Using Two Combo Amps

[Lostgallifreyan]

Adding an identical combo amp should give you +6dB. Increasing the power from 100W to 200W alone will only give you +3dB. This is somewhat of an oversimplification as it's likely that a 200W combo will have a different speaker than a 100W combo.

That sounds odd to me. Wouldn't both conditions produce the +3 dB increase? It amounts to two ways to double power.. When adding an identical thing gets a 6 dB rise, it's usually like adding a tape track or mixing two signals, on the basis that it's doubling the voltage. A second (and equal) combo wouldn't be doing this.

Anything more than 3dB extra from ganging driver arrays might be more to do with increased directionality from a wavefront that is wider at source, assuming they're closely set together and not cancelling at frequencies various due to mismatched distances.

 

[Engineer_Josh]

I always wondered about tying something like four Rumble 100's together via the send/returns.
A scaleable solution for about any venue and failover with not a lot of loss in capability if one died.

pretty sure one of the TB’ers uses two rumble 100’s as his gigging rig

 

[rtslinger]

I have done it and used it live sounded great
Peavey MAX 112 200w and a Fender Rumble 100 100w 1*15 I did not do it for more volume I wanted the low end of the 15"

 

[oldcatfish]

Hi folks. I have a question for you experts out there. I have never gigged in any situation where I needed anything larger than a combo amp. If I needed more "oomph" I just ran out of a D.I. from my pedalboard or out to the FOH from the line out of my amp. I was just wondering, theoretically (because I don't have a practical need to do this right now), could I add a second combo amp and get the same coverage as having a larger amp and multiple cabs? I'm mean, would two 100-watt combos give the same coverage and output as a 200-watt amp? I mean, I have a perfectly good combo and I would rarely use anything bigger. But if I had "Combo A" at home and "Combo B" at a rehearsal location, and I needed to cover a larger gig, could the two be used together, either by feeding the line out from one to the other, or by splitting off the stereo outputs of my rack's mixer? Just wondering.....

—I have found the easiest and most reliable method for me is just to use an effects pedal with a stereo output. Bass into effects pedal, each output to separate amp. It works even with the pedal in bypass and with two different amps.

 

[G-Dog]

Not sure you could do that [chain 4 Rumble 100s] because when you use the Effects-in/return, you are totally bypassing the preamp of the slave amp. You are using the preamp from the 1st amp, the "master amp" and delivering that to the power-section only of the 2nd amp, the "slave amp". So the effects send/out of the second amp is not going to have a signal to connect to the power section of the 3rd amp, let alone the 4th. ... ... ...

That's my thinking, too, Rip. The slave has no preamp signal to send to another slave, so you need a splitter somewhere to run two sets of master/slaves.

... ... ... Actually, depending on how the amp is wired, you might be able to do that. If so, then the 2nd rumble's preamp would be running into the power section of the third amp and the third one's preamp would be running the power section of the 4th. It "might" be possible. If they were all Rumble 100's you could theoretically use the same settings on the first three amps to get close to the sound from the first. Of course you'd have to balance all 4 master volumes...that would really be a mess. And God help you if you have to track down a hum.

Per the Rumble 100 block diagram, I don't believe it would work that way. In fact, going from FX Send of the master to FX Return of the slave on these Rumbles gives the master total control of the slave. None of the controls on the slave have any effect.

It's very efficient that way, having just 1 set of controls for two amps. Actually, if you chain two Rumble 200s or 500s together, you could then add extension cabs to both of them, thus running 4 sets of speakers at higher wattage than the 2 amps alone. (200 runs at 140W alone and the 500 at 350W, until you add an 8 ohm cab to get nameplate power)
.

 

[JACKSON JS1XM]

ABY Box with a boost pedal, EQ & power up for volume at each combo.

 

[basscooker]

Marshall Micro Bass for giggles. Worked ok. Even both amps full tilt is only about 60 watts. No fx return to use, so balancing the second amp was tricky. The preamps are stacked, so the second amp was a bit noisy.

 

[JACKSON JS1XM]

The way I see it, each of the combos produces 100W of theoretical power (Rumble 100's or whatever the amps being used are) at whatever efficiency the speakers are capable of. Loudness & volume are more a function of the distances where the sound is measured anywhere in the venue, so acoustics of the building come into play for efficiency, whether it's carpeted or a concrete floor to absorb sound. The difference in volume for decibel loudness is more a function of covering the cubic footage of the venue. With 2 combos, let's say your room is 22x20x8, that's 440 sq ft or 3,520 cu ft of venue/garage. 2, 100W combos are going to cover that area better than 1, 100W combo with 2 speakers at 50W per speaker. With the latter rig, One of those speakers is 20-ish feet away from the other at 50W, as opposed to both speakers getting the amps full 100W. The 2 combos are not only louder by their 3-6 dB level, the 12 or 15 inch speaker only has to cover 1/2 the room instead. It's really about the efficiency of where anyone is in the room & relative coverage of square footage.

A simple way to see it. Use a smartphone meter and measure the decibel level 6 inches in front of a combo amp and then walk across to the furthest point in the room. the decibel level will drop -6 dB over that 20-25 feet. Put 2 combos at each end of the room and either has in theory the volume/loudness in dB that each combo is capable right in front of the speaker. At the midpoint, there are going to be sound at the same output, hopefully the sound waves aren't cancelling each other out.

 

[garp]

For some gigs, I've been using a pair of Fender Bassman 150 combos, fed by a Line 6 Bass PODxt. I like the redundancy factor.

