Mod circuits from Daveplaysbass

[Ken Baker]

This is the place to look for circuits from Daveplaysbass, the gentleman who originally created all the single coil (non-K model) mods.

Ken...

[daveplaysbass]

Here is the latest version of the Coil Mod document. From best I can tell this is Version 4 which was recently updated. There is a new mod in this one that uses a push-pull volume pot along with the 3 position coil switch. It gives both Single Coil options along with Series and Parallel.

COIL MOD DOCUMENT Version 4.1
https://drive.google.com/open?id=1JDqxz2bWiiV_kq0QY0DqeLVZ7HlWHEIH


As of 12/28/2017 here is an updated Preamp Mod version with a huge bloviation opamps for those who care. If nothing else this gave me a chance to collect multiple thoughts in one place. I have found over the years that explaining an engineering problem to someone else forces me to think through it better. This document drove me into some corners a little more than I had done previously. Also, after taking the engineering manager lobotomy six years ago, I think I am missing the gory details of circuit design. And I am hoping the lobotomy was not 100% successful -:).

PREAMP MOD DOCUMENT Version 2.2
https://drive.google.com/open?id=1hwnRvHrkf1x-eweWK164SLw85YUUO_uG


Here is a detailed document of what I am calling the "Super Mod" which is Coil Mod 10.1 and Preamp mods with pictures, graphs, and charts.

SUPER MOD DOCUMENT VERSION 2 (UPDATED 3/21/2020)
https://drive.google.com/file/d/1cRxzzFhpfnheV-91Xwpn8uvW-LSDxXOE/view?usp=sharing

[godblender]

^^^^ These are outstanding and include the exact wiring schematics I've been looking for the past week. Thank you.

[jamjax]

Dave, thanks for documenting all of these mods for the community!
Ken, thanks for hosting and facilitating! (I especially liked the topical CAPTCHA question when I registered.)

I made my first bass purchase in March and thanks in a large part to this forum I settled on a 1998 L-2500. It plays and sounds great but I can't leave it alone knowing how many sounds are trapped inside. I plan to try out the super mod (just the coil rewiring part, so maybe it's just the 10.1 mod from the other doc). I have a few questions and observations, some of which could be trivial but which may be helpful to the next solder slinger.

• The super mod doc is based on a Tribute, but mine is a USA L-2500 and some of the wires are differently colored. "Bridge_Pup_Green" in the schematic is white on mine. "Neck_Pup_Red" is white. "Pup_Select_Out_White" is yellow. Attached is a picture of my stock control cavity.
• Push/Pull Pot: Dave's docs go into detail on the specifics of the 4PDT switch but the push/pull potentiometer's specs are omitted. I took a gamble on shaft length, etc., and settled on this one: Bourns PDB183-GTR02-254A2 from Mouser for $5. It would be helpful to have specs (and part number options) in the docs, since others might know less than I do (and it still took me some time to track this one down). I haven't installed it, so I'm not sure I've got the right one yet.
• 4PDT Switch: It can be hard to find one of these which one can buy individually. I also was incredulous at the price and spent an uneconomical amount of time trying to hunt down a bargain (which I never found). Unless someone else finds a great bargain for you (the next tinkerer reading my post), just stop searching and pay the $25 plus shipping for one of these things. (You may find a better price until you realize you have to buy a minimum of 1000). I got this one: C&K 7411SYZQE from Mouser.

Shipping from Mouser was 7 or $8 to VA, USA.

Questions:

• The subject Tribute's pickup cavities were described as being shielded. How did they do it at the factory? (Anybody got pics?) I can have a go with some shielding paint or copper tape (both of which I have), but I wouldn't mind emulating the stock approach.
• Curious: How am I supposed to interpret the numbers on the switch's diagram in the doc? (There are 1s, 2s, and 3s, and sometimes comma-separated combinations.) I stared at it for a minute and didn't understand those labels. UPDATE: I understand now: The numbers are each shown between two contacts. If a given number exists between contacts, those contacts are bridged when the switch is in that position number.

