#1
Well I've been running this same setup for a while ignorantly and just want to see if I'm taking a major risk here. When my Vox VT100 broke a while ago I gutted it and wired its 2x12", 16ohm speakers in series without realizing that it created a 32 ohm cab. I've been running my Bugera V55 at 16ohms into this setup for quite a while now with no negative effects that I can find. Am I running any serious risks here?

Thanks in advance.
SLAP energy drinks ftw.
#2
Wut? You mean it didn't explode and kill your dog? You sure it's not a Vox in disguise?

But srsly, if nothing's happened, you just wore down your tubes a bit more than usual.
Gear:
- Bugera 333
- VJ & VJ cab
- Jackson JS30
- TS9

Bugera Users Militia. We are horrible people. With a sprinkler fetish.
~ BUM: For all things extinguishing

Rackmount Tube Amp Project <<< Updates!
#3
Quote by Kanthras
Wut? You mean it didn't explode and kill your dog? You sure it's not a Vox in disguise?

But srsly, if nothing's happened, you just wore down your tubes a bit more than usual.


Thanks for the response. Everything I seem to be finding implies that running a lower head ohm into a higher cab rating is ok. My case for instance, or a 4ohm head into an 8ohm cab, etc etc. The main risk would be running an 8ohm head into a 4ohm cab, right? Is there anything wrong with continuing to run it this way since I really like the sound?
SLAP energy drinks ftw.
#4
Quote by ianae86
Thanks for the response. Everything I seem to be finding implies that running a lower head ohm into a higher cab rating is ok. My case for instance, or a 4ohm head into an 8ohm cab, etc etc. The main risk would be running an 8ohm head into a 4ohm cab, right? Is there anything wrong with continuing to run it this way since I really like the sound?
Actually, I'm pretty sure it's the other way around for tube amps. Running a lower impedance on the cab is a lot less risky than a higher impedance.

Anyway, I really wouldn't keep doing that since it's simply not good for the amp and the sound shouldn't be much different from a matched impedance.
Gear:
- Bugera 333
- VJ & VJ cab
- Jackson JS30
- TS9

Bugera Users Militia. We are horrible people. With a sprinkler fetish.
~ BUM: For all things extinguishing

Rackmount Tube Amp Project <<< Updates!
#5
Quote by Kanthras
Actually, I'm pretty sure it's the other way around for tube amps. Running a lower impedance on the cab is a lot less risky than a higher impedance.

Anyway, I really wouldn't keep doing that since it's simply not good for the amp and the sound shouldn't be much different from a matched impedance.


Hmm, that kinda sucks but I guess I'd rather take the time to rewire it then risk damage to a very expensive part. Just to make sure, any other input on the matter?
SLAP energy drinks ftw.
#6
You sure it didn't catch fire?
Gear:
- Bugera 333
- VJ & VJ cab
- Jackson JS30
- TS9

Bugera Users Militia. We are horrible people. With a sprinkler fetish.
~ BUM: For all things extinguishing

Rackmount Tube Amp Project <<< Updates!
#7
You should re-wire it.

With tube amps when you mismatch impedance, either direction, the output transformer becomes less efficient and you get weird parasitic magnetic effects that generate heat. In some cases, this isn't a problem other than costing you volume and changing the frequency response of the amp. But in other cases the excess heat will cause the output transformer to blow. Old Marshalls were notorious for blowing transformers if you mismatched the cabinets.

So better safe than sorry.
GMW hot-rod telecaster
GMW soloist
PRS Custom 24
The Illegal Les Paul
CAE 3+SE
Soldano SM-100R
Splawn 4x12

“Life is on the wire…the rest is just waiting” - Papa Wallenda
Substitute the stage for the wire, and he's got it.
#8
Leave it the way it is. Then report back later. We need to experiment on somebody's equipment. And better yours than mine.

Or play it safe and rewire.
#9
Quote by fly135
Leave it the way it is. Then report back later. We need to experiment on somebody's equipment. And better yours than mine.

Or play it safe and rewire.
Gear:
- Bugera 333
- VJ & VJ cab
- Jackson JS30
- TS9

Bugera Users Militia. We are horrible people. With a sprinkler fetish.
~ BUM: For all things extinguishing

Rackmount Tube Amp Project <<< Updates!
#10
Quote by Kanthras
Actually, I'm pretty sure it's the other way around for tube amps. Running a lower impedance on the cab is a lot less risky than a higher impedance.

Anyway, I really wouldn't keep doing that since it's simply not good for the amp and the sound shouldn't be much different from a matched impedance.


This is correct. Higher impedances are more harmful than lower impedances, as they can cause inductive spikes in your transformer that can punch through and harm the windings. OT transformer replacement by a qualified tech will run you probably close to $500, part cost included.

Lower impedances simply cause the tubes to basically refuse to pass a given level of current. Of course its not smart to run a low-or-no load situation for an extended period of time, but it's not the tube amp death-sentence as some people claim.
Tastes like chicken, if chicken was a candy.
Last edited by ConfederateAxe at Sep 30, 2010,
#11
Quote by fly135
Leave it the way it is. Then report back later. We need to experiment on somebody's equipment. And better yours than mine.

Or play it safe and rewire.


