Weird behaviour on ROG English Channel

[Mark Hammer]

Once again, working my way through the "bin-o'-boards" and wired up a ROG English Channel today.  Nice little Vox emulation.  A pleasing bite to it.  I'm using Pablo de Luca's layout.  The first three J201s are nicely biased since I had some 10-turn trimmers available.  The last two FETs are a bit on the hot side of V+/2, since I only had cheaper trimmers to tweak, but they're not terribly far out of whack.  Everything on mine works fine with the exception of the Bass control, which provides a loss of lower bass and bump of mids when turned up full.  Weird.

The Duncan tonestack calculator provides the very same Vox tonestack and components-values as one of their choices, and diming the Bass control most definitely does NOT get that EQ curve.  Ifa big dip in mids when the Bass is cranked. anything, I ought to get

I've checked my wiring and will check my soldering, but in the meantime, does anybody else get anything like that?

[Rob Strand]

Do you have "bass lug 3" connected to ground.  I don't think it's explicitly marked on the layout.

[Mark Hammer]

Thanks for looking.
And yes, it is exactly as you describe.  At first I thought that I might have had some leads flipped around, but the bass control is wired correctly.

[Rob Strand]

At first I thought that I might have had some leads flipped around, but the bass control is wired correctly.

If the bass control is OK then maybe there's short or a line isn't cut on the PCB.

To get bass cut the point on the circuit (not the bass control) marked bass lug 1 would have to get connected to ground when the bass pot is on full.   That might happen if bass lug 1 and bass lug 2 are shorted.
Given those points are right next to each other on the PCB, that idea has a lot going for it.

[Mark Hammer]

I'm beginning to think that I simply flipped the two outside lugs.  What's deceptive is that the Treble control ends up boosting the bass when turned down, and doesn't just attenuate the treble.  As well, the Bass control reduces the mids and treble, and doesn't just increase bass.  As such, I guess it just works in ways I'm not used to.  Not much, or indeed any, experience with AC30s.

But I appreciate your efforts.  Thanks.

[Rob Strand]

See how you go.

As well, the Bass control reduces the mids and treble, and doesn't just increase bass

Yes.  It looks a bit weird but in practice when you combine the mid cut and bass boost it is
perceived as having more bass.  A bit like those scoop/contour controls on bass amps.