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Bass head that will handle three cabs


DeepEnd

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I'm doing research for a project at church and I need some advice. As the title says, I'm looking for a bass head that will run three cabs at once. Most heads I've seen will run two cabs with no problem but in this situation it may be necessary to run a third from the same amp. A further stipulation is that it has to be new and it has to be available from Guitar Center. Thanks in advance.

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Right. It comes down to the cabs impedance and the wattage you need. no more. Most output jacks are parallel but you can use a series cable easily enough or wire the cab jacks for series/parallel depending on the needs to get the right impedance which is the most critical item.

 

How well it may sound with say one cab in parallel with two others in series for example is questionable. Many solid state bass heads are variable voltage designs that can take a load from 16 to 2 ohms just like PA power heads can and the lower the impedance the higher the wattage they produce. Three 8 ohm cabs in parallel gives you 2 ohms. 3X16 ohms in parallel gives you 5.3 ohms which is close enough to 4 ohms. Tube heads on the other hand have transformers and therefore need specific impedances, especially if they have a coil tap switch.

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Let's assume we're talking 8 ohm cabinets. Three 8 ohm cabinets in parallel gives us a nominal impedance of 2.67 ohms. That's a bit higher than 2 ohms, but still well below 4 ohms, so you'd need an amp that's stable below 4 ohms, and that usually means down to 2 ohms. Old heads that would work include the Sunn Coliseum amps and the Gallien-Krueger GMT 600B, but those are 40 years old, and don't meet the criteria of being new and available from Guitar Center. I'm sure there are new amps that meet your criteria, but I haven't looked at new amps for a long time, having more than I need already.

 

If more than one of the cabinets is a 4 ohm cabinet, you're out of luck, I think. Two 8 ohm cabinets and one 4 ohm cabinet could work, but be aware that the cabinets would not share the load equally. In fact, that can be the case even when the cabs are the same impedance. I have two Sunn cabinets, the Model 215 and Model 410H, both 8 ohms, and the Model 215 is much louder than the Model 410H. That's not a problem for the amp, but it's something to be aware of. I find it best to use similar cabinets when powered from the same amp.

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There are probably a lot of used heavy stereo PA heads that would do the job just fine. You might need to run one of the cabinets on one channel and the other two on the opposite channel. Lot people trying to reduce the weight of their PA system, so these solid hard to kill clean amps are probably cheap. (And they would all be more power than most bass rigs need.)

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Some amps like some older Peavey stuff I've seen are stable into 2 Ohms so I know such amps do exist. I'd make sure the cabs were 8 Ohms minimum and that the amp could handle 2 Ohms. I specifically want an amp that has existing connections for three cabs. It looks like I'm going to have suck it up and research this on my own. Thanks anyway.

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????? The number of output jacks on an amps back panel don't mean jack. Pun intended.

 

The jacks in the back panel of most amps heads are connected directly together to the same circuit in a Y jack configuration. They don't go to separate transformers or separate circuits in most cases in a mono head. Stereo heads, yes, you have separate outputs on each. There are also some special configs that use resistive loads, but those are the exception. 95 percent of the bass heads have simple mono outputs from the same circuit. They usually have two to make it convenient plugging in two cabs, but that doesn't stop you from running more cabs.

 

You can run 10 cabs with a single output jack so long as the impedance matches. Cabs often have two jacks in parallel. These are for daisy chaining other cabs together. Plug the head into the first cab, use the second jack on the cab to connect the second cab, use the second jack on the second cab to connect the third cab, etc etc.

 

You of course have to be sure the jacks on the can aren't switched to split the speakers to stereo or in rare cases designed to change the cabs impedance. Its easy to check with a simple ohm meter plugging in the two cables and reading between the two tips to be sure it reads zero ohms.

 

If you need to match the heads impedance, then you would have to do some rewiring, either internally in the cabs to the jacks or externally to get the impedance to match the head. Most jacks will parallel the load bring the impedance down. You can wire the two jacks on a cab so they are in series. You have one that's an input, the second jack is switched and breaks the circuit and inserts the second cab in series with the first cab.