 

[LowActionHero]

I ran 2 identical combos (GK MB115) from a stereo pedal (Zoom B3).

Works great until your drummer trips over a cord,
then it works half as good.

 

[GregT]

I use a Rumble 200 and a Rumble 100. Effects send of one goes into the regular input of the other. I leave the EQ the same as usual on both of them and it works perfectly.

 

[themickster]

Here is post I wrote while back, where an isolation transformer worked :
Low-Wattage Tubesters Official Club

FYI, I believe the the Ebtech HE-2-XLR is being rebranded as the Morley MHE.

There's more than one way to skin a cat, and your way would be good for when there's no balanced line. I answered your bit about Return not killing the feed.

 

[Hasty]

If guitar players can figure it out... surely bass players can do it louder and better.

 

[pingvuiini]

I ran into that problem with my Eden Nemesis RS400 when I first got it back in 2008. The problem you're running into is that you are sending the signal out of the first one just fine and it's running your slave amp like it's supposed to do, but the signal return on the master amp is not getting any signal it back in. A simple Y-cord will fix that. Plug the Y cord into the effects-send and then run one short cord right back into the effects-return on that first combo. Run the second line from that Y-cord into the effects-in of the your second combo and everything should be working.

I just got a response from Gianfranco at GR Bass and he said to use a XLR to 1/4" cable to go from the DI of the master to the input of the slave. But the Y cable method sounds just as simple. Does it matter that the jack going into the master effects send is TRS? I much prefer the cable methods to the ABY pedal method dude to simplicity and less stuff to carry around and set up. Thanks!

 

[agedhorse]

I always wondered about tying something like four Rumble 100's together via the send/returns.
A scaleable solution for about any venue and failover with not a lot of loss in capability if one died.

It can be done, but not by linking sends and returns. A custom cable or splitter box would be needed to take the master send and split into the 4 returns.

Ground loops might or might not be an issue.

Everything @Wasnex said (always—such a resource ) and:

If both combos have available 1/4” outs and at least one of them uses a conventional 1/4” plug in one of those outs to connect the amplifier to its own speaker(s), you can unplug the speaker(s) of one combo and power it/them with the other using a male-to-male 1/4” coupler between the cable coming out of one amplifier and the cable going to the speaker(s) of the other.

Only if the amp can drive the lower rated load impedance, and you would need a female-female coupler. Note that any metal on the shell of the coupler (sleeve terminal) must NOT touch any metal on any amp or other cable.

Not sure you could do that because when you use the Effects-in/return, you are totally bypassing the preamp of the slave amp. You are using the preamp from the 1st amp, the "master amp" and delivering that to the power-section only of the 2nd amp, the "slave amp". So the effects send/out of the second amp is not going to have a signal to connect to the power section of the 3rd amp, let alone the 4th.

Actually, depending on how the amp is wired, you might be able to do that. If so, then the 2nd rumble's preamp would be running into the power section of the third amp and the third one's preamp would be running the power section of the 4th. It "might" be possible. If they were all Rumble 100's you could theoretically use the same settings on the first three amps to get close to the sound from the first. Of course you'd have to balance all 4 master volumes...that would really be a mess. And God help you if you have to track down a hum.

Correct.

A balanced line between the two will deal with that

Not happing on an MI amp.

That sounds odd to me. Wouldn't both conditions produce the +3 dB increase? It amounts to two ways to double power.. When adding an identical thing gets a 6 dB rise, it's usually like adding a tape track or mixing two signals, on the basis that it's doubling the voltage. A second (and equal) combo wouldn't be doing this.

Anything more than 3dB extra from ganging driver arrays might be more to do with increased directionality from a wavefront that is wider at source, assuming they're closely set together and not cancelling at frequencies various due to mismatched distances.

The result is +6dB, 3dB due to the increased power and ~3dB due to increased radiation area (with double the motor strength).

 

[agedhorse]

I just got a response from Gianfranco at GR Bass and he said to use a XLR to 1/4" cable to go from the DI of the master to the input of the slave. But the Y cable method sounds just as simple. Does it matter that the jack going into the master effects send is TRS? I much prefer the cable methods to the ABY pedal method dude to simplicity and less stuff to carry around and set up. Thanks!

IME, the effects send split into 2 effects returns is a better way because that guaranteed correct level and polarity.

 

[pingvuiini]

OK! I think I will go with this method for sure. What about the TRS vs TS of the effects send jack?? Does it make a difference??? Thanks!

 

[Lostgallifreyan]

The result is +6dB, 3dB due to the increased power and ~3dB due to increased radiation area (with double the motor strength).

Ok, that works for me. So long as there's no perception complications. An explanation based on the emission makes sense.

Is that extra ~3dB an approximation, or is it a specific, i.e. 3.162277.., square root of 10...? I'm trying to understand where it relates to things like the dB scales on Wikipedia, or if it even does so.

 

[H K]

I use a Rumble 200 and a Rumble 100. Effects send of one goes into the regular input of the other. I leave the EQ the same as usual on both of them and it works perfectly.

Could one theoretically run 4+ combos this way?

 

[Old Garage-Bander]

It can be done, but not by linking sends and returns. A custom cable or splitter box would be needed to take the master send and split into the 4 returns.

Ground loops might or might not be an issue.

Got it. Thanks for the input. Was just a thought experiment (brainfart) anyway.

Yup. Always the potential of ground loops.