Members lemur13 Posted February 21, 2015 Members Share Posted February 21, 2015 So here's the deal, I have two cabs (Acoustic B115 250w 8ohm, Marshall MC412 200w 16/4ohm solo or 8ohm stereo) and I'm trying to find a head that will feed both. I've tried to figure this out on my own but desperately need an expert opinion. Do I get an amp with 4ohm output and run the negative of Marshall's 8ohm stereo to the Acoustic? Do I need an amp with an extension jack because the wattage is different? What is the best way to match these? -Mike Link to comment Share on other sites More sharing options...
Members DeepEnd Posted February 22, 2015 Members Share Posted February 22, 2015 Set the Marshall MC412 to 16 Ohms and run the cabs in parallel. It will result in a 5 1/3 Ohm load. Most amps that will handle 4 Ohms will do nicely. Be advised though that the Acoustic will be absorbing more power than the Marshall and the volume probably won't match. That said, lots of guitarists use Fender Bassman cabs. I would, however, like to know why you want to use a pair of mismatched cabs, especially this particular pair? Link to comment Share on other sites More sharing options...
Members lemur13 Posted February 22, 2015 Author Members Share Posted February 22, 2015 Thanks for the reply. I don't exactly know what you mean by in parallel though. Is that running the second cab off the first intead of both directly into the head? I've wanted to pair a bass cab with my marshall for some time looking for more lower end in my tone. This just happens to be the one I keep around for my bass. Is there anything I can do for the volume ratio? I've heard about heads with separate jacks for two cabs, but I can't find anything like that... or I'm not searching the right terms. Link to comment Share on other sites More sharing options...
Members lemur13 Posted February 22, 2015 Author Members Share Posted February 22, 2015 My bass head is 4 ohms actually, that might be worth a try. Ha! Link to comment Share on other sites More sharing options...
Members lemur13 Posted February 22, 2015 Author Members Share Posted February 22, 2015 Sorry for the multiple posts, I just realize how ignorant I am. I have a 4 ohm bass head with two outputs, so I could run one to the Acoustic cab and the other to the Marshall at 16 ohms, right? But probably nothing I can do about the volume difference I'm guessing Link to comment Share on other sites More sharing options...
Members DeepEnd Posted February 22, 2015 Members Share Posted February 22, 2015 Yeah, typically (but not always) when an amp has outputs for two cabs the connections are in parallel. Here's an explanation of what parallel vs. serial means, with illustrations: http://cie-wc.edu/Series_Parallel_9_14.pdf. And no, there isn't anything practical you can do about the relative volume of the cabs.What are you planning to play through the rig? The Marshall cab is a guitar cab even though it has a closed back (bass cabs normally have a closed back, guitar cabs are often open backed). It could probably handle a bass as long as you don't go overboard in terms of volume. You can play a guitar through a bass head but you'll usually need external effects (reverb, chorus, distortion, etc. pedals) since bass amps normally don't have built-in effects. Link to comment Share on other sites More sharing options...
Members HoobaStunk Posted February 22, 2015 Members Share Posted February 22, 2015 Find an amp that has 2 speaker output jacks. Chances are extremely good that an amp with two speaker jacks will support operations with a 4 ohm load. Set the amp to "4 ohms" if there is an output transformer switch. Set the Marshall MC412 speaker cabinet to MONO and 16 ohms. Connect both speaker cabinets to the amp. The amp will be pushing a 5 ohm load. Link to comment Share on other sites More sharing options...
Members DeepEnd Posted February 22, 2015 Members Share Posted February 22, 2015 ^ Which is pretty much what I already told you. Still curious as to how you intend to use the rig. Link to comment Share on other sites More sharing options...
