Obey Your Master: The Art Of Amp Slaving

Posted on by Jay Hale

Orange cabinets

Back in the days before we had direct recording outs and stereo effects loops, if a guitarist wanted to take his favorite amp’s tone and make it LOUDER, it was done by something called amp slaving. This is accomplished by taking the signal of one amp and boosting it via the power section of  another amp. This method allow you to use the primary amp as you tone-generator, and the other amps to provide additional volume for larger venues. Using a more modern amp as the slave, you could take the out of the primary amp into the effects return of the secondary amp and bypass the preamp section of the slaved amp altogether. This maintains the “pure” tone of the primary amp, which is more often than not the goal of amp-slaving, and it’s a cool way of essentially combining the preamp section of one amp with the power section of another. For example, love your Marshall’s preamp response but wish you could hear it through a KT88 or 6L6 power amp instead?

Either way, you’re able to boost your volume appropriately when running an amp with more wattage as the slave. And you can use slaving for simple volume boosting or as a way of inserting insert effects into separate chains. These setups can be as basic or elaborate as you like. But first, there are a couple of things you have to consider as precautionary measures before ever attempting it.

“That’s right, my name is ‘Hot Plate” – and what?”

Please note –  and this is very important – if you’re considering doing this with an old-school amp without any type of direct out or effects loop, you can’t just bypass the amp’s speaker output without potentially seriously damaging – if not destroying – your amp’s output transformer! It needs to ‘see’ a speaker load, so you’ll need to employ a cab, the internal speaker of a combo, or better yet a load resistor box of some sort. There are many types on the market at various price points, like the THD Hotplate, the Radial JDX or the Palmer Speaker Simulator that will mimic a speaker load (at the correct ohmage) and spare your amp’s output transformer any serious damage. These units are also beneficial for silent recording, but that’s a topic all its own. Once you have that vital safety measure covered however, particularly if you’re using a tube amp – you get to experience one of the other main benefits of slaving: you can CRANK the tone-shaping amp’s power section to get maximum power stage distortion, the kind only a dimed amp can produce, considered by some to be the “Holy Grail” of rock guitar tone.

I’m little, but I might save your amp…

Slaving also allows more flexibility in that scenario. One could hypothetically have their 100-watt Marshall cranked with a speaker load, and slave, say, a 50-watt power amp to achieve power distortion and yet still maintain a manageable volume in a smaller venue too. That having been said, it’s usually about “MOAR VOLUME” and the ability to run more cabinets in various stage locations as well. After all, stories of EVH slaving his own “grail” Marshall into H&H power amps are not just legendary, they’re still in his touring rig to this day, for example powering cabs used as monitors for his brother Al, and for side fills if needed, etc. And since the power amps are only reproducing the “master” amp’s tone feed, the sound is consistent anywhere on stage.

If you do have an FX send and run stereo effects after the tone-shaping stage, you can have wet/dry/wet cabinet setups for sounds that are positively massive. This can be accomplished with a stereo effect (assuming it has a ‘dry’ output), a single stereo power amp and the cabinets. In this scenario the dry signal would go back to the tone shaping amp’s FX return and drive the center speaker, and the left and right outputs of the effect would go to each respective channel on the stereo power amp to provide the full effect, and drive more cabinets. The effect, particularly with time-based effects like chorusing, flanging and delays, can be quite dramatic, but pretty much everything sounds huge. If you have the capability and you feel like schlepping the extra gear around, it’s quite cool and useful, especially if your favorite amp can’t cut it by itself, and if you happen to have something else with a little more horsepower, so to speak.

What would your ideal amp-slaving rig involve?

You don’t have to go THIS nuts, but should you want to…

Written on March 3, 2013, by Jay Hale

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  • james

    So how much does the quality of the power section of the slaved amp effect the tone?
    I have a 120/60watts, all tube amp with a harsh preamp section. Could i buy a <15watt top of the range amp with a preamp i really like, and slave it into the power section of the big amp and get the same high quality preamp at 120/60watts for great tone and versatility? and if the 15 watt amp has a line out and fx loop, which is more accurately leveled and would I still need an attenuator?

    • Metal Punk

      The 120/60 watt tube amp would be great no doubt. As long as you have the ability to bypass the preamp of the 120/60 and put the signal into the poweramp. Line in of an effects loop or dedicated slave jack?? A competent amp tech could also wire an input to the poweramp.
      As for the 15 watt amp, good thought, but you still need a speaker connected to the amp, and cranked up a good 15 watt amp can be pretty loud. You would then need an attenuator to either reduce or eliminate the volume of that amp, or you could let it be heard. Obviously there are different options. I personally would think smaller amp like 5 watts or 1 watt, that will sound great driven hard, at listenable volume levels on its own, then amp it up with the 120/60 when you want more. Whatever you choose a line out and effects loop would be a serious plus. An attenuator would be a very good idea if you own any kind or size of tube amp, especially if it has a line out built into it and even better if the line out is appropriate for guitar amp input impedance so you can run one amp safely into another amps input and have fun with that as well, as you can access the preamp of the second amp as well as the Preamp of the first and sort of couple the sounds.

