- Last Updated: 10 April 2021 10 April 2021
Build Your Own Clone Amp Selector board
BYOC original design
If you have a dual-amp setup, you may well have experienced the shrieking of amps with a ground loop. You'll know if it happens! This pedal is designed to let you use two amps, but isolated from each other by transformers, with ground lift switches to get the best sound from your amps. For some reason, we always have to think about how to use this properly. Somehow it just takes an extra minute or two to hook up. Perhaps because it is a clever design that supports two similar but different functions. Let's start with the footswitches. They control where the signal(s) go to. The one on the left is labeled "Both". In one setting it routes the signal to both the A and B output jacks. In the other setting, it routes the signal to only the A or only the B output jack, whichever is selected by the A/B footswitch on the right. So that lets you send your signal to the A amp, the B amp, or both the A and B amp. No problem. If you want to use it that way, you connect your source signal to the A input jack and your A amp input to the A Out jack and your B amp input the B Out jack and switch away. So what is that B In jack for? It is for "stereo" operation. If you plug something into both the A In and B In jacks, then whatever is going into A In can only go to A Out and whatever is plugged into B In can only go to B Out. But whether anything goes to either A Out or B Out is controlled by the two footswitches. So you can have A only, B only, or both A and B going to their respective amps.
We'll skip the whole discussion about ground loops here. If you have a ground loop in a multi-amp setup, you'll know. If you don't have one, you're lucky (or smart). The two ground lift switches (one for each connected amp) give you the ability to select the best grounding configuration with the connected amps. You may notice no difference at all, or you may find one combination of the switch settings to be best (quietest). If you move your amps and plug them in to different power outlets (perhaps you play different venues), then you may need to change the switch settings to work better for the new power connections.
It's magic of the most arcane sort! However, there may be a catch. You *may* notice a little bit of change in your low lows or your high highs. The transformers in this design are TM018 transformers and have been used for many years in audio applications like this, and are considered "acceptable" for these uses (particularly in this price range). This is highly technical stuff, and datasheets don't cover it well enough to draw many conclusions. You just have to try it. We've never noticed a difference, but we rarely use them. We also don't do sophisticated studio recording or processing - just live. In a studio production setting, you may notice any changes more clearly. But then you probably wouldn't be using one of these in that setting anyway... YMMV.
Besides the TM018 transformers, there are metal film resistors, poly and electrolytic caps, and TL072 op amps. In this application, it is best to use the plastic jacks so that they are isolated from connection with the enclosure and not connecting their grounds.
Standard 2.1mm 9VDC center negative Boss-style power connector only. No battery clip. Special power circuitry is utilized for dual rail +9V/-9V operation internally.
Footswitches and ground lift switches are describe above.