Help wanted: Gibson Les Paul Recording wiring flaw

[pessukus]

Greetings to all "Nutz",

This is my first time posting but I have been reading this forum for years.

I have a question concerning the wiring in the 70's Gibson Les Paul Recording
(that's the one with the low impedance pickups). I have attached the Gibson
schematic for reference.

The "Tone switch", which is a regular 3-position Telecaster-type switch, has a
setting (associated with lugs 2 and 5 of the switch on the drawing) where both
pickups are selected in parallel, with a resistor in series with the neck
pickup and a capacitor in series with the bridge pickup. This gives a very
characteristic, "quacky" sound. However, it only achieves the intended effect

when the pickup selector (the toggle switch next to the neck pickup on the

drawing) is in the neck or the bridge position. When the toggle switch is in the

middle, the (almost) normal sound of both pickups in parallel results.

Would it be possible to alter the wiring so that the aforementioned position of
the "Tone switch" is completely independent of the position of the pickup
selector? I would guess that Gibson would have done it that way if there was an
obvious solution (since I can't think of any advantage to the current
arrangement), but you never know...

Thanks in advance for any and all insight,

Cheers!

[pessukus]

I don't know why the image appears at a 90° angle. I would gladly rectify it but I am afraid

I can't see how...

[newey]

pessukus-

Hello and Welcome to G-Nutz2!

No biggie to rotate it:



As for an answer to your question, we've had some fans of the LP Recording, and I've seen the wiring before, but it's been a few years, so let me take a look again to see what can be done with it.

[gckelloch]

Welcome, Pessukus. I don't get involved in wiring scheme stuff, but that's a great guitar. I do know that a poor quality transformer was used to convert the signal to Hi-Z. If you want to hear the pickups in all their glory, you should plug into a Lo-Z input.

[pessukus]

Hi gckelloch,

That's what I usually do: plug into a mic preamp input. It makes all the
difference. When plugged in a high-Z input, the internal transformer works but
it defeats the purpose of these pickups to a large extent. The incredible width
of the frequency response is lost and, especially with a long cable, the
"decade" switch and the treble control become much less useful, as the
frequencies they affect are already attenuated (which I believe is due to the
capacitance of the cable more than the quality of the transformer). A method
that works better is to use a transformer at the other end of the cable
(specifically a Shure A95U, which seems to be the only one with the right
specs), right before the high impedance input.

(You might already know all this if you've had experience with these pickups;
I'm just putting this information here in case anyone is interested.)

[Yogi B]

Oct 10, 2021 11:59:24 GMT -5 pessukus said:

Would it be possible to alter the wiring so that the aforementioned position of the "Tone switch" is completely independent of the position of the pickup selector? I would guess that Gibson would have done it that way if there was an obvious solution (since I can't think of any advantage to the current arrangement), but you never know...

I can't see a way, not with the stock switches at least.

The issue results from the toggle switch summing the parallel output of the two pickups 'before' the resistor & capacitor. Thus the result is the pickups in parallel in series with the parallel combination of the resistor & cap. The resistor is small enough that is mostly bypasses the effect of the capacitor, plus the additional impedance (from either R or C) has much less effect since it's only forming a voltage divider with the loading of controls rather than that of the individual pickups.

The solution would be to break the connection between the two centre lugs of the pickup toggle switch but only when the tone switch was in position 1, which would require the tone switch to have at least one extra pole (a 3P3T, rather than the standard DP3T).

---

For fun this is how they spin this functionality in the original owners manual (emphasis mine):

□ Tone Selector Switch The tone selector offers three distinct tonal capabilities. Position 1: This position engages both pickups into the tonal circuit. The signal output of both pickups are mixed together, bypassing the treble and bass controls. (The bass and treble controls will not function in this position.) The pickup selector toggle switch need not be in the center position to activate both pickups. If the toggle switch is placed in the center position, additional tonal effects may be achieved.

Gotta love them "additional tonal effects"!

[newey]

This description, from the Gibson manual, describes this better than I can:

Tone Selector Three settings: 1, 2, and 3. This switch does not actually change the tone produced by the instrument per se.. it acts as a bypass, inactivating certain controls - hence allowing quick and reversible changes between settings that would otherwise be impossible particular in a live setting. In position 2 (middle), nothing is bypassed. All controls function as described above. In position 1 the pickup selector switch and treble and bass controls are inactive - both pickups are selected by default. In position 3 only the treble and bass controls are bypassed.

