PickUp wiring help ...

TTony

I'm about to build a bass.  To be more precise I'm about to put together a bass from bits from Mr GSP, which seemed like a better option than buying a cheapo bass, particularly as he had pretty much all the bits and pieces that I'd need.

The pickups (Kent Armstrongs) have no wires on them at all, just some tags/terminals protruding through the bottom of the pickup units - which appear to be fully sealed.  Now, Graham told me that I'd need a wiring diagram, but I didn't appreciate quite what he meant!

Having Googled and googled, I could find no obvious wiring diagrams, so - Google having failed - I'm asking here!  


The Jazz unit has 4 small tags/terminals and 1 larger.  I'm guess that's to allow coil tapping, and that some standard 4core +1 hookup wire is all that I need.  But I need to work out which of the small terminals is which before I can wire the thing up.

Each of the Precision units has 2 of the smaller terminals, plus a larger one.

I'm guessing that the larger terminal is for the shield, but why's that necessary on the single coil Precision units?  And what's the best way, or indeed anyway, of working out which terminal is ground / hot?


I am tired, so maybe I'm just not thinking this through properly.

normula1

Assuming the Jazz is hum cancelling, what you'll need to do is find how which pair of the four terminals represents the individual coils and then determine their phase. This link has a method to do that http://www.guitar-repairs.co.uk/guitar_pickup_polarity_test.htm

Then wire the the two cold side of coils together and use the two hot side of the coils as output and ground. Unless you want to do some fancy coil splitting etc. I'll guess like you the larger terminal is ground.

For the Precision, do the same as above to determine phase and again join the two cold ends together and the hots as output and ground.

By hot I'm essentially meaning the connector that makes the multimeter have a positive reading and the other end of that coil becoming cold.

normula1

IIRC Kent Armstrong was the man behind WD Music in the UK or at least he was at one point, so it might be worth dropping them a line.

TTony

normula1 said:

IIRC Kent Armstrong was the man behind WD Music in the UK or at least he was at one point, so it might be worth dropping them a line.

I tried WD music in the US (which seems to be the distributor now).

On the plus side, they responded very quickly.

On the minus side, that's because it doesn't take long to type "err, dunno".


I shall go dig out my multimeter though, because the site you linked @normula1 looks like it might help.

Funkfingers

Photographs of the K.A. pickup soldering terminals will help. 

Your assumptions of four-conductor + shield format wiring are correct although, there are ways in which you could simplify things. 

If the plastic pickup covers are removable, inspect each coil to determine its start and end. If the pickups are sealed in epoxy resin, things could prove a little trickier. 

A dual coil J pickup could be configured in one of two ways: vertically stacked coils or side-by-side coils. The latter could be exploited by borrowing an idea from the old Adrian Legg customisation book. Essentially, the EA coil of one pickup plus the DG coil of the other. 

TTony

Funkfingers said:

Photographs of the K.A. pickup soldering terminals will help. 

Here you go @Funkfingers ...

Precision


If I put the multimeter across terminals 1&2, I get a reading of c4.81.  Likewise across terminals 3&4 (4.83).

If I join 2&3, and then test across terminals 1&4, I get a reading of 9.66.

At that point, I thought I'd won.  Except, I then joined 2&4, and testing across 1&3, and got a reading of 9.6 again.  

And I'm still unclear about the terminal marked X.  I'd assumed that was a shield, but I've not seen shield wires on single coils before?


Jazz


Points 1&2 = 8.10, and points 3&4 = 8.13 - so I'm assuming the start & end of each coil.

If I put a join across 2&3, and test across 1&4, reading =16.20

But I then joined 1&4 and tested across 2&3 and the reading was 16.14


Although the pickup covers look like they're in two parts and might separate, they don't actually come apart, so looking inside isn't possible.

ICBM

X is the shield connection and probably goes to a piece of tape either around the coil (Jazz) or in contact with the magnets (Precision).

