Problem with S2 LSB - serial # 905752

[Stefano]

Hello everyone,

I am facing a problem in 2 of 3 pickup selecting configurations: an awful scratching noise is produced when I strum the stings or pop (pull) the strings with a bit more strenght. I guess there must be a problem in the signal path of the bass pickup and when both pickups are selected, there is no problem when the treble pickup is selected.

What would you suggest? I have already made 50 turnings of all the pots and inverted the pickup signal cables on the board. The problem "migrates" with this operation, that means it is hearable when the treble pickup or both pickups are selected. Also, I replaced the opamps on the board a couple of years ago.

Futhermore, when knocking slightly on the back plate of the PF-6B board there is a crackling noise and this occurs when the pickup confirguration is the same as described above. The bass pickup hum balance trimpot is affected and makes a crackling noise when touched with a screwdriver. Apparently, the treble pickup hum balance trimpot has not this sort of problem.

I have already sent an email to Mica asking for advice, but maybe somebody here can help in the meantime.

Thanks a lot in advance.

Stefano

[JimmyJ]

Sorry to hear you are having trouble.  It sounds like you are experiencing a rare component failure.

Just to clarify ... when you swap the treble and bass pickup connectors at the board the noise moves from the bass output channel to the treble output channel?  And then the bass output channel is clean (although amplifying the treble pickup)?  If that is the case then it points to the bass pickup as being the source of the problem. 

Hopefully Mica will get you sorted out.

Jimmy J

[Stefano]

Thanks a lot for your input Jimmy!

I am not sure to understand: what do you mean by bass output channel and treble output channel?

If I swap the the treble and bass pickup connectors at the board the noise 'moves' from the bass pickup to the treble pickup (and the noise still remains with both pickups on), so that the single volume pots, the filters and the selector switch are 'inverted'. That is why I do not think that the pickups are the source of the problem. The problem is probably located in the bass pickup channel, a component failure, as you say, or a board problem, a cable issue in the signal path or a bad welding point.

Stefano

[JimmyJ]

It’s not easy to describe this accurately but I believe you already know how to troubleshoot the circuit. So it seems one channel of your preamp board is making the unwanted noise, correct?  The normally noisy bass pickup is clean when you swap the connectors, yes?


You mentioned that you had previously changed the opamp chips?  That’s the only serviceable thing you can try. There are 5 on the board, one for each “input” (bass, treble, hum coil) and two for each output (bass & treble). You can do some experimenting with those to see if you can isolate the problem.

You can also just plug in and tap around on the board with a pencil or plastic pen to see if you can identify the location of the fault. Highly doubt that it would be a solder joint issue. And if it is a FET (first transistor at each input) then you may need professional help. I’ve never tried to replace one of those and I fear I would make a mess of it.

Let us know what you find.
Jimmy J

[Scarlett]

Check the rainbow cable that plugs into the pf6.
are all pins intact?
I encountered a similar problem recently on a series and it was the result of 2 broken pins.

[Stefano]

It’s not easy to describe this accurately but I believe you already know how to troubleshoot the circuit. So it seems one channel of your preamp board is making the unwanted noise, correct?  The normally noisy bass pickup is clean when you swap the connectors, yes?

You mentioned that you had previously changed the opamp chips?  That’s the only serviceable thing you can try. There are 5 on the board, one for each “input” (bass, treble, hum coil) and two for each output (bass & treble). You can do some experimenting with those to see if you can isolate the problem.

You can also just plug in and tap around on the board with a pencil or plastic pen to see if you can identify the location of the fault. Highly doubt that it would be a solder joint issue. And if it is a FET (first transistor at each input) then you may need professional help. I’ve never tried to replace one of those and I fear I would make a mess of it.

Let us know what you find.
Jimmy J

Hi Jimmy,

thanks again!

Yes, the normally noisy bass pickup is clean when you swap the connectors. Then the noise is hearable on the treble pickup and with both pickups selected.

I have experimented with the opamp chips, but the problem still remains. I will try and tap around on the board to see if I can identify the location of the problem, but I believe I need professional help to find and resolve the issue.

Stefano

[Stefano]

Check the rainbow cable that plugs into the pf6.
are all pins intact?
I encountered a similar problem recently on a series and it was the result of 2 broken pins.

Hi Scarlett,

thanks for your input!

Yes, I have checked the rainbow cable and it seems ok, all the pins are intact.

Stefano

[matbard]

Stefano is a good friend and the owner of the Dragonslayer Series II. His baby deserves all the help we can provide

[Stefano]

Stefano is a good friend and the owner of the Dragonslayer Series II. His baby deserves all the help we can provide

Thanks Matteo!

[Stefano]

Do you think it would be an option to send the PF-6B board to Alembic?

Thanks!

PS: no reaction from Alembic so far...

[StephenR]

Do you think it would be an option to send the PF-6B board to Alembic?

Thanks!

PS: no reaction from Alembic so far...

There was a post here last week about problems with the phone, email and internet access at Alembic. So far there. has been no update to the thread so it is hard to tell if it has been resolved.
https://club.alembic.com/index.php?topic=29055.0

Since you have already determined that the pickups are okay you should be able to send the PF-6B board in to be checked/repaired. Hang in there a bit longer and I am sure you will get an answer from Mica.

[mica]

Yes, you can send the preamp card to us for testing. Generally we Make sure you use the new address:

240 Classic Ct
Rohnert Park, CA 94928

I haven't seen an email, what email address did you send it to?

[Stefano]

Yes, you can send the preamp card to us for testing. Generally we Make sure you use the new address:

240 Classic Ct
Rohnert Park, CA 94928

I haven't seen an email, what email address did you send it to?

Thanks Mica!

Will send the preamp card to the new address for your attention.

I sent the email to help@alembic.com and mica@alembic.com exactly one week ago on April 23rd.

[Stefano]

Mica,

I just have sent my e-mail to the same addresses once again, just in case it got lost during the internet problems you were facing last week. You may also look in the spam folder.

Thanks for your kind support.

Stefano

[Stefano]

Hi,

just to let you know that Mica suggested to check the joints on the preamp card. So I asked my local luthier explaining the problem and he suggested to clean all the joints on the preamp card with alcohol. I tried that and it seems the problem is now resolved. There is no distorted sound anymore when I hit or strum the strings harder.

Thanks a lot to Mica and to all of you who have responded (special thanks to Jimmy J!), the S2 sounds as it should now! If you play an Alembic Series bass all my other basses seem to sound 'banal' in comparison...

All the best,
Stefano