In most cases you will want to split the guitar signal to run two different amps. For this you need a so-called AB-box. An AB-box can be used to switch from one amplifier to the other and back, using only one amp at each given moment. A good example would be a Lehle Little Lehle II.
If you need to run the same signal into two amps at the same time, your switching device gains an addition letter "Y", making it an ABY-box or a splitter.
Do you switch between amps or do you run two amps concurrently?
If both amps are always used simultaneously, you can employ a Lehle P-Split to split a single signal safely into two feeds.
If the last block on your pedalboard is a stereo effect (like a reverb), you should instead add a Lehle P-Iso ground isolator box in front of the input of one of the amps to avoid the danger of ground hum loops. The P-Iso is like a downscaled version of the P-Split, without the larger unit’s parallel output and the phase reverse switch.
If you plan to use one or the other amp alone for certain songs in your set, while running both at the same time for other songs, you can choose between:
Custom Boards only supplies ABY-boxes that won’t add any ground loop hum to your system. These pedals either include isolation transformers or feature special switching to make ground loops impossible. Many ABY-boxes also sport phase switches, which make it possible to solve phase problems between two different amplifiers.
Are you planning to use more than two amps?
It is possible to use more than two amps with a split signal. An important rule of thumb is to be careful that only one of the amplifiers shares a common ground with the guitar and effects. All other amps have to be connected via isolation transformers to avoid any possibility of ground loops.
This is easy to achieve by using several Lehle P-Split boxes in series, until you have as many isolated splits as you require. If you need to switch amplifiers on and off during your set, we’d recommend using any Lehle product marked as “SGoS” – which stands for Second Generation of Switching. SGoS-boxes can be programmed to synchronize with each other, making it possible to switch several amp feeds on or off with just one single step on a footswitch.
What about more than one instrument?
If you use different guitars for different songs, or if you have to switch between electric bass and a bass synth, an AB-box will give you a much smoother experience than having to unplug and plug your instrument cable. For two different instruments a Lehle Little Lehle II is the easiest solution.
If you require more inputs we’d recommend using a Lehle 3@1 SGoS as it features two adjustable inputs, which means that you can plug the lowest output instrument feed into Input C and then use the level controls in Inputs A and B to adjust the other instrument levels to match. This way your effects – or the input of a mixing console – will react similarly to any of the three instruments.
If you need to run a synthesizer and a guitar into the same effect chain and/or amp you could choose a Lehle Parallel L-mixer. Simply connect one of the instruments to the Parallel L’s Return-input and use it’s level control to adjust the balance between the two instruments.
What about phase issues?
Phase problems are often spotted simply by listening to the mix of two (or more) amps. If your signal sounds fat and juicy through a single amplifier, but always turns thin and tinny when played through multiple amps, chances are that you have a phasing issue with at least one amp. Simplified drastically, you could think of the problem as the guitar speakers of the different amps moving in opposite directions, resulting in the two signals cancelling each other out. If you mike up two amps who are not in phase your tracks would look like this in a DAW:
All of Lehle’s splitters and ABY-boxes are equipped with phase reversal switches, allowing you to bring two amplifiers into phase easily. When two amplifiers run in phase, the resulting sound is usually fat and juicy.
Will these devices change my sound?
Specially-selected and sensitive high-impedance isolation transformers are at the core of Lehle’s ABY-boxes and splitters. This transformer is passive – meaning it doesn’t require power to function – and doesn’t add any impedance load on your precious signal. This is why you should never use cheap passive splitters, because virtually all of them have been designed for low-impedance, line-level signals, which will suck the lifeblood out of your guitar tones.
Due to their passive nature, though, Lehle products won’t work against the negative effects of long cables and/or long effect chains, which will attenuate the signal’s treble content. If you have long cable runs and/or lots of true bypass effects, you should add high-quality buffer amps between the splitter outputs and the amp inputs to help against audible signal loss.
Can I use an isolation transformer as a DI-box?
Yes, you can. Using the ISO-output (isolated) found on Lehle products will transform an unbalanced signal to an electronically balanced (shielded) signal, which can in turn be transported onwards using a balanced cable with TRS-plugs (also called stereo-plugs).
Can I fold a stereo signal into a mono-feed using a Lehle P-Split?
Yes, you can. In this case you should plug the left channel into the Lehle’s regular input and the right channel into the DIR-jack. This method works best with a single stereo source – like a stereo effect or something like a synth – because both channels will have the same nominal impedance.
Will a Lehle P-Split or a P-Iso work for reamping?
Yes, they will. Most studios will record a completely clean DI-box signal in parallel with the effected and amplified sound, because it enables them to try different effect and amp setups during mixdown. This is process is called reamping. Connect your audio interface’s output to the input of the Lehle, and then run the output signal off of the ISO-output to the amp.
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