A question about L-2000 pre-amp (treble sweep).

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A question about L-2000 pre-amp (treble sweep).

Postby Stevedude » Fri Aug 29, 2014 2:38 pm

Hello Kan and everyone,

A question about the pre-amp treble sweep on my newly acquired L-2000.

When I put it in serial, the treble increases or decreases smoothly & properly as I turn on the treble knob.

But if I put it in parallel connection, then turning the treble knob doesn't do much.
The treble level doesn't change much, if at all, when I turn the knob from 10 to around 2 (10 being max treble).
It may change a little, but it's almost unnoticeable.
Then at around 1, the treble level goes down noticeably for the first time.
And at treble knob 0, the treble goes abrupt 0, producing muffled tone (like tone knob at 0 on a passive bass).

Simply out, turning treble knob in parallel connection from 10 (max) to around 2 doesn't do anything.
Then from 2 to 1, the treble goes down little but at least it's noticeable.
And then the knob at 0, producing muffled tone very abruptly.

Is this normal?
Since the treble sweep is working properly in serial connection, I assume it may be normal that has something to do with the nature of parallel connection.
But I would like to hear your opinion on this matter.

Thank you so much.
PS: I shielded the control cavity today with copper foil from Stew Mac. It took longer than usual due to odd shape of the cavity and the bird-nest wiring (OMG, all them wires~ :shock:).
I had to be real careful not to knock any wire/connection off while shielding, but it's done and the bass is a lot quieter now. ;)
FYI. The treble sweep issue mentioned above was there before shielding. So it was not something that occurred during shielding.
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Re: A question about L-2000 pre-amp (treble sweep).

Postby GeorgeB » Fri Aug 29, 2014 4:27 pm

The reduced function of the passive(!) treble control in parallel mode is normal because it interacts strongly with the characteristics of the pickups which change a lot between the two configurations. In parallel mode you'd need a lower value pot resistance and a higher value tone capacitor to have as strong an effect but then it would be not usable at all in series mode.
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Re: A question about L-2000 pre-amp (treble sweep).

Postby Ken Baker » Fri Aug 29, 2014 4:53 pm

GeorgeB, I don't agree, based on my experience with the L series Tri-Tone circuit. It's just a simple 250K/.047mfd treble cut. I've found it to be smooth and effective in action, and not at all dissimilar from, say, a Jazz Bass circuit (which uses the same values).

Stevedude:

Below are two drawing versions of the same circuit for a modern L-2000 without OMG caps. Choose whichever works best for you, or use both, and compare with the actual wiring in your bass. Pay particular attention to the treble pot, which is the middle pot in both drawings. Look for any differences and go from there.

I'm thinking that if there are no wiring faults, that the treble pot itself could be faulty, or maybe just badly gunked up with grunge that's affecting proper action.

Each image below is also a link to the PDF version of the image.

Image

Image

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Re: A question about L-2000 pre-amp (treble sweep).

Postby Stevedude » Fri Aug 29, 2014 6:41 pm

Thanks so much George and Ken.

I'm not 100% certain, of course, but I am doubtful that the treble pot is faulty because as I mentioned it works perfectly fine when the pickups are in serial.
The lack of range in treble happens ONLY in parallel mode.
So maybe, George has a valid point, or there's a faulty wiring/connection somewhere.

Regardless, I will check the wiring by those two diagrams and report back.
(Boy, with that mess of wires, it won't be easy to follow the wirings... :cry:)

Thanks again gentlemen.

Steve ;)
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Re: A question about L-2000 pre-amp (treble sweep).

Postby Stevedude » Fri Aug 29, 2014 8:26 pm

Okay, I just finished comparing the wiring between my L-2000 and those 2 diagrams and here's what I found.

There was ONE discrepancy between my bass and those diagrams.
On the diagrams provided by Ken, there is a 10K resister between the yellow wire from "SW" terminal of circuit board (#5 in 2nd diagram) and the pre-amp switch terminal (top left corner of the switch body).
That 10K resister is missing in the wiring of my L-2000.
The yellow wire from the circuit board is connected to the pre-amp switch terminal directly WITHOUT that 10K resister in between.

My circuit board is version 1.3 and the board on the diagram shows version 1.1.
So I don't know if that missing 10K resister is normal difference between v.1.1 and v.1.3.
And also I don't know if that missing resister is the cause of this very limited treble sweep range ONLY in parallel mode.

Is this missing 10K resister a problem?
Can this be the cause of very limited treble sweep range ONLY in parallel mode?

I will really appreciate your input.
Thanks so much~!

Steve

PS: FYI. THAT was the wire that got under the switch unit at the factory during installation and got wedged between bass body and switch unit.
By getting wedged, the insulation on the wire got ripped and exposed wire made contact to the shell of the switch unit and caused loud buzzing when I touched the preamp toggle in preamp "On" position.
I freed the wedged wire when I first bought the bass and discovered the issue, but is it ever possible that initial short (or grounding problem - loud buzzing) caused by faulty installation damaged the circuit board and created this problem is treble sweep?
Last edited by Stevedude on Sat Aug 30, 2014 6:19 am, edited 1 time in total.
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Re: A question about L-2000 pre-amp (treble sweep).

