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bass amp ohmages


Guest five years
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Guest five years

what's the deal?

anyone able to explain fairly basically? or link something that does? i've been looking all afternoon, without anything particularly helpful.

i basically wanna know what the relationship between watts from my head into the cab is and how not to blow anything!!

a 1600watts head is with no load, correct?

meaning it'll go to 800watts with an 8 ohm cab?

400w with a 4ohm cab?

cheers.

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Your bass amp will be rated at a certain wattage into a certain load. Normally its about 4 ohms for musical instrument stuff.

When you double that load (put your head into an 8 ohm cab, say) you'll ROUGHLY reduce the power output by about half. This isn't all bad however, because it doesn't work the amp so hard and it'll run cooler. Likewise, if you half the impedance (say 2 ohms) you'll get a bit short of double the power. And, this pushes the amp harder.

One thing to note is that not all amps are rated for going into 2 ohm loads. Generally this pushes the amp quite hard and will increase the Total Harmonic Distortion. If the amps not rated for it, you could be seeing smoke :)

Note that this doesn't apply to valve amps. Valve amps are designed to run into a certain load, and modern amps have switches in the back for transformers which let it use different loads of speaker cabinets.

What bass amp do you have fiveyears, and what cabinet are you thinking of putting it through?

Oh, incedentally, with no load thats basically an impedance of infinity, meaning that your 1600watt head will put out 0 watts :) And with 0 impedance (a wire going from on terminal to another, or a short circuit) your amp will put out much more than its rating...but only for a second or two as the fuse goes and/or your amp goes to the repair shop. But why do I mention this? Because if you use standard jack connectors on your speaker wire, the ends of this connector short circuit brieflt every time you unplug them from the speaker, so its a good safety precaution to always make sure your amps off before unplugging your speaker, and also to unplug the cable from your amp before unpluging your speaker.

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Guest five years

i've played it through one preamp/channel into a 4x8 cab

it's an ampeg svt 4 pro, i just got spooked by the manual that says be sure that the cab you use can take the power, especially in "mono-bridge" mode, which obviously uses both the preamps in the head, meaning it's louder, and presumably running more efficiently and safer than using just one preamp. i just don't wanna blow anything!

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what's the deal?

anyone able to explain fairly basically? or link something that does? i've been looking all afternoon' date=' without anything particularly helpful.

i basically wanna know what the relationship between watts from my head into the cab is and how not to blow anything!!

a 1600watts head is with no load, correct?

meaning it'll go to 800watts with an 8 ohm cab?

400w with a 4ohm cab?

cheers.[/quote']

Wattage means nothing without load. 1600 watts in this case (being an Ampeg) is most probably going into 8 ohms.

Not all amps can handle 2 ohms so I wouldn't even try.

It's not a simple linear relationship, the impedance of the amp is in parallel with the speaker load (so you have to use 1/R1+1/R2=1/RT, not the series R1+R2=RT)

The manual is the best place to look. It's normally tucked away at the back among the technical specifications.

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So its this amp, right?

http://www.ampeg.com/products.htm?product=112&catid=31

RMS Power Output (8 Ohms): 300 x2 /900 (mono-bridged @ 8 Ohms)

RMS Power Output (4 Ohms): 490 x2 /1200 (mono-bridged @ 4 Ohms)

RMS Power Output (2 Ohms): 600x2

Ok, so this is the info you need. If you tell me what wattage is your bass cab rated at, and what impedance is it rated at I can tell you right away what if its safe to use.

That bass amps complicated...You've got two individual power amps in that thing, k?

*If you plug an 8 ohm cab into either output, its best to make sure the cab can handle 300 watts.

*If you plug a 4 ohm cab into either output, you need to make sure it can handle 490 watts.

*If you plug a 2 ohm cab into either output, you need to make sure it can handle 600 watts.

A common misconception is that you need to use both outputs, you do not. Its perfectly safe to use only one power amp.

Now, if you use the Bridge-Mono mode, it effectively ties both power amps together, and I assume theres a dedicated output for this mode.

*If you run bridge mono and plug an 8 ohm cab into the output, it must be able to handle 900 watts.

*If you run bridge-mono and plug a 4 ohm cab into the output, if must be able to handle 1200 watts.

*Do NOT run anything lower than 4 ohms from the bridge mono output!

Note, using bridge mono is NOT more efficient, and is definately NOT safer. I can point you to an article explaining why if you really want, its basically more catastrophic if something goes wrong.

If you're running more than one cab into any of the outputs, refer to soundians post on calculating the resultant impedance from the two cabs.

I'd recommend for safest use, use the onboard limiter, use only one of the amps, do not run bridge-mono, and study your manual well :)

Good luck!

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