G&L L2000 (1992) MFD pickup distortion?

[Jeremy Allen]

Hey gang, I've had this bass for several years, and this has always perplexed me: I cannot avoid a distorted/"clipped preamp" tone when I really dig in with my right hand. Just to get ahead of it--yes, I know these are hot pickups; I always run them passive, and regardless of serial or parallel mode I get this response. It happens even with the input gain on the amp/preamp set super low (which I've tried, in order to isolate the sound)--even with no signal clippage being possible or being indicated, this sound is there when I really dig in on the strings.

It almost sounds like a mechanical response, almost like I'm making something in the pickup rattle, although it is only audible in the signal chain (not acoustically, in the room, if I turn all volume off).

Any thoughts or experience with something like this? Thank you...

 

[sunbeast]

Hey gang, I've had this bass for several years, and this has always perplexed me: I cannot avoid a distorted/"clipped preamp" tone when I really dig in with my right hand. Just to get ahead of it--yes, I know these are hot pickups; I always run them passive, and regardless of serial or parallel mode I get this response. It happens even with the input gain on the amp/preamp set super low (which I've tried, in order to isolate the sound)--even with no signal clippage being possible or being indicated, this sound is there when I really dig in on the strings.

It almost sounds like a mechanical response, almost like I'm making something in the pickup rattle, although it is only audible in the signal chain (not acoustically, in the room, if I turn all volume off).

Any thoughts or experience with something like this? Thank you...

Is it with both pickups or just one?

Have you tried dropping the pickups heights? I found these pickups can be pretty saturated if you put them too close to the strings, and their tone really opens up when you drop them.

Also try removing the battery- even in passive mode there is connection to the pre (shouldn't matter, but easy to test).

Some eras of G&L used springs to suspend the pickups and these could potentially be picked up by the pickup (it was not an uncommon issue talked about on the G&L forums over the years- search for "spring ping"). Usually it sounds like a monotone high-pitch ringing sound though that follows your playing. The fix is to dampen the springs with foam or just replace them with foam entirely.

Microphonics in general could cause issues like this if your pickups are microphonic (also not uncommon from older G&Ls, tap on the bass body while muting the strings and if you hear clear pinging through the amp then your pickups are probably somewhat microphonic). Make sure the copper plate on the bottom of each pickup is glued firmly in place (I had one come loose on an SB-2 pickup coil and cause microphonic issues).

Distortion sounds can also happen if you have a weak solder joint or frayed wire in the signal chain.

 

[mellowgerman]

Maybe it could be a failing solder joint in the preamp itself? Might be worth having a tech take a look who's experienced with active preamps

Edit: Looks like @sunbeast beat me to it by a few seconds

 

[Jeremy Allen]

Thank you for the excellent replies!

The issue is mostly in the bridge pickup, though the E string on the neck pickup is brutal.

I took the battery out (forgot there was even one in there, it's been dead forever, ouch), no luck. No spring ping, no microphonics.

Lowering the pickups, though--magic! I ended up dropping them quite a bit, a little at a time, and the problem is gone. THANK YOU.

I have to say, it sounds like a different bass, in a good way! I had not expected such a pleasant surprise.

Thanks, friends--

 

[sunbeast]

Thank you for the excellent replies!

The issue is mostly in the bridge pickup, though the E string on the neck pickup is brutal.

I took the battery out (forgot there was even one in there, it's been dead forever, ouch), no luck. No spring ping, no microphonics.

Lowering the pickups, though--magic! I ended up dropping them quite a bit, a little at a time, and the problem is gone. THANK YOU.

I have to say, it sounds like a different bass, in a good way! I had not expected such a pleasant surprise.

Thanks, friends--

Glad that helped! I played a 1982 L2000 as my main bass for years and had the pickups dropped almost as low as they could go, which for me sounded fantastic and helped tame some of that overabundance of chunky midrange that these pickups can have while still having plenty of overall output!

 

[mellowgerman]

Worth mentioning, a dead battery will also cause distortion in a preamp, so that could also have contributed to the issue. In any case, very happy to hear it's resolved!

 

[sunbeast]

Worth mentioning, a dead battery will also cause distortion in a preamp, so that could also have contributed to the issue. In any case, very happy to hear it's resolved!

The G&L preamp has a "passive" setting, though the way the circuit is wired the pickups are still connected to the preamp even in passive mode. I seem to recall that testing my old L2000 in passive mode that I heard some slight change when removing the battery, but it could have been my imagination. In any case I just left the battery out of that bass since I never used the active preamp anyway.

 

[Stylee Mousse]

As an MFD lifer I have to reiterate: pickup height is the biggest mod of all.