 

If the cabs only have one input jack, then you can so this same thing with either a breakout box or specialized cable that connects the cabs in series or parallel. You run one cable from the head to the box, and the box will either act like a three way Y jack or a series parallel connection. The most it may cost you is a couple of 1/4" jacks. The box doesn't need to be shielded but having it made of metal saves you from extra wiring having a common ground.

 

You can also just wire the cable itself soldering extra 1/4" plugs to it. Have one plug at the end for the head, Connect two sets of wires to one plug, have the second lead go to another plug in parallel and act as a Y jack. You can even do a third this way if the impedance allows you. This is the same as you have for Guitar pedals power supply daisy chained together in parallel.

 

The difference with cabs is you can connect to 1/4" plugs in series. You have to have both cabs plugged into the cable to get continuity of course.

 

The rest is just ohms law at work and matching the cabs to run efficiently. With 3 cabs, you may have two cabs that are louder then the third. Connecting the two cans in series will drop the SPL level of the two because the wattage is split between the two. Connected with the third in parallel may give you a good balance between the third "If" you need a series parallel connection to match the heads impedance.

 

Again, knowing what impedance the cabs have, the number of speakers in each cab is essential in advising what may work before you begin. You must know these details first, then purchase the head that will handle the load.

 

the number of jacks on the head doesn't even come into the picture. They are simply a convenience having more.

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Some amps like some older Peavey stuff I've seen are stable into 2 Ohms so I know such amps do exist. I'd make sure the cabs were 8 Ohms minimum and that the amp could handle 2 Ohms. I specifically want an amp that has existing connections for three cabs. It looks like I'm going to have suck it up and research this on my own. Thanks anyway.

 

Seems like the easiest way would be to call or email Guitar Center and ask them.

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????? The number of output jacks on an amps back panel don't mean jack. Pun intended. . . .

If an amp has only a single output jack I would infer that the manufacturer advises caution when connecting multiple cabs, otherwise there would be more jacks since it really doesn't cost that much to add another. In any event, the vast majority of amps won't handle the 2 2/3 Ohm load produced by three 8 Ohm cabs in parallel. It would be necessary to cobble together something with either three 8 or 4 Ohm cabs in series for 12-24 Ohms or three 16 Ohm cabs in parallel for 5 1/3 Ohms. Personally, I prefer to avoid unnecessary cobbling when I can.

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My Ampeg Portaflex has one 1/4" phone plug out and beside it is a Speakon out. The amp will safely drive a 4 ohm load. By the way, the manufacturer specs the amp at 300 watts at 8 ohms and 500 watts at 4 ohms. It's not a direct ratio. A lot depends upon the amp's power supply being able to keep up with demand. The amp doesn't care what is connected up as long as the minimum impedance is met. (Might be a problem with way too large an impedance.)

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If an amp has only a single output jack I would infer that the manufacturer advises caution when connecting multiple cabs,

 

No, that's usually infers they designed to head to run with their matching cab. Caution is a matter of a musician knowing how to match impedances and wattages. No more no less.

 

During my amp repair days I only came across a few oddball amps out of the thousands that had three jacks. One was either an old Acoustic or Standell bass head and one was an Acoustic PA head. The PA head was designed to run two Column cabs and a single monitor. Cant remember what the bass head was supposed to drive. Both date back to the late 60's so its been a very long time. The PA head was crap by the way. I sole one to my friend as a monitor head and they ran three monitor cabs off it.

 

The reason why most usually have two jacks simple. Extra jacks take up space in a crowded chassis and having an even number adds up mathematically to match cab impedances in most cases. Cabs are daisy chained to each other. They have two jacks because it cuts down on the length of cable needed to drive them and its not what you call cobbling them together. Its how all cabs you see stacked on stages are connected. 4 short cables are better then 4 long cables from the head, especially running high wattage. Its critical to run short cables whenever possible especially with bass to minimize the cable resistance which adds additional load to the power amp.

