MK-1 Preamp Anatomy (INTRODUCTION)

The heart of many Cort and several other brands of basses is a Bartolini MK-1 preamp.

I've read tons of comments on this little thing.... basically soo many that I've decided to make a full and NEUTRAL reverse engineering of the whole device.  

This will be time consuming , boring and potentially destructive for my bass..... but the other face of the medal is that....once done I will have FULL CONTROL of my tone and infinite possibilities of modifications & optimizations.

Yes because little thing not buried into a black epoxy block is ideal for being optimised...

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Where to start?  

Pretty simple ...

Let's remove  the cavity cover... for a first overview  of the electronics.

This super mess is the  ..... electronics:
:-)

You can notice the cavity is  shielded with some microns of conductive paint.
(I will review the whole shielding later , not on the top of my list for now ;-)
Lets remove the preamp and perform some initial review.
There is a small adhesive foam to remove to expose the component side of the preamp.

HI-DEF pic of the connector \ rear side side:

HI-DEF pic of the component side:

The signal pocessing is performed "left to right" as we will see in next posts.
The 3 active components are the omnipresent TL062 dual Operational Amps.

What to say?  was TL062 engineered in mid 1970...used in tons of battery powered music devices .... for decades and decades .... till now ! It has a trade off to consider:

• Very low power used
• Relative acceptable-noticeable Noise Level
• Low cost
• Easy replacement

Yes ... easy replacement:
I will definitely replace them at the end of the reverse engineering with something more actual, like a triade of super expensive LT1352 ....


Generally speaking:

• The leftmost Opamp 1 is used as pickups 1st stage amplifier & mixer.

• The center Opamp 2 is  a decoupler and a  Baxandall "Bass & Treble" Equalizer.

• The rightmost (half used) Opamp 3  is a Baxandall Mid Range Equalizer.

• The diode  soldered "on the fly"  in parallel with the power supply is to me useless as in my bass there is a schottky idiode in the battery cavity able to protect the circuit.

• The smd circuitry is using  a medium density scale so with some care is fully possible to apply some modifications , upgrades and of course some repair.

In the next post we'll see an overall description of the whole circuitry reversed engiinered.


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:-)