Les Paul Custom Questions 1992

[joelorigo]

I have a 92 left handed Les Paul Custom that I have a few questions about.

I was wondering if I could add push/pull pots to split the pickup coils. It’s all stock so I’m assuming it has the 498T and 490R (which I’ve gathered are what they used back then).
It looks like it's a single shielded wire from the pickups connecting to the volume pots, so not splittable, right? Not 4 wires?

Also, what pots were stock back then? I ask because I’m looking into ways to brighten up the neck pickup and if they are 300K, maybe one thing to try is 500K. If they are already 500K, does anyone go to 1M? (I’m also learning about some other things to try on a another site's thread) The pits have this number on them:

440-71079A R13792

I found a coupe of things searching that. Both are suggesting 500K and/or 100K ().
www.mylespaul.com/threads/unknown-pot-numbers.78790/
www.vintageguitarandbass.com/gibson/potentiometer/description/71079

Finally, I’m assuming it’s modern wiring, right? Not 50’s? Looks like it as I compare it to a "modern vs 50's diagram" I found. Asking that because I’m interested in a treble bleed I I've read that the 50's wiring also include it.

[newey]

You are correct, no coil cutting possible, unless you're inclined to perform some surgery on the pickups. Conversion to 4-wires can be done, but I've never done it, so not much I can tell you except it sounds like it would be a delicate operation, and might go either way.

If you really want to have coil splits, easiest route is to replace the pickups with the "modern" 4-wire versions, saving the original ones in case you ever want to take it back to original.

I don't believe the pots would have been 100K, 500K sounds more likely.

As for pot values and brightness, your neck pickup has 2 pots, and while the factory certainly used identical values for both the V and T controls, there's no reason you have to do so. And, it is the parallel resistance of the two pots with which we are concerned, not the individual resistance of one.

So, assume Gibson made the thing with 500K pots. The overall resistance of both in parallel is 250KΩ. If Gibson used two 300KΩ pots, then it's 150K.

If you replace both pots with 1MΩ ones, the combo is 500K- and will probably be significantly brighter. Change one pot of the two to 1M, leaving the other at 500K, gives you 333K. Is the difference between the 2 500K pots (assuming that's what the originals are) at 250K combined resistance going to sound audibly different than 333K? I dunno, maybe.

Now, if the originals were instead 300K, and you replace one with a 1M pot, you get 230KΩ The 2 500K pots would be 250K, and I guarantee you can't hear the difference between 230K and 250K. That difference is within the margin of tolerance for the pots anyway.

I have a Strat-ish guitar with a dual-lipstick tube HB at the bridge position. The lipstick tube HB is already pretty bright for a HB, and I put 1MΩ V and T pots in it. It is very bright, but again, this was a bright pickup to start. But simply turning the tone control down a couple of notches puts it in a sweet spot.

That's the thing about brightness. It's hard to get if you don't have it to start with, but easy to get rid of when you don't want it.

[JohnH]

I have a '91 Gibson LP studio. Obviously, a more modest model than yours but it has a similar metal control plate and the wiring looks similar.

I rewired but I do recall some 300k pots. It looks like there may be some writing on them?. Or you could measure, if you can get hold of a multi-meter? Even the cheapest one will be fine and you don't have to unsolder anything. (we can step through how)

I did a 4 wire conversion, but id agree it has some risk.

A quick fix to add brightness is to unsolder one end of the tone caps.

[joelorigo]

Mar 3, 2021 21:11:54 GMT -5 newey said:

You are correct, no coil cutting possible, unless you're inclined to perform some surgery on the pickups. Conversion to 4-wires can be done, but I've never done it, so not much I can tell you except it sounds like it would be a delicate operation, and might go either way.

If you really want to have coil splits, easiest route is to replace the pickups with the "modern" 4-wire versions, saving the original ones in case you ever want to take it back to original.

I will think about replacing the pickups. I have an SG that has these same pickups (I assume - a Standard from 2005) so it would be nice to change one of them.

[joelorigo]

Mar 3, 2021 21:11:54 GMT -5 newey said:

I don't believe the pots would have been 100K, 500K sounds more likely.