Lol! I can vouch that in 4 months of use, I've not had a single issue. Don't have any more speaker wire at the moment so I think I'm going to just hook it up to one of the 85 watt, 16ohm speakers for now. I'll let you know if I can tell I was losing volume with the mismatched ohms.
SLAP energy drinks ftw.
#12
Well there isn't a real noticeable difference tone wise. I'm sure I'll break down and wire them up in parallel at 8ohms pretty soon here but the 1x12 setup doesn't sound drastically thinner. Thanks for the info guys. If nothing else I feel good knowing I won't destroy anything now, haha.
SLAP energy drinks ftw.
#13
One more bit of feedback. Got both speakers wired up in parallel @ 8ohms and its noticeably louder. Definitely an improvement. Thanks again to everyone for stopping me from prolonging my stupidity! haha
SLAP energy drinks ftw.
#14
Quote by fly135
Leave it the way it is. Then report back later. We need to experiment on somebody's equipment. And better yours than mine.

Or play it safe and rewire.

! !


But yeah, like said, the opposite scenario would not be good. Potentially deadly on an SS amp. I've got some amp+fire experience under ma belt.
#15
Quote by 311ZOSOVHJH
! !


But yeah, like said, the opposite scenario would not be good. Potentially deadly on an SS amp. I've got some amp+fire experience under ma belt.


There is so much mixed info on this matter its really hard to tell. Like I said, I can vouch that I ran it like this for 4 months or so without a hiccup. Maybe I got lucky, maybe its not as bad as some people think. There are reports of guys running a similar setup for years. But then you also have people reporting that it'll destroy your OT rapidly. Either way, its a good peace of mind to have everything matched now.
SLAP energy drinks ftw.
#16
Quote by ConfederateAxe
This is correct. Higher impedances are more harmful than lower impedances, as they can cause inductive spikes in your transformer that can punch through and harm the windings. OT transformer replacement by a qualified tech will run you probably close to $500, part cost included.

Lower impedances simply cause the tubes to basically refuse to pass a given level of current. Of course its not smart to run a low-or-no load situation for an extended period of time, but it's not the tube amp death-sentence as some people claim.


This is where I get confused. When you say "lower impedance/higher impedance" are you talking numerically. For instance, 4ohms is a lower impedance then 8ohms or is it one of those screwy systems where 8ohms is actually a lower impedance then 4ohms?
SLAP energy drinks ftw.
#17
Quote by ConfederateAxe
This is correct. Higher impedances are more harmful than lower impedances, as they can cause inductive spikes in your transformer that can punch through and harm the windings. OT transformer replacement by a qualified tech will run you probably close to $500, part cost included.


lolwut. I got my OT swapped by a guy for $3000 Jamaican which is about $40 US, and the transformer itself (Weber) was about $80 after shipping and customs. $500 for an OT and swap is highway robbery unless you're getting a DeYoung or something high end like that.
Quote by DeathByDestroyr
What the hell is a G&L.



Quote by Flux'D
Gay & Lesbian I think, the box smelled funny
Greg what did you send me??
#18
Quote by Raijouta
lolwut. I got my OT swapped by a guy for $3000 Jamaican which is about $40 US, and the transformer itself (Weber) was about $80 after shipping and customs. $500 for an OT and swap is highway robbery unless you're getting a DeYoung or something high end like that.


That's more along the lines of what I was thinking. I couldn't imagine one part of an amp costing nearly twice as much as my amp itself, haha.
SLAP energy drinks ftw.
#19
Quote by 311ZOSOVHJH
! !


But yeah, like said, the opposite scenario would not be good. Potentially deadly on an SS amp. I've got some amp+fire experience under ma belt.
Yeah, running lower impedance than rated on an SS amp = fried transistors before you can say fuuuuuuu.
Gear:
- Bugera 333
- VJ & VJ cab
- Jackson JS30
- TS9

Bugera Users Militia. We are horrible people. With a sprinkler fetish.
~ BUM: For all things extinguishing

Rackmount Tube Amp Project <<< Updates!
#20
Quote by Raijouta
lolwut. I got my OT swapped by a guy for $3000 Jamaican which is about $40 US, and the transformer itself (Weber) was about $80 after shipping and customs. $500 for an OT and swap is highway robbery unless you're getting a DeYoung or something high end like that.


What wattage is your amp? A 15W transformer is not as expensive as a 100 Watt.

I agree $500 is rediculously expensive, but unfortunately that's what kind of cheese guys over here in California like to charge for tech work, so I tend to forget that other places do it much cheaper. It's common to see $90 and $120 an hour bench fees. That figure was also taking into account a higher end transformer, which, if you're gonna replace an OT, I'd say upgrade while you're at it. I'm not saying it would cost right at $500, but $350 is a solid estimate of total cost of a $170 transformer plus the labor to install it. At least out here...
Tastes like chicken, if chicken was a candy.
Last edited by ConfederateAxe at Oct 1, 2010,
#21
Rewire, fo sho. You may notice an increase in output.

I think what needs to be said here is...

from amp to cab...
1:2 is safe to run, but because it's a mismatch, it still stresses the amp out more than it should.
2:1 is unsafe, definitely will damage something with extended use.

any bigger mismatch ratios are sure to be dangerous as well.
#22
Quote by ianae86
This is where I get confused. When you say "lower impedance/higher impedance" are you talking numerically. For instance, 4ohms is a lower impedance then 8ohms or is it one of those screwy systems where 8ohms is actually a lower impedance then 4ohms?
You got it right. 4 ohms is a lower impedance than 8 ohms. On a SS amp a higher impedance is almost always ok. But the theory on tubes amps is different. A match is recommended, but presumably going lower is better than going higher on a mismatch.