Any chance of hurting my old Dano DM 25 running it into my 1x15 Weber CA15 cab? It sure sounds good. The old Jensen in the Dano is very bright and I don't want to blow it. Danos, like the Silvertone below, have a wonderful tremolo, and I can run the amp full out without worrying about blowing the 15.
8ohm amp into 4ohm cab?
- Thread starter Brick
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Daddy Elmis
Tele-Holic
an amp rated at 8 ohm load running into a 4 ohm cabinet is in danger of frying. It will certainly tax the tubes, trannies, caps, etc., and you'll find out if there are any weak links.
I'd recommend against it if you like the amp and want to avoid a rebuild.
I'd recommend against it if you like the amp and want to avoid a rebuild.
sticko
Tele-Meister
image removed
the guy who invented fire
Tele-Holic
Brick,
Some people will disagree with me on this but belive me when I tell you thats it's ok...A tube amp can handle up to a 100% impedence mismatch as long as the impedence does not go below 2 ohms (2 ohms is almost a "dead short" and going below that would not be good). in fact going down(from 16 to 8, from 8 to 4 or from 4 to 2) will drive the power section a little harder giving a tone that some people really like. There are many people that have done and do this all the time...Alvin Lee (Ten Years After) always does this...He mismatches the impedence on his Marshall heads down 100% (Just as you have done) to get a little extra drive. EVH has done this, Jimi, did it, Jeff has done it, Jimmy does it. A Fender 3x10 Bandmaster comes from the factory mismatched...it has a 4 ohm output transformer, and the impedence from 3 10's is 2.66 ohms, look at that...it's almost 100% mismatch, and I belive if you ask around, a 3x10 Bandmaster has got a "Grind" that NO other tweed Fender has. That said going up in mismatch (from 2 to 4, from 4 to 8 or from 8 to 16) will not hurt the amp, but it will be missing something...it will lack punch. I say it again...IT WILL NOT HURT THE AMP, AS LONG AS YOU DO NOT GO MORE THAT 100% IN EITHER DIRECTION!!! The exceptions to this rule are any and all amps as that runs EL-84 power tubes...it would take a while to explain it but in short, EL-84 run wide open ALL THE TIME and an impedence would cause bad things to happen.
The guy who invented fire
Some people will disagree with me on this but belive me when I tell you thats it's ok...A tube amp can handle up to a 100% impedence mismatch as long as the impedence does not go below 2 ohms (2 ohms is almost a "dead short" and going below that would not be good). in fact going down(from 16 to 8, from 8 to 4 or from 4 to 2) will drive the power section a little harder giving a tone that some people really like. There are many people that have done and do this all the time...Alvin Lee (Ten Years After) always does this...He mismatches the impedence on his Marshall heads down 100% (Just as you have done) to get a little extra drive. EVH has done this, Jimi, did it, Jeff has done it, Jimmy does it. A Fender 3x10 Bandmaster comes from the factory mismatched...it has a 4 ohm output transformer, and the impedence from 3 10's is 2.66 ohms, look at that...it's almost 100% mismatch, and I belive if you ask around, a 3x10 Bandmaster has got a "Grind" that NO other tweed Fender has. That said going up in mismatch (from 2 to 4, from 4 to 8 or from 8 to 16) will not hurt the amp, but it will be missing something...it will lack punch. I say it again...IT WILL NOT HURT THE AMP, AS LONG AS YOU DO NOT GO MORE THAT 100% IN EITHER DIRECTION!!! The exceptions to this rule are any and all amps as that runs EL-84 power tubes...it would take a while to explain it but in short, EL-84 run wide open ALL THE TIME and an impedence would cause bad things to happen.
The guy who invented fire
jjmantele
Tele-Holic
Ohms
Fender BF and SF combo amps (at least) have the "ext" speaker output in the back which, when used, is wired parallel to the existing speaker. That means you will have 4 ohms when you add an 8ohm extension cab to an existing 8 ohm speaker (for example.) This is the factory setup so it is not too bad nor unsafe. If you have no speakers plugged in, in error, the jack shorts which is 0 ohms since this is safer than infinity ohms. So going "down" in ohms is thought to be generally "safer" than going up. SS amps are the opposite. That's why you see "minimum" ohms figures on the backs of SS amps like PA's and home stereos. On a tube amp, when you go up, you create risk of blowing the output tranny. I don't know if 100% "up" is always safe but Fender felt that going 100% "down" was safe, at least in the BF/SF days.
