Guitar Routing Box (Part 1)
If you undertook last month's project and converted your guitar to stereo, build a routing box to provide ultimate panning flexibility
In last month's issue I discussed the possibility of pick-up and amp selection, controlled by footswitches. "DAISY" is the result of many hours of thought and trial and error, to produce a flexible routing box with a minimum of wiring problems, and at a reasonable price. There were certain problems encountered in building the prototype, the major one being where to obtain a good-looking, thin, flat box, long enough to allow for separate operation of four foot-switches. After trying electricians' "Adaptable Boxes", which are virtually unobtainable, and aluminium radio chassis, which are too soft and always seem to look like radio chassis whatever you do to them, I found a case No. C-3. available through your local radio shop, from Norman Rose Ltd.
I cut both lid and base to practically half-size for the sake of appearance and stability, but if you have limited metalwork skill, leave it full-size. (Although the base is aluminium, the top is fairly hard steel.) The second problem was that of indicating which way the switches were "pointing". As this is essentially a signal routing box, it seemed obvious to use spare contacts on the switches to operate lights, as in recording desks.
To keep heating effects to a minimum, the lights are relatively new components called Light Emitting Diodes. As long as you remember to connect the lead called "Anode" to the + wire of the power supply through a suitable resistor, and not to bend the leads sharply near the body, they should cause no trouble. The anode of the R.S. Components LED 4-586 475 is the shorter lead. Others may vary - ask for written lead identification — don't guess. Most L.E.D.'s will work happily from a 6 volt D.C. supply via a resistor of about 120 to 150 ohms/1 watt, for each L.E.D. and taking about 25 m.a. each. With all lights on, total current is 100 m.a. You could power this off (say) a 6 volt Lantern battery, but it is not going to last very long.
It appears that the simplest way of getting 6 volts D.C. from mains is some form of battery eliminator. As it only supplies the indicators, the fact that the D.C. supply can be rather "rough" from these eliminators is irrelevent. The most suitable type is the A.C. 101 C., again from Norman Rose. This is rated at 500 m.a. and is required to only 100 m.a. so there should be no problems about fitting it inside an enclosed cabinet.
It also occurred to me that some of you might not wish to be involved with do-it-yourself projects including mains voltage wiring — quite right too! The advantage of using a battery eliminator is that all the mains wiring is done for you. Mains wires go in one end, and + and - 6 volts comes out the other. All you have to do is screw or glue the entire eliminator inside the switch box, cut the mains wires short and connect them correctly to the mains socket on the side of the box. You will also need to connect a wire from the earth terminal of the socket FIRMLY to the box, preferably with a crimp tag and a spiked washer between tag and chassis.
Any radio, television, or electrical engineer can check whether you have done all this correctly and safely. You also need a wire from the chassis to the -6 volt supply, but note that none of the jack or switch connections go to the chassis. Apart from the fact that audio wiring is inside an earthed metal box, any direct earthing required will be provided by the amp to which it is connected.
IF YOU SCREW THE BATTERY ELIMINATOR IN PLACE, DO SO WITH ITS COVER OFF, TO ENSURE THAT SCREWS DO NOT TOUCH ANY (MAINS) WIRING, then replace cover before starting rest of wiring. The mains plug for this switch box should be fitted with a fuse not larger than 3 amps.
Before you wire anything, drill all the holes, check each component for fit and remove it again. You will find a library book on "O-Level" PRACTICAL metalwork, and a 1/2 inch or 11mm chassis punch (Home Radio Ltd.) a great help for this part. The odd shaped hole for the mains connector must be filed or nibbled out from a round hole and should be cut first. Nibbling tools are made for radio work and for installing windows in the sides of vans.
Wire in the following order:—
Diagram 1 - Mains socket, power supply, earth tags, metal screen, L.E.D.'s, and indicator wiring.
Diagram 2 — Input jacks.
Diagram 3 — Input jacks to switches 1 and 3, and links on switch 4.
Diagram 4 — Switches 1 and 3 to switch 4.
Diagram 5 - Switch 4 to switch 2 and output jacks, and input jacks to output jacks.
Get an engineer to check mains wiring, and screw on lid.
Components for DAISY:
4 Light emitting diodes see text
4 switches, 2 pole changeover, foot operated as used on fuzz boxes etc.
4 mono jacks, insulated from chassis
1 A-type stereo jack, insulated from chassis
4 Resistors 150 ohms 1 watt
Small piece of aluminium for internal screen
Norman Rose case C.3.
Norman Rose Battery eliminator A.C. 101 C.
Mains chassis connector, plug and lead.
Assorted screws, earthing tags, and wire.
This is only a few of the possibilities.
Stereo lead in from stereo wired guitar — Guitar selector switch in centre position — Switches 1 and 3 route pickup 1 to output 1 and/or pickup 2 to output 2. Switch 4 routes P/u 1 to o/p 2 and P/u 2 to o/p 1. Switch 2 routes whatever pick-up(s) selected, to both outputs.
By using two mono leads from guitar to box, one or both input channels may go through different effects boxes.
A mono guitar may be put through two different effects, by expanding its output into 2 leads using a split lead in reverse, or a 1 into 2 adaptor from Hi Fi shops.
You may have fuzz into right-hand amp and phase and reverb into left-hand amp and by pressing switch 4, change them over to opposite sides of the stage.
A guitar solo may be directed to right stage, left or centre. I am sure you will find many more tricks — Good luck, and let us know if you hit on anything really good.
If you have hum troubles when two different amps are connected, try disconnecting the "earth" lead to ONE of the output sockets at point X. Alternatively, break both leads to one of the jacks and insert the same transformer as used in the Hum Loop Isolator. (Point X to pins 1 and 5/other lead — pin 4/pin 6 to Tip connection on jack socket/pin 8 — jack body connection). You should not fit the 22 K resistor or any other additional components. There may be, with some amps, a slight increase in treble from omitting the 22K damping resistor and/or loss of volume when the "LINK" switch is pressed. Next month I shall describe a simple addition, based on the "Blob" circuitry, which runs off the existing 6 volt supply, and solves both these problems.
Feature by Stephen Delft
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