Alembic jazz bass preamp issue

[miamigroove]

Greetings!
New member here in need of urgent assistance. I have a very BELOVED 70's jazz bass that has Alembic pickups and preamp system installed by the previous owner. The preamp still passes signal OK but it has developed an intermittent "popping" sound which has rendered my bass unusable at the moment.  :'(

I've eliminated the amp, cabling, phone jacks, and 9V battery as possibilities so it must be something faulty within the preamp itself. I've attached a few photos and a short video demonstrating the issue below this message.

A) Is it possible to repair this preamp?

B) In the unfortunate event that the preamp cannot be repaired, is it possible to use the active Alembic pickups with another preamp or convert them to passive use?

My preference is to get it back working again as it was. This bass has served me well for many years now. Thank you!

https://www.dropbox.com/s/apgnesgmpe5sys7/1ABAF987-6147-4775-A5DB-5366D7DD4596.heic?dl=0
https://www.dropbox.com/s/u7mtzt8nks37qt6/7E89A8B3-7EE9-4669-83B7-07A3EDF2B486.heic?dl=0
https://www.dropbox.com/s/5mo16vw55s9qtdi/37D3E49C-27A8-4501-8527-03A28FAFF354.heic?dl=0
https://www.dropbox.com/s/q1uvujzr21dkdab/768AFA6C-C7BC-49D7-9ED7-42E6DFFF0840.heic?dl=0
https://www.dropbox.com/s/lengjxcvzyufv9c/E3F397C2-84D0-4155-AC76-E91C83795097.heic?dl=0
https://www.dropbox.com/s/kseypc7862q28xa/Alembic%20preamp%20popping%202?dl=0

[mica]

Likely the jack or the cable. Can you wiggle the cable in the jack and get the popping sound?

I know you said you checked the cable but note that many cables, especially some expensive/premium cables use connectors that don't comply with the standard. The Switchcraft jack you have does comply. Some of the connectors are slightly too long, or and so concave that they miss the contacts on the jack. So first I would suggest using a super cheap cable since they tend to not be a problem on that front.
Now, you can "tune" the jack with pliers and make the contacts hit where they need to on your cable. But you can break the jack doing this. New jacks are available in our online store. The original jack is probably this one: https://alembic.stores.yahoo.net/1moouja.html but we now use this one if there is enough room as it's even more durable: https://alembic.stores.yahoo.net/1moouhedu.html
All the parts are still made so anything that needs replacing is available. You really can't use these pickups passive as they are too low impedance.

[miamigroove]

100% sure it's not the cable. Same result with every cable i've tried (well over 10 different cables). Both cheap and expensive ones.

I brought it to a local tech who suggested it could be the jack as well so he replaced the jack already with a new USA switchcraft. Unfortunately, it did not fix the problem, it continued as before. Again, the bass does pass signal when played but it randomly sends a DC-like pulse (aka crackling, popping) along with the regular output signal which usually clips the amplifier. It even happens when the bass is stationary on the stand and not moving at all.

How can I get the preamp repaired? Tried calling a few times and left a voice message.

[mica]

Can you post an image of the electronics install?

[miamigroove]

As you wish. But please respectfully understand it is definitely NOT the patch cable or 1/4" jack that is causing the problem. I am 100% certain it's something failing in the preamp electronics that is responsible.

https://www.dropbox.com/s/p2ilfrburfs272a/0427E699-D433-4468-88BE-AEC84AA29A1E.heic?dl=0
https://www.dropbox.com/s/3jmymnimq3vvx70/BAFBDBF5-4F78-4575-8603-21C00971F82F.heic?dl=0
https://www.dropbox.com/s/ldxrbeqx97nc5a4/BD5A5E0B-362E-4DE2-BE9C-A8596566E354.heic?dl=0
https://www.dropbox.com/s/mb04bw90240xykt/E2E6A00E-5552-4AE7-908C-8114DB50DA66.heic?dl=0
https://www.dropbox.com/s/yfw3ws00t36nvns/F5D0B4C8-5ACF-4239-9B16-9F25624F0689.heic?dl=0

[JimmyJ]

Odd looking solder work on those boards, as if somebody has reheated all the joints - maybe looking for a cold one?  Picture 1 below does not look like factory work.  And that spot picture 2 looks like it NEEDS some solder.  Maybe plug it in and poke around on those boards with a nylon or wooden stick to see if you can get it to pop?

Jimmy J

[xlrogue6]

The solder on the sleeve terminal of the jack looks iffy, I'd redo that. I would also remove all of the excess flux from the PC board (Q-tips and isopropyl alcohol will do the trick). I agree with Jimmy's assessment that the board has been resoldered.

[miamigroove]

{taking a deep breath here........}

First, some history. This is no ordinary bass, it is a VERY special instrument to me. This bass went on tour with many top tier R&B bands back in the day (Four Tops, Temptations, Diana Ross, etc) the neck is a one-of-a-kind made by Philip Kubicki in the early 80's. The body is a mid-70's Jazz and the bass just feels and sounds amazing. Its better than any off the shelf Geddy Lee j-bass i've ever tried. Everyone i've ever let touch it has asked to buy it from me and the original owner still says he would buy it back if I ever sold it. This instrument has been well-maintained and faithful for 20+ years. In other words, this bass really means a lot to me.

I agree its not a pretty solder job but the reason i'm 100% sure that its not a mechanical joint failure is because you can consistently repeat the failure. If the bass is placed in a stand, ***COMPLETELY STATIONARY*** you will hear the component failing. Every few seconds it just sends a "pop" out. It's extremely consistent, verifiable and repeatable, unlike a bad jack or solder joint which is random and intermittent and would only occur when the bass is played, shaken or moved.

Can someone please help me with the following:

1. How can I send the preamp in for repair?
2. If it is deemed unrepairable, can I use another preamp with these pickups?

[MuseChaser]

First, anything is repairable. Secondly, there's nothing particularly magic about electronic circuitry.... it just takes time and patience to inspect, troubleshoot, and verify components. I agree that the solder work has definitely been retouched since original manufacture, and pretty hamfistedly, and maybe more than once. Clean up the boards with isopropyl alcohol (preferably 91%, not typical rubbing alcohol) as already suggested. You're discounting mechanical problems too early. Maybe a weak ground is causing a component cap to cycle and discharge causing the pop, or a voltage regulator to swing when it should remain stable...I have no idea really, other than I know it isn't as simple as "bad mechanical connections only cause random intermittent events." Any capacitor that's almost 50 years old can be suspect. I've done complete preamp and power amp circuit board repopulations on Dynaco integrated amps, rather than try and figure out which pesky cap, resistor, diode, or whatever is causing a problem. It's relatively cheap to do, and just takes time.

If you don't want to mess with it, any competent audio repair facility should be able to troubleshoot and repair your circuit for you.

[JimmyJ]

That's a lovely description of this historic axe and we all understand how important it is to you.  As stated, you will definitely be able to repair it and get it back to spec, eventually.  It will take some electronics work by somebody and patients by you.  Whether or not Mica and crew are able to do it, you'll need to wait and see.  But aside from the unusually bad soldering on the trace side of those boards, all the components are replaceable.  They are neither "potted" in epoxy nor unmarked. 

If Alembic themselves are unable to do the work then you should seek out some local talent - find out who's the best amp repair guy in Miami.  I am SURE there are some great guys there with all the music that happens in that town.  And they should be able to work through the boards for you and get that thing running.


Jimmy J