The coil connections will give the same resistance whichever order they're connected in - the only difference is the phase of the coils, which will determine whether it's hum-cancelling or not. If it differs slightly its just a metering error. Usually they are wound in the same direction but with opposite magnetic polarities, so they need to be connected in opposite directions, ie 2-3 or 1-4 for the series link.

If you want to check the polarity of all the coils you can do it with the multimeter. Connect the meter to the coil you're testing with clips, and set it to read resistance. Put the pickup face up and touch the polepieces with a screwdriver, first making an 'on' movement and then an 'off' movement. The resistance reading will deflect away from the static value and then return to it - the direction of change tells you the polarity of the coil, ie you want them all to go high when putting the screwdriver on and low when lifting off, or vice versa. Swap the connections on any coils that do the opposite. That should give you pickups that are both in phase with themselves and hum-cancelling, and in phase with each other.

Funkfingers

Epoxy potting, as anticipated.

The first thing that I would try is to offer up the top of the J pickup to the top of one half of the P pickup. Move the P along the length of the J. If there is magnetic attraction on one half of the J pickup and rejection on the other half, the J pickup has side-by-side coils. 

The big terminal that you have labelled X is the shield connection. On the J pickup, the likeliest connection sequence is:
X & 4 = Ground
3 & 2 = Series link
1 = Hot output.

This presumes that you desire series interconnection of the J pickup coils and simple two conductor output cable.


On the P pickup, you have to wonder whether there is any significance to the positioning of the start/end terminals? From a winding perspective, it would be physically easier to start a coil closer to the centre line of the bobbin and attach the finish end further out, towards the outer edge.

The most practical solution is to just solder on some 4-con + shield cable to the pickups. Fasten them into their respective cavities. Sort out the interconnection permutations at the control cavity end.

TTony

Thanks gents 

Funkfingers said

The first thing that I would try is to offer up the top of the J pickup to the top of one half of the P pickup. Move the P along the length of the J. If there is magnetic attraction on one half of the J pickup and rejection on the other half, the J pickup has side-by-side coils. 

@Funkfingers ;
Now it gets interesting ..
The strongest reaction that I get between the pickups is an attraction between 1 P and the J, and rejection between the other P & J.  The reaction is constant along the full length of the J.

ICBM said:

the direction of change tells you the polarity of the coil, ie you want them all to go high when putting the screwdriver on and low when lifting off, or vice versa. Swap the connections on any coils that do the opposite. That should give you pickups that are both in phase with themselves and hum-cancelling, and in phase with each other.

@ICBM ;
That advice worked (no big surprise there!).
I get a -ve deflection on both units when the I connect the multimeter the same way on both p'ups (ie red to 1, black to 2 on p'up 1, and then red to 3, black to 4 on p'up 2).

Funkfingers

TTony said:

attraction between 1 P and the J, and rejection between the other P & J. 

That means;
1) your J pickup has stacked coils. 
2) no smartass Adrian Legg coil permutations.
3) not even worth coil-splitting or series/parallel switching of the J pickup, really.

TTony said:

The reaction is constant along the full length of the J.

This suggests blade polepieces and ceramic bar magnets rather than eight individual rod magnets. Expect snappy, modern sounds rather than traditional, vintage ones.

TTony

Thanks again @funkfingers -   a fair bit of decoding done there


I was planning on keeping the wiring simple  on this - I was just wanted to get it right (first time) as well as simple!

Funkfingers

My fear is that the soldering eyelets might be vulnerable to compression in the pickup cavities. It would be desirable to solder once with adequate strain relief and, then, leave things alone.

impmann

Wow... Tony... rare pickups. Those are hand wound units by Kent himself back in the day (probably 80s) when he was based near Ashford, Kent.

Kent used to supply grey multicore shielded cable with these pickups (I may even have some in a drawer). Often he'd wire taps into his pickups (proper taps not coil splits) for different sound options. I'd suggest using that approach and then you can experiment at the control cavity end, rather than keep soldering/desoldering the tabs on the base of the pickups.

Very cool!

