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Old 09-19-2012, 08:41 PM   #1
DrewMeyer
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Mismatched Ohms?

Okay, here's the deal. I want to use my bandmaster head for gigs but don't want to haul around my 2x12 cab and am planning on using a 1x12 instead. So I have the Fender Bandmaster rated at 45 watts with a 4 ohm out. I have a 1x12 cabinet rated at 16 ohms. Would it damage the cabinet to run the 4 ohm out into the 16ohm speaker? I don't know much about ohms and stuff so thanks!
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Old 09-19-2012, 08:45 PM   #2
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I'll let ragingkitty or gumbilicious or cathbard handle this but my gut reaction is....



you'll be fine WITH THAT AMP but it will stress the output transformer of your amp and ultimately your tubes.

play at your own risk and don't come back to us if something breaks.

I always say Match.




Edit: Don't do this at home kids
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Old 09-19-2012, 08:50 PM   #3
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Quote:
Originally Posted by 311ZOSOVHJH
I'll let ragingkitty or gumbilicious or cathbard handle this but my gut reaction is....



you'll be fine but it will stress the output transformer of your amp and ultimately your tubes.

play at your own risk and don't come back to us if something breaks.

I always say Match.

Darn 4 ohm output. Is it possible to find a 4 ohm 12" speaker?
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Old 09-19-2012, 08:55 PM   #4
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I guess the next question is ....


how good are the cabs and speakers you have now?

how attached are you to them?

if this is part of a longer term solution then that makes a difference.

why not just sell what you have and get what you need - in other words.







-----------------------------
Here is the official maths approved by UG amp overloards

For Tube amps:
Amp Head Ohms > Cab Ohms = Possible blown Power Valves and/or Output Transformer.
Amp Head Ohms < Cab Ohms = Strain on the Output Transformer, Power loss.
*Some amps can take a 1 step mismatch but not all.

For Solid State Amps:
Amp Head Ohms > Cab Ohms = Broken amp
Amp Head Ohms < Cab Ohms = Power change, no strain
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Old 09-19-2012, 08:59 PM   #5
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fishy.....both a 1x12 in 16 ohm and an amp with only 1, 4 ohm output is very strange. did you modify anything?

generally the standard given only 1 option is 8. even 1 4 ohm speaker is unusual.

from my understanding, it is better to have a lower ohms number out of the amp going into the cab and the reverse.

BUT, always match. im just saying i think its harder on the amp if your amp ohms were 16 going into 4 ohms rather than the other way. i may be wrong on this.

________

yes it puts unneeded stress on the output transformer and tubes etc. will your amp explode? no. can something bad potentially happen and this being the cause? yes.

just the other day when i was transporting my amp the ohms switch on the back went to 4. was running it inot my 8 ohm cab for a week in my bedroom!!!!!!

i was freaked when i saw that. no damage, no tonal change. i really couldnt tell at all. sure it wasnt ideal though.
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Old 09-19-2012, 09:03 PM   #6
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Normally you can safe mismatch 1 rating higher.

So if you have the head set on 4 you could run a 4 ohm cab or an 8 ohm cab.

Going to 16 ohm... Not sure on that.
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Old 09-19-2012, 09:05 PM   #7
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yeah im sure its common sense to say the further away you get the more the negative effect.
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Old 09-19-2012, 09:08 PM   #8
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Right.


I guess I was thinking of something like this:

https://taweber.powweb.com/store/zmatch.htm


Or this:

http://www.tonebone.com/tb-cabbone.htm


Or this (new cab):
http://www.ultimate-guitar.com/foru...d.php?t=1387138


(can't speak to why you only have a 4 ohm tap now) - maybe a mod to the OT wiring would fix that even easier
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Old 09-19-2012, 09:24 PM   #9
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Can't go higher. Would need an OT.
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Old 09-19-2012, 09:45 PM   #10
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Quote:
Originally Posted by ikey_
fishy.....both a 1x12 in 16 ohm and an amp with only 1, 4 ohm output is very strange. did you modify anything?

generally the standard given only 1 option is 8. even 1 4 ohm speaker is unusual.


Nothing strange. 4 ohm outputs were pretty common back in those days. And there are plenty of 12" speakers that come in 16ohm.


TS - A 2 to 1 mismatch is usually okay, but even then there can be issues.

Connecting a 16ohm speaker to a 4ohm tap can be a bit risky though.
Your amp is expecting to see an impedance of 4ohms. When you stick a 16ohm impedance in there, the total output power is reduced, the tone can change a bit, and there will be a greater strain on the output section of the amp.
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Old 09-19-2012, 10:08 PM   #11
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Quote:
Originally Posted by DrewMeyer
Would it damage the cabinet to run the 4 ohm out into the 16ohm speaker? I don't know much about ohms and stuff so thanks!


