L-1000 wiring figured out

[Wild Rice Chris]

I posted this over on The Dude Pit, but thought some folks over here may be interested.

I was looking at the drawing and thinking about what the switch really does...
http://www.glguitars.com/schematics...tic_drawing.pdf

There is no way to wire in a capacitor to provide a bass boost in a passive circuit. I was looking at the switch and this is what I get.


1. Pickup coils in parallel. Just what they say it is.

2. The yellow is connected to the black which is connected to ground (the cap is shorted out by the switch). Classic single-coil mode by shorting out one coil. Again, just what they say it is.

3. Yellow and black are connected. These go through the .1 cap and then to ground. This puts the coils in series, with the series connection going to ground through the .1 cap. So the lower frequencies act as though the coils are connected in series (which they are!) while the upper frequencies are only coming from one coil. Bam, instant bass boost.

[Scutterflux]

That's a really cool idea! I always wondered how they claimed to boost the bass.

[Wild Rice Chris]

I've started wiring guitars that way and really like it better on a guitar than a bass.

Still cool wherever.

[kraigo]

This thread has interested me for a long time, short as it is. I've got a few basses that I'm working on and I loved the switching scheme of my old L-1000.

My question is: Since the coils are in series at that point and this is alternating current, how is the cap affecting just one coil? As far as I can figure out, at that point both coils are one circuit and there's no way to isolate one coil from the other.

Like I said, I'm genuinely curious and I've got a few projects that are sort of dependent on the answer, so if anyone can explain it to me, I'm very interested.

KO

[sunbeast]

The wording is a little weird in the original post. The cap cuts the highs from the grounded coil before it runs that coil in series through the 2nd coil, so the 2nd coil doesn't see the cap. The cap is attached to the connection between the 2 coils (there is a jumper wire on any series/parallel switch, which is where you add this cap- you just decide which coil you want to have the full signal from and make that the following coil). I've also used this idea on a couple of different instruments, and it really makes for some unique and useful sounds in lots of applications. It works really well when used with 2 single coil pickups as well- you can add a switch that puts the 2 pickups in series (like the S1 switching on some Fender Jazz basses), but with a cap in the series connection that cuts the highs from the neck pickup. It gives you the clarity and growl of the soloed bridge pickup, but with the added depth of the neck pickup (whereas the series setting on a J bass can be really muddy/middy).

Karl

[DavePlaysBass]

The single coil with bass boost is great on a sweet spot or bridge MFD IMO. I also find that it works well with the neck pup but sometimes I roll back the passive bass cut a bit to keep it from being overly boomy. There is a link to a document up top that goes into coil stuff. But it sounds like you understand the single coils with bass boost arrangement.

[DavePlaysBass]

Originally Posted by kraigo

My question is: Since the coils are in series at that point and this is alternating current, how is the cap affecting just one coil? As far as I can figure out, at that point both coils are one circuit and there's no way to isolate one coil from the other.

The coil that the capacitor is in parallel with is the coil that gets its highs sucked out. It is kinda the same thing as excessive winding capacitance which is what determines the peak or resonant frequency of a pickup. By using a 0.1uF cap in parallel, you are essentially setting the peak resonant point of the coil at a much lower frequency than it normally is and from that point forward the highes are gone.

The other coil sees the capacitor as essentially a short. This is like an AC coupled signal. If the capacitor was made smaller in value, at some point it would roll off the lows for the other coil (not the highes).

You can do the same thing by having the capacitor go from the top of the series connected coils to the mid point, but then you are sucking the highs out of the top coil and getting full range on the bottom coil. This trick can be helpful if you want both pickups in this mode to be hum bucking (which they naturally are not because the cap messes with the hole hum bucking equation). There's some info up top on the hum bucking thing if that is of interest.

Dave

[kraigo]

Thanks for the clarification folks. The Artcore's new pickup (SGD Lutherie neo pickup) is installed and the electronics are pulled out through the F-hole. I'll install the pickup this morning and play with my wiring harness a bit to ensure my theory works in practice. Your help is _MUCH_ appreciated.

In rereading the posts, are we saying that one of the coils is shorted with a cap?

KO

[sunbeast]

Yes- the series connection between 2 coils is essentially a jumper from the hot (or end) output on one coil to the cold (beginning) wire of the second coil- there is only one capacitor which is attched directly to this jumper with the other end connected to ground. The first coil shunts high frequencies to ground through the capacitor in much the same way that a tone control does when rolled all the way off. The 2nd coil sees the capacitor as a "short" in that it is another connection to ground in the circuit- but probably has very little noticeable effect on the tone from the 2nd coil due to the high value.

Karl