This is my plan of attack:

**1. Desolder paralled 2uf/0.2uf cap combos from each filter section**

Why ?

Just pull IC2 and IC3 and lift one side of the frequency/gain setting resistors that would be lifted anyway to adjust to the required value, IE R21 where it connects to C11||C55 and either side of R23 for the sub band as an example.

**5. Adjust 5k62 series resistor(s) - (R44, R42, R40, R38, R36) based on 470k rev log pot center values (use Harpo's spreadsheet)**

> Use 20k multiturn trimmers, using DMM preset each value to calculated values using Harpo's spreadsheet

> Fit trimmers in R44, R42, R40, R38, R36 positions

substituting the 5K62 series resistors (ment for 500k rev.log pots with 10% value at 50% rotation) with -depending on value needed- 10K or 20K trimmers, trimmers pretrimmed to the calculated value and fitted in R45, R43, R41, R39, R37 positions would give you some spare 5k62 resistors and a cleaner layout. YMMV.

Hey Harpo,

I've spent the last few days reworking my left channel as per all the discussed recommendations, I had to use a lot of multiturn trimmers due to the 'non standard' resistor values required.

I have calculated resistor values against real-world values for 2uf & 0.2uf paralleled caps. 5k6 series resistor values were also calculated and set with trimmers based upon your spreadsheet.

All trimmers were pretrimmed and checked with a DMM before fitting to the circuit.

These are my calculations:

**Calculated resistor values adjusted for paralled caps (2uf/0.2uf):**10 - C55+C11 = 2.1 - R21 - Calculated Resistor Value = 7.58

10 - C12+C19 = 0.201 - R23 - Calculated Resistor Value = 79.18

40 - C54+C9 = 1.991 - R18 - Calculated Resistor Value = 2.00

40 - C18+C10 = 0.201 - R20 - Calculated Resistor Value = 19.80

160 - C53+C7 = 1.975 - R15 - Calculated Resistor Value = 503.66R

160 - C17+C8 = 0.203 - R17 - Calculated Resistor Value = 4.90

640 - C52+C5 = 1.979 - R12 - Calculated Resistor Value = 125.66R

640 - C16+C16 = 0.201 - R14 - Calculated Resistor Value = 1.24

1280 - C51+C3 = 1.973 - R9 - Calculated Resistor Value = 63.02R

** 470k rev Log pot, center indent adjusted values:**Sub - R44 - 445,000 - 56,800 - R45 = 10,300

40 Hz - R42 - 472,000 - 54,600 - R43 = 12,500

160 Hz - R40 - 483,000 - 55,600 - R41 = 11,500

640 Hz - R38 - 451,000 - 54,400 - R39 = 12,700

2.56 kHz - R36 - 481,000 - 61,000 - R37 = 6,100

R fb = 67,100

Attached is the new frequency plot. Still not flat, but the curve looks 'healthy'... Do you think adjusting the series resistors will get me closer, or more component tweaking? I've been meticulous about making sure every trimmer was set to the correct value.

The only thing I didn't touch in this whole process was the air band, is any tweaking required here? As you can see this is a bit of a boost up high

Any thoughts about where to go from here? This has been quite a learning process. The circuit board is starting to look a bit like a charred mess from soldering and desoldering so many times! I'm really determined to get this right....