Impedance questions...

Hi! I'm new in this world and I'm sorry I could not wait to write...
I'm the happy owner of a '64 Bandmaster, rated 4ohms as far as I know.
The point is: what ohmage should the cab be? Can it be 8 or 16ohm and, if not, why?
Thank you SOOOOO much!

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Go for it Bass...

Drum roll... enter 1bass... nice cue, Lee :lol:

Riz, if you can stomach it, have a look at my thread on this forum, "Some impedance theory". There is also a link to an excellent site on this subject. Between them, you'll get some insight on how it goes.

Unfortunately, Riz, your exact Q is the one bit where I think one thing (4ohm amp output into 2ohm cab is safer than 4ohm output into 8ohm cab) and David's site says the exact opposite. Almost everybody agrees that Fender amp transformers are sturdy enough to cope with a mismatch so you'll be OK but a 4ohm cab load (matching the amp) is preferable if you can do it.

I really need to clear this up with David. I think it's fair to say that he walks the walk whereas I just read the talk. There is another site that agrees with my way round, though.

FWIW (1): My thinking goes like this. The fastest way to frazzle your valve amp's OPT is to run it with no cab connected, agreed? Many old amps even have a warning sticker on this (eg my '69 Laney). That being so, what is the impedance an amp 'sees' when no speakers are connected? To me, it's nigh on infinite and the tubes work like billy-oh to meet this load - taking themselves, the OPT and gawd knows what else out in the process. Hence, a 4ohm output tap like your Fender creates more work (and possible sparks) if connected to a 16ohm cab. Obviously, 4 to 16 is a lot better than 4 to infinity - but that's my thinking.

Major caveat; I'm not an exp on this - just an interested reader. I'll get back with any ops I retrieve.

FWIW (2): I have my Marshall (supposedly very likely to blow up on a mismatch) at 8 into a 16 cab. No ill effects, so the Fender (or any other valve amp) could tolerate a 4-8, 8-16 mismatch or vice-versa. I don't want to recommend it, though, as a smoking amp often results in a punch in my mouth. As soon as I get more ops, I'll post them up.

BTW, somebody please post a "God, that was boring" to my 'theory' thread. At least I'll know I didn't type it for nothing... :P [/i]

thanks to everyone!
anyway, here is my experience. I posted my question here because I had read stuff on the net that worried me.
I have, like said, this bandmaster head, plugged into a crap marshall 1987 cab, which is rated 16ohm 400w and sucks. At the moment money is on holiday so I cannot buy another one.
Well, I never had troubles. The point is that when I tried to change the tubes coz the other were a bit old, the local shop gave me some gt 6L6B that started to glow for the first half an hour, then went tback to the right temperature at their own will. I don't know if that depended on the bad tube quality, on the cab ohms, or on the fact that hte guys at the shop did not know that 6L6B's have to be biased lower, as I then found out. And seenms like on fenders this can't be done...
So, I put my old 6l6gc on it and it works. I'll buy JJ soon...
Don't know if everything I just wrote can be of any interest, but at least I shared it with someone who can understand all this!
I can't yet.
Regards from Italy

i always thought that 2ohm amp into 4 ohm cab was a no no.
the amp (output transformer) works harder the drive the 4ohms, i thought the other way round was ok, like 16ohm into an 8ohm cab, either way i wouldnt risk my Partridge OT to any mismatched cab, very good post though Bass.

do i get anything for a 200 post??? probably not, i bet the next flag is on the 1000.

Lee, what you say is what I think. It is best that everything matches of course. If not, setting the amp to more ohms than the cab presents is safer (in my theory, anyway). So, 8ohm tap to 16ohm cab is better than vice versa.

Riz, your cab is not that awful - thousands of people have bought it and like it. Your problem is that you have a 4ohm head into a 16ohm cab. For one thing, this risks damage but there is another point. Impedance mismatching affects the tone, as well as the efficiency.

Riz, if I were you, I would do something very simple and easily reversed if want to sell things later. Simply have you cab's wiring altered so that all drivers are wired in parallel. If all "+" terminals and "-" terminals are linked by wiring, the cab becomes a 16/4, or a 4ohm cab. Perfect match for the Bandmaster's 4ohm tap. Just a thought.

Thanks Bass, I've been looking around in the net and that is what I planned to do.
Like you said, that Marshall cab can be good for some people, I was I bit rough last time. Well I think the speakers are too hard and they might be perfect for some music but not for my taste; the point is that it is a mistreated cab so it's full of buzzes and stuff, which make things worst obviously.
I'll do the job as soon as I can and post the results.
Thank to everyone!

Riz, glad you're thinking that route - it makes the most sense. In my previous post (apart from terrible typos) I made a dreadful mixup. I meant to say that (to my theory) a 16ohm tap to 8 ohm cab is safer than 8ohm tap to 16ohm cab.

Yeesh :oops: , this kind of mis-type is so easily done - no wonder there are opposing ops on the subject. FWIW, I think the 'tone improvement' argument for deliberate mismatching is horse. If at all possible, get the cab(s) to match the output impedance. Your research has been well worthwhile Riz.

Of course, some speakers suit one player more than another but I think this little mod at least allows you to check everything in its most favourable setting. If it still fails to meet, at least you know you've given it a chance.

Hi everyone. I just bought a 2001 reissue of Gibson's J160e--the guitar John Lennon and George Harrison made famous--but it's not one of the signature series. It sounds great acoustically, and it's very playable. But when I plug it into my Fender Blues Jr. it distorts like crazy. Is this an impedance problem? And if so, what can be done about it? I'm not even sure if it has a p90 or p100 pickup. It looks just like the one in the pictures of the signature Peace series, which Gibson says is a p100 and Musician's Friend says is a p90. Any help much appreciated.

Cat, I don't know about the guitar itself, but an impedance problem is an issue between the amplifier and the speakers. If your Strat sounds fine (using the same input lead), then it isn't impedance. Have you tried eq adjustment with any success? Also, contact Gibson for advice; I hear their e-support is quite good.

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