Members kadrocker Posted August 13, 2012 Members Share Posted August 13, 2012 I've never really been a gear nut so I never really thought about asking this..... I have a Fender Super Champ XD amp, which is 8 ohms. I have a 4x12 cab that has Celestion speakers. (all 8 ohm) so I know I can put them together with no problem. Now, just say I want to buy a head, either tube or solid state, does it have to be 8 ohms? Can it be more or less without damage? What's the deal? probably a common question but I can't use the search feature with my phone. Thanks for the help. Link to comment Share on other sites More sharing options...
Members Mike LX-R Posted August 13, 2012 Members Share Posted August 13, 2012 I've never really been a gear nut so I never really thought about asking this.....I have a Fender Super Champ XD amp, which is 8 ohms. I have a 4x12 cab that has Celestion speakers. (all 8 ohm) so I know I can put them together with no problem. Now, just say I want to buy a head, either tube or solid state, does it have to be 8 ohms? Can it be more or less without damage? What's the deal? probably a common question but I can't use the search feature with my phone.Thanks for the help. Don't assume that because the speakers are all 8 ohm that the cab is safe to run. It depends on how it's wired i.e. series vs. parallel. If the cab says 8ohm on the input then yes, you're fine, and yes your amp should have an 8 ohm jack. Typically you should just avoid mismatched impedance. I'm sure guys will pop in here telling you about acceptable tolerances, but just give the amp the load it wants. Link to comment Share on other sites More sharing options...
Members guitarbilly74 Posted August 13, 2012 Members Share Posted August 13, 2012 Don't assume that because the speakers are all 8 ohm that the cab is safe to run. It depends on how it's wired i.e. series vs. parallel. If the cab says 8ohm on the input then yes, you're fine, and yes your amp should have an 8 ohm jack. Typically you should just avoid mismatched impedance. I'm sure guys will pop in here telling you about acceptable tolerances, but just give the amp the load it wants. With a 4x12 cab with 8ohms speakers, it is pretty safe to assume the cab is 8ohms, since the possible impedance would be either 2,8 or 32 ohms and no one really wires guitar cabs for 2 or 32 ohms. As far as tolerances, mismatching one up (4ohms amp into 8ohms cab) or one down (16ohm amp into 8om cab) is generally safe, but it will depend on how strong the amp's transformers are. Also, the amp will sound slightly different. Your best bet is to get an amp with a multi-tap transformer and select the 8ohms tap for a perfect match. There are so many amps available with that feature, it simply doesn't make sense to buy one without it. The above is for tube amps only, with SS amps you don't have to worry about a mismatch, but bear in mind the power cuts in half every time you double the impedance. A SS amp rated at 100w @4ohm, would be 50w @ 8ohms and 25w @16ohms. Link to comment Share on other sites More sharing options...
Members guitarcapo Posted August 13, 2012 Members Share Posted August 13, 2012 The speaker is rated for "impedance" and not "resistance" so basically it's frequency related. People will tell you otherwise but basically since the impedance rating is based on an arbitrary single frequency, all changing the rating does is alter the frequency response and possibly efficiency depending on which frequencies you are putting through the amp. Given that, it's pretty safe to go a step away from the recommended impedance your amp asks for. In my experience, amps sound brighter when you use a speaker rated at a lower impedance than the amp calls for...and darker if you go higher. Link to comment Share on other sites More sharing options...
Members Mike LX-R Posted August 13, 2012 Members Share Posted August 13, 2012 With a 4x12 cab with 8ohms speakers, it is pretty safe to assume the cab is 8ohms, since the possible impedance would be either 2,8 or 32 ohms and no one really wires guitar cabs for 2 or 32 ohms. That makes sense and I didn't bother to add it up. I know this is unlikely, and I only ask for the sake of my own curiosity, but could you wire each side left/right in series and then jumper the two sides together in parallel to get 4 ohms? Link to comment Share on other sites More sharing options...
Members GCDEF Posted August 13, 2012 Members Share Posted August 13, 2012 That makes sense and I didn't bother to add it up. I know this is unlikely, and I only ask for the sake of my own curiosity, but could you wire each side left/right in series and then jumper the two sides together in parallel to get 4 ohms? No. That's series/parallel wiring, which is how it's going to be wired, but you'd still end up with 8 ohms. If you did parallel first, you'd have two 8s wired together to get 4, then connect the two 4s together to get 8. If you did the series first, you'd have two 8s wired in series to get 16, then wire the two 16s in parallel to get 8. As mentioned, 2, 8 and 32 are your only options with 4 8 ohm speakers. Link to comment Share on other sites More sharing options...
Members guitarbilly74 Posted August 13, 2012 Members Share Posted August 13, 2012 That makes sense and I didn't bother to add it up. I know this is unlikely, and I only ask for the sake of my own curiosity, but could you wire each side left/right in series and then jumper the two sides together in parallel to get 4 ohms? That's probably how the cab is wired .. but it's 8ohms not 4. if you wire each side in series, you will have 16ohms per side. Once you combine both sides in parallel you get 8ohm. Link to comment Share on other sites More sharing options...
Members Mike LX-R Posted August 13, 2012 Members Share Posted August 13, 2012 That's probably how the cab is wired .. but it's 8ohms not 4. if you wire each side in series, you will have 16ohms per side. Once you combine both sides in parallel you get 8ohm. my noobishness still shines through from time to time.. Link to comment Share on other sites More sharing options...
Members BC Audio Posted August 13, 2012 Members Share Posted August 13, 2012 ...no one really wires guitar cabs for 2 or 32 ohms... Fender did! - e.g. Super Reverb, four 8 ohm 10" spkrs wired in parallel = 2 ohms(!). I guess no one ever told Leo that he didn't have to wire all speakers in parallel. Link to comment Share on other sites More sharing options...
Members Rock Hardness Posted August 13, 2012 Members Share Posted August 13, 2012 No. That's series/parallel wiring, which is how it's going to be wired, but you'd still end up with 8 ohms. If you did parallel first, you'd have two 8s wired together to get 4, then connect the two 4s together to get 8. If you did the series first, you'd have two 8s wired in series to get 16, then wire the two 16s in parallel to get 8.As mentioned, 2, 8 and 32 are your only options with 4 8 ohm speakers. How do stereo cabs work? Some of the newer 1960 Marshalls have that option, yes?(Though I don't get why you would want to...no seperation. Or is it to "blend" a pair, which seems contrary to the term "stereo". Hmmm...) Anyone use this option? Mine are either pretty old, or newly built to look really old. Link to comment Share on other sites More sharing options...
Members BC Audio Posted August 14, 2012 Members Share Posted August 14, 2012 I use a stereo cab when I run a two-amp rig. Works great. It's not really "stereo" but a compact (is a 4x12 ever compact?) way to get two amps on a small stage. My personal 2x12s are set up that way, too. (The ones I sell are mono with two jacks for daisy chaining.) It works by splitting up the left and right sets of speakers. In the newer Marshalls, each pair consists of two 16-ohm speakers in parallel for 8 ohms. In "stereo" mode, the two pairs are separated, and each of the two jacks feeds one side. In "mono" mode, the left jack feeds both sides in parallel for 4 ohms; the right jack feeds both sides in series for 16 ohms. Link to comment Share on other sites More sharing options...
Members Rock Hardness Posted August 15, 2012 Members Share Posted August 15, 2012 Thanks for this^^^ Link to comment Share on other sites More sharing options...
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