Members Belva Posted November 22, 2008 Members Share Posted November 22, 2008 Much has been said recently about making sure speaker impedance is correct for the amp you're using. Yet I see amps out there that have 8 ohm speakers in them & a 2nd ext speaker jack marked 4 ohms. Obviously this is a parallel jack. Pignose G40 is just one example. Other amps have an impedance selector of some sort. What gives? Wouldn't you lose sound quality or volume if you go messing with your load? Do some output trannies just not care what they get? I'm a tron noob. Any light you shed will be greatly appreciated. Link to comment Share on other sites More sharing options...
Members metalhobo Posted November 23, 2008 Members Share Posted November 23, 2008 Much has been said recently about making sure speaker impedance is correct for the amp you're using. Yet I see amps out there that have 8 ohm speakers in them & a 2nd ext speaker jack marked 4 ohms. Obviously this is a parallel jack. Pignose G40 is just one example. Other amps have an impedance selector of some sort. What gives? Wouldn't you lose sound quality or volume if you go messing with your load? Do some output trannies just not care what they get? I'm a tron noob. Any light you shed will be greatly appreciated. Many output trannies have secondary taps so you can have multiple output impedances. Link to comment Share on other sites More sharing options...
Members Belva Posted November 23, 2008 Author Members Share Posted November 23, 2008 So the ext. jack would be hooked up to this secondary tap? Link to comment Share on other sites More sharing options...
Members Snakebite4767 Posted November 23, 2008 Members Share Posted November 23, 2008 The different speaker jacks on the back of your amp should say what they expect to feed.... 4 ohm, 8 ohm, 16 ohm are the most common. Each of these jacks, in turn, should be hooked to the amps output transformer secondary winding tap of the same value. Now days, many output transformers have only one output on the secondary side, and that output is usually 4, 8, or 16 ohm. It cost more to build a multi tap transformer so you don't always find amps with many different outputs. If the amp wants to look at.... say, an 8 ohm output, then you can feed one 8 ohm speaker, or two 4 ohm speakers hooked in series, or two 16 ohm speakers hooked in parrallel. When you start stacking speakers the OVERALL wattage that the speaker system can handle will increase. Say you have two 16 ohm-50 watt speakers hooked in parrallel. The resulting system will be equal to an 8 ohm load, that will handle 100 watts. Tube type power amps are more forgiving than solid state power amps when it comes to a mismatch of the output impedance.... but the best thing to do is make sure that the load is correct for the amp. If for some reason (can't think of a good one), you were going to mismatch the load, then it would be better to use the higher impedance. This would be less likely to destroy the power output device in the amp. Going to a lower number...say the output called for a 16 ohm load, and you hooked up a 8 ohm load, would put a heavier load on your power output stage, and be more likely to burn it out. Snakebite Link to comment Share on other sites More sharing options...
Moderators isaac42 Posted November 23, 2008 Moderators Share Posted November 23, 2008 Many solid state amps will have two output jacks, often labeled 8 ohms, 4 ohms minimum. What this usually means is that the amp is stable down to 4 ohms, and you can plug an 8 ohm speaker off of each jack, or one 4 ohm speaker off of either. Higher impedances are safe, but you'll pay a price in loss of power. If the amp has an impedance selector switch, it is almost surely a tube amp, with an output transformer. There are lots of opinions, but all agree that matching is best, that is, an 8 ohm speaker with the selector set at 8, a 4 ohm speaker with the selector set at 4, two 8 ohm speakers with the selector set at 4, and so on. Most also agree that a mismatch of -50% to +100% is usually okay, though not ideal. So, if you have a 6 ohm speaker, it will probably be fine on either 4 or 8 ohms. Many say that, for tube amps, lower is better, that is, if you can't match exactly, set the selector to the next higher impedance. So the 6 ohm load would be better fed by the 8 ohm setting than the 4. Most output jacks are simply wired in parallel. In such cases, it makes no difference which jack you plug into. The only exceptions I know of are old Sunn tube amps. The are wired with one jack connected to either the 8 or 16 ohm tap of the output transformer, depending on which speaker they were intended to power, and the other jack wired via a switching jack to the next lower tap. So, if the outputs are labeled something like 8 OHM SPEAKER and 4 OHM EXTERNAL SPEAKER, plugging into the 8 ohm jack connects the speaker to the 8 ohm tap on the transformer. Plugging into the 4 ohm jack connects to the 4 ohm tap, and also connects the 8 ohm jack to the 4 ohm jack via the switching contacts on the 4 ohm jack. So, if you plug an 8 ohm speaker into the 8 ohm jack, it is connected to the 8 ohm tap. If you then plug a second 8 ohm speaker into the external speaker jack, both speakers will be connected to the 4 ohm tap, which is as it should be because two 8 ohm speakers in parallel form a 4 ohm load. If you happened to have a 4 ohm speaker, you'd plug it directly into the 4 OHM EXTERNAL SPEAKER jack. This is a bit complicated, but don't sweat it. Most amps are not wired this way. Link to comment Share on other sites More sharing options...
Members Belva Posted November 23, 2008 Author Members Share Posted November 23, 2008 That makes it a little easier. Thanks all Link to comment Share on other sites More sharing options...
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