Sunday, June 19, 2016

Playing with Two Amps. Stereo vs Slaving and Fun With FX Loops

 WARNING:  Never power on your amp and play it without a speaker connected.  Always have a speaker connected (or a speaker load).  If you don't you will fry your amp and it will be costly. 

Stereo Rigs

There are lots of options when you realize you want to start playing with two amps live.  The tone you can dial in with two differently voiced amps and cabinets can be very full and amazing.  You may never go back to playing a single amp again.  Although lunging around two heads and cabs to every show is not for everyone.  Let's look at some options on connecting your stereo rig.

The easiest and cheapest route is to simply get a Y instrument cable and plug straight in.  It is highly likely you will run into ground hum.  You can buy an audio isolation transformer to remedy this.  However this method leaves you with the fewest options.
Y Cable
 The next option is to get a ABY box, which will allow you to switch between amps or play both at the same time or just one amp at a time.  This gives you a lot of control over the voicing and dynamics.  Not all ABY boxes are created equal however.  The best ones will offer you a ground lift to defeat ground hum.  The Radial Big Shot seems to be one of the better boxes on the market.  
Now lets say you like playing with a lot of modulation or delay effect pedals.  Many of these offer stereo outputs which can sound huge and psychedelic.  Pop a stereo Chorus, Tremolo, Flanger, Phaser, or Delay at the end of your FX chain to split the signal to both amps.  Again, you'll probably have ground hum, so try to find an audio isolation transformer to plug one of the outs into.
Through a Stereo Pedal

Amp Slaving and Daisy Chaining

Now lets talk about Slaving, Daisy Chaining and FX Loops.  Slaving is basically taking one amp and sending it's preamp to the power amp of another amp, bypassing the preamp of the slave amp.  Why would you want to do this?  Seems like a waste right?  Well, it can be a solution to a problem I run into a lot here in Japan.  Most clubs have a backline of amps which depending on the venue, that amp might not have enough volume or power you're looking for.  I like the dirty sound of most of the Marshalls these clubs have, but sometimes they are lower wattage or under serviced and just not cutting it.  In this case I'll take the FX loop send of my Marshall (master amp) and run it into the FX loop return of another amp(slave amp).  It simply uses the power amp of the slave amp to boost the volume.  Sometimes you might want to do this for a smaller low wattage amp that has great tone, but low volume.  Maybe you might get a different EQ from the slave amp's speakers.  Hell, I've been know to use a bass amp as a slave amp.  Sometimes the other amp might not have the distortion tone you're looking for, but it has the power.  In my case, most clubs in Japan have a Roland Jazz Chorus.  Great loud clean amp, but the distortion channel just isn't my thing. It should be noted the slave amp will usually not have EQ control.  We are bypassing it. 
Amp Slaving
So that's one solution for an under powered amp,  but if we have a lot of effect pedals, we can also run a "wet"(effect pedals into)amp and a "dry" amp(no effects).  This will give you the clarity of your normal guitar tone with all the effect pedals only going into the slave amp.  It will sound like two different amps and offer more depth of sound.  To do this, we again run the FX loop send of the Master amp into our modulation or time based effect pedals, then into the FX loop return of the Slave amp. 
"wet" "dry" amp slaving
There is another method to linking amps that don't have an FX loop.  We can daisy chain most amps with dual inputs, such as an old Marshall JMP or most Fender styled amps.  JMPs  have 4 inputs.  A low and high input for two channels, bright and normal.  Many people "jumped" these channels by linking a patch cord from the low input of the bright channel to the high input of the normal channel.  This allowed both channels to mix, offering more tone control.  We can use this same idea and take the lower input of one amp and link it to another amps input.  This will run through the second amps preamp, so we can dial each amp.  Hendrix was know to do this with two or three JMP heads.  Sometimes he simply used the Y cable technique. 
Daisy chaining or Linking amps

FX Loops

Lastly, since we're on the topic of FX Loops, lets clarify what they are and what's going on with them.  Your amp has a preamp which controls your EQ and a lot of times the gain or drive of the amp.  A lot of people like the sound of preamp distortion, so this is the source of that.  When we use effect pedals, sometimes we want our delays, reverbs or modulation pedals to come after the amp distortion.  To do this, we can take the send of the FX loop into the input of the pedal or pedals we want to come after the amp distortion, and take the output of the last pedal back into the FX loop return.  Sometimes these "send" and "returns" are labeled differently, such as "preamp out".   Most people prefer the sound of their tubescreamers, fuzzs, and distortion or boost pedals in front of the amp.  Going into the regular guitar input.  Because these gain pedals interact with the preamp.  Lots of people like the clarity of delays or modulation pedals, coming after this distortion or gain.  Some pedals you many find are over powering in the FX loop.  I perfer my Phase 90 in front of my amp.  In the FX loop it is just too overbearing for my tastes.  Maybe try an EQ pedal in the FX loop, and dial in your tone even more.  Or boost it.  There are no real rules, so experiment and have fun. 
FX Loop configuration
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  1. Wow, really liked your explanation of the many possible setups! Curious though, my Marshall head has a SEND output. I also have a Roland JC120 with two MAIN IN jacks on back of the amp. Seems these main ones should work to connect into from the Marshall FX Send? Thx

    1. Not familiar with that being labeled on the JC120. Seems like the same thing, just a different label.

  2. If anyone still monitors this thread...I'm wanting to Master/Slave 2 small combo Bass amps...identical amps - say, 200Watts each and a single 15" speaker in each - and use the FX loop in the manner described here...use the Send from the Master to the Return of the Slave, just for the power reinforcement...I've been told that once you plug a 1/4" jack into the Master's Send, you silence the amp - unless the amp 'sees' a cable in it's Return...anyone know if this is the case?

    1. Sorry I didn't see this earlier. I doubt it would silence the master amp. But there could be a design I'm not familiar with. Give it a try.