Lower them and everything works.

 

[lowfreqgeek]

Worth mentioning, a dead battery will also cause distortion in a preamp, so that could also have contributed to the issue. In any case, very happy to hear it's resolved!

This is because the supply rails of the opamp are at 0V and the output topology of the LM4250 starts clipping as soon as the voltage of the output pin hits a diode drop above or below ground. The MFD pickups certainly can put out more voltage than a diode drop, so you end up clipping the signal. The only way to resolve it is to either use a battery to maintain the rails at a high enough voltage or to pull the opamp out of the circuit. Pulling a battery out of the bass alone will not fix it.

 

[Ricky Rioli]

Lowering the pickups, though--magic! I ended up dropping them quite a bit, a little at a time, and the problem is gone. THANK YOU.

On the BassesByLeo forum (sadly now shuttered) main-man Ken's standard advice for MFD pickups was: first drop them as low as they will go, and then gradually raise them until you get the tone you want.

 

[sunbeast]

This is because the supply rails of the opamp are at 0V and the output topology of the LM4250 starts clipping as soon as the voltage of the output pin hits a diode drop above or below ground. The MFD pickups certainly can put out more voltage than a diode drop, so you end up clipping the signal. The only way to resolve it is to either use a battery to maintain the rails at a high enough voltage or to pull the opamp out of the circuit. Pulling a battery out of the bass alone will not fix it.

Are we talking about the L2000 in passive mode like the OP, or in active mode which the OP never uses? I played my L-series basses in passive with no batteries for years without issue.

 

[LowActionHero]

Thank you for the excellent replies!

The issue is mostly in the bridge pickup, though the E string on the neck pickup is brutal.

I took the battery out (forgot there was even one in there, it's been dead forever, ouch), no luck. No spring ping, no microphonics.

Lowering the pickups, though--magic! I ended up dropping them quite a bit, a little at a time, and the problem is gone. THANK YOU.

I have to say, it sounds like a different bass, in a good way! I had not expected such a pleasant surprise.

Thanks, friends--

That's a common first 'mod' for G&Ls. I had the same problem when I first bought my L2000

 

[TomB]

Here and there over time in the club thread you’ll see the suggestion that you reduce the bass’ volume control. I always run MFD’s at around 75% (L1000). The dual tone controls allow for fine adjustment after that without losing character.

 

[lowfreqgeek]

Are we talking about the L2000 in passive mode like the OP, or in active mode which the OP never uses? I played my L-series basses in passive with no batteries for years without issue.

Passive mode. It was most noticeable in the studio environment. I reviewed the schematic of the LM4250 and did a circuit simulation of the cascode push-pull output stage, which confirmed my analysis and what my ears were hearing. Maybe I'll put it on a scope one of these days, but a basic review of the circuit is enough to see it.

 

[sunbeast]

Passive mode. It was most noticeable in the studio environment. I reviewed the schematic of the LM4250 and did a circuit simulation of the cascode push-pull output stage, which confirmed my analysis and what my ears were hearing. Maybe I'll put it on a scope one of these days, but a basic review of the circuit is enough

the output of the preamp (and presumably the LM) is disconnected from the output jack when in passive mode, only the input of the preamp remains connected to the volume control/pickup switch output. Are you saying that amplifier distortion could somehow still make it into the signal from just having an input connected? I never noticed any distortion from my L-series instruments when playing in passive mode with no battery installed FWIW, though may have noticed a slight tonal difference between having the battery connected and not (could have been my mind playing tricks though, as it was subtle). I ended up removing the preamp entirely from my 1982 bass as I never used it and utilized the extra switch to get separate coil switching per pickup.

 

[lowfreqgeek]

the output of the preamp (and presumably the LM) is disconnected from the output jack when in passive mode, only the input of the preamp remains connected to the volume control/pickup switch output. Are you saying that amplifier distortion could somehow still make it into the signal from just having an input connected? I never noticed any distortion from my L-series instruments when playing in passive mode with no battery installed FWIW, though may have noticed a slight tonal difference between having the battery connected and not (could have been my mind playing tricks though, as it was subtle). I ended up removing the preamp entirely from my 1982 bass as I never used it and utilized the extra switch to get separate coil switching per pickup.

You're right - it's the input that's still connected rather than the output. However, the issue remains with the rails collapsed when the input amplitude gets large enough. It's not amplifier distortion, but the PNP input transistors form a diode between the base and emitter when the base goes negative relative to the emitter voltage (in this case 0V). The diode clips the signal amplitude and causes distortion if there is no supply voltage - even in passive mode. Most passive pickups don't put out enough voltage to make that happen, it was certainly an issue on my L2500.