Help Wirring Bass Guitar on board preamp

Started by ilcaccillo, January 27, 2015, 11:48:48 PM

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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 (picture of the current layout attached).



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 I'm able to build fx pedals and other audio electronic projects although I'm still learning and I don't know electronically how an amplifier, buffer or active tone circuit works. That's why I'm asking for your help.

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

Black (ground connection to VOL Pot case)
Yellow Stripped (ground connection to Tone Pot case)
Orange stripped
Blue Stripped
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

The 3 Way DPDT Switch has already a Jumper soldered between 3 pins, picture attached.


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

Thank you so much


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:



New Corrected schematic with re designed layout


ok, don't know how much help i can be, but for the sake of dragging this into the light, ill do what i can...
1. i'll guess that the passive wiring and pots REPLACED the active circuit, rather than were incorporated/separated from it...
2. the dpdt is what i'd do if i wanted to coil cut one (down) or both (up) pickups. that would mean the pickups should have 4 conductors each rather than 2...
3. green and yellow wires (also INPUT)at the far left of circuit are all inputs... one for each pickup? is a pretty safe bet...
4. red wire probably power... +18v ... to power the +pins of the opamps
5. white wire might be half of a voltage divider, with orange being the cap from v ref, but theres a missing 27k to +18 to make it a voltage divider/ to set the audio at 1/2 the voltage(+9v) 
6. brown wire looks like op amp - /  battery negative same spot as the jack ring... maybee?
7. then theres a crapload of outputs... voilet,blue,bluestriped... grey blueblack .... orange striped.... maybee switches were present to pick btween the blue and bluestriped, or maybee one or the other gets connected to violet via a switch for different volumes...
8. violet may go into green out violet to in green, maybee a tone pot in between? not sure a guess...
9. same above guesses for the grey blueblack orange striped, they may have all been set up to a switch to take out from blue black (in phase) or orange striped (out of phase) of one of the pickups... and possibly grey to a switch that either leaves it open or connects it to blueblack for a slight vol cut/boost?
well... it's a start... i wouldn't be surprised if i'm totally off on some of those guesses, but thats GOOD if i am. in my experience, people love to correct me... so the wronger i am the more replies you'll get!  ;). whew!!! good luck mate!
might be easier to just start from scratch and wire up a new active circuit... rather than banging your head against this thing...  :-\  :)
nothing says forever like a solid block of liquid nails!!!


Hi Quackzed ,
thanks so much for your reply and help.

It seems that IC2 is the input Buffer.
IC1B is most likelly and summing output unity gain inverting stage

IC1A, IC1C, IC1D seem to form a State Variable Filter

I re-drawn the schematic with a new layout, using the previous PAD??? as the input.

I re-traced the board also 2 times, looking for mistakes of my original tracing.
I found an important mistake there was a resistor missing, it's 2K Resistor and connects IC1B Pin6 to R12 and C5.
IC1D and IC1C were wrongly placed in the first schematic, they are swapped now.
And the C8 capacitor is 22nf and not 22uF.

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