Crate Power Block ohm question.

[johnnyseven]

The speaker output of my Crate Power Block is 8 Ohms, but can anyone tell me if it would be safe to run into a 16 Ohm cab?

[Johno]

The speaker output of my Crate Power Block is 8 Ohms, but can anyone tell me if it would be safe to run into a 16 Ohm cab?

yes thats fine, just never the other way around.

[Gabriel]

The entire I had mine I used a 16 ohm cab with it, just don't run it at 4 ohms as that puts some stress on it (at least so I've heard/read).

[johnnyseven]

Thanks chaps. I'm taking it to practice tonight, i've always shyed away from using it with anything other than 8 ohms - at least I know I can use it if the only cab they have is 16 ohms.

[willlin]

No matter how many times people tell me about the amp ohm load thing, I cannot for the life of me remember which way round it goes.

[Thom]

No matter how many times people tell me about the amp ohm load thing, I cannot for the life of me remember which way round it goes.

The opposite way to what most people think...some useful info here:

Q: I have an amp that specifies it wants to see an 8 ohm load. Is it OK to hook a 4 ohm, 2 ohm, or 16 ohm load to it? Will I blow up anything? (substitute any numbers you want)
A: "It depends." Typically, with Fender amps, you are OK going either one step up or one rung down-- either half, or double. In an old Fender amp requesting 8 ohms, you should be fine with either 4 ohms or 16 ohms. By "fine," I mean "not exceedingly likely to blow anything up." As always, there are no guarantees. With the upward mismatch (i.e. the load is double what's specified), you're in slightly more danger. With half the requested load, your risk is very low. Going too far beyond the "half or double" rule of thumb is asking for trouble. This applies mainly to Fender amps, but to many others as well. Any amp with robust transformers (Traynor, Ampeg, etc) will usually be pretty tolerant of a reasonable (i.e. 100% either direction) mismatch.

Q: My dad is an electronics engineer, and he told me that upward mismatches are safer (i.e. 4 ohm output into 16 ohm load), and this 80-year-old TV repair guy I'm friends with says the opposite-- that downward mismatches (i.e. 8 ohm output into 2 ohm load) are safer. The old dude probably just has alzheimer's, right?
A: No. The answer to this question depends on whether you're talking about tube or solid-state technology, and this is the source of the confusion. Solid-state amps typically have a very LOW output impedance, and will easily drive a load many times higher than their output impedance. In fact, they're usually happiest this way, and having a load with too LOW an impedance is dangerous-- dead shorts will kill a solid-state amp, and open circuits will be fine.

Tube amps are the opposite. Tube amps prefer if the output impedance of the amp and the load are matched as close as possible; however, to some degree they are fairly tolerant of loads that are lower in impedance than the source. Loads whose impedance are way higher than the amp's output impedance will cause what's called flyback voltages in the output transformer. This can lead to arcing, and can burn the insulation off the transformer's windings, causing death to the transformer. Tube amps are the opposite of solid-state, as a rule: they'd rather see a dead short on the output than an open circuit. Fender amps have a shorting jack on their speaker outputs for this reason-- If the speaker comes unplugged, it shorts the output transformer secondary, which will 'buy you some time' until you figure out that there's no speaker connected.

Q: I have an amp that wants to see 4 ohms, but my only cab right now is 16 ohms. Can I hook it up just to see what the amp sounds like and make sure it works? Is there any way to minimize the chance of damage?
A: Do so at your own risk. If the numbers were reversed (16 ohm amp, 4 ohm speaker), you'd likely be fine if you were reasonable with the demands placed on the amp--your tubes would wear a bit faster, probably. However, upward mismatches like the one in this example are more dangerous for the output transformer. The greater the upward mismatch, the greater the flyback voltages. At low volumes you would be fine. The higher the volume, the more voltage swing you're causing at the output tubes, and the greater the flyback voltages will be. I won't say it's "never OK," or that it will cause instant death to every amp-- but proceed with caution.

For the Crate, the inputs are a min input as it's solid state so a 16 ohm will be fine.

[willlin]

Ah useful, ta.

When I bought my Marshall I unknowingly used it with mismatched impedance (8 ohm output into a 16 ohm speaker) for a couple of weeks until I took the back off and realised. Apparety a whole load of the JVMs came from the factory plugged in wrong.

[Doog]

The only problem is you'll lose volume or at least clean headroom not matching impedances.