Marshalls have impedance switches on the back. I have read that Marshalls "don't like" impedance mis-matches but I'm no authority.
Going "down" makes the tubes wear faster.
Fender BF and SF combo amps (at least) have the "ext" speaker output in the back which, when used, is wired parallel to the existing speaker. That means you will have 4 ohms when you add an 8ohm extension cab to an existing 8 ohm speaker (for example.) This is the factory setup so it is not too bad nor unsafe. If you have no speakers plugged in, in error, the jack shorts which is 0 ohms since this is safer than infinity ohms. So going "down" in ohms is thought to be generally "safer" than going up. SS amps are the opposite. That's why you see "minimum" ohms figures on the backs of SS amps like PA's and home stereos. On a tube amp, when you go up, you create risk of blowing the output tranny. I don't know if 100% "up" is always safe but Fender felt that going 100% "down" was safe, at least in the BF/SF days.
Marshalls have impedance switches on the back. I have read that Marshalls "don't like" impedance mis-matches but I'm no authority.
Going "down" makes the tubes wear faster.
Russinator
Tele-Holic
- Joined
- Mar 2, 2003
- Posts
- 504
Hmmmm...
this is somewhat akin to choosing to be shot between a .22 or a 9mm.
this is somewhat akin to choosing to be shot between a .22 or a 9mm.
guywhoinventedfire worte: "The exceptions to this rule are any and all amps as that runs EL-84 power tubes...it would take a while to explain it but in short, EL-84 run wide open ALL THE TIME and an impedence would cause bad things to happen."
El84's do not 'run wide open all the time'. If the amp is designed and set up to run in Class A operation, then the tubebs...whatever power tube...will be 'on' full time. However, most amps we play on, and that includes the majority of the purported 'Class A--EL84 amps', are running in Class AB and therefore the tubes are on for half a cycle and off for the other half.
As for impedance mismatches, vintage Fenders are designed to tolerate no more than 100% mismatch either way. The external speaker jacks and the set OPT impedance demands that these amps tolerate this. The exceptions to the rule are the Champs and the Super REverb. Impedance mismatches will affect the sound. An 8 ohm dpeaker impedance on a 4 ohm Fender amp will yield a darker sound.
To my understanding, Marshalls do not tolerate mismatches well. When running 2 16 ohm cabs, for instance, one would want to set the impedance at the amp for 8 ohms. People who play these amps know this, and any mismatch would knowingly be risky. Granted, the sound would be different, but the amp is put at risk.
El84's do not 'run wide open all the time'. If the amp is designed and set up to run in Class A operation, then the tubebs...whatever power tube...will be 'on' full time. However, most amps we play on, and that includes the majority of the purported 'Class A--EL84 amps', are running in Class AB and therefore the tubes are on for half a cycle and off for the other half.
As for impedance mismatches, vintage Fenders are designed to tolerate no more than 100% mismatch either way. The external speaker jacks and the set OPT impedance demands that these amps tolerate this. The exceptions to the rule are the Champs and the Super REverb. Impedance mismatches will affect the sound. An 8 ohm dpeaker impedance on a 4 ohm Fender amp will yield a darker sound.
To my understanding, Marshalls do not tolerate mismatches well. When running 2 16 ohm cabs, for instance, one would want to set the impedance at the amp for 8 ohms. People who play these amps know this, and any mismatch would knowingly be risky. Granted, the sound would be different, but the amp is put at risk.
Daddy Elmis
Tele-Holic
Re: Ohms
Now this is the opposite of my understanding. I thought reducing impedence (going from 8 to 4 or 2, etc.) on an amp rated for 8 ohms runs the risk of frying the OT. Certainly most commercial amps have tolerance, but reduced impedence means the amp is running harder because it faces less resistence. Not having any speaker load, I thought, meant immediately frying your OT on power up.
I could, however, be wrong.
jjmantele said:
Now this is the opposite of my understanding. I thought reducing impedence (going from 8 to 4 or 2, etc.) on an amp rated for 8 ohms runs the risk of frying the OT. Certainly most commercial amps have tolerance, but reduced impedence means the amp is running harder because it faces less resistence. Not having any speaker load, I thought, meant immediately frying your OT on power up.
