Adding an LED Indicator
I enjoy my VHT Special 6, and I can’t find many things that I would change about it. The one most annoying thing isn’t exactly related to the amp except that the footswitch that was sent with it is just a switch in a metal cone. Occasionally, I get caught trying to play a guitar solo without the boost enabled. I found that the switch of the original footswitch pedal is already modifiable to make it work with just a battery, an LED, a current limiting resistor, and a 1/4″ stereo audio jack.
Originally, I assumed that when the switch was closed the boost was enabled. I built a whole circuit and enclosed it in the enclosure. The 1/4″ stereo jack was used to connect the switch to the amp, and it also turned on the power supply which powered a transistor to invert the LED. Once assembled I found that I didn’t even need the transistor inverter. I already had the hole drilled for the jack so I kept it in. Here me out on this one…You could simply connect the switch to the original cable and opt not to install the jack, but if the button is pushed in this manner, the LED will illuminate. The stereo jack serves two purposes: it connects the switch to the amp, and it completes the negative path from the battery to ground to enable to LED to illuminate.
The original switch is a single pole dual throw (SPDT) switch with the ground soldered to the outside tab of the switch. The common is from the amp’s circuitry that, when grounded, disables the boost. In order for an LED indicator to work, the common connection has to be the ground. The image in the second paragraph shows this connection. I just desoldered the switch and removed it from the original footswitch housing because I chose to install it in a small box from Radio Shack. The enclosure is a 3″ x 2″ x 1″ plastic box. You might want to consider a larger box. It’s possible to fit it all in there, but it’s a tight squeeze, and the final layout is asymmetrical.
The image to the left shows the schematic of how the new switch will work. When a mono guitar plug is inserted into the stereo jack, it completes the ground path for the battery. When the footswitch is pressed, it toggles between the amp circuit being grounded (boost off, LED off) and the LED being grounded (boost on, LED on). When the boost is off, the LED is not connected; It is left floating, which like like having an infinite sized resistor that completely block current flow through the resistor.
Bill of Materials (Radio Shack)
You’ll want to do a dry layout before drilling holes in your box. I placed my 9v battery between the two screw posts on one end of the box. Then I laid out the jack, switch, and LED holder to make sure nothing touched. By following the wiring diagram, you’ll make each connection as shown. I used a bottom made of metal (not the original supplied one), so I hot glued the switch contacts. I also hot glued the battery wires down to ensure that they don’t get pulled out on accident. I drilled pilot holes using a 1/8″ drill bit, then I used a stepper bit and a whirly gig to take each hole to its final size. I decided to solder all the parts together after I installed them into the box.
This was an easy and cool project. It took about an hour to make the whole thing once I decided on the design. Once completed, you’ll never have to guess or audibly check to see if your boost is on. The LED will tell you!