Power amplifier modes explained

hello YouTube Bruno loose here with glb productions thanks for joining me in this video I'd like to discuss a topic that I get questions on all the time and that is power amplifier modes now I did go over this in my video that I did recently on how to connect an amplifier in bridge mono but I thought that I break this topic out into its own video which will also give you guys a platform to ask me questions specifically on this topic so before we start just to be clear when we say power amplifiers we are talking about two channel sound reinforcement power amplifiers like these QSC plx series amps that you see behind me so without further ado let's get on with this video now let's begin with the most common mode that we have and that is stereo now I thought that this mode should actually be called independent mode because a lot of people think that you need to use the two channels as a left and a right channel but as we'll see there are actually many many different ways of deploying them so if you look at my little diagram here you can see that in this mode the two channels are fully independent meaning that each one has its own level control and its own processing when we say processing we're referring to things like high or low pass filters some amplifiers have built-in compression or limiting that sort of thing they are completely independent and they are set separately for the two channels the settings on channel one do not affect the settings on channel two and vice versa now this mode is probably the most versatile because you effectively have two mono power amplifiers that you can deploy in whatever way you want now the most common will definitely be this one here in which they are deployed as front of house left and front of house right so here you have your signals coming in from your mixer you have your left and your right main outputs those go to channels 1 & 2 the output of channel one goes to front of house left and the output of channel 2 goes to front of house right of course it could be the other way around but typically one is left and two is right I've shown four speakers here of course you could run any number you could run one speaker aside if it was a small system or you could run any number depending on the sort of coverage that you need it the point is is that here left and right are completely independent and they have their own level control and processing another way that you can deploy the two channels is to use one channel for your mains or front-of-house and the other channel to run stage monitors this is a very common setup with stereo powered mixes which have two channels and typically they're required to run the whole show so let's have a look at how this would work coming in to channel one you will have a mono signal of some kind it could be your left your right or a mono some of the two now if you're using a stereo mixer and you want to deploy it this way you have to leave all of your pan controls at 12 o'clock because obviously if you're using your left output and you Pan stuff to the right won't appear in your front-of-house feed so left right all mono comes in to channel one and you then daily change the two speakers together in this case I've written in front of house left and right but notice that they are still in mono the left and the right simply refers to the physical position of the speaker's visibie the audience they are daisy chained together and they are considered mono the other channel you will connect a box end from your mixer and you will use that for your stage monitors obviously in this case you only have a single oxide and therefore you only have one monitor mix but this is a very common setup for small PA systems using a single power amplifier or as I mentioned earlier a powered mixer which has two channels in it internal power amplifier now let's discuss two other ways of setting this up using the stereo mode that are most definitely not stereo the first is to use one channel to run your full range speakers and the other channel to run your subwoofer now in this one here you can see channel one is fed full-range signal either the left right or a mono sum of the two and it is used to power both the front of house left and front of house right speakers once again these are daisy chained together they are in mono alright channel 2 is fed a subwoofer signal now this can be derived from the output of an active crossover or it can be derived from a digital signal processor like a dbx drive rack this signal is then used to drive the subwoofer now one of the interesting things about this setup is that it gives you interesting options for playing with impedance typically front of house full range speakers will be 8 ohms right professional cabinets are usually 8 ohms with the exceptions of large DJ type door woofer cabinets which are 4 ohms those are usually designed to be run without a subwoofer to make setup more easier easier so if you combine two of those you will have a combined impedance of 4 ohms which obviously raises the power output of that channel right lower impedance higher power this is assuming your amplifiers designed to run into 4 ohms you can then run a subwoofer which is 4 ohms now you can get professional subwoofers that are configured as 4 ohms and those four arms subs are typically for running in this type of situation where you're using one channel to run your front of house full range and the other one to run a subwoofer of course you can also run an 8 ohm sub it depends on the exact power requirements of your system as well as the coverage that you need so for more information on how to match speakers and power amplifiers please see my dedicated video on that topic the last configuration that we're going to look at for stereo mode is this one in which you are using both channels to run a buy amplified speaker now speakers that are buy amplified have the ability to take two amplifier channels right one to run the lows and one to run the highs or if it's a 3-way speaker to run both the mid and the hinds right I can think of a number of large speaker cabinets for example the pv sp2 that are configured this way a lot of stage monitors can also be run by amplified if you want the maximum power output from them so in this case channel 1 would be fed a