Boss - PQ-3B Bass Parametric Equalizer [schematic]

[Bernardduur]

I already posted it at the workbench; small update!

I have a Boss PQ-3B on my bench right now; want to make it into a guitar parametric EQ instead of the bass version it is now. Could not find any schematics so I tried to trace it.

For most parts the unit is identical to the PQ-4; instead of the low / presence knob the low is made parametric. This is done by adding one more stage (total of 3 stages; low, middle, high). This stages differ from the PQ-4

Stage(s)

High uses 3.3 nF
Middle uses 22 nF
Low uses 120 nF caps as the unmarked cap section

PQ4 schematic

[analogguru]

Sooo..... if I got everything right, than it should lokk like in the schematic below....

enjoy,
analogguru

[Bernardduur]

Yep

I used the next values for my "guitar" version; dunno if they are close to a real guitar freq but it works really well

High = 6.8 nF
Middle = 33 nF
Low = 150 nF

Just copied the PQ4 values.

[Krinkle]

I really want to build a PQ4.

Where can I get concentric pots?

Darrin

[Dirk_Hendrik]