Members squish_man24 Posted February 19, 2007 Members Share Posted February 19, 2007 What are Ohms? What do they do to the amps. If I had a 4 Ohms head connected to an 8 Ohms cab, what are the problems? What difference would I get connecting an 4 Ohms cab? I never really learned about these. Link to comment Share on other sites More sharing options...
Members SoundwaveLove Posted February 19, 2007 Members Share Posted February 19, 2007 You never want less ohms on your cab then your amp. More is OK. If you connect cabs in series the ohms add to each other, if you connect in parallel they go down. Link to comment Share on other sites More sharing options...
Members bassplayinguy Posted February 19, 2007 Members Share Posted February 19, 2007 What are Ohms? What do they do to the amps. If I had a 4 Ohms head connected to an 8 Ohms cab, what are the problems? What difference would I get connecting an 4 Ohms cab? I never really learned about these. oh dear god no!........ Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted February 19, 2007 CMS Author Share Posted February 19, 2007 What are Ohms? What do they do to the amps. If I had a 4 Ohms head connected to an 8 Ohms cab, what are the problems? What difference would I get connecting an 4 Ohms cab? I never really learned about these. An ohm is a unit of either resistance or impedance, in the case of speakers and amplifiers, it's impedance. A speaker presents a certain impedance, which is how hard the amplifier must 'push' its voltage through the speaker, so to speak. The lower the impedance, the greater the amount of power the amplifier can produce...but only to a point..that point being where it passes more current than the components are designed to handle. So...the manufacturer will state a minimum impedance the amp can be hooked up to. Higher impedance is fine, it only reduces the amount of power, and therefore heat, the amp generates. An 8 ohm speaker hooked to an amp rated for a 4 ohm minimum load is fine...it'll produce about half of the power it would produce into an 4 ohm cabinet. Everything I just wrote applies to solid state amplifiers. Tube amplifiers usually have impedance matching output transformers. They produce the same power into whatever impedance the transformer is rated to handle. Another difference is that solid state amps can have no speaker hooked up at all, and will not be damaged, but a tube amp can be damaged if a signal is passed to it but there's no speaker load present. Link to comment Share on other sites More sharing options...
Members bassplayinguy Posted February 19, 2007 Members Share Posted February 19, 2007 if you want the scientific explanation of ohms, wrap your head around this: http://en.wikipedia.org/wiki/Electrical_impedance I took a year of electronics engineering in college and still managed to only touch the tip of the iceberg when it comes to everything that is resistance related. Link to comment Share on other sites More sharing options...
Members squish_man24 Posted February 19, 2007 Author Members Share Posted February 19, 2007 An ohm is a unit of either resistance or impedance, in the case of speakers and amplifiers, it's impedance. A speaker presents a certain impedance, which is how hard the amplifier must 'push' its voltage through the speaker, so to speak. The lower the impedance, the greater the amount of power the amplifier can produce...but only to a point..that point being where it passes more current than the components are designed to handle. So...the manufacturer will state a minimum impedance the amp can be hooked up to. Higher impedance is fine, it only reduces the amount of power, and therefore heat, the amp generates. An 8 ohm speaker hooked to an amp rated for a 4 ohm minimum load is fine...it'll produce about half of the power it would produce into an 4 ohm cabinet.Everything I just wrote applies to solid state amplifiers. Tube amplifiers usually have impedance matching output transformers. They produce the same power into whatever impedance the transformer is rated to handle. Another difference is that solid state amps can have no speaker hooked up at all, and will not be damaged, but a tube amp can be damaged if a signal is passed to it but there's no speaker load present. So basically, i am only producing half the volume I am able to using a 8 ohm cab and a 4 ohm head? That clears things up a bit. Is it possible ( i jknow it's kind of rare) to hook a 4 ohm head up to a 2 ohm cab? Link to comment Share on other sites More sharing options...
Members squish_man24 Posted February 19, 2007 Author Members Share Posted February 19, 2007 if you want the scientific explanation of ohms, wrap your head around this:http://en.wikipedia.org/wiki/Electrical_impedanceI took a year of electronics engineering in college and still managed to only touch the tip of the iceberg when it comes to everything that is resistance related. wow...that looked like a bunch of equations that made no sese to me. I haven't taken physics in about 2 years, so I'll skip wikipedia, haha. Thanks for the input though Link to comment Share on other sites More sharing options...
Members bassplayinguy Posted February 19, 2007 Members Share Posted February 19, 2007 So basically, i am only producing half the volume I am able to using a 8 ohm cab and a 4 ohm head? That clears things up a bit. Is it possible ( i jknow it's kind of rare) to hook a 4 ohm head up to a 2 ohm cab? 2 ohm heads are pretty rare. and they get hot fast. The higher the ohm rating (impedance) the cooler the head runs generally. If you have (2) 4 ohm cabs, running them together will give you a total impedance of 4 ohms. Thus getting more power to each cab. if youre out to get the most volume out of your amp, run a cab that has the same rating as the head is rated for. A 4ohm head running a 4 ohm cab will be alot more efficient that running a 4 ohm head with an 8 ohm cab. But running a 4 ohm head with a 2 ohm cab will make it run rediculously hot and burn itself out. Then you end up with smoke and no amp Link to comment Share on other sites More sharing options...