Members lemur13 Posted February 23, 2015 Author Members Share Posted February 23, 2015 First of all, you were a tremendous help and thank you. The plan is to play all intruments through one setup that is heavy on the bass end. I have a schecter omen-6 as my primary and an ibanez 7-string that I like for heavier tunes. Bass, keyboard and viola will be used to but I'll probably unhook the marshall for the bass. All are being used for post-metal type tunes in a home studio, but I want something unique, versatile and ubiquitous in case of shows. Link to comment Share on other sites More sharing options...
Members lemur13 Posted February 23, 2015 Author Members Share Posted February 23, 2015 A lot of it is going to be repetitious on the low end so I don't anticipate too much activity in the high, no screaming solos or anything like that. My only concern is being able to keep palm mutes with that tight -chunk- flavor and hopefully chords don't become a wall of sound. I'm trying not to rely too heavily on effects, but I'll probably end up with some sort of chorus and reverb through the loop, and a metal zone mt2 and danelectro black coffee for distortion. The end result hopefully being something in the vein of Isis (post-metal/shoegaze) with a bit of folk influence. Think of 'Fiddler on the Roof' if it was scored by Tool. All this is to be recorded in my basement on a korg 8-track with sennheiser's on the cabs and an akg 420 dynamic for ambient. Does that help? Link to comment Share on other sites More sharing options...
Members DeepEnd Posted February 23, 2015 Members Share Posted February 23, 2015 . . . The plan is to play all intruments through one setup that is heavy on the bass end. . . . I want something unique' date=' versatile and ubiquitous in case of shows.[/quote'] Back in the day (late 50's-early 70's), Fender made an amp called the Bandmaster Reverb, essentially a guitar amp with bass speakers. My college roommate always wanted one. Sounds like you're planning something similar. As I mentioned, plenty of guitarists using bass cabs; I used a bass amp and modelling pedal myself until I got a proper guitar amp. Best of luck with the recording project and possible shows. Link to comment Share on other sites More sharing options...
Members lemur13 Posted February 23, 2015 Author Members Share Posted February 23, 2015 I checked some out on youtube, and wow... Those do sound really smooth. It's exactly what I want the cleans to sound like. If I could get a thick overdriven sound that stops on a dime to come out of that thing as well it would be perfect. Thanks for all the help, man. Take care Link to comment Share on other sites More sharing options...
Members WRGKMC Posted February 23, 2015 Members Share Posted February 23, 2015 Woah hold on here. You have a Marshall cabs that's 16 or 4 ohm (2X8 stereo) and another cab that's 8 ohms. If you run the Marshall at 16 ohms and use the additional 8 ohm cab it gives you 5.33 ohms which is an oddball impedance. It should be fine for most transistor heads that will run between 4~16 ohms. Some tube heads like Marshalls have to be run at exact impedances with their transformers or you'll damage the head. Others tube heads like some older Fender heads are rated for 4 ohms can run between 4~8 ohms OK but no higher or you risk taking out the power tubes. In all cases check your amp head manual and make sure the speaker cabs total impedance falls between its min and max ratings. Link to comment Share on other sites More sharing options...
Members r0bo01 Posted February 23, 2015 Members Share Posted February 23, 2015 What wrg said. 8 ohms prolly upper limit for a 4 ohm tube power section head. which is what you'll be getting when you unplug the marshall for playing bass (personally, i'd leave it hooked up. you might like the top end it gives...).anyway, good luck with your project! Link to comment Share on other sites More sharing options...