This was for the original Recording models. On later models, the pickup selector was moved to the bought and the tone control positions were numbered reversed from the above, so the position pessukus is describing is called "Position 1" in the above description, but became "position 3" by the time of his guitar.

According to the description above, however, the toggle switch is bypassed (and that's what the schematic shows as well) in that position, so the sound should be the same regardless of the toggle's postion. So, your description has me a bit mystified.

EDIT: Ninja'd by Yogi B

[Deleted]

Some years ago i was reading about the LP Recording and Professional also Personal
i cant find the site off hand

From what i recall of the image id seen
the Treble was before the Bass

and i dont recall the Tone Switch

[pessukus]

Yogi B:

I only vaguely understood what was causing the issue, so I appreciate your
description of it. I did expect that an additional pole would be necessary.

"Additional tonal effects" is a good one indeed…

newey:

I too was mystified by the Gibson literature concerning that switch when I
first got the guitar. As you can see from the extracts you and Yogi B posted,
it is rather confusing.

[newey]

Oct 11, 2021 7:44:41 GMT -5 pessukus said:

"Additional tonal effects" is a good one indeed…

Yes it is. And in looking at the schematic, I can't figure out what they would be. The decade switch is in the circuit in the center position of the 3-way toggle, and that would vary the tone, but it looks to me like it is in the circuit at the other switch positions as well, so I'm lost on where those additional tone options are coming from.

If you are truly getting a different tone in the center position with the tone switch set to that option, I would suspect that (perhaps) at some point Gibson changed the wiring from what is shown in the schematic??? Have you checked the wiring in your guitar against that schematic? We already know some changes were made during the years this was produced.

[pessukus]

newey:

My comment was sarcastic: those "additional tonal effects" are imperceptible
except under the most favorable of conditions (they, or rather it, sounds just
like the regular "both pickups in parallel" setting — Yogi B's description of
the issue seems to explain why). Gibson's attempt at disguising this quirk as a
feature was therefore ludicrous.

The wiring in my guitar is as per the schematic, and I am pretty sure that all
LPR's are wired this way. The sentence in the extract that you posted which
says that the pickup selector is inactive in that position of the "tone switch"
is simply wrong. Apparently, one cannot trust Gibson to explain how their
products work.

[pessukus]

BTW, as far as I know, the only difference in the wiring of the first and
second versions of the LPR was the change from having the transformer on a
switch vs on two separate jacks, although they also might have changed the
value of the treble control's capacitor, as I recall seeing a different value in
another schematic.

[newey]

Well, they also moved the pickup selector to the bout, as you noted yours has. Not a change to the wiring, of course, just a change to the layout.

But, maybe Yogi B or one of our other more clever members can explain it, but as I view the schematic, the toggle switch should be bypassed by that setting on the tone switch, so the sound should be the same for all three positions of the pickup selector. Not clear to me why you're hearing a difference with the pickup selector in the middle position.

[Yogi B]

Oct 11, 2021 11:33:51 GMT -5 newey said:

But, maybe Yogi B or one of our other more clever members can explain it, but as I view the schematic, the toggle switch should be bypassed by that setting on the tone switch, so the sound should be the same for all three positions of the pickup selector.

It is bypassed in so far as it can no longer disconnect the pickups from the output, however it is not entirely removed from the circuit. As such it can still connect the two 'hot' leads of the pickups together in the centre position, additionally it selects with which pickup(s) the decade switch is directly in parallel. (This secondary quirk likely has only a pretty subtle audible effect, so I'm not surprised that it hasn't been noted.)

Below is a simplified diagram of what's going on with the tone switch fixed in position #1.

With the toggle switch down: ((Bridge + Decade Switch) × C1) + (Neck × R1)

then, in the centre position: (Bridge + Neck + Decade Switch) × (C1 + R1)

finally, the toggle switch up: (Bridge × C1) + ((Neck + Decade Switch) × R1)

The primary purpose of R1 & C1 is to affect how the neck & bridge pickups mix in parallel, but in the centre position the pickups are already directly joined via the toggle switch. Thus those components could only ever affect the combined parallel signal, rather than how that parallel signal is composed.

[newey]

Oct 12, 2021 23:07:28 GMT -5 Yogi B said:

Thus those components could only ever affect the combined parallel signal, rather than how that parallel signal is composed.

AHA! That is what I was missing.

In any event, it looks like there is no easy way to do what pessukus wants to do here, without a major rewiring anyway.

[Deleted]

i did think i posted here but the Tone Switch is some thing new from what ive seen
i want to try and find the site i used to read about this Guitar