Les Paul Lo-Z pickups

[DeepFrequency]

The rule of thumb for volume control value is to find a pot value that is between 35 to 50 times the total DC resistance of the pickup coil or coils if wired in series. This will give you a resistance range in which to find a standard pot value.

Joseph J. Rogowski

Earlier in this thread the Les Paul low-z pickup (just one) was determined to be about 10ohms. Times 50: 500ohms or .5K Pot. is that correct per your formula? The schematic posted for two of these pickups is 2.5K. All help appreciate here as this is not my field. Would applying the guitar notion that if you had 250K pots but wanted more control use 500K pots work as well here? i.e. a 2.5K pot to a 5K pot? I ask because I have 5K pots and can't find the lower value.

[DeepFrequency]

Major break through on how the Les Paul pickups were wired with the coil taps and 8 wires per pickup. Using the photo from Fly Guitars webpage and the schematic I colored the schematic as suggested by Dave and the drawing did not match the photo. So I colored the drawing to match the photos then traced back the circuit following what pickup and what coil were put into play in the 3 "Tone" choice switch. Like I said big break thru!!


First off the Brown leads go to the Phase switch, The unseen Brown to the unseen Selector Switch. The drawing has them as Green so the Drawing is backwards.

So look at the photo and you see two gangs of 6 lugs each: They run off into two large black wires to the pickup selector switch at the top of the bass. The connections to the 12 lugs are far from what is pictured in the drawing AND why when I wired per the drawing is sounded all flat with no tone change at all.

Looking at the photo left to right Position #1 is Bridge pickup (photo top row of gangs - with the brown leads as per interpreted drawing)
POSITION #1 BRIDGE RED/BLUE: IN RED 500 TOP COIL - OUT BLUE 750 BOTTOM COIL ~ NECK GREEN/BLUE: IN GREEN 1000 TOP COIL - OUT BLUE 750 BOTTOM COIL.

POSITION #2 BRIDGE GREEN/RED: IN GREEN 1000 TOP COIL - OUT RED 500 BOTTOM COIL ~ NECK RED/GREEN: IN RED 500 TOP COIL - OUT GREEN 1000 BOTTOM COIL

POSITION #3 BRIDGE BLUE/GREEN: IN BLUE 750 TOP COIL - OUT GREEN 1000 BOTTOM COIL ~ NECK BLUE/RED: IN BLUE 750 TOP COIL - OUT RED 500 BOTTOM COIL

When pictured as I did ruff in the drawing below the relative size of over-laying coils and their positions bridge/neck light a bulb in my head. In particular the Position #1 Neck GREEN/TOP coil over BLUE/BOTTOM coil. I immediately recognized that this was the heavy "full bass" setting I had loved so much. My other two "middle" settings could be any combination of the remaining. And the OUT-OF-PHASE any of the sets. Imagine however all of these could be had IN and OUT of PHASE with the 2 pickups that's a whole lot of love. I hope my pix post below.

[DeepFrequency]

[bbsailor]

Earlier in this thread the Les Paul low-z pickup (just one) was determined to be about 10ohms. Times 50: 500ohms or .5K Pot. is that correct per your formula? The schematic posted for two of these pickups is 2.5K. All help appreciate here as this is not my field. Would applying the guitar notion that if you had 250K pots but wanted more control use 500K pots work as well here? i.e. a 2.5K pot to a 5K pot? I ask because I have 5K pots and can't find the lower value.

Consider the total load on the pickup that includes the volume pot or pots values when used in parallel with the actual amplifier input impedance. Most guitar amps have a 1M input impedance so the total load on a Fender pickup is 250K pot in parallel with 1M ohm amp input impedance. This turns out to be R1 times R2 divided by R1 plus R2 or 200K total load of parallel resistance. Now, low impedance XLR inputs have about a 2400 ohm actual input impedance to be about 10 times higher than the actual output impedance of low Z mics or guitar pickups usually rated at 150 ohms, called nominal rating, but many go as high as 300 ohms actual mic impedance. If you use a 2.5K ohm pot that is in parallel with 2400 ohm XLR input impedance you will have an actual load of about 1.25K ohms.

Here is a quick test you can do to see how the pot loads the pickup output level. Use two alligator clip wires and play a note or chord and the alligator clip the end lugs of the pot across the pickup output and listen for any signal loss. Once the pot is installed, if the pot value is too high you may not have a smooth and continuous volume control adjustment. I would say that a pot value between 1K and 2.5K should get you in the neighborhood of the proper value for your 10 ohm pickup. Remember also that when two 2.5K pots are in parallel their combined value is 1.25K but also in parallel with the XLR input impedance of 2400 ohms. Try the 2.5K ohm or the 5K ohm pots and let your ear be the judge.