Members burdizzos Posted February 19, 2007 Members Share Posted February 19, 2007 So basically, i am only producing half the volume I am able to using a 8 ohm cab and a 4 ohm head? That clears things up a bit. Is it possible ( i jknow it's kind of rare) to hook a 4 ohm head up to a 2 ohm cab? No, half the power, not volume, very different things. Also, most amps will put out more than half of the 4 ohm rating into an 8 ohm load. Link to comment Share on other sites More sharing options...
Members squish_man24 Posted February 19, 2007 Author Members Share Posted February 19, 2007 Ahh, i understand now. So having 2 8ohm cabs running through a 4 ohms head is Ok, but if I want the msot out of everything, get the same independance. Link to comment Share on other sites More sharing options...
Members Smokinfiddler Posted February 19, 2007 Members Share Posted February 19, 2007 that is what the skinny little indian guru dude does on the mountein peak when he meditates, he goes he goes OHMMMMMMM....OHMMMMMMM....OHMMMMMMM:D Link to comment Share on other sites More sharing options...
Members mlwarriner Posted February 20, 2007 Members Share Posted February 20, 2007 Ahh, i understand now. So having 2 8ohm cabs running through a 4 ohms head is Ok, but if I want the msot out of everything, get the same independance. having two 8-ohm cabs connected to a 4-ohm head is (typically) presenting the head with a 4-ohm load. and while it's generally OK to run more ohms in your cabs than your head is rated for, this (essentially) goes right out the window if you're discussing all-tube heads. everything i've ever heard/read/seen says to be sure and match your cabinets exactly with your head when dealing with all-tubes. Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted February 20, 2007 CMS Author Share Posted February 20, 2007 Ahh, i understand now. So having 2 8ohm cabs running through a 4 ohms head is Ok, but if I want the msot out of everything, get the same independance. Two 8 ohm cabs in parallel would be a 4 ohm load. Independence is a town in Missouri, impedance is the subject we were discussing. Link to comment Share on other sites More sharing options...
Members prosigna Posted February 20, 2007 Members Share Posted February 20, 2007 Some cabinets have 8 of these, some only have 4. If you run 4+4 in parallel you will only get 2. If you run them in series you will get 8. Funny creatures these ohms. Here is a good picture of one: or maybe that is a gnohm (or a gnome whatever) Link to comment Share on other sites More sharing options...
Members T-bolt Posted February 20, 2007 Members Share Posted February 20, 2007 Font enlarged and bolded for importance. Note that this applies to amps with a tube power section... hybrids with a tube preamp but solid-state power sections don't have this issue. Link to comment Share on other sites More sharing options...
Members georgestrings Posted February 20, 2007 Members Share Posted February 20, 2007 2 ohm heads are pretty rare. and they get hot fast. The higher the ohm rating (impedance) the cooler the head runs generally. If you have (2) 4 ohm cabs, running them together will give you a total impedance of 4 ohms. Thus getting more power to each cab. if youre out to get the most volume out of your amp, run a cab that has the same rating as the head is rated for. A 4ohm head running a 4 ohm cab will be alot more efficient that running a 4 ohm head with an 8 ohm cab. But running a 4 ohm head with a 2 ohm cab will make it run rediculously hot and burn itself out. Then you end up with smoke and no amp The 1st part of your post is dead wrong - there are quite a few 2 ohm capable amps - Peavey, Genz-Benz, and Carvin all make them, just off the top of my head... Furthermore, running (2) 4 ohm cabs makes for a 2 ohm overall load... Personally, I prefer a 2 ohm capable head, and to use 4 ohm cabs with such a head - that way, I get a decent amount of wattage out of 1 cab, and can still kick some major ass with two cabs at 2 ohms... Now, the 2nd part of your post is pretty much on the mark... - georgestrings Link to comment Share on other sites More sharing options...
Members georgestrings Posted February 20, 2007 Members Share Posted February 20, 2007 Font enlarged and bolded for importance. Note that this applies to amps with a tube power section... hybrids with a tube preamp but solid-state power sections don't have this issue. Absolutely correct... - georgestrings Link to comment Share on other sites More sharing options...
Moderators isaac42 Posted February 20, 2007 Moderators Share Posted February 20, 2007 Ahh, i understand now. So having 2 8ohm cabs running through a 4 ohms head is Ok, but if I want the msot out of everything, get the same independance. This is correct. Note that running two 8 ohm cabs in parallel is a 4 ohm load, so that is the same impedance. Link to comment Share on other sites More sharing options...