As for pot values and brightness, your neck pickup has 2 pots, and while the factory certainly used identical values for both the V and T controls, there's no reason you have to do so. And, it is the parallel resistance of the two pots with which we are concerned, not the individual resistance of one.

So, assume Gibson made the thing with 500K pots. The overall resistance of both in parallel is 250KΩ. If Gibson used two 300KΩ pots, then it's 150K.

If you replace both pots with 1MΩ ones, the combo is 500K- and will probably be significantly brighter. Change one pot of the two to 1M, leaving the other at 500K, gives you 333K. Is the difference between the 2 500K pots (assuming that's what the originals are) at 250K combined resistance going to sound audibly different than 333K? I dunno, maybe.

Now, if the originals were instead 300K, and you replace one with a 1M pot, you get 230KΩ The 2 500K pots would be 250K, and I guarantee you can't hear the difference between 230K and 250K. That difference is within the margin of tolerance for the pots anyway.

I have a Strat-ish guitar with a dual-lipstick tube HB at the bridge position. The lipstick tube HB is already pretty bright for a HB, and I put 1MΩ V and T pots in it. It is very bright, but again, this was a bright pickup to start. But simply turning the tone control down a couple of notches puts it in a sweet spot.

That's the thing about brightness. It's hard to get if you don't have it to start with, but easy to get rid of when you don't want it.

I didn't not know that about the parallel wiring.

And I get what you're saying about the brightness issue.

[joelorigo]

Mar 4, 2021 5:30:48 GMT -5 JohnH said:

I have a '91 Gibson LP studio. Obviously, a more modest model than yours but it has a similar metal control plate and the wiring looks similar.

I rewired but I do recall some 300k pots. It looks like there may be some writing on them?. Or you could measure, if you can get hold of a multi-meter? Even the cheapest one will be fine and you don't have to unsolder anything. (we can step through how)

I did a 4 wire conversion, but id agree it has some risk.

A quick fix to add brightness is to unsolder one end of the tone caps.

I do have a multimeter! Please tell me how to measure. (The only writing I see on the pots is this: 440-71079A R13792)

And I don't plan on attempting a 4 wire conversion.

I will add the unsoldering of the neck pickup tone cap to my list of things to try.

[JohnH]

OK great

We can work out the values of all the pots, allowing for the fact that they are wired in:

Tone pots:

1. Set meter to 2M ohm
2. Measure across the two outer lugs and this is the pot ohms. In this case, the tone cap stops any influence of the rest of the circuit on the reading.

Volume pots:

3. Set the switch to the pickup to be tested.

4. Set your meter to a 200k ohms setting and connect across hot and ground at the jack, or between tip and barrel of a cord plugged into the jack.

5. Sweep the tone pot - there should be no change (this makes sure the tone cap is ok)

6. Set knobs to max
you are now reading just under the pickup ohms, maybe 7 or 8 k. You can change to a 20k setting to confirm. Add 2% for a very good estimate of pickup ohms. eg, if you read 6.8k at this stage, a good estimate of the pickup is 6.8 x 1.02 = 6.9k.

7. Now back to 200k, and sweep the volume pot from max to min. The reading will start as in 6 above, rise to a maximum then fall to zero at minimum. Record the maximum reading and where it happens on the pot knob turn. If its at half turn, knob at 5, you have a linear pot (common on LP's of that period). If its at about about 7 on the knob, then you have a log pot.

8. Take the maximum reading from point 7 that you found, multiply by 4 and subtract the pickup estimate. eg, say you read 130k maximum and the pickup was worked out at 7k. Your pot is then (130 x 4) - 7 = 513k

[JohnH]

Just another thought about brightness:

What length guitar cord do you use? A typical 20' cord will sound more muted than a typical 10'. It's very noticeable, due to capacitance of the cable from the guitar to the amp or to the first buffered pedal . If you use pedals and they are all true bypass and all off, then the second cable adds more capacitance. A buffered pedal in the chain together with a shorter cord from the guitar may fix this.

