Saturday, 4 October 2014

3 Pickup Wiring

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

The Impossible Circuit

In the course of experimenting with different wiring configurations I accidentally discovered that its possible to get sound from a pickup even when only one of the ends of the coil is connected.

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.

So the circuit actually looks like the diagram to the right. It's kind of interesting but not really of much practical use. I only discovered it because my switching rig lets me configure circuits that should never exist and I accidentally configured it with the lead going to the positive terminal instead of the negative.

What it does illustrate is that sometimes you have to be careful of  cable placement because it can have unintended consequences.

Tuesday, 30 September 2014

Converting Shielded Pickups for Phase Switching

I was going to write a massively complicated post about all the wiring options for three pickups and the rig that I have made for testing out the different sounds, but that is going to have to wait because I have realised I have a problem with the Vanson P90 pickups.

One of the things that I want to do with the pickups is to switch the phase. There is nothing complicated about phase switching, you just switch the positive and the earth wire on one pickup and then it will be out of phase relative to the others.When pickups are out of phase they tend to be a little quieter and have less bass.

The only problem is that the earth wire on the Vanson P90s is connected to the metal case. When wired in phase, the case reduces electromagnetic hum. When wired out of phase it does the opposite and acts like an antenna.

The only way to fix this is to replace the two wires with three. One for each end of the pickup coil and the  other connected to the case so that the case can be grounded independently of the pickup wires.

The pickup cover is connected to the base of the pickup with a couple of blobs of solder. My soldering iron was not hot enough to melt the solder so I used a craft knife to carefully cut through the solder so I could get inside the pickup.

I was surprised to see that the pickup wasn't much bigger than a strat pickup inside the cover, I was expecting something a little fatter. You can see that there are two wires coming out of the pickup. The black wire is soldered to the case and the cable shield. The white wire is connected to the cable core.

I cut the wires off, leaving myself a little slack and attached a two core shielded cable. The shield wire I connected to the pickup base. It was a challenge to solder it it because the base sucks the heat out of the soldering iron. In the end I laid the cable in the gutter between the edge of the base and the magnets and then laid some solder on top of it. When I melted the solder it solidified almost immediately the heat was off and held the wire in place

For the other wires, I cut a short length of shrink wrap and slid it on. Then I twisted the ends of the wires together (black to blue, white to red) and applied a little solder. After the solder cooled I slid the shrink wrap over the joint and applied some heat with the iron.

I re-assembled the case and applied a bit of solder to stick it back together.

So far so good. I just have two more to do and then I can get on with the rest of the wiring.

Monday, 18 August 2014

Nevada Les Paul

A few months ago I spotted this really sexy looking beast of a guitar on Ebay. It was some sort of cheap chinese Black Gibson ES175 clone. With three humbucker sized P90s and a Bigsby B6. I put in a lowball bid and failed to win it. But as time went on I kept thinking about it. Even though it was pretty beat up and had electrical tape all over it, it was still a very striking guitar.

Then one day as I was thinking about it I was hit with the inspiration to convert my Nevada Les Paul. The Nevada isn't a semi acoustic, but it is the right shape and colour and desperately in need of TLC. The Nevada was a guitar I picked up from the local cash converters for a whim. I hadn't really thought about what I was going to do with it other than do some coil tapping and splitting but restyling it to a carry three p90s and a Bigsby seemed like an fun project.

I ordered three p90 pickups from Vanson guitars on Ebay and a Bigsby B70. For the wiring I had no fixed plan but thought I would try out a 4 pole 11 throw rotary switch. I also managed to get old of an old soviet military 5 pole 11 throw switch which would allow me ultimate freedom, but unfortunately was too big to fit in the body.

I thought the main challenge would be cutting a hole for the middle pickup but in the end it was planning the wiring that would be the hard part. But more on that later.

Cutting the hole for the pickup turned out to be easier than I thought it would be because the guitar isn't solid all the way through. I was able to cut through the arched top just using a dremmel tool. After getting the hole in place all I needed to do was drill two holes in the body for the pickup mounting screws to fit in and there was enough room to fit the pickup.