Postby Ken Baker » Fri Aug 29, 2014 9:41 pm

Stevedude wrote:Okay, I just finished comparing the wiring between my L-2000 and those 2 diagrams and here's what I found.

There was ONE discrepancy between my bass and those diagrams.
On the diagrams provided by Ken, there is a 10K register between the yellow wire from "SW" terminal of circuit board (#5 in 2nd diagram) and the pre-amp switch terminal (top left corner of the switch body).
That 10K register is missing in the wiring of my L-2000.
The yellow wire from the circuit board is connected to the pre-amp switch terminal directly WITHOUT that 10K register in between.

My circuit board is version 1.3 and the board on the diagram shows version 1.1.
So I don't know if that missing 10K register is normal difference between v.1.1 and v.1.3.
And also I don't know if that missing register is the cause of this very limited treble sweep range ONLY in parallel mode.


That 10K resistor is part of the "Active with Treble Boost" setting and should have no effect on what you're experiencing. Remember that the controls on the bass are passive and are totally separate from the preamp. In fact, you could strip the preamp out of the circuit and those controls should work just fine.

PS: FYI. THAT was the wire that got under the switch unit at the factory during installation and got wedged between bass body and switch unit.
By getting wedged, the insulation on the wire got ripped and exposed wire made contact to the shell of the switch unit and caused loud buzzing when I touched the preamp toggle in preamp "On" position.
I freed the wedged wire when I first bought the bass and discovered the issue, but is it ever possible that initial short (or grounding problem - loud buzzing) caused by faulty installation damaged the circuit board and created this problem is treble sweep?


No, that was a separate issue. If I were to guess, I'd say that the yellow wire and the missing 10K resistor are from a previous owner mucking around in there.

I asked Paul about this earlier today and he got back to me when I was out. His response:

Paul Gagon wrote:This does not sound normal. My guess is there is something goofy with the wiring on the series/parallel switch. Shoot him a wiring diagram and have him check it out.


That's from the designer of the modern L Series circuit. So recheck wiring, looking closely through the rat's nest at the series/parallel switch.

Also, please understand that this is the Internet and that we don't have hands on your bass for troubleshooting.

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Re: A question about L-2000 pre-amp (treble sweep).

Postby Stevedude » Fri Aug 29, 2014 10:05 pm

Ken Baker wrote:No, that was a separate issue. If I were to guess, I'd say that the yellow wire and the missing 10K resistor are from a previous owner mucking around in there.

Thanks Ken, but one problem.
This is a brand new L-2000 made in Feb 13, 2014 that I bought less than a month ago from Guitar Center. I am the first owner.
Thus, the messed up wire and missing 10K register came straight from G&L factory.
In this case, do I need to put a 10K register on that wire?
If I do it myself, will it void warranty?

Paul Gagon wrote:This does not sound normal. My guess is there is something goofy with the wiring on the series/parallel switch. Shoot him a wiring diagram and have him check it out.

Ken Baker wrote:That's from the designer of the modern L Series circuit. So recheck wiring, looking closely through the rat's nest at the series/parallel switch.

I checked twice and found no discrepancy, but I will check it again tomorrow morning just to be 200% sure.

Ken Baker wrote:Also, please understand that this is the Internet and that we don't have hands on your bass for troubleshooting.

Of course I understand.
Thanks again Ken.

Steve
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Re: A question about L-2000 pre-amp (treble sweep).

Postby Ken Baker » Fri Aug 29, 2014 10:45 pm

Stevedude wrote:This is a brand new L-2000 made in Feb 13, 2014 that I bought less than a month ago from Guitar Center. I am the first owner.
Thus, the messed up wire and missing 10K register came straight from G&L factory.
In this case, do I need to put a 10K register on that wire?
If I do it myself, will it void warranty?


I missed that this was a brand new bass. Looking back on your original post, it's clear that it is new. Sorry I missed it. That changes things.

You have a warranty and I strongly suggest that you exercise it. Guitar Center isn't going to be the place to go for a G&L warranty fix, so you need to contact G&L directly. Contact Chris Robosan at 1-714-897-6766 x156 or you can email him. Be sure to mention that the bass is new from Guitar Center. You can also tell him that I recommended that you contact him for service on this issue. You should tell him of the pinched wire, the missing resistor, and the missing shielding that you had to install.

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Re: A question about L-2000 pre-amp (treble sweep).

Postby Stevedude » Fri Aug 29, 2014 11:12 pm

Thanks again Ken.

I checked the wiring again (couldn't wait until tomorrow morning even though it's now 2 AM EST :shock: ) and still found no discrepancy.
I will contact Chris Robosan as you suggested via email.

By the way, if I need to ship the bass to G&L, do I need to take the shielding off?
(If I need to ship it, I really hope I won't need to pay for it...)

Have a wonderful Labor Day weekend Ken.

Steve :)
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Re: A question about L-2000 pre-amp (treble sweep).

Postby Ken Baker » Fri Aug 29, 2014 11:35 pm

I've emailed Chris and given him a heads up on what you've done. He won't be back in until 9/2.

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