Members DeepEnd Posted February 24, 2015 Members Share Posted February 24, 2015 . . . Some tube heads like Marshalls have to be run at exact impedances with their transformers or you'll damage the head. . . . . . . In all cases check your amp head manual and make sure the speaker cabs total impedance falls between its min and max ratings. Except that actual speakers aren't resistors and impedance varies with frequency. Here, for example, is an impedance plot for the speaker in a Marshall MG10 amp: Note that there's a substantial peak at just above 100 Hz, and troughs at 10 Hz and about 275 Hz, and that the impedance rises above that. An "8 Ohm" speaker can run from 5 Ohms or so on up to 30 or 40 Ohms easily. Real amps are designed for real speakers. Any amp that isn't is frankly not worth buying because it's a self-destruct device The OP has already said his/her bass head is rated for 4 Ohms so as long as he/she uses that head or another quality amp rated for 4 Ohms there won't be a problem. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted February 25, 2015 Members Share Posted February 25, 2015 Except that actual speakers aren't resistors and impedance varies with frequency. Here, for example, is an impedance plot for the speaker in a Marshall MG10 amp: Note that there's a substantial peak at just above 100 Hz, and troughs at 10 Hz and about 275 Hz, and that the impedance rises above that. An "8 Ohm" speaker can run from 5 Ohms or so on up to 30 or 40 Ohms easily. Real amps are designed for real speakers. Any amp that isn't is frankly not worth buying because it's a self-destruct device The OP has already said his/her bass head is rated for 4 Ohms so as long as he/she uses that head or another quality amp rated for 4 Ohms there won't be a problem. Yes impedance changes based on frequency but a transformer in certain tube amps don't change. They want to see a specific load all the time weather sound is passing through it or not. Without the proper load the power tubes can degenerate and go bad and cause damage. Transistor amps are a different animal and can vary their outputs with load changes. The power tubes in a tube amp are before the transformer and when the secondary isn't seeing the right load it pulls or fails to pull the right amount or voltage and current from the primary and all that backs up into your tubes and power supply. Again this is a matter of amp design and just how far the load is actually off (by the way its not just impedance load, the DC resistance is a real item as well and is factored into the design. Its just the push gets much harder when you're dealing with inductance. Link to comment Share on other sites More sharing options...
Members DeepEnd Posted February 25, 2015 Members Share Posted February 25, 2015 Again, IMHO, an amp that finicky simply isn't worth buying, at least to me. I want an amp designed for real speakers, not idealized engineering notions. Apparently the best advice for the OP is to avoid tube amps in general like the plague. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted February 26, 2015 Members Share Posted February 26, 2015 Marshall tube heads have been used for decades. They have an impedance selector for 4, 8 or 16 ohms and run fine when that impedance is matched. If you're running the head flat out pushing a full stack you better be dam sure you're running the right impedance load or you take a chance on cooking the tubes prematurely. Once the power tubes blow its a roll of the dice what may be taken out with them. As I said before some heads have a much wider tolerance for loading. A Fender Bandmaster or Bassman head for example can run between 4~8 ohms. You try and run them at 16 and you'll cook the tubes and blow the grid resistors in approximately 40 to 80 hours operation or less. If you want solid state they don't use a transformer and don't have the same impedance loading issues. Voltage and current change with load changes and so lone as the power transistors can handle the current changes and not overheat you're not going to damage them. Some have no problem running above their rated impedance. You can even run some with no load and have no ill effects. Something like a Valvestate will run between 4 and 16 ohms with no problems. Other older designs like the old Vox amps would actually catch on fire if you improperly loaded them. This should be serious stuff and advice shouldn't be given lightly. People have allot of cash wrapped up in their gear and in a case like this where you don't even know what head the guys using you cant advise him on what is safe and what is not. There are too many different circuits being used in amps to guess. It all comes down to proper balance for a particular circuit design. If you want a specific amp because you like that amps sound, you simply adhere to the manufacturers specifications and don't do stupid stuff with it. Chances are it will last you a lifetime. If you want it to run it with different cabs you simply stick to running it within proper specs and you wont have a problem. If you don't know these basics, Don't be temped to connect additional cabs until you're 100% sure that amp can handle that load. That's all there is to it. Link to comment Share on other sites More sharing options...
Members DeepEnd Posted February 26, 2015 Members Share Posted February 26, 2015 All the more reason I'm glad all my amps are SS. The next time someone asks a question like this one I'm going to tell him that if he has a tube amp he needs to either give up on using multiple cabs or pitch in into the nearest landfill. Link to comment Share on other sites More sharing options...
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