1980 Series 1 Truss Rod, Filter and Hum Cancellation Problem

[Picure]

I finally got my 1980 Series 1 Point Bass today and man it is fun to play this beast!

However I came across some problems while digging deeper into this bass.

First of all, the bass has a really straight neck but the truss rod on the bass side is completely loose, and the treble side has just a bit of tension. The E string hits the frets more frequently because I play with a pick most of the time. I dunno if this is a problem being that this bass has travelled from California to Taiwan where Taiwan is known for it's humidity. However, I wish to have more truss rod margin because right now I am unable to adjust the truss rod.

Secondly, my neck filter has noise. When I turn the filter for the neck pickup, I can hear "dirt" in it. Like an old uncleaned volume pot. And sometimes, I get a very large volume drop on my neck pickup. However I found that exercising the filter pot didn't do any good so I opened the back plate and found that something was wrong with 2 transistors (shown in the picture next to the screwdriver head) because when I pushed down on these 2 transistors, it cleaned up the filter pot but not completely.




Pushing down on these 2 transistors also temporarily fixed another problem I had with the neck hum cancellation pot on the rear of the bass. Because the neck hum cancellation pot for some reason cut the volume of the neck pickup by almost 90%.

Right now it seems to be working as it should but I am worried that these two transistors would fail me again. Does anyone know what kind of transistors are these and where I could get replacement ones to repair my preamp card?

Finally, im not sure if this is inherent in Alembic basses but I found that like my Mosrite bass, the tone of the strings sounds drastically different between up picking and down picking when playing with a plectrum.

And... is it possible to purchase a new Q Switch? It seems like my neck Q switch is a bit bent

Videos of the Filter and Hum Cancellation problem:

Filter Problem
https://youtu.be/g7PzGHlYqIo

Hum Cancellation Problem
https://youtu.be/C7xNiZBEdVU

Thanks!

[JimmyJ]

Hey Jack,

I'll jump in with a couple ideas.  Nice looking axe and we all want to help you get it running to spec.

Regarding the action; this may seem dumb but I recommend raising the bridge a turn or two.  (Take the string tension off first so that the nuts below the bridge will follow the head of the bolt upwards.  I also like to tighten the nut against the bridge after moving it.)  Once you've done this you should be able to utilize the truss rods to correctly oppose the tension of the strings.

The behavior of your board is unusual and I can't explain it.  Those FET cans should be solidly mounted on their 6 legs.  You could take the board off the brass plate and inspect the (very small) solder points.  But before you do that, exercise the nearby pickup connectors. and also press on the opamp chips which are in sockets to be sure it wasn't just the physical pressure on the board that was changing things. 


I also can't figure out how the hum balance could work like a p/u volume...  We need expert advice on that so perhaps Mica will jump in with some ideas...

I'm not licensed to operate a plectrum so can't speak directly to your last question.  But I will say that these basses have such a wide range of frequency response and dynamics that they expose both good and bad things about our playing techniques.  Experiment with exactly where you're plucking the string and you'll see what I mean.  Along with balancing the pickup levels to your liking you'll likely find a sweet spot to create the tone you're looking for.  And hopefully balance out the up and down strokes. Keep in mind that theses basses are slightly offset to the left - the bridge is not at the end of the body as on your Jazz bass for instance...

Jimmy J

[Picure]

Thanks for your reply JimmyJ!

It seems like my bridge has already been raised by the previous owner, but I will raise it a bit more and see what happens.

About the FET cans, they seem to be solidly mounted on the board. I also have cleaned the nearby pickup connectors with contact cleaner. Right now it is working perfectly. Im just afraid that the FET cans will fail sometime down the line because I have a Vox Jaguar organ that has a ton of these FET cans and they go bad pretty often and with a few love taps, they come back to life.

[JimmyJ]

I've been playing these basses since 1975 (although currently my oldest is an '80) and never had a problem with these FETs.  But definitely tap and poke around on your board to see if you can recreate the failure.  Could be that it hadn't been played for a long time and you've simply revived a few of these electrical contacts.

Since these are handmade instruments there's no common "correct" bridge height.  It varies from one bass to another.  Once you get the action the way you like it, spend some time playing the bass to be sure you love it.  And then consider investing in a 2nd preamp board - which you could use as your main board if you're concerned about the original.  If you want to go a step further you could consider getting a new set of "hyper-matched" pickups.

Let us know how it goes!
Jimmy J

[gtrguy]

You might try using a VOM on the transistor leads by clipping one to the front leg and testing the back side of the board leg by contacting it or the trace hooked up to it. You may have to adjust the ohm settings to bypass whatever else is in line, either by adjusting up or down, so that you get a good test for continuity. Of course, if it is now working OK, this won't tell you anything.

A tech would probably just re-solder all those joints, just to make sure.

[mica]

We had some messages back and forth this morning, and I've had my dad take a look at the videos you sent and read this thread. He think you've gotten excellent advice already.

