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[Stephen Kirby]

I used to use a PLX3602 on subs.  At some point I replaced it with a Crest Pro 9200.  The first gig with it was a club we played every month and just used two 1-18s.  In the first set the keyboard player did an organ rush (glissando from the low end of the keyboard) and immediately looked up at me with this "what did you do with the PA?" look on his face.  Then he came over and asked during the break.  Same settings and levels we always used in there.  But when he mashed the low end of the keyboard you could feel it in the floor.  If wasn't that it was louder, but it was noticeably more solid.  All this by way of saying that as good as the PLX are (and even though I've migrated to powered tops and monitors I've kept the 3602 as a back up to the sub amp and to have just in case for other things) they tend to be somewhat limited, don't tolerate low line voltage well, and just don't work on subs as well as some alternatives.  Splitting one between top and sub duty might just not give you the clarity and reserves you need at some point.

[Alex Magor]

I used to use a PLX3602 on subs.  At some point I replaced it with a Crest Pro 9200.  The first gig with it was a club we played every month and just used two 1-18s.  In the first set the keyboard player did an organ rush (glissando from the low end of the keyboard) and immediately looked up at me with this "what did you do with the PA?" look on his face.  Then he came over and asked during the break.  Same settings and levels we always used in there.  But when he mashed the low end of the keyboard you could feel it in the floor.  If wasn't that it was louder, but it was noticeably more solid.  All this by way of saying that as good as the PLX are (and even though I've migrated to powered tops and monitors I've kept the 3602 as a back up to the sub amp and to have just in case for other things) they tend to be somewhat limited, don't tolerate low line voltage well, and just don't work on subs as well as some alternatives.  Splitting one between top and sub duty might just not give you the clarity and reserves you need at some point.

Should I use 1 Crest amp for both tops and bottoms or would I be better off using 1 amp for tops and 1 amp for bottoms?

[Luke Geis]

Depends?

If the subs and the tops are all 8 ohm's you can run a mono system that has the tops on one channel and the subs on the other. This will put a 4 ohm load on the amp and will work quite well. Now if the subs and tops are 4 ohm's each, you may want to reconsider? I am not sure if your amp is rated down to 2 ohm's per channel? If it is rated for 2 ohm loads in dual channel mode, then you will again be alright to run everything off the one amp.

I usually suggest running a dedicated amp for tops and for subs. Two reasons:

1. If the amps breaks down or you loose a channel, you can at least get through the gig in limp mode. You will have to reconfigure things to make it work, but at least you can if you have a good working amp.

2. Proper powering of your speakers. As we know, having an amp that is too small is not going to hurt anything, but trying to get the SPL out of an amp that may be grossly under powered is not ideal; especially when you run it into clipping! If you use a dedicated amp approach, you can power each part of the system as it was designed to be. This is of course more ideal. It truly depends on how closely rated your tops are vs your subs. If you need the same power going to each half of the system, it is not as big of a deal, but you are still better off with an amp dedicated to each half ( as per point # 1 ).

A third and possibly more debatable reason is that using subs on one half of an amp and tops on the other will present an uneven load to the amp. If you have the subs going full bore, it is likely that the top swill be pulled back a little to achieve balance. This means one channel of the amp will always be working a little harder than the other. This probably doesn't have any negative implications in the short term, but my bet is that in the long term it will. With one side always working harder, there will be more heat on one half and eventual failure will occur on that side sooner. Perhaps not though?

[Dave Garoutte]

A third and possibly more debatable reason is that using subs on one half of an amp and tops on the other will present an uneven load to the amp. If you have the subs going full bore, it is likely that the top swill be pulled back a little to achieve balance. This means one channel of the amp will always be working a little harder than the other. This probably doesn't have any negative implications in the short term, but my bet is that in the long term it will. With one side always working harder, there will be more heat on one half and eventual failure will occur on that side sooner. Perhaps not though?

