Inspired by the Beavis Board and other similar designs, I finally got around to building my own effects circuit test box.
+9VDC in from an adapter goes to a MadBean Road Rage board, which uses a TC1044 and a voltage regulator to provide 9V, 12V, ~18V and -9V — the leftmost knob is a rotary switch. Power then goes to a voltage sag knob before it heads to the outside world.
I used a four-output speaker connection panel from Radio Shack for my connections to the external circuit. From top to bottom it goes: power, ground, circuit input, circuit output. The 1PDT switch is there to select whether circuit output or test probe output goes to the out-to-amplifier jack, but I haven’t wired in the test probe yet.
Here I am testing Channel 1 of my MadBean Aristocrat board. Sounds great configured for overdrive with a B250K Gain pot. I’ll try the B100K later today.
It’s great to “rock it before you box it”. Not only do you make sure the circuit is functional before you spend a lot of time cramming the board into the enclosure and wiring up the jacks and the switches, but you can make subtle tweaks much more easily, too.
Of course if you really wanna tweak an effects circuit before you even heat up your soldering iron, you can breadboard it first. A friend of mine has expressed interest in the Echoplex preamp booster, so I put this together last night. (Notice that I have the voltage selector knob on the left in 18V position.)
It’s essentially the schematic for the MadBean FatPants board, but I replaced all the potentiometers with median-value resistors.
The problem with working on these guitar projects at night is that, unless you live by yourself in an underground bunker, you can never properly test them at serious volume when you’re finished. I could tell there was a boost, but I couldn’t tell how much it was fattening up the sound or if I even liked it.
Sounded great this morning when I finally had a chance to crank up the amp! I’ll grab some pots and alligator clip leads and head over to my friend’s place later this week to see if he likes it.