OK so I just had another play with the tone controls of my LB30 and noticed some strange behavior.
- Middle knob attenuates highs.
Putting mids on full sounds like I've turned the Tone knob of my bass all the way to 0.
Or, if I first turn Highs up to 12 o'clock and then turn the Middle up, the treble content will begin to reduce.
- The Bright switch appears to engage when in the DOWN position
However, the manual says it's engaged when in the UP position
I believe it's a MK1; made in PRC and Middle control is first. But it behaves nothing like my Fender Bassman, nor anyone else's LB30 experiences! I bought it secondhand so maybe it had some "modifications" in a previous life...?
If the Mid control comes first, I think it's probably a Mk1. But it's possible there are more variations of this amp.
It's possible the tone stack is damaged, but I suspect it's fine. I agree it does not sound or respond exactly like a Fender tone stack. This is because different values were chose for the components and probably because of the added Mid-Shift and Bass-Shift circuits.
FYI if you want an amp that sounds and responds very similar to a blackface Fender, try the Orange AD200B with the Master maxed out.
FYI, The bright switch on some of my Ashdowns works in reverse as well. Also, the Hi Low inputs are reversed on my LB30 Mk2. I have just come to the conclusion Ashdowns are quirky and inconsistent...and yes it used to bug the crap out of me, like ants on my brain
If you play around with the Fender tone stack calculator I set up, this is the curve with the Bass and Treble fully CCW and the Mid at 5
As you see the high end is emphasized and does not roll off.
If you adjust the mid control, it does not modify shape of the curve, it just changes the level of gain. So the same shape simply moves up or down on the graph.
If you turn up the Bass and Treble you start to get a mid scoop. This is Bass 5, Mid 5, and Treble 2
As a mentioned this model is not a perfect copy of the LB30 tone stack because it's missing various components. But hopefully it gives you a decent approximation for what is going on when you twist the knobs. Use your ears and learn how the controls interact. Also learn the range in which the controls are actually functional.
Another aspect of this tone stack that I find a bit confusing is the Mid-Shift switch. IMHO the Mid-Shift actually modifies the curve of the Bass control rather than the curve of the Mid control. If you turn the Bass control fully CCW the Mid-Shift has no impact on the sound. In one position the Bass control reaches further into the mids, so the sound is less mid-scooped. In the other position the upper cutoff of the Bass control is moved to a lower frequency.
Essentially, in one position the Bass control creates a curve similar to the purple line and in the other position you get something like the black line.
This is about the closest I can get the calculator to flat
. As far as "flat" goes, the Fender style tone circuit doesn't do truly flat no matter where you set the controls - probably the main reason that Ampeg dominated the bass amp market over the weirdarse EQ on the Bassman. I have no idea why Ashdown thought it was a good idea to copy a failed design - maybe they expected most of these to end up as guitar amps like the Bassmans? But as you've see you can get a great tone out of them if you get out of the "flat at noon" mindset 
.