Members bassplayinguy Posted February 20, 2007 Members Share Posted February 20, 2007 The 1st part of your post is dead wrong - there are quite a few 2 ohm capable amps - Peavey, Genz-Benz, and Carvin all make them, just off the top of my head... Furthermore, running (2) 4 ohm cabs makes for a 2 ohm overall load... Personally, I prefer a 2 ohm capable head, and to use 4 ohm cabs with such a head - that way, I get a decent amount of wattage out of 1 cab, and can still kick some major ass with two cabs at 2 ohms...Now, the 2nd part of your post is pretty much on the mark... - georgestrings Call it dead wrong all you want. (my SVT 4 is 2 ohm capable) I was just putting it that way so that he doesnt try running 2 ohms without checking to see if his amp can handle it. Its a fast way to wreck a head. I also say that because most beginner and middle of the road heads are usually only 4 ohm capable. And just because it says 2 ohms capable doesnt mean it can handle playing a full night at gig volume. Hence the extra cooling and testing the Genz Benz guys talk about when they say their amp is stable at 2 ohms. I know I dont trust my Ampeg at 2 ohms for more than a couple hours. Link to comment Share on other sites More sharing options...
Members georgestrings Posted February 20, 2007 Members Share Posted February 20, 2007 Call it dead wrong all you want. (my SVT 4 is 2 ohm capable) I was just putting it that way so that he doesnt try running 2 ohms without checking to see if his amp can handle it. Its a fast way to wreck a head. I also say that because most beginner and middle of the road heads are usually only 4 ohm capable. And just because it says 2 ohms capable doesnt mean it can handle playing a full night at gig volume. Hence the extra cooling and testing the Genz Benz guys talk about when they say their amp is stable at 2 ohms. I know I dont trust my Ampeg at 2 ohms for more than a couple hours. Maybe you can point out what is actually right with the below quote, because I'm not seeing it: "2 ohm heads are pretty rare. and they get hot fast. The higher the ohm rating (impedance) the cooler the head runs generally. If you have (2) 4 ohm cabs, running them together will give you a total impedance of 4 ohms. Thus getting more power to each cab." FWIW, 2 ohm heads don't get any hotter than any other heads, are not all that rare - and (2) 4 ohm cabs ran together work out to a total impedence of TWO ohms, not 4 ohms, like you erroneously posted... Face it, you were wrong - and now are being too stubborn to admit it... I've run several Peavey 2 ohm capable heads at 2 ohms and high volumes for many, MANY gigs - and in some hot clubs - and NEVER had a problem doing so... There are actually a fair amount of 2 ohm capable amps... - georgestrings Link to comment Share on other sites More sharing options...
Members CaptianGalatica Posted February 20, 2007 Members Share Posted February 20, 2007 I think also letting your tube amp warm up with no signal going to it hurts it because i remember i did that once with my v4b and the tubes lit up a weird color and then didn't work right when i put a speaker into it and flipped it on. I was getting no signal at first but then i did get an "off" tone that came in but thankfully it got better after i played it for like 10 mins. hey, give me a break its my first tube amp..... Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted February 20, 2007 CMS Author Share Posted February 20, 2007 I think also letting your tube amp warm up with no signal going to it hurts it because i remember i did that once with my v4b and the tubes lit up a weird color and then didn't work right when i put a speaker into it and flipped it on. I was getting no signal at first but then i did get an "off" tone that came in but thankfully it got better after i played it for like 10 mins. hey, give me a break its my first tube amp..... There is absolutely no problem with letting a tube amp warm up with no signal. Link to comment Share on other sites More sharing options...
Members georgestrings Posted February 20, 2007 Members Share Posted February 20, 2007 There is absolutely no problem with letting a tube amp warm up with no signal. I was thinking the same thing - as long as it's in standby, I'd say no harm, no foul... - georgestrings Link to comment Share on other sites More sharing options...
Members Rippin' Robin Posted February 20, 2007 Members Share Posted February 20, 2007 I think also letting your tube amp warm up with no signal going to it hurts it because i remember i did that once with my v4b and the tubes lit up a weird color and then didn't work right when i put a speaker into it and flipped it on. I was getting no signal at first but then i did get an "off" tone that came in but thankfully it got better after i played it for like 10 mins. hey, give me a break its my first tube amp..... Just to be on the safe side, NEVER run an all-tube head without a speaker load*). There are some situations where it's acceptable and safe. But to be safest, just DON'T run it without a speaker*), even if it's on stand-by. It might be safe, but next thing you'll know you forgot you didn't plug the speaker it, flip it on and ruin something. *)Or suitable dummy load, such as a powerbrake Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted February 20, 2007 CMS Author Share Posted February 20, 2007 I was thinking the same thing - as long as it's in standby, I'd say no harm, no foul...- georgestrings Venturing further out onto the ledge, you don't even need a speaker load if there's no signal present. Link to comment Share on other sites More sharing options...
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