 

This is common with PA gear too. Your power amps are kept on stage with shorter cable runs to the cabs. The mixer may be 150' away and the mics are run to the board through a snake, and then the line level mixer output comes back through the snake to feed the power amps on stage.

 

In any case, you may want to think about getting a Bi Amp bass head. My buddy uses a Peavey bi amp model. Very well built too. I did some service work on it awhile back and its built with the highest grade parts. (unlike their cheaper stuff which is all bottom of the barrel components) You can run two cabs for the lows and run the third as the mid/highs. The crossover is wide enough to get down to 500hz on the high side and the low side will easily overlap the highs up to 2K if I remember right.

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Thanks but the powers that be decided to go a different direction so we never bought the amp or cabs.

 

That's probably for the best. 3 bass cabs ( I am assuming in 3 different locations) would be a nightmare.

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That's probably for the best. 3 bass cabs ( I am assuming in 3 different locations) would be a nightmare.

This would have actually been for an organ. One speaker close to it and aimed at the person playing as a monitor and one on either side aimed at the congregation, plus a feed for the PA.

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This would have actually been for an organ. One speaker close to it and aimed at the person playing as a monitor and one on either side aimed at the congregation, plus a feed for the PA.

 

There are all kinds of ways around that... but it sounds like your church already decided on a solution. Still, had we known what the actual scenario was from the beginning we could have offered better / more appropriate solutions. :idea::)

 

 

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I'm doing research for a project at church and I need some advice. As the title says' date=' I'm looking for a bass head that will run three cabs at once. Most heads I've seen will run two cabs with no problem but in this situation it may be necessary to run a third from the same amp. A further stipulation is that it has to be new and it has to be available from Guitar Center. Thanks in advance.[/quote']

 

 

There's a couple of basshead I know that just won't quit, and will run to 2 ohms. Parallel up 3 8-10 cabs and go to town.

 

In a church setting that would be a long run for 1/4 speaker cables. I think.

 

http://ashdownmusic.com/products/1/Bass-Amplification/1/Custom-Shop/10/CTM100/

 

http://ashdownmusic.com/products/1/Bass-Amplification/2/ABM/140/ABM1200EVO-IV/

 

http://www.ampeg.com/products/heritage/svtcl/

 

http://www.aguilaramp.com/products_amplifiers_db751.htm

 

get your wallet out for these babies and then take up a second collect for some nice cabs.

 

The deal si you'd be way better running a couple of powered sub woofers off the PA. It's hard to tell the direction of low frequencies anyway.

 

How ever these are kill bass heads. :D

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. . . Still' date=' had we known what the actual scenario was from the beginning we could have offered better / more appropriate solutions. :idea::)[/quote']

Thanks but honestly I'm inclined to doubt it. ;)

 

There's a couple of basshead I know that just won't quit' date=' and will run to 2 ohms. Parallel up 3 8-10 cabs and go to town. . . .[/quote']

Thanks but, as I mentioned already, the decision has already been made so it's moot at this point.

 

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They bought an electronic organ with a built-in amp and had the speakers installed where the pipes used to be. My idea of a keyboard or organ plus a bass amp and cabs could have saved us 2/3 of the cost but the decision had pretty much already been made by then.

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Allot of churches run a 70V system so they can run multiple extension speakers all around the hall off a single power amp. Anytime you have long speaker cable distances, converting the output to high voltage low current preserves the fidelity. (like low impedance mic cables) The speakers each have their own transformer that convert the 70V line back to the proper speaker impedance. The good part is you aren't constrained to running a specific number of cabs based on their impedance. The main 70v line can run multiple step down transformers depending on the type of step transformer used at the amp. Big theatres and ball parks use allot of 70V gear too. you can run more cabs much more efficiently. I think my 2000w Crown PA power head even has a 70V tap built into it. Makes permanent installations allot easier and cable costs allot lower too.

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