[joelorigo]

Tone pots measure:
Neck .460
Bridge .422

So probably 500K for them?

Using the formula above for the volume pots above I get:
Neck 276
Bridge 270

So probably 250K for them? And the maxim reading was at about 5 on the knob, so looks like linear. 

Interestingly, the bridge pickup is 13.2 and the neck is 7.8 for their individual readings.

[joelorigo]

Mar 4, 2021 15:59:19 GMT -5 JohnH said:

Just another thought about brightness:

What length guitar cord do you use? A typical 20' cord will sound more muted than a typical 10'. It's very noticeable, due to capacitance of the cable from the guitar to the amp or to the first buffered pedal . If you use pedals and they are all true bypass and all off, then the second cable adds more capacitance. A buffered pedal in the chain together with a shorter cord from the guitar may fix this.

I mostly have 6-12' cords. I have the same opinion of the neck pickup with various setups, both with a cable directly into the amp and with a string of several pedals. I am also planing on making some cables using low capacitance wire.
guitar.com/guides/diy-workshop/diy-workshop-how-to-make-your-own-guitar-cable/

[JohnH]

Good results! and it's a neat set of tests isn't it?

I reckon the pots were nominally 500k tone, and maybe 300k linear volume, and that was a common recipe. Having seen your results, I think I had it too. Many pots end up as less than the nominal value.

[joelorigo]

Yeah that is neat!

Yea, 500 & 300 make more sense.

Thanks guys!

[joelorigo]

Oh! If I do decide to replace any of the pots in this guitar, they need to be the long shaft type?

[JohnH]

yes definitely long shaft, on these the shaft has to reach through not only a thick top but also through the metal plate, if you want to keep it. I kept mine and changed to some nice new long-shaft 500k log pots.

[joelorigo]

Thanks!

[newey]

Mar 4, 2021 14:57:53 GMT -5 JohnH said:

We can work out the values of all the pots, allowing for the fact that they are wired in:

Tone pots:

1. Set meter to 2M ohm
2. Measure across the two outer lugs and this is the pot ohms. In this case, the tone cap stops any influence of the rest of the circuit on the reading.

Volume pots:

3. Set the switch to the pickup to be tested.

4. Set your meter to a 200k ohms setting and connect across hot and ground at the jack, or between tip and barrel of a cord plugged into the jack.

5. Sweep the tone pot - there should be no change (this makes sure the tone cap is ok)

6. Set knobs to max
you are now reading just under the pickup ohms, maybe 7 or 8 k. You can change to a 20k setting to confirm. Add 2% for a very good estimate of pickup ohms. eg, if you read 6.8k at this stage, a good estimate of the pickup is 6.8 x 1.02 = 6.9k.

7. Now back to 200k, and sweep the volume pot from max to min. The reading will start as in 6 above, rise to a maximum then fall to zero at minimum. Record the maximum reading and where it happens on the pot knob turn. If its at half turn, knob at 5, you have a linear pot (common on LP's of that period). If its at about about 7 on the knob, then you have a log pot.

8. Take the maximum reading from point 7 that you found, multiply by 4 and subtract the pickup estimate. eg, say you read 130k maximum and the pickup was worked out at 7k. Your pot is then (130 x 4) - 7 = 513k

JohnH- That is the clearest explanation of the "brain scan through a nostril" procedure I have seen, at least for an LP-type HH setup. With your permission, I think we should repost this in references, as it's more straightforward than ChrisK's post, which has slipped way down the list anyway. The only thing I would add would be a line about auto-ranging meters not needing to be set, since many nowadays are auto-ranging.

[JohnH]

Thanks newey,

A couple of years ago I added a slightly longer version to update Chris' Strat version of this procedure, as a 2nd post of his thread. The one here above is a bit terser, having written it out a number of times elsewhere. I always want to give credit to Chris as the inventor.

It should work with any guitar, unless there is a treble bleed circuit, to give a pot value within 1k. There's one final step if we want to find a really accurate pickup value instead of just adding 2%, which I put on Chris' thread. How about I try to put all that together in a new and concise Reference thread?

[newey]

Yes, by all means please do so.