One the challenges I had with wiring the three pickups on my Les Paul was choosing what options to use. Ive always like having some of the different phase options and have installed phase switching on all my guitars but one of the issues I have is that if there are too many options its easy to lose track of the combination of switches to set.
Brian May for instance has a switch to turn each pickup on or off and another switch to set the phase. All the pickups are wired in series. That gives him 64 different ways of of configuring his pickups but he still doesn't have access to all of the tones available. Not only that but he uses only 8 different configurations on his songs.
I thought it would be much simpler to have a single rotary switch that would give access to all the tones I need. No phase switches or series parallel switches to confuse things.
However there was still the issue of which tones to select. There are 35 different sounds possible with three pickups. I needed to be able to wire all of them up and then compare them.
There are two wires from each pickup and when they are wired up in parallel they will either be connected to ground or to the positive terminal. When they are connected in series then one of the wires from one pickup will be connected to one of the wires of the other.
So I got myself some 4 way slider switches and built a little circuit board that would allow me to connect any of the six strings to either hot, ground or one of two jumpers.
I used some terminal blocks so that I could connect it to the pickups without soldering as it is only intended to be connected temporarily.
I wrote a short computer program to generate a spreadsheet with every
possible valid wiring combination. This generated over 1200 different ways of wiring the 35 tones.
If you look at the circuit diagram of the switchboard you can see that each string from each pickup can be connected to "+","a","b" or "-" I could have also have included an option to leave the wire disconnected but I would have needed a 5 way slider switch. It wasn't necessary to have an option to leave a wire disconnected because having both wires of a pickup connected to "-" is the same as switching it off.
So for instance if I wanted to make just the bridge pickup active I could connected set the switches as follows +----- but that is not the only way I could configure that particular pickup circuit, the following would also work. -+---- because even though the phase is reversed it does not affect the sound when there is just the one pickup. I could also use +-aaaa +-baba or a number of other combinations.
The ability to wire up in multiple ways is helpful when wiring to a rotary switch with just 4 poles because if you can pick circuits where one of the pickups is wired the same way on every throw then you don't need to wire that pickup to the poles on the switch. You can get away with 4 wires instead of six.
Here is the Spreadsheet of Wiring Options that I generated. I went through each of the pickup configurations and set the switches to the first option that came up and recorded a snatch of music in Riffworks. Once I had recorded all 35 different tones I listened to them all and picked the 11 I liked best. I've put them on this you tube video.
Bear in mind that these tones were recorded without the volume controls installed. Adding volume and tone controls will also affect the sound. Ive been considering using noload pots so that they will not affect the sound when the volume is set to full. With hindsight I should probably have tested with the volume controls in place. Perhaps the next version of my rig will have volume controls built in or I could simply add a 250k resistor between the pickup wires to simulate having volume controls in place at full volume.
My next post will go into a bit more detail about selecting the sounds and how I was able to shoehorn these circuits onto a 4 pole switch.
If you have actually read this far and have any questions, please leave a comment and I'll do my best to answer
Friday, 3 October 2014
After the initial WTF and some checking of my wiring I realised what was going on. You can see from this diagram that one end of the pickup is connected to the positive terminal. The other is disconnected and the wire connected to the earth is connected to the metal pickup cover.
Testing with a multimeter confirmed that there was no electrical connection between the case and the disconnected wire and yet when I plugged the guitar into my amp I could hear sound at a much lower volume than normal.
So if the pickup is not connected to earth how is the sound getting through? What is not shown on this diagram is that all three wires are in a single two core shielded cable. The close proximity of the wires meant that together they were acting like a capacitor. A capacitor blocks DC which is why the meter didn't detect any electrical connection, but it does let alternating current pass.
What it does illustrate is that sometimes you have to be careful of cable placement because it can have unintended consequences.