He does want you to check the shield on the pickup wires. If one is frayed, it may cause a short and show the symptom in your video.

For the filter pot, you need to turn it back and forth at least 100 times, maybe more. It should clean right up. If it doesn't you will need to replace this part.

As far as I know from our earlier conversations, the plan is to play a gig next week then send the card to us for a complete test. My dad asked that I give the card directly to him for the testing.

[sonofa_lembic]

I recently had virtually the same issue with an older Series I I had in stock.  Drop in pickup volume with a lot of noise.  Your pickup has a short in it.  It is common for them to short out within the final inch of shielding before the connector.  I solved my issue by trimming the wires back about 1.5" and then attaching a new Molex terminal and crimp ends.  It is likely only one of your pickups that is affected, but it messes up the hum canceller and the balance between the bass and treble.  I determined which pickup was bad by swapping the terminals and messing around with the trim pots, but whichever pickup appears to have the weak signal, just try trimming the wire back until you are past the short.  Alembic made me some pre wired connectors to use, but I was able to find the parts I needed at Frys, and I just attached the new Molex connector myself.  Mica says you need a special crimping tool to crimp the metal clips on the wires, but if you are careful, you can do it with fine needle nose pliers. 
As to your neck issue, I suggest you run a heavier gauge set of strings for a while.  They will create the bow your neck needs, and it may help the neck wood to take the bend permanently.  Any time you go to an island or along the equator, you are asking for neck issues due to the humidity. 

[Picure]

We had some messages back and forth this morning, and I've had my dad take a look at the videos you sent and read this thread. He think you've gotten excellent advice already.

He does want you to check the shield on the pickup wires. If one is frayed, it may cause a short and show the symptom in your video.

For the filter pot, you need to turn it back and forth at least 100 times, maybe more. It should clean right up. If it doesn't you will need to replace this part.

As far as I know from our earlier conversations, the plan is to play a gig next week then send the card to us for a complete test. My dad asked that I give the card directly to him for the testing.

Thank you very much Mica! I will "exorcise" the filter pot further and let you know the results. And you are correct about the wires being a bit frayed at the connecting end of the pickup connector. Ill see if I can repair it or tape it up or something to keep some tension on the wire.

About shipping the card in for test, I will give you a heads up via FB when I send it in.

Thanks!

[Picure]

I recently had virtually the same issue with an older Series I I had in stock.  Drop in pickup volume with a lot of noise.  Your pickup has a short in it.  It is common for them to short out within the final inch of shielding before the connector.  I solved my issue by trimming the wires back about 1.5" and then attaching a new Molex terminal and crimp ends.  It is likely only one of your pickups that is affected, but it messes up the hum canceller and the balance between the bass and treble.  I determined which pickup was bad by swapping the terminals and messing around with the trim pots, but whichever pickup appears to have the weak signal, just try trimming the wire back until you are past the short.  Alembic made me some pre wired connectors to use, but I was able to find the parts I needed at Frys, and I just attached the new Molex connector myself.  Mica says you need a special crimping tool to crimp the metal clips on the wires, but if you are careful, you can do it with fine needle nose pliers. 
As to your neck issue, I suggest you run a heavier gauge set of strings for a while.  They will create the bow your neck needs, and it may help the neck wood to take the bend permanently.  Any time you go to an island or along the equator, you are asking for neck issues due to the humidity.

Thanks for the tip! However, I think the wire has no more slack to be trimmed. Therefor for now I maybe have to just tape it up or solder the connection point as it is.

Thanks!

[sonofa_lembic]

Trust me, it is your pickup wire, and not the card.  I sent my card up and went through a bunch of dead ends before I figured it out.  If you don't have any slack left, then just splice in a new length of wire with a connector end on it.  At Frys, they have computer connectors that have small wires with the Molex end already installed.  You can just clip those wires off the Frys part, and use them to splice in to your pickup wires.  Here is a photo of a three lead wire from Frys, but they have plenty of two lead ones to use.  Just make sure you use some shrink tubing to isolate the hot wire from the ground wire.  A little solder, and you are good to go. 

[Picure]

Trust me, it is your pickup wire, and not the card.  I sent my card up and went through a bunch of dead ends before I figured it out.  If you don't have any slack left, then just splice in a new length of wire with a connector end on it.  At Frys, they have computer connectors that have small wires with the Molex end already installed.  You can just clip those wires off the Frys part, and use them to splice in to your pickup wires.  Here is a photo of a three lead wire from Frys, but they have plenty of two lead ones to use.  Just make sure you use some shrink tubing to isolate the hot wire from the ground wire.  A little solder, and you are good to go.

Thanks a lot! I finally figured out the problem while noodling around some more on the bass. It turns our that my neck filter knob was just a fraction loose from the bass and when turning the neck filter, it moved the wires inside a bit causing the noise. After I tightened the fastening nut for the neck filter, the noise was completely gone, super clean. 

[mario_farufyno]

you guys on this club are amazing