I hope this helps? Let us know what you try.

Joseph J. Rogowski

[DeepFrequency]

Consider the total load on the pickup that includes the volume pot or pots values when used in parallel with the actual amplifier input impedance. Most guitar amps have a 1M input impedance so the total load on a Fender pickup is 250K pot in parallel with 1M ohm amp input impedance. This turns out to be R1 times R2 divided by R1 plus R2 or 200K total load of parallel resistance. Now, low impedance XLR inputs have about a 2400 ohm actual input impedance to be about 10 times higher than the actual output impedance of low Z mics or guitar pickups usually rated at 150 ohms, called nominal rating, but many go as high as 300 ohms actual mic impedance. If you use a 2.5K ohm pot that is in parallel with 2400 ohm XLR input impedance you will have an actual load of about 1.25K ohms.

Here is a quick test you can do to see how the pot loads the pickup output level. Use two alligator clip wires and play a note or chord and the alligator clip the end lugs of the pot across the pickup output and listen for any signal loss. Once the pot is installed, if the pot value is too high you may not have a smooth and continuous volume control adjustment. I would say that a pot value between 1K and 2.5K should get you in the neighborhood of the proper value for your 10 ohm pickup. Remember also that when two 2.5K pots are in parallel their combined value is 1.25K but also in parallel with the XLR input impedance of 2400 ohms. Try the 2.5K ohm or the 5K ohm pots and let your ear be the judge.

I hope this helps? Let us know what you try.

Joseph J. Rogowski

Big help, even with the parts that are over my head. I do grok the gist of what we are driving at. I really do appreciate your interest and help with this. I also notice we are both "ski's". To add my small understanding of electrics, would the pots wired in series add vs half the value? I made a speaker cab and ran into this ohms there.

EDIT: to add to the complete picture here when I use this rig I always use a small ac powered mixer. The stereo 1/4" jacks into the two inputs of the mixer and a single line out to my amp. Why, because this gives me better volume control over the two mis-matched pickups and my present (and many new small bass amps) amp has only one input.

EDITagain: rereading your post I am seeing XLR Low-z INPUT....there is no Low-z INPUT in my rig...I use an inline transformer to change the Low-z at the end of my cable to 1/4" input High-z. I used to have an amp with a built in low-z transformer to the 2nd channel, but sold it off years ago.

[Mike Sulzer]

There is a bit more to this. First consider a standard high impedance pickup. The impedance is only approximately equal to the coil resistance at very low frequencies. As the frequency increases it becomes inductive, rising in frequency, due to the coil inductance, and then the impedance maximizes at the frequency of the resonance composed of the coil inductance and the capacitance, cable and coil. The volume pot affects the Q of the resonance, that is, the width of the peak in frequency response. But also so does the tone pot since it must be considered as part of the load. (The tone capacitor has a low impedance at the resonant frequency and so it can be represented as a short at the resonant frequency.) That is, the resistance of the tone pot needs to be put in parallel with the rest. For a low impedance pickup, you would have to look carefully at the tone circuit, if any, to figure out how to compute the load.

Consider the total load on the pickup that includes the volume pot or pots values when used in parallel with the actual amplifier input impedance. Most guitar amps have a 1M input impedance so the total load on a Fender pickup is 250K pot in parallel with 1M ohm amp input impedance. This turns out to be R1 times R2 divided by R1 plus R2 or 200K total load of parallel resistance. Now, low impedance XLR inputs have about a 2400 ohm actual input impedance to be about 10 times higher than the actual output impedance of low Z mics or guitar pickups usually rated at 150 ohms, called nominal rating, but many go as high as 300 ohms actual mic impedance. If you use a 2.5K ohm pot that is in parallel with 2400 ohm XLR input impedance you will have an actual load of about 1.25K ohms.

Here is a quick test you can do to see how the pot loads the pickup output level. Use two alligator clip wires and play a note or chord and the alligator clip the end lugs of the pot across the pickup output and listen for any signal loss. Once the pot is installed, if the pot value is too high you may not have a smooth and continuous volume control adjustment. I would say that a pot value between 1K and 2.5K should get you in the neighborhood of the proper value for your 10 ohm pickup. Remember also that when two 2.5K pots are in parallel their combined value is 1.25K but also in parallel with the XLR input impedance of 2400 ohms. Try the 2.5K ohm or the 5K ohm pots and let your ear be the judge.

I hope this helps? Let us know what you try.

