HELP - Volume drop on L2000 bass

Seeing as how we are fortunate to count Paul Gagon as a member here, it seemed like a good time to give him a home to stretch out in and relax a little. Maybe exercise the grey matter and present a little history of the guitar and bass (amps too!) from his perspective as one of the eminent designers of our time.

Got questions? Great! Good questions might be, "What kind of windings are on the S500 pickup and why?" Or, "What was the thought process behind the MJ-4?" Troubleshooting questions should remain in the regular forums (he reads those too). Finally, please be mindful of how I feel about tech questions via PM or email.

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HELP - Volume drop on L2000 bass

Postby murger » Tue Apr 04, 2017 3:28 pm

Just wondering if someone has any ideas - I have a Trib L2000 that I bought 2nd hand - great bass!!! Played it one night at practice - everything is fine. Picked it up the next day, plugged it in and noticed a significant drop in volume, both in passive and active modes. Changed the battery - same thing. Tried a new patch cord - ditto. Tried a different amp - same thing. Tried another bass I borrowed to check the amps - lots of volume from the amps, so that's not it.
I dropped it off to the local guitar tech - he can't figure out what's going on. So before I get brave and start some major surgery to find which component is the culprit, I thought I'd ask for some input from the experts!!!
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Re: HELP - Volume drop on L2000 bass

Postby Ken Baker » Tue Apr 04, 2017 4:29 pm

Okay - lemme get this off before I take off to see Adam Savage at OCPAC.

When you plug in a cable, does the plug feel at all loose in the jack? I ask because the barrel jacks are a point of failure. If they get loose all kinds of crappy thing can happen.

Ken...
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Re: HELP - Volume drop on L2000 bass

Postby murger » Wed Apr 05, 2017 4:07 am

Nope - good and tight - good clean contacts.
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Re: HELP - Volume drop on L2000 bass

Postby TDR1138 » Wed Apr 05, 2017 6:57 am

I had an L-1500 that had similar symptoms. It turned out that the bass control pot was the culprit by making contact with the conductive paint in the cavity. Basically, it had rotated slightly in the hole and one of the tabs on the pot was touching the conductive paint in the cavity and grounding the circuit. So, I'd start by opening up the cavity, checking all of your connections and making sure there aren't any unwanted connections, too. After that, if you're still having problems, I'd start with a new volume pot and work from there.
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Re: HELP - Volume drop on L2000 bass

Postby murger » Wed Apr 05, 2017 7:23 am

Will do - I'll keep you posted! :D :D :D
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Re: HELP - Volume drop on L2000 bass

Postby murger » Wed Apr 05, 2017 3:07 pm

Nope - checked clearance on all pots (checked everything) - nothing shorting out - next idea???
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Re: HELP - Volume drop on L2000 bass

Postby Ken Baker » Wed Apr 05, 2017 3:58 pm

Things to look into:

1. Remove the battery and put the bass in passive mode. What happens here?

2. Does the problem occur at all pickup selections - neck, both, bridge?

3. There should be a notable difference in volume between series and parallel modes, with series being the louder of the two. Still, parallel should get plenty loud. What happens when you switch modes?

4. Do all the controls work as expected? Vol, treble, bass? Remember that EQ is cut only.

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Re: HELP - Volume drop on L2000 bass

Postby Paul Gagon » Thu Apr 06, 2017 8:56 am

You already have a lot of excellent suggestions, but if you are a bit handy with an ohm meter, let's look at something important. The DC resistance of an L-2000 pickup is around 8.4k (when configured in series mode). When a single pickup is connected to the controls is drops to around 8.1k. So, here's what we can do. Plug an instrument cord into the output of your bass and connect the other end to an ohm meter. Select either the neck or bridge pickup, set the coil configuration switch to series mode, switch to passive mode, and turn all controls to maximum. You should read a resistance of between 8.0k ohms and 8.2k ohms. You can switch between the neck and bridge pickup to see how closely they are matched. If you read a resistance that is a lot lower than this or reads way higher ( like 250k) you have a pickup that has gone bad.

While the ohm meter is still connected, you can check the resistance of each pickup in parallel mode. You should read around 2k for each pickup individually. If you set your pickup selector to use both neck and bridge pickup together then you will read around 4k in series mode and 1k in parallel mode.

All this is just trying to see if there is a problem that has developed in the pickup coils. By the way, this isn't a typical problem that comes up often but I have run into it a time or two. Check this out and let us all know what you find.

Thanks,
Paul
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Re: HELP - Volume drop on L2000 bass

Postby murger » Thu Apr 06, 2017 9:59 am

Awesome! I'll keep you posted on what i find - much thanks for the great suggestions!
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Re: HELP - Volume drop on L2000 bass

Postby Tomvl » Thu Apr 06, 2017 11:26 pm

Paul Gagon wrote:You already have a lot of excellent suggestions, but if you are a bit handy with an ohm meter, let's look at something important. The DC resistance of an L-2000 pickup is around 8.4k (when configured in series mode). When a single pickup is connected to the controls is drops to around 8.1k. So, here's what we can do. Plug an instrument cord into the output of your bass and connect the other end to an ohm meter. Select either the neck or bridge pickup, set the coil configuration switch to series mode, switch to passive mode, and turn all controls to maximum. You should read a resistance of between 8.0k ohms and 8.2k ohms. You can switch between the neck and bridge pickup to see how closely they are matched. If you read a resistance that is a lot lower than this or reads way higher ( like 250k) you have a pickup that has gone bad.

While the ohm meter is still connected, you can check the resistance of each pickup in parallel mode. You should read around 2k for each pickup individually. If you set your pickup selector to use both neck and bridge pickup together then you will read around 4k in series mode and 1k in parallel mode.

All this is just trying to see if there is a problem that has developed in the pickup coils. By the way, this isn't a typical problem that comes up often but I have run into it a time or two. Check this out and let us all know what you find.

Thanks,
Paul


Paul is the same DC resistance for a L-2500 Pickup ? If not , which are the valued ?
Anything below 500 Hz
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