a single 200 watt sub will effectivly push out 150-200 watts with a 2 ohm load.

Most good car stereo equiptment is built to withstand low ohm loads, but home stereo stuff, i'm not so sure about.

What kind of amp and the specs?

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Posts: 354
I don't have a specific amp y

I don't have a specific amp yet. The idea is that I have a couple of detachable boom-box speakers from a defunct boom-box. I am looking for an amplifier circuit to build that

1) Runs on batteries (so I don't have to build a dual-rail supply)

2)can drive these speakers

Most circuits I've found on the web that can drive 4 ohm speakers require a dual power supply. Most circuits that are battery powered are for small 8-16 ohm speakers, or for headphones (32 ohms and higher).

I'm not looking for high power; I'm sure just a couple of watts would be fine for my purposes.

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use mine

You could use my amp design for that. It can drive a 4 ohm load, but you have to limit the power supply voltage to no more than 25V. It'll give you 56W per channel and it's very clean. About the size of a 3x5 card.

However it doesn't run on batteries. There's a reason why they all want dual rail power supplies and that is you'll get much better quality sound out of it. With a single rail, you have to offset the ground halway between the rail voltage and 0 in order to properly represent an AC waveform.

Dr. Bob

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How about using this cap in y

How about using this cap in your project? Wink

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That looks like a high voltag

That looks like a high voltage cap. My current cap bank is excessive as it is.

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Wow - nicely layed out. I mu

Wow - nicely layed out. I must get myself a drill / taps etc so I can lay out board nicely in a case. I get a bit nerveous electrical taping 240V stuff...

Yes, that is a high voltage capacitor. I was reading some posts in a electronics forum and that came up. I don't think it has a very large capacitance...

In my powersupply I wanted to use a toroidal transformer - but they are £15 - 25 here.. I like there build in thermal cut out (self destruct). Are they used for audio applications for there low noise?

What value caps are you using? What formulas did you use to work out there values - or is there a rough law of thumb?

Oh - the only caps I have are these...so I need some more Wink (Battery for size)

All rather pathetic, except for the large 400wv one.. (Whats WV anyway??)

I'll probally end up using some filter caps I scavanged from an ATX PSU, rated at 200V @ 6800uF.

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Re: Wow - nicely layed out. I mu

martakz wrote:

Wow - nicely layed out. I must get myself a drill / taps etc so I can lay out board nicely in a case. I get a bit nerveous electrical taping 240V stuff...

I just bought some perfboard and cut it out for that.

Quote:

Yes, that is a high voltage capacitor. I was reading some posts in a electronics forum and that came up. I don't think it has a very large capacitance...

Cap size increases with both voltage and capacity. a 3V 1 farad cap is the size of your thumb, but a 12V 1 farad cap is like two soup cans stacked on top.

Quote:

In my powersupply I wanted to use a toroidal transformer - but they are £15 - 25 here.. I like there build in thermal cut out (self destruct). Are they used for audio applications for there low noise?

Torroids are more compact, lower noise, lower distortion, and more efficient (less heat). However the "noise" generated by them is generally irrelevant to most audio applications. Many people use them anyway because they don't know any better. I used that one because I was interested in low heat output. BTW: That torroid cost $45 USD

Quote:

What value caps are you using?

4700 micro farad, 50V, low leakage.

Quote:

What formulas did you use to work out there values - or is there a rough law of thumb?

You have to figure out how much current they need to supply while the input voltage is below the required voltage.

Quote:

All rather pathetic, except for the large 400wv one.. (Whats WV anyway??)

I don't know what wv referrs to. Probably safe to assume voltage.

Quote:

I'll probally end up using some filter caps I scavanged from an ATX PSU, rated at 200V @ 6800uF.

Voltage only needs to be rated higher than your supply voltage. There is no reason to use a higher rating. Caps are pretty cheap, you should just buy new ones as they do lose their value over time.

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