The other bit of woodwork that needed doing was to fit couple of pieces of dowling into the holes left after removing the stop tailpiece. I left these 24 hours to let the glue dry before attaching the new Bigsby B70 tremelo. The Bigsby conveniently covered the slots so I didn't bother painting them.

I put the dremel to use again to cut the scratch plate to fit three pickups. its not the neatest job but only noticeable close up.

With the guitar all styled out. The next step was to plan the wiring. This turned out to be very challenging. When I wired up the Gretch I only had two pickups to contend with. I'd come up with a clever way of planning the wiring but with only 4 poles on my switch and 6 wires plus a huge number of wiring options for three pickups it wasn't easy.

The 11 way switch combined with phase switches on the volume controls would allow me access to most of the 35 tones that are possible with a 3 pickup guitar . However the type of rotary switch has limitations that means that it is not possible to do every possible combination. Also how do you choose which tones you want easy access to?

There is still a lot of thought that will need to go into the wiring and a little experimentation before I commit to a wiring scheme.

More on the wiring in the next post.

Sunday, 4 May 2014

Gretsch G5265 Baritone Switch Replacement

When I started (and abandoned)  this blog over a year ago I thought I would be posting about one of the various project guitars that I have. In particular the nasty Les Paul clone with the crazy sustainer I've been building.

I certainly would never have predicted that my first post would be about a Gretsch Baritone G5265 Jet. The thought of actually owning one never really entered my mind back then let alone the thought of modifying one. Yet here I am.

Its a lovely guitar but it has one rather annoying feature, the three way selector switch. When I'm strumming I frequently knock the switch into the neck position. To be fair its more the fault of my playing style, but when seated its where my hand naturally falls.

So I thought to myself, why not replace it with a a rotary switch instead. Then I thought why have a three way switch when I could have a 6 way switch to give me every combination that you can have with two pickups.
I googled around to see if I could find a wiring diagram that would help with some success but the one I found didn't have the selections in the order I wanted. So I decided instead to work it out from first principles.

The approach I took was to draw a schematic for each circuit I wanted to make then I could colour in a block diagram of the switch to show which terminals should be wired together. With the block diagram complete I could apply the colour codes to a representation of the switch. With all the planning in place soldering the switch was as simple as painting by numbers.

Have a look at the embedded slides to see the documentation

When it came to wiring up I used some solid core jumper leads that had sleeves of the right colour. The solid cores made it possible for me to connect everything together before applying the solder so I could double check. There it is on the left looking like the console of the tardis

Once all the wires are soldered in, its simply a case of attaching the wires from the pickups and the controls to the appropriate tabs on the switch.

Identifying the cables wasn't too difficult. You can identify them by looking at how they are attached to the three way switch.  The white cable going to the central contact of the three way switch is hot going down to the controls and jack socket and the other two white wires are for either pickup.

One error I made was that I didn't pre-tin the terminals or the wires. Had I done so, then I wouldn't have had a dead connection on one of the positions. The green jumper had a dry joint that wasn't making contact so position 3 was not working. I had to take the switch out and do some probing with a multi-tester before I worked out what was wrong. To resolve it I just reheated the joint.

The switch came with a chicken head knob, but I thought it looked awful so I bought a Gretsch knob from ebay. I had to dremmel out the hole a little as it didn't fit in the switch shaft very well but once it was on it was a really good fit.
 The switch adds a lot of variety to the sounds and the out of phase settings are pretty unique. Not great dry, but they work well with distortion. There is quite a big different in volume between the settings and I think if I had been able to test out the different settings in advance I might have chosen a different  order. The good news is that the way I have documented the switch connections means that it is trivial to change the layout. I can simply change the order of the columns on my block diagram and its painting by numbers. If I had decided I didn't need six settings I could wire up a 4 way or 5 way switch using the same diagram, just skipping the positions I don't need.