Members broknstuff Posted August 23, 2006 Members Share Posted August 23, 2006 This is a really dumb post, but I've always wondered and now actually might need to know, so here goes: So me and my band member bought the crate powerblock as a backup in case something happens during a gig. I just realized that now in this band I'm just using a 2x12 (4x12 is in different city, 2x12 fits my needs better). I loaded it with 2 v30's in parallel, and a total load of 8 ohms, and 120 volts. Now I just realized at 8 ohms the powerblock is 150 watts, and my cab can only handle 120. I would only be using the powerblock live, so in those situations I would be turning it up. Is there any device to put between a head and speaker to knock off some wattage and make this possible? If not the powerblock can also do 75 watts stereo. Now I'm not sure if that will be loud enough, but if it is should I just put a load box on the other stereo output? Also can an 4 ohm speaker out go into a 8 ohm cab, or is it the other way around? (Can someone clear up the safe/unsafe mismatch again?) I know if not I could just plug it to the P.A. with the powerblock, but I'd rather run it through a guitar cab because that sounds better than straight to a P.A., and also to put less load on the sometimes not so outstanding p.a. systems... One final question about the impedence mismatch, I know there is a safe mismatch and an unsafe mismatch. Let's say your forced in a situation where you can only use the 'unsafe mismatch', is there a device to put between head and cabs to be able to change the impedence. (Dumb question, but I was just always curious on this one). Thanks for the help... Link to comment Share on other sites More sharing options...
Members Thunnar Posted August 23, 2006 Members Share Posted August 23, 2006 I don't know the exact answer, but I know it's not a dumb question. In fact, it's a damn good electircal question. What is the relationship between Ohms and Watts in a speaker?What happens if the impedance remains the same but the current increases? Now you got me wondering:freak: Link to comment Share on other sites More sharing options...
Members 496dart Posted August 23, 2006 Members Share Posted August 23, 2006 id run it at 150--i really doubt that little Crate will actually produce that. Run it at 8 ohms--or 4 if you have to (the amp). Link to comment Share on other sites More sharing options...
Members walfordr Posted August 23, 2006 Members Share Posted August 23, 2006 The power handling capability of speakers is often understated and the power output of SS amplifiers overstated. I think youd be pretty safe. To be sure you can use the inbuilt feature of the amp that reduces the power output - the volume knob. Just turn it down slightly and you'll definitely be safe. Impedance matching is completely different in SS amps and tube amps. For a SS amp there is a minimum impedance below which you should not go - the amp basically puts out a constant voltage so the current and hence the power output will increase as you reduce the impedance of the load. Below a certain level of load impedance the current will be too high for the power transistors which will blow - end of amp! A higher an impedance will just result in less power output and cannot damage the amp. You can run most SS amps without a load at all. The simple versions of the relevant equations are: V=I*R so I = V/R Power, W = V*I or W = (V*V)/R For a tube amp it is much more complex because of the OT and any mismatching will result in a reduced power output. To much of a mismatch in either direction can result in damage. Link to comment Share on other sites More sharing options...
Members ToneGrail Posted August 24, 2006 Members Share Posted August 24, 2006 I would run it at 8ohms and just don't turn it up all the way. Link to comment Share on other sites More sharing options...
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