fleabag Posted September 1, 2011 Share Posted September 1, 2011 Just need something clearing up .. If the spec of a 2 channel power amp is say : 2x300W RMS at 4 ohms 2x200W RMS at 8 ohms bridge 600W RMS at 8 ohms. Does this mean it wont bridge into 4 ohms ? Its not mentioned in the spec Here's some spec from the same manufacturer, but different power amp 2x250W RMS at 4 ohms 2x150W RMS at 8 ohms Bridge 500W RMS 4 ohms so does this mean this one wont bridge into 8 ohms ? Quote Link to comment Share on other sites More sharing options...
alexclaber Posted September 1, 2011 Share Posted September 1, 2011 If each side will run down to 4 ohms then it'll bridge into 8 ohms, whilst if each side runs down to 2 ohms it'll bridge into 4 ohms. With solidstate amps you can run any higher impedance than the minimum load, even hundreds of ohms, you just get less power with increasing impedance. Quote Link to comment Share on other sites More sharing options...
fleabag Posted September 1, 2011 Author Share Posted September 1, 2011 (edited) Cheers Alex I posted those specs direct from the ads. It seems to me then that the 2nd spec listed is a typo. Perhaps it should read Bridge 500 watts into 8 ohms ? Edited September 1, 2011 by fleabag Quote Link to comment Share on other sites More sharing options...
JTUK Posted September 2, 2011 Share Posted September 2, 2011 I am pretty well certain that my amp run 200 per side into 4ohms.. when bridged it runs 400 into 4 ohms.. I run 4 ohms of cabs of either side to get 200 stereo or 4ohms of cab to get 400w bridged. Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted September 2, 2011 Share Posted September 2, 2011 If your amp is 200W into 4ohms stereo it will give 400W bridged into 8. It may well also give 400W bridged into 4ohms. This is because of the power supply. Solid state amps are limited by the voltage they run at. Running them as a bridge means the voltage is effectively doubled which theoretically gives 4x the power (power is Vsquared/R). In practice asking them to provide masses of extra power demands a lot more current which could damage the output devices or more likely simply demand more than the power supply can provide. Protection circuits may cut in too. Running bridged into 4ohms is much like running an unbridged amp into 2 ohms. You might be trying to draw more power than the amp is happy with and may in extreme cases damage it. You need to check the handbook as each amp is designed differently. Generally the more expensive amps have bigger power supplies, better output devices and better protection though you don't always get what you pay for. Power supplies can always provide high currents for brief periods. This enables some manufacturers to claim greater power outputs than the amp could manage over an extended period even if they are 'RMS' values. Quote Link to comment Share on other sites More sharing options...
fleabag Posted September 2, 2011 Author Share Posted September 2, 2011 Thanks chaps Well if either of those amps can do each channel into 4 ohms , EG run 2 cabs, each with 4 ohms, then surley it can run 1 x 4 ohm speaker with the channels bridged, no ? Its not like I'm asking the amp to run lower than 4 ohms using a single 4 ohm cab, so i assume its no big deal Quote Link to comment Share on other sites More sharing options...
alexclaber Posted September 2, 2011 Share Posted September 2, 2011 Indeed, if you can bridge an amp into 4 ohms then it's 2 ohm stable in used in parallel. Some amps don't have enough current delivery to develop any more power into 2 ohms than 4 ohms, hence bridged into 4 ohm output can be the same as bridged into 8 ohms. [url="http://www.swrsound.com/support/manuals/html/sm400om.php"]http://www.swrsound.com/support/manuals/html/sm400om.php[/url] Interesting to note that the bridged output is lower than you'd normally expect, whilst with power amps it's usually a bit higher than double the unbridged power. Presumably this is down to the power supply design? Quote Link to comment Share on other sites More sharing options...
alexclaber Posted September 2, 2011 Share Posted September 2, 2011 [quote name='fleabag' post='1359684' date='Sep 2 2011, 11:37 AM']Thanks chaps Well if either of those amps can do each channel into 4 ohms , EG run 2 cabs, each with 4 ohms, then surley it can run 1 x 4 ohm speaker with the channels bridged, no ? Its not like I'm asking the amp to run lower than 4 ohms using a single 4 ohm cab, so i assume its no big deal[/quote] No. When you run an amp bridged, each side of the amp only sees half of the load impedance. So when you bridge into 4 ohms, the left of the amp sees 2 ohms and the right of the amp sees 2 ohms. Quote Link to comment Share on other sites More sharing options...
fleabag Posted September 2, 2011 Author Share Posted September 2, 2011 Ooooer So the specs on the 2 amps above could be correct and not typos ? One of them will bridge to 4 ohms, and other only bridges to 8 ohms , despite both being able to run each channel separately into 4 ohms ? I hate tech Quote Link to comment Share on other sites More sharing options...
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