Liquid Pickups

[Mike Sulzer]

That's a drawing from the 1976 Bartolini patent (#3983777). That's one of their single coil pickups.

24 is the flat pole top. 26 is the coil, and 22 is a ceramic magnet. The poles were "T" shaped.

I guess the first thing that that flat magnetic top does is guide permanent flux away from the string by diverting it sideways (through the top) so it can loop around to the magnet more easily. Of course, with that big ceramic magnet, there is still plenty of field strength I suppose. The second thing it does is to guide flux from the vibrating string outward and so back around to the string with less passing through the coil. This weakens the output; I do not see any sense in that.

[Possum]

The flux goes up from the edges of the steel baseplate, but without a baseplate the flux goes down below the poles and isn't restricted in its flow. By restriction I didn't mean it kills the magnetism is just stop its and sends it straight back up from the edges and it doesn't flow below the baseplate. You can plainly hear the differences. Putting a baseplate on a Strat bridge doesn't make it sound like a Tele, it just makes it sound bad and cold to my ears, it feels tight, doesn't have any give to it. Bartolini design is one I wouldn't make, that kind of thing just sounds too "hi-fi" for me. But there is a similar pickup, the old Kay flattop or Stratotones that have a wide flat alnico magnet, but it doesn't protrude above the coil and the coil is very short and wide, now those DO sound good and I make them. Bartolini seems to like hi-fi tones from what I remember of his designs, very flat sounding.

[David Schwab]

The flux goes up from the edges of the steel baseplate, but without a baseplate the flux goes down below the poles and isn't restricted in its flow.

You got strings under the pickup? Then who cares. The field under the pickup loops back up to the top. If it's extending under the pickup that's doing nothing for you and is a waste of the magnetic field. The difference you are hearing is an increase in inductance from the added steel. Adding a steel baseplate to a Strat makes it warmer, not colder. it makes it louder too. But you might have to tweak your designs to take advantage of changes like that.

The Bart design was supposed to sound hi-fi, and like an acoustic guitar. Acoustic guitars are not flat sounding, but they don't have that upper midrange peak like on a Strat. The peak is much higher and smoother. Listen to Tuck Andress. That's not a "flat" sound at all. You just like certain tones over others. That's personal preference.

[Possum]

Build a Tele bridge pickup, play it without a baseplate, then put a baseplate on it, you'll hear and feel the tone become constricted is the only way I can describe it, its kind of like the mids get lost or sound "hard." Better yet do it with a Strat bridge, putting a baseplate on, it stops a full moving field that surrounds the top and bottom of the poles, and so then you're only getting a moving field from the top down the the edge, its a totally different feel and sound. Baseplates also boost the gauss at the poles. If you've not tried it yourself you won't know the effect. I made pickups for a guy who played for Curtis Salgado about 9 years ago, he had a baseplate on his Strat bridge and I suggested he take it off, which he did and was suprised how much better it sounded and felt, it used to be a fad back then to use plates on them started by Fralin, no one seems to use them these days.

I think a good way to describe what it does is it kills "sag" in the pickup, you could really double this effect by cutting a solid steel top plate and putting it on a Tele bridge, it would get very flat and hi-fi sounding, also very weak since you've put magnetic barriers on top and bottom so the flux is mostly going from baseplate edge to top plate edge and almost nothing beyond....

[David Schwab]

...it stops a full moving field that surrounds the top and bottom of the poles, and so then you're only getting a moving field from the top down the the edge, its a totally different feel and sound....

Moving field? It's doing nothing of the kind. It's a static field. The strings are moving.

It does sound different, because of the change in inductance. That generally makes the pickup louder and increases the low end.

[rjb]

Build a Tele bridge pickup, play it without a baseplate....

Looks like the thread's theme has switched from liquid pickups to Tele bridges.
Time sure flies. Is it time for Summer reruns already?

FWIW, Bill Lawrence said the bridge material has a big effect on the sound. Back in 2009.
Fender Telecaster® Electric Guitar Central -- No. 1 in the World

[David Schwab]

FWIW, Bill Lawrence said the bridge material has a big effect on the sound. Back in 2009.
Fender Telecaster® Electric Guitar Central -- No. 1 in the World

Right, the bridge is made from steel.

They make those half bridge Teles, and they sound different, as does the brass bridge on my Tele.

