Help Wirring Bass Guitar on board preamp

Hi,
I'm repairing at the moment  an Oakland & Co Bass. I'm having a lot of difficulties in trying to wire the active preamp circuit.
There's not much info around on these bass guitars, and no schematics.
The Active  Bass preamp circuit uses 2 IC's, the TL064 and a TL061.
It seems a  similar layout  to a MEC bass preamp, although the MEC uses TL064 and TL062, couldn't find a schematic on the MEC unfortunately.

Someone in the past messed around with the wiring of the active circuit and some wires were cut also.

I did a reverse engineering on the circuit and drawn a schematic of it (attached) , with the color of all the wires that come out of the board.
I would like to ask if someone could help me out of point me in the right direction of where to connected the wires.
The active part has a DPTP 3 way switch and a Dual gand 56K Pot.
The passive part has an 250K volume pot and an 500K Tone pot. The passive circuit is wired and working (will attach picture of the current layout  in a reply post).

I just don't really know where to connect the wires coming out of the preamp board and how to integrate this circuit into the passive circuitry already in place.

 

I know how to read schematics, and M able to build most of the projects of this forum although Im still learning and I don't know electronically how an amplifier, buffer or active tone circuit works. Thats why I'm asking for your help.

The wires coming out of the preamp board have this colors:

Yellow
Green
White
Blue/Black
Grey
Black (ground connection to VOL Pot case)
Brown
Yellow Stripped (ground connection to Tone Pot case)
Orange stripped
Orange
Violet
Blue Stripped
Blue
Red  (+Voltage from the Batteries)
PAD??? (pad on the pcb , it seems a wire was cut from here)

Some of them should connect to the 3 way DPDT switch (the switch that turns the active circuit on or of)
Others to the Dual gang pot
and the rest to the others part of the circuit like the pickup selector switch, volume pot, tone pot, output jack

It would be great if someone could have a look into the schematic and give some tips and direction

Thank you so much

Here is the present wiring layout of the passive circuitry that is working.

The 3 Way DPDT Switch that should be used to turn on of off the Active Circuitry has already a Jumper soldered between 3 pins.

Picture attached

I redrawn the schematic with Eagle and replaced the hand drawn one in the first post.

Here are also some pics of the PCB top and bottom:


 

   

Bigger Schematic File

Green is an input for a capacitive (piezo) pick-up.... does that make any sense?

However IC1C has no DC feedback/bias, which would be bad, so there is something missing (a resistor from pin 1 to pin 2).

Yellow is another pickup input, with the same objections. IC1B is perhaps a buffer and perhaps a mixer, with output at Vio.

PAD? is a high-impedance input to the mixer.

IC1D is a mixer. Output is Org/Str.

The power supply seems to be single 18V positive, but these opamps won't work unless their inputs are biased up half-way.

There's much too much incomplete or missing to make any good guesses.

You might get more response on a bassist's forum where somebody may have actually seen this thing in working order.

It would probably much easier to make a much better preamp from scratch
though I like the hand drawn pcb!
Check out Albert Kreuzers onboard preamp for one.
http://www.albertkreuzer.com/pics/el/pre/schem/onboard_sch.gif

Though you had to drop the passive wiring (at least of the tone knob)

PRR said:

Green is an input for a capacitive (piezo) pick-up.... does that make any sense?

However IC1C has no DC feedback/bias, which would be bad, so there is something missing (a resistor from pin 1 to pin 2).

Yellow is another pickup input, with the same objections. IC1B is perhaps a buffer and perhaps a mixer, with output at Vio.

PAD? is a high-impedance input to the mixer.

IC1D is a mixer. Output is Org/Str.

The power supply seems to be single 18V positive, but these opamps won't work unless their inputs are biased up half-way.

There's much too much incomplete or missing to make any good guesses.

You might get more response on a bassist's forum where somebody may have actually seen this thing in working order.

Click to expand...

Hello PPR,
thank you so much for your input.

"However IC1C has no DC feedback/bias, which would be bad, so there is something missing (a resistor from pin 1 to pin 2)"

I will re-check that maybe I missed something. Thank you

"The power supply seems to be single 18V positive, but these opamps won't work unless their inputs are biased up half-way. "

Can you please explain me what that means? is there something probably missing in the circuit here also?
Sorry if this is a basic question, Im learning as I go sorry for that, and thank for your patience.

I've posted also in a bass forum, but not much luck at the moment, this is an obscure brand so not many people heard about this basses.

The owner of the bass really wants it to be wired as was originally so doing another preamp and replace this one is out of the question. But thanks anyway  L´Andratté.

How about Blue and Blue-Striped, they seem to be connected to a switch maybe that would switch between the 2 different resistor values, does that make sense?

Also the brown wire, were youl make sense to connect it?

Thank you

Hi.  Just thought I'd update this thread with the progress made over at music-electronics-forum.com since PRR is quite a sharp tack, and I'd love to see Paul take a crack at this puzzle again.

I've attached a hand drawn sketch.  I'm kicking myself now for not including the resistor and cap values, but they can be figured out by cross referencing the original poster's stuff.

We determined that the original schematic/trace had a bunch of errors - the pins numbers on my sketch reflect the corrections.

The dual gang pot connections on my sketch are total guesses.  Please feel free to rearrange those.  Same for the switch that connects all the "blue" wires.  That again is just an educated guess.

We now need to incorporate all these "loose" components available:
-dual 50k pot
-DPDT (on-off-on) mini toggle that already has some jumpers on it
-a lone resistor-to-ground
-a lone cap-to-ground

I have guessed that these components connect the yellow/grey, violet/green, and 3 blue (blue, blue striped, blue/black) wires to allow some control over the state variable filter.

Looking for anyone else to contribute ideas as to how this was originally wired.

Maybe there should be connections to the 3rd lugs of the pots that I left open.  Maybe the resistor/cap-to-ground attaches there?

Obviously the resistor and capacitor values are helpful clues... sorry I did not include them, but you can get them from the original poster's schematics.  (I think IC1 sections C and D are swapped on the poster's original schematic.)

I have already posted my suggestions on another forum...  so won't repeat myself.

Yes that appears to be a SVF (thus the apparent lack of local DC feedback, which comes from global DC feedback).

Good luck guessing the traffic control.  I've already posted my best guesses elsewhere.

JR

JohnRoberts said:

I have already posted my suggestions on another forum...  so won't repeat myself.

Yes that appears to be a SVF (thus the apparent lack of local DC feedback, which comes from global DC feedback).

Good luck guessing the traffic control.  I've already posted my best guesses elsewhere.

JR

Click to expand...

Thank you so much John,
I've already seen your posts and Replied with a new schematic.
Thank you all for your help.
Will continue to post at this thread:

http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=7&t=713&p=8219#p8219

Updated Schematic
- there was a resistor missing, it's 2K Resistor and connects IC1B Pin6 to R12 and C5. Fixed
- IC1D and IC1C were wrongly placed in the first schematic, they are swapped now.Fixed
- C8 capacitor is 22nf and not 22uF. Fixed
- new Layout with IC2 as input buffer

I fixed all these mistakes in the schematic, it makes much more sense now, it's much clearer and easy to follow.