Funkfingers

impmann said:

Wow... Tony... rare pickups. Those are hand wound units by Kent himself back in the day (probably 80s) when he was based near Ashford, Kent.

This might explain Kent Armstrong logo self-adhesive labels with the "SKY" model reference. Could those be prototypes? The out-of-focus handwritten info might shed some light.

TTony

Funkfingers said:

My fear is that the soldering eyelets might be vulnerable to compression in the pickup cavities. It would be desirable to solder once with adequate strain relief and, then, leave things alone.

Will do.  They'll be resting on some foam at the bottom of the cavities, so the eyelets should have enough protection.  

But I'll double check.

impmann said:

Wow... Tony... rare pickups. Those are hand wound units by Kent himself back in the day (probably 80s) when he was based near Ashford, Kent.

Kent used to supply grey multicore shielded cable with these pickups (I may even have some in a drawer). Often he'd wire taps into his pickups (proper taps not coil splits) for different sound options. I'd suggest using that approach and then you can experiment at the control cavity end, rather than keep soldering/desoldering the tabs on the base of the pickups.

Very cool!

Cheers for the info @impmann. ;

I was reliably informed that these were hand would units - and probably fairly "vintage" too.    Now, if you had a bit of wire in a drawer somewhere, that'd be  nicely appropriate!

impmann

TTony said:

impmann said:

Wow... Tony... rare pickups. Those are hand wound units by Kent himself back in the day (probably 80s) when he was based near Ashford, Kent.

Kent used to supply grey multicore shielded cable with these pickups (I may even have some in a drawer). Often he'd wire taps into his pickups (proper taps not coil splits) for different sound options. I'd suggest using that approach and then you can experiment at the control cavity end, rather than keep soldering/desoldering the tabs on the base of the pickups.

Very cool!

Cheers for the info @impmann. ;;

I was reliably informed that these were hand would units - and probably fairly "vintage" too.    Now, if you had a bit of wire in a drawer somewhere, that'd be  nicely appropriate!

I shall have a look this evening.

You can tell these are Kent's own handiwork from the handwriting - if they are machine-made, far eastern pickups these labels are printed. Interestingly he uses the word "Sky" on the base, which was the branding used on the early far eastern stuff he had made - again, these had printed labels and weren't constructed like this.

Kent's Handwriting:



Machine-made, far eastern stuff:



Nothing wrong with the Far Eastern stuff, just not as nice or bespoke.

EDIT: Sky pickups labelling

TTony

Funkfingers said:

This might explain Kent Armstrong logo self-adhesive labels with the "SKY" model reference. Could those be prototypes? The out-of-focus handwritten info might shed some light.

Who are you calling "out of focus" ??


Could be "SKY" or "$KT" , or "8KY" ... and Sq Jig underneath?




This one looks like "8£T", but could also be SKT.  Doesn't look so much like "Y" at the end on this one.



Looks pretty clearly like 6KT on this unit.    So I'm guessing that the others are probably 8KT

impmann

8KT - 8k ohms Total.

On the Jazz unit the bottom word is "Bridge".

You could email Kent himsef for advice - details here:

http://www.kentarmstrongpickups.com/

Funkfingers

impmann said:

You could email Kent himself for advice

Good suggestion.

1) The pickups may be more valuable than first imagined.
2) As good as they probably are, the sound might not be what you had in mind for your project bass guitar.

impmann said:

8KT - 8k ohms Total.

By this logic, the legend on the J Stack ought to read 16KT. Probably an oversight.

TTony

impmann said:

You could email Kent himsef for advice - details here:

http://www.kentarmstrongpickups.com/

Ahhhh - perfect, thanks  Tim!

My Googling to date had just taken me to kentarmstrong.com (and WD) rather than to the man  himself.

TTony

Funkfingers said:

1) The pickups may be more valuable than first imagined.
2) As good as they probably are, the sound might not be what you had in mind for your project bass guitar.

OK, you've got me a little worried now.

If they have some sort of collectible value,  I wonder whether I should actually use them!