Transformer VS Speaker Impedance Solved and Explained!

[spookstrickland]

I found this great video that finally explains mathematically whether or not your can run too high or too low of impedance on a tube amp.  Check it out at about the 6 minute mark.

[RAGER]

The real pertinent information for most people is at 11:00 min mark.

[RacerX]

Why make it seem so complicated?

The impedance load of the combination of all connected speaker cabinets can be equal to or higher (BUT NOT LOWER) than the minimum impedance load recommended for the tube amplifier in question.

That means it is NEVER advisable to run too low of a load on a tube amplifier.

[Jake]

Yeah, but it's really not demonstrated in a way that is "so complicated." That gentleman kindly explains the WHY of that (obvious) conclusion, which you have also been able to grasp.

Good link. Applauded.

[RacerX]

"Because you'll blow your tranny" was always plenty for me.

[RAGER]

For those that don't care about how or why tune it at the 11:00 min mark.  Those that do want to know how and or why tune in at the 6:00 min mark.

[Jake]

That's pretty neat for you. But then you really have nothing to add to a thread that has explained it's title -- implying a more in depth look into the process. Maybe just move on instead?

[RacerX]

I already have, but I found it impossible to pass up the opportunity to make a "blow your tranny" pun.

[Ayek]

Very interesting.  It's just a shame that the guy in the video is WRONG. What the guy is saying would be right if he was talking about general electrical principals, but it can't be applied in the same way to tubes. I can't explain it as well as them in the know about tubes, but it's been explained on here before. I think Dunwich Nick was the last one to lay down the science. The output current of tubes is self limiting so won't produce an excess current by a too low impedance speaker. It's a higher risk to connect a too high impedance speaker due to the potential flyback voltage which can definitely damage the output transformer.
Long story short, anyone can put a video youtube. Ain't gonna make them right

[Mr. Foxen]

yeah, someone covers it in comments. Basically, looks at the output jacks of an amp, see that they short with nothing plugged in. Short is lowest impedance possible, and that is to protect the amp from being run with nothing plugged in. If there is a lead in and nothing on the other end, that is where the amp death happens. The main clue this is wrong is how he constantly talks about impedance as if it were a single figure.

But yeah, I have a fair stock of spare iron and a guy that does rewinds, so go ahead with the believing this stuff over actually looking at your equipment.

[dunwichamps]

Yea the problem with running an impedance greater than the tap impedance is that it results in flyback voltage on the primary side of the transformer. Now a 2:1 mismatch is usually not a big deal but you can see that as you go larger you cause more and more issues. An infinite impedance on the secondary side is the real problem and it results in an arc in the OT if sufficient power is attempting to be passed from the primary to the secondary. A short in the secondary is a better scenario since it will not result in arcing on the primary side hence why old Fenders had shorting jacks on their outputs.

[Mr. Foxen]

Sort of concerning that the comments are lapping up the wrong info.

[Ayek]

Problem is it's conveyed convincingly and has little drawings and stuff

[RacerX]

This begs the question:

Is it safe for me to continue using the rule of thumb of never running less of a total speaker load than the minimum impedance load recommended for the tube amplifier in question, in complete & total (not to mention willful) ignorance as to the details?

[jibberish]

rule of thumb:

tube amp, never open circuit
solid state amp, never short circuit

eased rule of thumb:

tube amp: if you are going to vary impedance, go low, not hi to play it safe
ss amp: if you are going to vary impedance, go hi not low to play it safe

[RAGER]

Or how about this rule of thumb.

Match you impedance or suffer tone, efficiency , and damage to your gear. One will suffer.

To each your own. I know what works for me.

Next argument. Do I run my amps at 16 ohms or 4 ohms

[jibberish]

well bad tone is different than melting down your outputs.
let's not digress too much here cap'n obvious.


you cannot hurt shit by running SS into hi impedance. nada.  you nailed it tho: max power transfer is not achieved. in other words the current drive ability is strangled out and the power output drops, and that mismatch strangles the tone.

rule of thumb is for like ok. I have a 6 ohm speaker cab and I have a 4 or 8 ohm tap. which do I choose.  there is a very clear choice here. you would use the 8ohm tap.
so don't make fun of rules of thumb for when shit happens at any time. the simple : SS no short/tube no open will save risking catastrophic fuck-ups, and you don't have to think. just do.

also, to answer your facetious question about 4 or 16 ohms.   from a matter of xformer winding efficiency, considering they are impedance matching from usually much higher impedance on the tube out, and you are already short on turns on the output side, I would go 16ohms and get more turns and a better turns ratio from primary to secondary.
[/smarty-pants answer]

[Lumpy]

A correct match isn't hard to do. Just assemble the right equipment. Newbs are usually oblivious, until after they've made purchases.