Ohms and why they are important. (Guitar amps)

Alrighty, I've learned an important lesson tonight. I was going to post this in the guitar gear thread but rather than talk about gear per se, I want to talk about ohms.

Don't just reach behind your 60W tube amp to plug things in. Look WITH YOUR EYES, don't go by feel.

A few days ago I plugged my amp in after moving it to a different corner and noodled around for a while. A little with headphones, a little without. The next day same thing. No issues. Today I turn on the amp and everything is at 15% volume even at levels on 10. This amp SCREAMS through a 2x12 cab and I keep it at 2 max. Bad cable? Bad tube? Bad cord?

Let's investigate:

Hmmm, let's focus on figure 30, the loudspeaker outputs. 4/8/16 Ohm outputs in that order.

What's this at the bottom of the cab?

Well I'll be damned. That explains a lack of sound. I have two 16 Ohm speakers and I was running 4 Ohms out (far left output) instead of 16 ohms out (far right). Apparently, I didn't pay attention a few days ago when I did it and curiously I don't remember a pop, burning smell, sound......nothing. Just didn't have volume today though I've played it for days like this with no issue. I guess it just caught up with the weak link.

I've never seen that happen before but I understand matching things so they place nice. Can anybody else explain in more detail what exactly went on here and any bets on if the amp is hurt or just that speaker wire is toast?

Do you have a cat? Because my speaker wires looked exactly like that shortly after my wife brought one home...

Remember basic electronics: "Virginia International Raceway"--- V=IR

V is for the volts that jolt.

I is the current, (the mils that kill)

R is the resistance.

your amp is putting out a given voltage, and your speaker resistance "should be" relatively constant at the 16 ohm neighborhood.

If you are burning up wires, it's because your resistance is too low, not because your amp expects it to be too low(the selected output), but because a speaker is shorting internally or along the wire path to the speaker

WilD wrote: Do you have a cat? Because my speaker wires looked exactly like that shortly after my wife brought one home...

We dont thank God. Have a little dog but it was pressed against the wall. I also thought about rodents but no evidence of that either. Its weird that I just dont remember any smell or pop and I dont leave it on when I am away.

crankwalk wrote: Have a little dog but it was pressed against the wall.

That's an odd place to keep a dog...

If you ran 4 ohm speaker(s) into the 8 or 16 ohm output you could have fried something, but going the other way would only reduce the volume. You have to keep in mind whether your speakers are wired in series or parallel though - two 16 ohm speakers in parallel = 8 ohms combined.

Pete Gossett wrote:

crankwalk wrote: Have a little dog but it was pressed against the wall.

That's an odd place to keep a dog... If you ran 4 ohm speaker(s) into the 8 or 16 ohm output you could have fried something, but going the other way would only reduce the volume. You have to keep in mind whether your speakers are wired in series or parallel though - two 16 ohm speakers in parallel = 8 ohms combined.

Ha! The amp was pressed against the wall. Dog was on the couch.

I believe they are wired in parallel so 2 X 16 Ohm Speaker = 8 Ohm Load.

But I had the output cable at 4 ohms.

Should I normally be plugging it in to 8 Ohms or 16 then?

In reply to crankwalk:

If they're both 16 ohm speakers, and they're wired in parallel, then yes the 8 ohm jack would be correct. Though using the 16 ohm jack wouldn't hurt anything, it would just reduce the output volume.

Pete Gossett wrote: In reply to crankwalk: If they're both 16 ohm speakers, and they're wired in parallel, then yes the 8 ohm jack would be correct. Though using the 16 ohm jack wouldn't hurt anything, it would just reduce the output volume.

That's what I was thinking. Thanks Pete!