If I had an all tube bass head (SVT-VR, or possibly a Bassman300, both 300w @ 4ohms), could I reliably power a Basson B412 guitar cab that runs at 300w @ 8ohms? By reliably I mean without putting too much stress on the amp, or something of that nature. Any info/thoughts are welcome (keeping in mind I already have the guitar cab, and don't really have the money to buy the SVT (or Bassman) and a new bass cab for it).
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Impedence question (Very specific situation)
- Thread starter Siafu666
- Start date
You shouldn't. I've seen people use SVT's with 8 ohm cabs before and they've been OK, but according to the experts on here, it does take its toll on the amp and could cause tube and transformer failure.
yea, as long as you're going from a low to high impedance, its actually ok for tube amps, i.e. 4 ohm tap on the amp to an 8 ohm cab. its only when the cab is trying to draw more power from the head that you get in a world of trouble. still, like with like impedances is the safest bet.
besides, bass amp + guitar cab = muddy muddy mud w/ sloppy low end.
besides, bass amp + guitar cab = muddy muddy mud w/ sloppy low end.
Personally, I wouldn't with the SVT.
I'd also sell the guitar cab and save up for a bass cab. There's plenty to be had for a song right here on TB.
Even if the cab is rated to 300W, more than likely, you'll end up killing speakers in no time, unless this is only going to be used as the "highs" on a bi-amp type rig, or at lower volumes.
All of that's not even considering the possibility of damaging the OT and power tubes in the SVT, if that's what you get.
If you get the Bassman 300, it has taps for 8-, 4-, and 2- ohm loads, so as long as you can put the selector in the right place, you'll be OK there.
I'd also sell the guitar cab and save up for a bass cab. There's plenty to be had for a song right here on TB.
Even if the cab is rated to 300W, more than likely, you'll end up killing speakers in no time, unless this is only going to be used as the "highs" on a bi-amp type rig, or at lower volumes.
All of that's not even considering the possibility of damaging the OT and power tubes in the SVT, if that's what you get.
If you get the Bassman 300, it has taps for 8-, 4-, and 2- ohm loads, so as long as you can put the selector in the right place, you'll be OK there.
From what I understood having a higher impedance was worse for tube amps? (but its fine for SS).
I wouldn't risk it with my SVT anyways! Not to mention the cab wouldn't handle the lows very well.
There are plenty of good cheap bass cabs out there. Peavey are a personal favourite of mine
Mismatch in either direction can be a very bad thing. I also won't risk it on my SVT. Or any of my tube amps, for that matter.
If somehow I was forced to have a mismatched load, though, I believe it's considered safe to have the mismatch be to the lower impedence. I.e if you have 8- and 4- ohm taps on the head, you'd be better off running a 2 ohm cab than a 16 ohm one.
I think.
Probably. But I never do that myself anyway. And I never really pay attention when the gurus say about itActually no, you are certainly frying your amp then
.
Actually no, you are certainly frying your amp then
Lower impedance is certainly bad for SS amps, and they can handle higher impedances, just the power output is reduced as the impedance increases.
With amps which use output transformers a higher impedance is also damaging (from what I remember)
If an amp is rated for a 4ohm load, that is the lowed impedance it can operate at without causing failure. You will have no issues going to an 8ohm load. You will need more volume / gain, however you shouldn't have any issue.
However, never go to a lower impedance than what your amp is rated for. In this case, 2ohm. For you, 2ohm = FAIL
However, never go to a lower impedance than what your amp is rated for. In this case, 2ohm. For you, 2ohm = FAIL
I think i misunderstand your question. If you power an 8 ohm cab in you will throw the impedance off. Use ohms law (physics book stuff). Using series or parallel wiring, and if you do not exceed the rated impedance of your head, i'd say try it.
Hi.
This EXACTLY same question pops up quite frequently and personally I think that any impedance mismatch with a tube amp is a very good thing. It brings the food to the starving techs table and might feed his/her family too.
People who don't know a squat about amplifiers or how to use them, should be then encouraged to abuse the heck out of them, but at the same time adviced to sell them cheap or to give them away for free. Preferably even before they break them down with their ignorance.
Just my 0.02€
Sam
This EXACTLY same question pops up quite frequently and personally I think that any impedance mismatch with a tube amp is a very good thing. It brings the food to the starving techs table and might feed his/her family too.
People who don't know a squat about amplifiers or how to use them, should be then encouraged to abuse the heck out of them, but at the same time adviced to sell them cheap or to give them away for free. Preferably even before they break them down with their ignorance.
Just my 0.02€
Sam
Just ignore him, he's grumpy.
Don't do it. Tube amp= match impedance. SS amp= matched or higher impedance.
Don't do it. Tube amp= match impedance. SS amp= matched or higher impedance.
I think so also, Ray.
Actually no, you are certainly frying your amp then
These kinds of opinions are a recipe for disaster; someone could take them as accurate and do some serious damage to their gear. Youve got it reversed; speakers don't "draw" power, in fact they resist current flow to varying degrees which is measured in impedance.
Too low of an impedance/resistance is far less damaging than too high, although matching impedance is the best idea, and will provide the best tube amp performance (at least from an efficiency standpoint; personal tone preferences may vary).
Heres a real world example of the which is safer, higher or lower impedance theory taken to the extremes of high and low impedance.
Old Fender amps actually defaulted to a dead short (+/- 0 impedance) as a protection device for amps running without a load attached. OK for an accidental speaker disconnect, or turning it on and wondering why there is no sound; not advisable for sustained running but certainly safer than an infinite (open circuit) load.
As a side note, Ive read that MarkBass touts the ability to short the outputs on their new (well, newer) tube head as some sort of "state of the art" protection circuitry, like its magic or something. I find that amusing.
Im not flaming MarkBass, I like their stuff in general and the tube amp in particular has some very impressive technological features, but the ability to safely short outputs on a tube amp isnt one of them.
I'd like to hear how running less of a load (higher impedence) can damage a transformer. Let's say, for example, I'm running a tube amp with a 4 ohm output plugged into a 8 ohm load, or 16 or 32. The output will be less, of course, but how does the "damage" occur? 
The OPT presents a load to the output tubes. That has to match what the tube were designed for. If it does not, the tubes will be damaged. That can cause them to fail and short out causing damage to the OPT. If the transformer is not loaded by a speaker, the signal can "bounce" back into the primary causing high voltage spikes. These can damage the insulation within the OPT as well as damaging the tubes causing them to short out and so on. Very skimpy explanation for sure but I hope you get the idea. if you have a tube amp, especially for bass, you should operate it with the correct load.
Paul
Paul
