Let’s argue about impedance mismatch

  • Thread starter Thread starter Bad Brain
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Bad Brain

Bad Brain

Well-known member
I’ve read so many differing opinions on this. Can anyone set the record straight? I ran my 2203 circuit at 8ohms out into a 16ohm attenuater for around an hour before I realized it. Master vol was about 2.5. Think I’ve damaged anything? Maybe I smelt something a little funny…I’ve heard high mismatch is the death knell for Marshalls ? Everything seems okay though, sounds good, etc. Is this so called flyback voltage bad stuff or what?!
 
Never with Marshalls

Sometimes with boogies

I hear very little sound difference in the room but can hear a bit close miced
 
This is what I follow take it for what you will.

Amp set to 4ohm and your good for 4 and 8 ohm cabs. 8 ohm amp and your good for 8 and 16ohm cabs. 16ohm amp goes to 16ohm cab. Ideally you’d have them match. Personally I’d worry more about the original screen grids, bias filter caps, and questionable power tubes than I would a mismatch going up if that makes sense. No load or a load under what the amps impedance switch is set to is where things go bad typically.
 
Chubbs said:
This is what I follow take it for what you will.

Amp set to 4ohm and your good for 4 and 8 ohm cabs. 8 ohm amp and your good for 8 and 16ohm cabs. 16ohm amp goes to 16ohm cab. Ideally you’d have them match. Personally I’d worry more about the original screen grids, bias filter caps, and questionable power tubes than I would a mismatch going up if that makes sense. No load or a load under what the amps impedance switch is set to is where things go bad typically.
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That’s what I always thought. But I read this. Sounds like one step is not too much a concern though. But another place said Marshalls are sensitive. ?

“The bottom line is the greater the low impedance mismatch, the harder your amp works, and the greater the high impedance mismatch, the more likely you are to burn out your output transformer and/or power tubes. For tube amps a low mismatch is safer than a high mismatch, that's why most speaker jacks have a shorting switch--a short is better than an open circuit. The opposite is generally true for solid state amps--a short will burn out their output transistors. ”

https://robrobinette.com/How_Amps_Work.htm
 
I'm watching this thread !! I try to match the impedance but don't get ulcers over it although I know the cabinets do sound different .
Here' s food for thought ---How many guy s have amp switchers where you are changing or running multiple cabinets? I'll guarantee the impedances are all over the place on most of them .
 
You can even run 2 mismatched cabs; 4 ohm out into an 8 ohm cab, and a 16 ohm cab. Total impedance the amp sees is 5.33.
 
I have been wondering with my Captor X about running my head @ 8ohms to the 8ohm Captor, then out to a 16ohm cab. I can't find clear enough info for me to risk it.
 
A trip down memory lane . So of the best tones are mismatched cabinets, 100 plus watt heads into beat up greenback cabinets. You might even have a potentiometer between the head and cabinet. Most glorious tones on the planet— right until the rig melted down!!!! Oh yeah!!!

Brings a tear to my eye!
 
SoooRad said:
I have been wondering with my Captor X about running my head @ 8ohms to the 8ohm Captor, then out to a 16ohm cab. I can't find clear enough info for me to risk it.
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That won't damage anything from what I understand, but it decreases attenuation.
 
I ran a 4 ohm Bassman into an 8 ohm cab, and it rocked.
Pretty sure it's ok to run a cab with higher rating than what the amp is set at. The amp will be a bit quieter.
I've read from Soldano and a bunch of other folks that the other way around, unlike what was posted in that Robinette blurb up there, can mess your amp up.
"Using a lower impedance speaker than recommended by the amplifier can lead to increased current draw and overheating, potentially damaging the amplifier."

"connecting speakers with lower impedance than the amplifier was designed for will cause more current to be drawn and cause the output transistors to get hotter than normal, plus higher distortion than with the correct speakers."
 
LPMojoGL said:
I ran a 4 ohm Bassman into an 8 ohm cab, and it rocked.
Pretty sure it's ok to run a cab with higher rating than what the amp is set at. The amp will be a bit quieter.
I've read from Soldano and a bunch of other folks that the other way around, unlike what was posted in that Robinette blurb up there, can mess your amp up.
"Using a lower impedance speaker than recommended by the amplifier can lead to increased current draw and overheating, potentially damaging the amplifier."

"connecting speakers with lower impedance than the amplifier was designed for will cause more current to be drawn and cause the output transistors to get hotter than normal, plus higher distortion than with the correct speakers."
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I think he's saying the same thing "The increase in primary current will cause the output transformer to run hotter" but I'm not clear why this wouldn't also potentially damage the OT. On the high mismatch problem is "Flyback voltage"
 
I just take a Viagra and I never have any problems! You guys are crazy and dumb in my opinion??????
 
SoooRad said:
I have been wondering with my Captor X about running my head @ 8ohms to the 8ohm Captor, then out to a 16ohm cab. I can't find clear enough info for me to risk it.
Click to expand...

As long as you’re using your amp’s 8 ohm out into an 8 ohm captor, you are good to go. The cab impedance doesn’t matter much in that case
 
for a few years in the early 90’s I ran Bassman heads (4Ohms optimal) into 16 Ohm Marshall 4x12’s. Never had an issue. I definitely wouldn’t want it to be the other way around. Some tranny’s can handle a one level mismatch in either direction But I would always err on the side of the amp never being higher than the cabinet.
 
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