Flubby Bass - troubleshooting the cause

[Vertigo]

I have a new preamp (a Demeter) and the bass response on the dirty channels is incredibly loose. I've tried it through a dedicated power amp, and through the power sections of several other amps with the same results. I've tried it with the bass and mids rolled all the way down and with the gain down to about 30%...still flubby.

I'd like to learn what the cause is and fix it if possible. I wish I could knock up a schematic real quick, but they way it's built makes it pretty tough to access the underside of the board and there are enough standup resistors that I can't trace them because all the soldering is done under the board as well.

So where should I start? how can you tell if it's caused by the tone stack, by filtering or something else?

[pdf64]

Generally, overdrive preamps have shelf and high pass filters associated with the early stages. So work you way from the input to the 3rd stage, and if there’s nothing to roll off the sub sonics and low bass, it may be worth tinkering.
Or just use a pedal

[Stevem]

Not surprised, as the first thing that gets overwhelming as you add gain stages is the low end!

Go find yourself on line the schematic for a a Pig Nose GV40.
The designer addresses this issue in the make up of the preamp circuit.
I have this amp and it does a nice job of keeping the low end tight within the preamp section.

If your inclined more towards blues tone and response, there’s a simple 1 resistor mod and a change of V2 to a 12AT7 that works very nice also.