Is there anywhere you can think of that a short could exist and result in this issue?
a short between opamps output and non-inverting input (unity gain follower) would be missing the LPF part and drop in level would be higher. Same with shunt arm open circuit for the HPF part from overheating caps (you'd have to fry both caps by too long soldering. Only one dead cap would shift frequency response one octave up, not two), so this would be a more unlikely reason.
Also, could it possibly be an issue around the sub band ?
easy enough for you to double check the 10Hz band with the pcb right before your eyes...
maybe a slack workaround but would changing the value of the 5k62 resistor help get me to 0db ?
decreasing R43 will get you closer, but the peak in the center of the dip will be boosted as well.
Thanks Harpo, I'll need to look at this closer, I've been working on the right channel far too long so I decided to leave it for a while and start fixing up the left channel based upon your spreadsheet (wish I had have seen it first time round...). I wanted to adjust the resistor values on each band to try and get 0db center ident for each freq...
Based upon your spreadsheet, I ended up with the following values:
SUB = R pot total: 445,000, R pot center: 56,300, R series: 10,470
40Hz = R pot total: 472,000, R pot center: 54,500, R series 12,270
160Hz = R pot total: 483,000, R pot center: 56,600, R series: 10,170
640Hz = R pot total: 451,000, R pot center: 54,100, R series: 12,670
2.56 Khz = R pot total: 481,000, R pot center: 60,700, R series: 6,070
R fb = 66,770
Since the R series values are so 'irregular' I had to put a few resistors in series to get to the desired values. I replaced R30 & R48 with a 68k resistor (closest to 66770ohms I had) - is there any impact not using an exact value for R30 & R48? The only audiable effect I can hear is that the output is slightly hotter than before
Attached is my frequency response after these resistor value changes, its certainly better but far from flat... I am starting to think that trying to get the center ident to track perfectly at 0db is not a worthwhile exercise. I wanted to use this EQ in a mastering chain but I don't think i'm going to get its response flat enough. The low end roll off seems really unusual too.
How does the plot for the left channel look? Am I being pedantic or have I missed something / misinterpreted your instructions?
Back to working on Right channel later today.... sorry for all the long winded questions