Damage the cabinet? Probably not.

Damage the output transfoemer of your head? Probably yes.

2:1 mismatch is marginal, depending on the construction quality of your OT. A good construction OT at 2:1 will stress a little but be ok.

4:1 is asking for trouble, even with a good quality OT. The chance of flashover between windings is not to be ignored even if you think its working well for a while.
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Old 09-19-2012, 10:36 PM   #12
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On a real Bandmaster it will be fine. From silverfaces on it is pushing the friendship a little more than a blackface but old Fenders will cope with a mismatch in that direction fine, it just won't be quite as loud. The old blackfaces didn't really give a shit what was plugged into them, they'll even soak up a 2 ohm load if they have to.
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Old 09-19-2012, 10:47 PM   #13
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^i would be a bit worried about the amount of 'flyback' voltage with such a mismatch. wouldn't this cause arcing across the pins of the output tubes?

would a schematic show diodes hooked up between the output tubes and ground to help stop this?

Quote:
Originally Posted by ikey_
fishy.....both a 1x12 in 16 ohm and an amp with only 1, 4 ohm output is very strange. did you modify anything?


old fenders are just like that, not unusual for them to have a single 4 ohm out, with no impedance switch to change impedance nonetheless. so if you got an extra extension cab... you just ran it mismatched.

yup, that is the way it wuz back then... didn't have school buses,
had to walk buck naked in the snow uphill both ways...

Quote:
Originally Posted by TS
Okay, here's the deal. I want to use my bandmaster head for gigs but don't want to haul around my 2x12 cab and am planning on using a 1x12 instead. So I have the Fender Bandmaster rated at 45 watts with a 4 ohm out. I have a 1x12 cabinet rated at 16 ohms. Would it damage the cabinet to run the 4 ohm out into the 16ohm speaker? I don't know much about ohms and stuff so thanks!


the only way to tell how it will handle a mismatch is to get someone more knowledgeable than me to see how much the over-engineered the design. it seems like fender made pretty robust amps back then cuz any extra extension cab would automatically cause a mismatch.

that being said, i wouldn't wanna mismatch it that bad.

i'd say either get a 2x12 with two 8 ohm speakers wired in parallel (which you don't wanna do cuz it's too big), or replace the speaker with a 4 ohm speaker (which is kinda hard to find, but they are out there) or get one of the impedance matchers that 311 showed.

or just take your chances, i'd hate to do that with a vintage amp though. you'll be hard pressed to find a trannie like the original
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Last edited by gumbilicious : 09-19-2012 at 10:54 PM.
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Old 09-19-2012, 11:12 PM   #14
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Nah, not really. They'll run find with quite a big mismatch. It aint a Bugera.
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Old 09-19-2012, 11:31 PM   #15
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Still its best to match if possible, or at least be close.

On a Bandmaster with a 16ohm speaker the power tubes will be seeing a 16,000 ohm load instead of the intended 4,000 ohm. Which could affect the high end tone, and will probably result in a slightly lowered output.

I never recommend more than a 2:1 mismatch, even though the old fenders were built like tanks, and could probably handle it, its still not good for them.......

Best option is to just match the impedance if possible. That way everything is working as intended. Tubes are happy, transformers are happy, and you'll be happy.......

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Old 09-19-2012, 11:36 PM   #16
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No argument that it's better to match it all up for a few reasons. It'll cope but it will sound better matched.
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Old 09-20-2012, 08:44 PM   #17
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So then it's fine? By the way, I already have a 2x12 cab rated at 4 ohms that I use at home, but I needed something to use at small gigs when I don't feel like hauling around my giant cab, at least until I can afford a used Vox AC15. I wouldn't be using the amp through the 16 ohm speaker more than 4 hours a week, at most.
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Old 09-20-2012, 09:49 PM   #18
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I think the answer is still the same.

Your amp may handle that mismatch but I don't think it is fair to try to get us to say it is fine. If the OT blows on your first gig you are looking at $100 - $300 worth of repairs.

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Old 09-20-2012, 10:09 PM   #19
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Quote:
Originally Posted by 311ZOSOVHJH
I think the answer is still the same.

Your amp may handle that mismatch but I don't think it is fair to try to get us to say it is fine. If the OT blows on your first gig you are looking at $100 - $300 worth of repairs.


Hm well thats not what I want to have. I'll stick with not using the 16 ohm cab then.
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Old 09-20-2012, 10:27 PM   #20
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What about my questions in post #4 and my suggestions in post #8?
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