Guest Post: How to Use Amps and Iso Cabs on Stage, Part 1

Kevin McPeak at work.

Kevin McPeak is the Creative Director at EastLake Church in Chula Vista, California. He is a proponent of both tubes and digits.  You can follow Kevin on Twitter @kevinmcpeak or find him on Facebook.  Kevin has kindly agreed to lend us some of his expertise in technical issues and will be posting from time to time.

Q: I play electric guitar and love my amp sound, but we donʼt use amps on stage because of stage volume. Is there some way I can use my amp so it does not impact stage volume?

Well, first off, letʼs identify the problem, because that will help us find a solution. The reasons that our mix engineer wants us to keep stage volume under control are many:

  • stage volume blurs front of house (FOH) mix clarity
  • stage volume creates ever-increasing demand for volume from stage monitors
  • stage volume leads to “hot spots” and “cold spots” where instruments are either too loud or too soft
  • stage volume dramatically limits the FOH engineerʼs ability to create a thoughtfully and musically designed mix.

So letʼs be clear: amps arenʼt the problem in and of themselves; the problem is that amps tend to get treated like personal monitors and turned up too loud. Furthermore, many amps donʼt sound their best without running at a decent volume. How the heck do we solve the problem?

First, you may want to give amp modeling a shot. The technology of amp modeling has come a long way in the past few years, so if you tried it before and you didnʼt like it, you might want to try it again. The versatility and tone quality of most amp modelers has gotten quite good.

But letʼs say that youʼre like me and youʼre one of those finicky tube amp people. Youʼve spent a lot of time on your tone and have finally found something you want to stick with, but itʼs dependent upon that magical combination of guitar, whiz-bang pedals, and amp. And at least for me, part of getting the tone I like involves turning up the amp a bit and letting the tubes do what they do, and that requires me to run at a higher volume. When thatʼs the case, what can you do to keep your tone intact but keep the FOH engineer from throwing darts at you?

A few years back, I decided to solve this by purchasing an isolation cabinet for my beloved amp. An isolation cabinet – also commonly called an iso cab – is an enclosed box within which a speaker and a microphone are mounted. The iso cab also commonly features sound baffling to help reduce the amount of sound that emanates from the cabinet once itʼs closed up.

What does it look like? Iʼm glad you asked. First off, hereʼs how it looks from the outside (itʼs the box on the bottom):

As you can see, it functions much like any other speaker cabinet in an important way: It gives me something to set my amp on. (After all, we couldnʼt put these tube amps directly on the floor, could we?) Bear in mind that the cabinet is a completely enclosed box. But how do we see whatʼs inside? Check out the picture below:

Once you open up the cabinet door, you can see the microphone and stand that are used to pick up the natural tone of the amp and speaker. (See below for a closer look.)

The idea is then to take the microphoneʼs signal from the iso cab and send it back to the mixer, where the FOH engineer can use as much – or sometimes as little – of it as he/she needs to create a workable mix. But the use of the iso cab allows me to open up and let the amp sing a little bit without generating angry looks from everyone else in the room.

For the tone purists, itʼs reasonable to ask if the iso cabs alter the sound in any way. The short answer is that they do. My experience has been that iso cabs can inhibit spaciousness a bit, but thatʼs not unreasonable if you consider that the sound is being picked up in a small, padded box. However, for the purposes of live sound, the benefit thatʼs gained by using a favorite amp more than offsets a modest alteration in tone.

So, if youʼve got a favorite tube amp that you want to use in a live setting but your FOH engineer keeps giving you the stinkeye when you bring it in, itʼs time to start thinking about getting yourself an isolation cabinet so you can turn it up to 11 and let that amp sing.

Have another technical question you would like Kevin to answer?  Post your question in the comments.

5 thoughts on “Guest Post: How to Use Amps and Iso Cabs on Stage, Part 1

  1. As a member of the Eastlake worship team, a FOH engineer and, finally, guitar player who occasionally uses Kevin’s rig when he’s away for other things, I can say that this totally works.

    There is definitely some tone loss when going to an iso cab, but for all intents and purposes, it sounds perfect. Also, the general congregation will NEVER know that you’ve lost 2.5dB at 1kHz and most of the 200-250Hz range that you would get out of a big 4×12 cab (do people actually use those at church???).

    I will say that I still refuse to run amp modeling myself. I can always hear the difference, even if other couldn’t and as a self-avowed tone snob, I just can’t give in that far. Maybe one day we’ll get there, but not yet.

  2. Hi, guys! My amp is a Line 6 DT25 hybrid combo…digital preamp, tube power amp. We’re starting to go less and less on stage volume, but we aren’t going to in-ear monitors just yet. My amp has a cabinet simulated Line Out that sounds very good. Since I wouldn’t be mic’ing my amp, but using the cab simulated Line Out, would you recommend an iso box for my application? Thanks!

    • Hi Wes,

      Thanks for your question. Here’s my two cents (and it might be worth less than that): Line 6 does a great job of designing their amps with the cabinet simulation in mind, so I think you’re probably in very good shape by using the cab simulator line out that they provide. Ultimately, your best bet is to do an A/B comparison between the line out and a mic’ed cabinet, but I would expect that in your case you’ll be pretty close in tone between the two. If you do go with an iso cab, I would anticipate that you’ll notice at least some difference between the sound of the DT25’s built-in speaker and the iso cab, insofar as the DT25 will probably sound a little more open and spacious.

      A reasonably short rant: Lots of players are quick to gripe about the various amp/cabinet simulator products. In some cases, their opinion is based on older technology from earlier generations of gear. In other cases, they just haven’t spent enough time working with the equipment to dial in tone that they’re happy with, which is sometimes not unreasonable because the presets on some of the gear can be pretty clunky sounding. Of course, there are some guys (like me) that have a particular tube amp they love and the only way to get the tone they want is to use an iso cab. But I do think that it’s worth spending the time with the amp/cab simulators to mess around with the settings and dial in what sounds best. In working with a few guys at our church who use them, my observation is that they usually sound bad because they’re throwing too much processing on the signal. Not everything needs compression, gating, chorus, and a stomp box emulator.

      In summary: I’ll bet that if you’re happy with the DT25’s sound on its own, you’ll be pretty happy with it’s cabinet simulator line out. If not, connect to the PA, sit in the house, and dial in your settings until you’re happy. (I still do this from time to time to make sure I haven’t let my tone drift.)

      Best of luck to you!


      • Thanks, Kevin! So far, I haven’t been disappointed with the cab simulated Line Out on the DT25. Although it’s a little brighter through our PA system (EQ flat) than what I thought. I assumed it would be a little darker and more compressed, but I was wrong:)

        If we do go to a silent stage, I think I’d prefer to get an ISO cab to keep the DT25’s tubes in the equation, versus not using the DT25 at all and just going from the HD500 to our PA system and using in-ears.


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