low signal and channel 2 would be fed a mid and high signal now obviously in order to get these two signals you would need either an active crossover or a DSP that is set up to do this right so loes you would run a low-pass filter and highs mids you would run a high-pass filter the exact crossover frequency would depend on the design of your cabinet and it's requirements so as you can see channel one feeds the lows and channel two feeds the mid and the highs now let's move on to the second main type of power amplifier mode parallel now the difference between stereo and parallel is that the two amplifier channels are connected internally a signal to either channel feeds both channels so whatever you send to channel one feeds both channels one and two and vice versa separate level controls and processing so things like your high-pass filter limiters are still set independently now this mode is probably the least glamorous of the three right and typically this is used in larger systems where you want to avoid having to run jumpers between multiple amplifier channels so here are a couple of creative examples as to how this might be run the first is where you would use them to run a large PA system where you have a combination of long throw speakers and short throw speakers so in this case you would send a full range signal to the amp the signal would then be split internally this is done within the amplifier there's no additional wiring needed channel one would feed your left long throw for example and channel 2 would feed your left short throw now this is just an example there are many many different ways of using the two channels if you are running a very large system for example where you had four cabinets beside you might simply connect two cabinets to channel one and two cabinets to channel two all the cabinet's are the same you just point them in whatever direction you need to get the appropriate coverage another way is with stage monitors now in this case the amplifier is fed a signal that is derived from an aux end in two wages a power with channel one and two edges are powered with channel two and these could be strung across the front of the stage for example I've done big band concerts like this where everybody needs to hear the singer and they just want a whole bunch of wedges across the front the stage pointing back at the band so that's parallel mode relatively simple straightforward utilitarian but still very important especially in larger systems and finally the most mysterious and exciting of the modes to many people we have bridge or bridge mono mode now in the case of bridge mono mode what you're doing is you are using the two amplifier channels effectively as one large amplifier now in order to understand this you have to understand what the amplifier is actually doing to the loudspeaker : under normal circumstances when you present a positive voltage to the input of the amplifier the amplifier channel generates an electro-motive force that moves the loudspeaker cone forwards when you present a negative voltage to the input of the amplifier it moves the owner backwards now on JBL this is the other way around for a long time and now they've come into line with other people when you bridge an amplifier what you're doing is you are using channel 1 to push the amplifier cone and you're using channel 2 to pull the amplifier cone now this is not a perfect analogy but I think you get the idea in practice the way that it works is this a signal is presented to the amplifier which consists of channel 1 and channel 2 the signal going to channel 2 is inverted in polarity meaning the waveform is flipped upside down so as you can see the outputs look like this the waveform the channel 1 produces is identical in polarity to the input waveform the waveform the channel 2 produces is inverted in polarity it's flipped upside down channel 1 is connected to the positive terminal of the loudspeaker and channel 2 is connected to the negative terminal of the same loudspeaker now the net result of this is that you get double the output voltage because you're using two channels instead of one to drive a single loudspeaker you get four times the peak power and three times the sustained power and as a result you can have very very large increases in power output as an example the lower amplifier and this rack the QSC plx 1602 it's 300 watts per channel into 8 ohms when you bridge the amplifier into 8 ohms you get 1,100 watts so you can drive thousands and thousands of watts into a single loudspeaker as a result you really want to be careful the other thing is that you have double the normal minimum impedance so if the amplifier could normally run into 2 ohms per channel in bridge model you'd only be able to run the amplifier into a 4 ohm minimum load now the exact minimum load will depend on your amplifier so please consult the specification sheet now how do you hook this up in practice you would run a full range signal to the input of the amplifier now in some amplifiers you can use either channel other amplifiers it will specify that you use channel 1 input and level control and the channel 2 input is not used the level control is typically turned all the way down the wiring between the amplifier and the loudspeaker is proprietary typically if the amplifier has binding posts you would connect to the 2 red binding posts if the amplifier has speakon connectors the usual arrangement is that they would use plus 1 and plus 2 on channel 1 speakon now for more information on this please watch my video how to set up an amplifier in bridge mono mode so that's a brief rundown of the three different power amplifier modes that there are stereo parallel and bridge mono I hope that this video was helpful if you have questions or comments please leave them below if you like what you see and you'd like to support the channel please remember to subscribe and also please consider signing up to become a patron by on my patreon page this is Bruno loose for GLB productions thanks very much for watching and I'll see you in the next video bye bye you

Channel: GLB Productions

Views: 227,529

Keywords: sound reinforcement, power amplifiers, stereo, parallel, bridge mono, impedance, loudspeakers, bridge

Id: HKpV30pjvIo

Length: 16min 48sec (1008 seconds)

Published: Wed Apr 19 2017