      • Chris Bennett

        Hi, thanks for all the info people.
        Just got a VHT special 6 ultra head and cab, and have been trying to find out if I could link it to my fender blues deluxe and 112 extension. The VHT is 6 watts of hand wired, all tube tone and I also love the blues deluxe set up (the one I gig with).
        The VHT, although very loud for 6 watts, isn’t quite loud enough to give me the slight overdrive I like at gigging volume (not far of mind).
        I know I could milk it through the pa but after looking around on here, I think its time to experiment.
        Cheers!
        Just as a point of interest, if anyone is interested or has the time to take a look at the VHT special 6 or special 6 ultra amps they are unbelievably good especially considering the extremely low price. There is a lot written about its gain capability which is impresive but it is capable of incredible clean and slightly overdriven tones as well.
        I have been playing for over 40 years and I can honestly say I have never come across such value for money.
        Thanks again for the info.

  • MetalPunk

    Great article. Nice to hear more about this very cool technique. The THD Hotplate is an excellent device, that has many possibilities when you start to look deeper into how to use it in a re-amping setup. The limitation seems to be only that the line out of the Thd has a wide range in an attempt to accommodate multiple devices, such as power amps, and rack mount gear or other devices which operate at line level, or higher signal levels, as well as lower level signals like the input jack on a guitar or bass amp. This leaves the output Volume control of the Thd line out in a rather narrow range for adjusting to the front end of another amp. The Radial XAmp Re-amping device is helpful here. It allows you to use the full range of the Thd line out volume control to feed the input of the second guitar amp. The XAmp is basically a step down transformer that takes a hot signal and tames it down to feed into other devices, like the ( line out ) of an amp, not the speaker out, meant to run into a mixer or recording console at line level, and can step that signal down into a useable signal like guitar amp instrument in signal.
    Are you still with me? I hope so. When running one amp hard into the hotplate, then sending the line out signal to the XAmp then to the input of a second amp, watch out, there is something very good happening here. Now you can use the entire range of the Thd line out volume control as well as the volume on the XAmp , and leave the controls of both amps set in place as they are now more like tone controls than volume controls, and you can make the amps sound like a very wide array of incredible sounds. Thumbs up to both products and a Big Thanks for making such amazing and high quality useable items to shape sound with. Tools of the trade.

    • Dave B

      With the XAmp can send the line level signal from the line out of the Hot Plate to some guitar pedals? ( like a clean boost, delay, reverb etc…)?

  • Joe

    The Radial JDX does NOT provide a load. Do not use the JDX the way described in this article, it is dangerous.

    • Sancho Rodríguez

      Sure enough – page one of the manual:

      This is not a load box.

      http://www.radialeng.com/pdfs/manual-jdx.pdf

    • Chris Basden

      I’m glad you said that!! I don’t own the JDX, but from what I remembered it was built as a DI that goes in between your speaker and power amp, not as a speaker-replacement! I’m a bit miffed that they haven’t edited the post to reflect that; if people aren’t careful, they could really be in deep trouble with this advice!

  • casecandy

    I’ve always wanted to run a ’70s Orange OR120 into two Orange PPC412s, and then run it into another ’70s Orange OR Slave Unit with its own pair of PPC412s… would be loud!

    • SeymourDuncanBlog

      AND GLORIOUS!

  • Victor Tomkinson

    I play baritone guitar and I use a Blackstar HT club 40 for tone shaping slaved to a Trace Elliott bass rig with a 4×10 speaker. Using the bass rig gives me the low end for the baritone guitar. I use the acive bass input on the Trace so that I can use the graphic equalizer. Adjusting the amps relative levels and the graphic equalizer on the Trace head gives me a huge amount of control over the frequency spectrum.

  • Nolalander

    I was thinking about running a line out from the new Fender Bassbreaker 10″ 007 into the effects return of a Fender Hot Rod Deluxe. Do I need an attenuator to do this? Can I do this and still get sound from the bassbreaker’s speaker: it would be wonderful to hear the 10″ and 12″ inch speaker together. Anybody?

    • SeymourDuncanBlog

      You’d have to look at the manual from the Bassbreaker to see what level the line out is. It should work, but check for sure. Just don’t use the speaker out!

  • Darren

    Hi Guys, Im looking to run a Fender blues Jnr into a Custom Hiwatt 100w Combo ala Noel Gallagher. It looks to me like he uses the THD Hotplate to do this but I am unsure how to do it and definitely do not want to damage the Hiwatt. Thanks

    • SeymourDuncanBlog

      You may want to contact HiWatt to see if there is a way to safely do this.

      • Darren

        could i not just take the out BJ into the hotplate and then feed the line out signal into the front of the Hiwatt?

  • Scott LaBenne

    I’ve used 15-watt Peavey transistor amps (dry) cranked with a line-out running to a 1965 Fender Twin Reverb cranked to about 9. No effects pedals necessary. Oh, and a ’62 Reissue Strat. These three pieces of equipment will give you everything you have ever dreamed of.