[Possum]

Of course the field moves with the strings ;-) but nothing below the baseplate moves, the plate stops the field, its a magnetic block. Nope, just a change in inductance can be done by winding it differently, you can wind it to increase the inductance but it wont sound like you put a baseplate on it. and actually putting a baseplate on a Tele bridge lowers the inductance. AC resistance tho goes up a little bit. Meters don't tell you what it sounds like. Really you should play a Tele bridge without a baseplate then put one on, you'll notice the feel is completely different on both that matches my visualization of the plate stopping flow below the poles, in fact some people call these "reflector" plates, which magnetically is kind of what they do. Kills sag. I'm sure Leo only put them on since they called them elevator plates, just put there to have a solid adjustable platform most likely, but I'm sure he probably tried one without baseplate or we would see them on vintage strat pickups; in fact Spence sent me a photo of a vintage strat pickup that did have a baseplate on it, pretty rare, guess they didn't like it either.

Its true the actual steel Telecaster bridge plate with saddles, does interact magnetically with the pickup itself, whether you can hear this or not I don't know. I do know that the cheap flat chrome plated brass bridge plates don't make the guitar sound like a Tele at all to me. For true Tele bridge tone you also need only 3 saddles which also gives you more sustain than the 6 saddles some of the modern ones use. You can measure gauss on the steel plate itself tho its very low. Its also a good idea for vintage purists to use magnetic steel adjustment screws because they too conduct some magnetism, good idea on Strats and Teles because thats what they used and you can get gauss readings on steel strat screws too.

[Possum]

I'm getting awfully tired of this double posting bug.....

[Mike Sulzer]

Of course the field moves with the strings ;-) ... and actually putting a baseplate on a Tele bridge lowers the inductance. AC resistance tho goes up a little bit.

It would be more accurate to say that the inductance reading that you got with your Extech decreased. The actual inductance probably did not decrease, but rather probably increased a bit. You lowered the Q of the pickup by increasing the losses by eddy currents in the base plate. The change in sound is caused both by the change in inductance (if significant) and the change in Q. I suspect the latter is more important, but this would require careful work to confirm.

Remember, your Extech can measure inductance and one type of loss. You have a series loss from the coil resistance. When you add an eddy current loss, that is a parallel loss. When both are present at once, the Extech readings are in error. This usually shows up as a decrease in apparent inductance. Although the readings are in error, they are consistent, and you can still use them to classify different pickups, etc., but you should be aware that they are not actual accurate values.

You should see less apparent change in the inductance by measuring at 120 HZ rather than 1 KHz. But you probably would not show up the change in loss as well either.

[David Schwab]

in fact some people call these "reflector" plates, which magnetically is kind of what they do. Kills sag.

They make the magnetic field at the top stronger, and probably "harder", which is what you are hearing. If you use weaker magnets it will compensate for the plate.

Here's a Strat pickup:



Here's the same pcikip with a steel plate on the bottom of the magnets:



I don't make any pickups with plates on the bottom, but this is my observation on them.

[Possum]

Mike, the change in sound isn't an inductance sound change, you can wind another pickup to increase inductance by using the same number of turns but a pattern to darken it up but you don't get the same tone you get by putting a baseplate on the pickup. Yes, the baseplate increases the gauss, its the "reflector plate" idea, but if you charge the magnets hotter you don't get a baseplate tone either, nor by making the magnets weaker charge. I did all this stuff a long time ago and spent about 3 years just on Tele bridge pickups alone and tried all kinds of things. I make a baseplateless Tele bridge pickup but in ten years I think I've sold only 2, probably because without a baseplate it just doesn't quite sound like a Tele anymore.

[Mike Sulzer]

Mike, the change in sound isn't an inductance sound change, ....

Yes, that is what I was saying; it is probably mostly due to losses from eddy currents, but I do not know for certain.

[ScottA]

A steel (i.e. ferromagnetic) base plate on a Tele pickup does increase inductance. It also modifies the magnetic field as the field tends to concentrate in the highly permeable steel material.

More windings also increase inductance, all other things being equal.

Both cause tonal changes, but by different mechanisms.

A ferromagnetic baseplate also results in an effective field strength increase as far as the strings see it, as David shows above.

Stronger magnets also result in a field strength increase.

Both cause tonal changes, but by different mechanisms.

I agree that the characteristic tone of a classic Tele bridge pickup is highly dependent on the influence of the plate, and that the character of the baseplate tone is unique to the baseplate configuration.

[Joe Gwinn]

Yes, that is what I was saying; it is probably mostly due to losses from eddy currents, but I do not know for certain.

One way to tell is to cut radial slits in the steel baseplate to interrupt any eddy currents therein. Ideally, the slits will be parallel to the magnetic flux and perpendicular to the eddy currents, so flux is unchanged while eddy currents are largely disrupted.