Switch Diagram from Doc

switch.png (143.86 KiB) Viewed 10294 times

7411 4PDT Switch Specs

7411_switch_specs.gif (83.47 KiB) Viewed 10294 times

Stock Control Cavity

control_cavity.jpg (132.74 KiB) Viewed 10288 times

[Ken Baker]

It's my bedtime....

Dave doesn't stop by all that often, so I'll try to field your questions.

Questions:

• The subject Tribute's pickup cavities were described as being shielded. How did they do it at the factory? (Anybody got pics?) I can have a go with some shielding paint or copper tape (both of which I have), but I wouldn't mind emulating the stock approach.

If any G&L cavity (USA or import) is shielded, it would be with shielding paint. Very dark gray - almost black. If you see bare wood or over-spray on bare wood from the paint shop, it isn't shielded. Paint is easier and quite effective, copper is prettier and arguably a better shield.

• Curious: How am I supposed to interpret the numbers on the switch's diagram in the doc? (There are 1s, 2s, and 3s, and sometimes comma-separated combinations.) I stared at it for a minute and didn't understand those labels.

The bold black numbers on Dave's drawings indicate switch position. Orient the physical switch like Dave's drawing; 4-across by 3-up/down, bottom view. Then wire the leads as shown, ignoring the lug numbers on the switch. Switch orientation isn't important because the switch is essentially two DPDT ON-ON-ON switches built into a single unit. Turn it 180° and it's the same. The internal shunts work the same way. Look here for more info.

Ken...

[daveplaysbass]

Push/Pull Pot: Dave's docs go into detail on the specifics of the 4PDT switch but the push/pull potentiometer's specs are omitted. I took a gamble on shaft length, etc., and settled on this one: Bourns PDB183-GTR02-254A2 from Mouser for $5. It would be helpful to have specs (and part number options) in the docs, since others might know less than I do (and it still took me some time to track this one down). I haven't installed it, so I'm not sure I've got the right one yet.

BOURNS 250K PUSH PULL SHORT SPLIT SHAFT AUDIO TAPER POT / POTENTIOMETER DPDT
https://www.ebay.com/itm/222438722380

If memory serves correct this required me to enlarge the "metric hole" used for the stock Tribute volume pot. I guessed when I bought this pot and it worked fine with the stock knob and the shaft length was proper. There is a picture of it being wired up in the Super Mod Document.

4PDT Switch: It can be hard to find one of these which one can buy individually. I also was incredulous at the price and spent an uneconomical amount of time trying to hunt down a bargain (which I never found). Unless someone else finds a great bargain for you (the next tinkerer reading my post), just stop searching and pay the $25 plus shipping for one of these things. (You may find a better price until you realize you have to buy a minimum of 1000). I got this one: C&K 7411SYZQE from Mouser.[/list]

Shipping from Mouser was 7 or $8 to VA, USA.

Nidec Copal Electronics 8A4101-Z
DP3T / 4PDT Switch @ Digi-Key for $12.51 plus postage

The Nidec Copal Electronics 8A4101-Z from Digi-Key is pretty affordable. I would call this a 4PDT on-on-on (4 pole, double throw, on-on-on) but the electronic industry more commonly refers to it as a DP3T (double throw, three pole, additional wire required, not worth going into but Google if interested). If using Google to buy one of these use "DP3T switch" search string. I think I mention this in one of the documents. Amazon has one. And Musician's Friend has a "4PDT on-on-on Dimarzio Pickup Selector Switch".

The subject Tribute's pickup cavities were described as being shielded. How did they do it at the factory? (Anybody got pics?) I can have a go with some shielding paint or copper tape (both of which I have), but I wouldn't mind emulating the stock approach.