If you swap amp channels from show to show to show, it will even out the 'wear'.

[Stephen Kirby]

In my experience the PLX will safely run at 2 ohms.  But there is a noticeable drop in sound quality.  It just sounded more strained and blurry when I tried it.  Thinking I could get more headroom with "more power" I actually got less.

If you're not running very hard you could get away with splitting duties between the channels of one amp.  Especially if it's a good robust amp.  PLX are good sounding and reliable, but I don't think of them as robust.  Kind of like conversations you read about here with folks replacing XTi's with iTech HDs.  The regular PowerLight series is QSCs robust touring versions.

As they say "it depends".  All the amps in the discussion are <25lbs.  Two in a rack compared to one isn't going to make or break a load in.  When I had a completely passive system I had the three mains amps and DSP in one rack and the monitor amps in another.  All one man lifts.  If all your gigs are in small rooms at moderate levels, then one amp is fine.  If you need to move people in a larger room (and many weddings I've played were in moderate sized hotel ballrooms) then two good amps is probably called for.

[Brian Jojade]

A third and possibly more debatable reason is that using subs on one half of an amp and tops on the other will present an uneven load to the amp. If you have the subs going full bore, it is likely that the top swill be pulled back a little to achieve balance. This means one channel of the amp will always be working a little harder than the other. This probably doesn't have any negative implications in the short term, but my bet is that in the long term it will. With one side always working harder, there will be more heat on one half and eventual failure will occur on that side sooner. Perhaps not though?

In a well designed amp, each channel functions independently, as long as there is sufficient power available.  I regularly will put a top on one side of an amp and the sub on the second side for each channel instead of one amp for tops and one amp for subs.  The primary reason to do this is to even out the current draw between the two amps when splitting circuits.  Interestingly enough, the average current draw for the tops is usually higher than it is for the subs.

As far as wear and tear on the amps, I doubt that matters even a little bit. At least not enough to create a measurable difference in the life of the amp.

[Luke Geis]

Hence why I said it was debatable. And of course if things are pretty well evened out, it is another non issue perhaps? My point being that if the amps halves are grossly different in terms of power delivery, can it and would it shorten life for one side?

Forget that all together. If you show up to a show with one amp and one amp only, then it fails, you are up a creek with nooooooooo paddles. At least with a second amp you have a backup plan that allows limp mode.

[Alex Magor]

Hence why I said it was debatable. And of course if things are pretty well evened out, it is another non issue perhaps? My point being that if the amps halves are grossly different in terms of power delivery, can it and would it shorten life for one side?

Forget that all together. If you show up to a show with one amp and one amp only, then it fails, you are up a creek with nooooooooo paddles. At least with a second amp you have a backup plan that allows limp mode.

Like I said I have a second amp as a backup which is used for monitors in case the main amp dies.  And I have a backup powered monitor as well. 

[Alex Magor]

Well we just had back to back wedding gigs and tried working off one amp the first gig and 2 amps the second gig and both of my partners said the second gig sounded better and that there was more power behind the sound.

[Brian Jojade]

Hence why I said it was debatable. And of course if things are pretty well evened out, it is another non issue perhaps? My point being that if the amps halves are grossly different in terms of power delivery, can it and would it shorten life for one side?

Forget that all together. If you show up to a show with one amp and one amp only, then it fails, you are up a creek with nooooooooo paddles. At least with a second amp you have a backup plan that allows limp mode.

When the amp is powered on, even with no load, there is a certain amount of wear and tear on the amp.  Driving speakers does heat up the transistors, which does cause failure eventually. However, unless you are driving your amplifier to the point of premature failure on the side you are using, the change of the lifespan of that side of the amp will be minimal, if even measurable.  An amp that is overloaded and driven hard, no matter what, will have a shortened lifespan.  An amp that is used within spec can last decades.  Proper storage conditions would have a greater impact on the life of the amp rather than measuring which side had more real life use out of it.

[ProSoundWeb Community]