I could, however, be wrong.
Mr. Droopy-Drawers
Tele-Meister
You might be perfectly safe. You would have to know the transformers, and how hot the tubes were running at the mismatched impedance. Play the amplifier for a long time, and then feel the core of either transformer. If they are just really warm, you're fine. If they are blistering hot, you got troubles . If you feel inclined (and have the capacity), measure some voltages and currents, and compare them to the tube manual recommendations. Chances are you're OK, but there is that one-in-a-million chance.
. If you feel inclined (and have the capacity), measure some voltages and currents, and compare them to the tube manual recommendations. Chances are you're OK, but there is that one-in-a-million chance. jjmantele
Tele-Holic
Re: Ohms
The tubes end up seeing less resistance (impedance since it's AC.) The transformer doesn’t care too much that the speaker ohms are less so long as the wattage is not excessive. With the speaker ohms too high, the tranny can't send enough of the input from the tubes to the output and "eddy" (sp?) currents result since the "excessive" input has no place to go. I think it's these currents that blow the tranny.
With SS amps, "low" ohms causes the power transistors to blow from what I heard.
Powering up (with the volume down) should never cause an OPT to blow from an ohms mis-match. With no volume, the speaker's ohms is not part of the equation.
Daddy Elmis said:
The tubes end up seeing less resistance (impedance since it's AC.) The transformer doesn’t care too much that the speaker ohms are less so long as the wattage is not excessive. With the speaker ohms too high, the tranny can't send enough of the input from the tubes to the output and "eddy" (sp?) currents result since the "excessive" input has no place to go. I think it's these currents that blow the tranny.
With SS amps, "low" ohms causes the power transistors to blow from what I heard.
Powering up (with the volume down) should never cause an OPT to blow from an ohms mis-match. With no volume, the speaker's ohms is not part of the equation.
Fender tube amps can handle such a mismatch without problem. You lose a bit of power (yes, even though you're running into a lower impedance speaker), but won't hurt the amp.
The Dano could likely handle it as well. Most of the budget tube amps were made with "loose" tolerances. When these amps were relatively new...Danos, Silvertones, Magnatones, Teiscos etc...we didn't worry too much about what speakers we plugged into them. We just plugged-and-played. Never blew any of them up as a result.
As said before, Marshalls are the best known amps that don't like impedance mismatches.
Don't worry about it. If it sounds good enjoy it - you're likely within a safe tolerance.
The Dano could likely handle it as well. Most of the budget tube amps were made with "loose" tolerances. When these amps were relatively new...Danos, Silvertones, Magnatones, Teiscos etc...we didn't worry too much about what speakers we plugged into them. We just plugged-and-played. Never blew any of them up as a result.
As said before, Marshalls are the best known amps that don't like impedance mismatches.
Don't worry about it. If it sounds good enjoy it - you're likely within a safe tolerance.
Ted Weber has a section in his Q&A concerning mismatches and it goes along with what I have been told by an amp tech in the past.
here is a sinp of his rather lengthy and detailed explaination:
"When you use a load that is lower than the intended load, the output has to drive the load (speaker) with more current because it is a lower impedance than is expected. Two inherent problems associated with transformers are flux leakage and regulation. Flux leakage is also referred to as leakage inductance. It is related to the current in the secondary, and these problems increase as the current increases. As the current draw in the secondary increases, the primary has a more difficult time transferring the signal to the secondary, so the secondary signal to the load gets squashed, or 'soft-clipped'. This soft clipping is called regulation. While regulation is desireable in a power supply, it is undesireable in a transformer"
It is about 3/4 of the way down the page below the second to last diagram.
(link removed)
here is a sinp of his rather lengthy and detailed explaination:
"When you use a load that is lower than the intended load, the output has to drive the load (speaker) with more current because it is a lower impedance than is expected. Two inherent problems associated with transformers are flux leakage and regulation. Flux leakage is also referred to as leakage inductance. It is related to the current in the secondary, and these problems increase as the current increases. As the current draw in the secondary increases, the primary has a more difficult time transferring the signal to the secondary, so the secondary signal to the load gets squashed, or 'soft-clipped'. This soft clipping is called regulation. While regulation is desireable in a power supply, it is undesireable in a transformer"
It is about 3/4 of the way down the page below the second to last diagram.
(link removed)