Joseph J. Rogowski

[DeepFrequency]

There is a bit more to this. First consider a standard high impedance pickup. The impedance is only approximately equal to the coil resistance at very low frequencies. As the frequency increases it becomes inductive, rising in frequency, due to the coil inductance, and then the impedance maximizes at the frequency of the resonance composed of the coil inductance and the capacitance, cable and coil. The volume pot affects the Q of the resonance, that is, the width of the peak in frequency response. But also so does the tone pot since it must be considered as part of the load. (The tone capacitor has a low impedance at the resonant frequency and so it can be represented as a short at the resonant frequency.) That is, the resistance of the tone pot needs to be put in parallel with the rest. For a low impedance pickup, you would have to look carefully at the tone circuit, if any, to figure out how to compute the load.

Wow, you guys are good. I serious did not understand a single word of what you said. Alex Dumble the fellow who put in this mod and who is supposedly world famous now understands this physics but I am lost. The odd part in this is for a fact Dumble left in the 250K original Gibson pots. They were 1967, marked so, and added value to the bass. He even replaced one with a 1969 pot to keep it close to the original date. That pot was in the low-z circuit.And it sounded gang busters. attached is the drawing I have come up with from the Gibson Ripper source which had the 4 position switch and the in-phase/out-phase, something I know Alex had as my positions 3-4. Together with the 500/750/1000 tap information I got here, and the combination of those that Gibson put in the Les Paul Recording bass I pieced together this. NOTE: The Gibson Humbucker (Gold color) is copied from my guitar, it is what Alex Dumble installed and has not been altered. Wish I had done the same with the low-z.

If curious minds what to see; Zip file is photos of my bass.

[DeepFrequency]

Success !!! Alex Dumble your imagination has come to life again. One day to clean all the old pots an re-wire the Humbucker circuit with a new On-On switch for that cuts the Gibson choke in and out. That was great, and the Humbucker sounds great again, with an .047 orange drop cap.

DAY TWO: With the all the parts and push-back wire in hand I solder up the 3 pole/4 position rotary switch to my diagram. Months of planning an years of waiting have all been worth it. I my plug 1967 Gibson EB-3 Alex Dumble Modified 1974 via it's XLR stereo jack to Y split to 1/4" plugs, to in-line Low-Z to High-Z transformer on 1/4" plug #1 and into 4 channel mixer channels 1 & 2. Out of the mixer/ Into my TC Electronics BH800 an VOILA!! Sound, Sound and More Sound. All 4 positions work....and with a few minutes of alligator clipping in a selection of different caps...lo and behold the Gibson schematic 4.7uf cap is the best. And the Kemet Aluminum Electrolytic 35v/4.7uf capacitor is the best sounding of the bunch. I want to thank everyone here on this thread for helping me complete this project. Perhaps one day you will hear this amazing sounding bass on a record somewhere.

P.S. the cool sound this bass gets is the combination of the very clean neck low-z pickup....which today I am leaning towards the cleanest #3 parallel position mixed together withe the Humbucker, choke on, .47uf orange drop tone turned a little bit in. I have La Bella "DeepTalkin'" Flatwound strings and run it all thru the mixer an TC Electronics BH800 and a 10" kevlar speaker in a Trace-Elliot BLX-80. It used to be an Ampeg B-15, with an Electro-Voice 15". The Trace-Elliot sounds better, a very tight speaker. The BH800 has the tone bumped just a little on the mid, mid-high, and high. Jack Bruce would have loved this little ax and rig.

[DeepFrequency]

Success !!! Alex Dumble your imagination has come to life again.

P.S. the cool sound this bass gets is the combination of the very clean neck low-z pickup.. Jack Bruce would have loved this little ax and rig.

The way this pickup is made there are TWO pickups stacked on top of each other, EACH of them with 3 taps Green/Blue/Red at 1500/750/500 (per entry found here in this thread). I had looked up how Gibson combined these in the Les Paul Studio/Recording bass. To make a visual reference I drew larger or smaller ovals and labeled them by color. Now that my pickup works I have a choice. At present it is in a fixed wiring state with the Green coil on top: Except Rotary Selector #2 then Red is the Top Coil pickup. AND Blue coil for ALL of the Bottom coil pickup choices on the Rotary selector. The Selector changes the two pickups from Series to Parallel or Series Out of Phase to In-Phase.

China sent Mini-Slide switches, On-On, by mistake. I find they will fit inside the available space in the cavity with the pots and wire loom. So I can make a modification similar to an Active pickups slide switch choice of Mids/Mid-Highs. In the first drawing I thought to access All the Bottom coil choices. But upon hearing the #2 Rotary choice of Red over Blue, it is a very full and bassy sound, I thought the Green might be More bassy but I would not need that. So I am opting to choose One Top coil change - Blue/Red: and One Bottom coil change - Green/Blue. More choices I think would be redundant and there is only room for two switches anyway. Attached is the drawing of my proposed addition. Also my initial drawing of the Les Paul bass combination of pickups. What I did not know about the Les Paul is whether the pairs were in Parallel or series which makes quite a difference.