No pics other than whats in the Super Mod document. You can see the black shielding paint in the wiring cavity. They also have it in the pickup cavities. And the pickup is grounded to the black cavity as I recall. I know not a very good explanation, but I am not in there. I believe the Tribute pickups have a 5th wire coming off it that is green that ties directly to painted cavity with a metal terminal and screw. That green wire is a direct short or connection to the green wire that goes from the pup cavity to the control cavity. That is why after I got into my first Korean Tribute long ago, I changed all the wiring diagrams to always have the green wire at "signal ground". The older US G&Ls do not have any of this.

Curious: How am I supposed to interpret the numbers on the switch's diagram in the doc? (There are 1s, 2s, and 3s, and sometimes comma-separated combinations.) I stared at it for a minute and didn't understand those labels. UPDATE: I understand now: The numbers are each shown between two contacts. If a given number exists between contacts, those contacts are bridged when the switch is in that position number.

The numbers are the toggle lever position: positions 1, 2, and 3. Since we are adding a 4PDT on-on-on switch, the on-on-on denotes there are three unique positions that the lever can take (versus the on-on or two unique positions in the stock series / parallel switch). The pictures you reference has 4 "columns" where each column is one of the 4 switches in the 4PDT switch. The center row represents the 4 switch poles. The top and bottom rows represent the throw positions that the pole can be connected to, which one depends on the lever position (1, 2, or 3). Each pole (middle row of terminals) is either making an electrical connection to the top throw or the bottom throw, again depending on the lever position (1, 2, or 3).

Here is a datasheet from CK Switches that may further explain. There are many varieties to see in this datasheet beyond the 4PDT and DPDT that are common in the bass world. Check out the 7411 variant on page F-5. This is the 4PDT on-on-on switch. https://www.ckswitches.com/media/1394/7000toggle.pdf

[Ken Baker]

I believe the Tribute pickups have a 5th wire coming off it that is green that ties directly to painted cavity with a metal terminal and screw. That green wire is a direct short or connection to the green wire that goes from the pup cavity to the control cavity. That is why after I got into my first Korean Tribute long ago, I changed all the wiring diagrams to always have the green wire at "signal ground". The older US G&Ls do not have any of this.

Might that extra green wire be the equivalent of the blue lead in the US -K models?

The non-K L series pickup has four leads; green & yellow and black & white. The green lead starts off at the coil and is a very short length to connect to one corner of the pickup's base plate. From the other corner of the base plate a long green lead extends into the cavity and is connected to ground. The other three leads run from the coils to the cavity.

The -K pickup has the same color leads as the non-K plus a blue lead. The green & yellow and black & white leads all run from the coils to the cavity. The blue lead runs from the base plate to the cavity and needs to be grounded.

In theory, the non-K pickup is ever so slightly unbalanced because of the base plate being in-circuit with one coil and not the other. The -K pickup is balanced because the base plate is not in circuit. The difference in impedance is so slight that it can't really be heard, but instrumentation can see it.

Ken...

[daveplaysbass]

Might that extra green wire be the equivalent of the blue lead in the US -K models?

The non-K L series pickup has four leads; green & yellow and black & white. The green lead starts off at the coil and is a very short length to connect to one corner of the pickup's base plate. From the other corner of the base plate a long green lead extends into the cavity and is connected to ground. The other three leads run from the coils to the cavity.

The -K pickup has the same color leads as the non-K plus a blue lead. The green & yellow and black & white leads all run from the coils to the cavity. The blue lead runs from the base plate to the cavity and needs to be grounded.

In theory, the non-K pickup is ever so slightly unbalanced because of the base plate being in-circuit with one coil and not the other. The -K pickup is balanced because the base plate is not in circuit. The difference in impedance is so slight that it can't really be heard, but instrumentation can see it.

Both make sense and achieve the grounding of the plate which is an improvement over the original design. The one thing to note is that usually there is a "single point ground" concept exercised or at least suggested with guitar wiring. To this end, the pup cavity ground wire is pulled to the control cavity tunnel and "grounded "on the back of a pot. This could be done with the green pup wire or with the blue wire you mention. In the G&Ls there are so many ground wires I don't try to get a true single point ground. I daisy chain the back of the pots together and use any of the three pot backs as "ground".