Questions about Series I Controls

[Bob Bell (kipknee)]

First, I've played an Alembic Spoiler for about 18 years now, so that's the bass that I'm familiar with.  However, I just graduated to a 1976 Series I a few days ago and I have a some questions about the controls layout.  Unlike the Spoiler, the Series I has separate volume/tone controls for each pickup.  The way they are wired seems backwards to me.  The neck pickup is controlled by the two pots nearest the input jack(s).  The bridge pickup is controlled by the other two pots (ie. the ones closest to the neck.)  Is that normal?  Did the pickups get switched around sometime during the last 26 years?  I pulled the back panel off the bass and the wiring seems undisturbed.
 
Second question is concerning the trim pots that are accessed at the back panel.  I'm assuming that two of them control the volume of each pickup (for proper blending) but what do the other two pots do?
 
Thanks in advance.
 
Bob/KipKnee

[Paul Lindemans (palembic)]

Hi Bob,
 
congratulations on your graduation!
Those pots are serving the hum-cancelling device = the third pick-up on your SI. There is a fine explenation on the club-board somewhere by Mica. Just wail around... you'll find it on the board.
 
CU
 
Paul

[Mark DuFresne (markus)]

Bob,
 
Sounds like someone crossed the pickup wiring. On mine, each pickup has a plug that connects to the preamp board. Could your two pickups be plugged in backwards?  
 
Paul's advice is good: seek the detailed description of your electronics elsewhere in this forum.
 
Mark

[Bob Bell (kipknee)]

I found Mica's post about the hum-cancelling trim pots (http://club.alembic.com/Images/394/1726.html) so that's a big help.
 
The pickup reversal has me still scratching my head.  I pulled the back-plate off and the pickup wires are color coded.  That is, the wires that come from each pickup has a tiny colored ring (blue or red) and the wires that come from the circuit board are also color coded blue and red.  According to the color coding, the pickups were plugged into the correct jacks of the circuit board.  I switched the pickups around so that it's opposite the color coding.  The volume/tone controls seem to make sense now, but the pickup selector switch (located on the lower horn) seems backwards now.  Generally speaking, there doesn't seem to be any problems with the pickups/electronics.  I'm almost wondering if it was wired backwards on purpose. The only other thing I can think of is that the pickups were removed and replaced incorrectly. Any thoughts?
 
 
Bob

[mica]

If you turn the pickup selector knob around, it might feel like it matches the arrangement you've found yourself with now. To really fix it, you'll have to rewire the pickup selector switch.
 

[Mark DuFresne (markus)]

Don't forget that since you have switched the PUPs to different channels in the electronics, you may need to tweak the gains and hum pots to bring it back to perfect. The gains are largely a matter of taste. As to hum -- it may be OK. Maybe listen for hum when you're giging in those electronically noisy rooms.
 
Of course, there's always the chance that the previous owner(s) never moved the trim pots when they switched the PUPs and you've just restored it to its original condition! ;-)

[Bob Bell (kipknee)]

I'm figuring on spending an afternoon tweaking this bass.  Although it doesn't look like the electronic circtuitry has been modified, I have no doubt that the original factory configuration/settings have long since gone by the wayside.  If I had more money, I'd send it up to Alembic and let them wave their magic-wands over it again.  In the meantime, I'll just trust my ears.  Rest assured, I will do NOTHING that requires a soldering iron or wire cutters.  (I know my limitations.)  Whatever I can't do by switching the pickups and/or adjusting the pots will remain undone until cash flow starts to move again.  There is no evidence that there is something wrong with the electronics.  I'm 99% sure it's just the pickups that got switched around.

[Paul Lindemans (palembic)]

Bob,
 
that's a wise thing to do.
I'm shure it will turn out for the best with that tiny bit of patience you always need when something really good is going to happen.
Look ... there is a whole lot of cash coming in at the horizon! Holidays!!!
;-)
Paul

[Bob Bell (kipknee)]

Good news!
 
I removed the pickups from the bass and switched their positions. Now all the color coded wires match up correctly. I also rotated the pickup selector switch 180 degrees.  (It appeared to have been switched around as well.)  Now all the controls and switches are back to stock and functioning perfectly.
 
I performed the trim-pot/hum-cancelling adjustments per Mica's instructions and I was amazed at how quiet the bass is now.  The only time I have a hint of noise is when the bridge pickup filter switch is in the lowest position.  I'm guessing this is just the nature of the original 1976 electronics.
 
Thanks to all for the input, assistance, information, etc.
 
Bob

[Paul Lindemans (palembic)]

All together: 3 x hurray for Bob!
;-)
 
Paul