Ruminating on the Trainwreck tone stack

[nee]

Greetings all!

There are a lot of posts about decreasing brightness/increasing bass in the 'Wreck. My own 'Wreck homage is not overly bright, but the biggest bother I had was with the bass pot. All the action seems to come between 0 - 3, and not much happens after that, and it doesn't really seem to boost bass as we know it.

Bass frequencies for the guitar come at around the 75Hz - 150Hz region, so increasing the bass capacitor does not help the situation. All this does is increase the very low stuff from 60Hz down, which is handy only if you're playing bass guitar. My quest was to try and shift that bass frequency up a little, and try and make the travel smoother.

All of this is a long winded way of saying I changed the slope resistor to about 60K, and the treble pot to 250Hz. This moves the mid frequency up a little, to a good scoopy freq of 600Hz or so, and the bass has more action over the all-important 100Hz - 120Hz range.

With the 'Wreck though "everything matters", and the increased oomph from the new tone stack drives the next stage harder, so for compensation I changed the 3rd stage grid resistor from 150K to 100K, which reduces gain slightly and also raises the frequency of the RC filter with the .002 cap.

It may seem there's no point in raising the bass at one point only to cut it later on, but I like having the bass knob operate over a useful range for guitar even if some of it is gently rolled off in the next stage,

YMMV, IMHO etc etc


IanG

[rooster]

Ian - Well, some have mixed things up here, it's true. The weird thing for me always is to read that the Express is 'too bright' and 'needs more bass'. (I realize you kind of said something a little different but you are in this general ballpark.) Have you seen that book by Merlin Blencowe? You should check it out sometime. He is online as the 'Valve Wizard', too, check that out as well maybe.

Anyway, I went throught that book cover to cover and it/he gave me a lot to consider and play with in regard to the two clones that I own.

For example, on my versions, I have always found the bass too much and also not having the greatest definition. This book made me rethink that and caused me to make some adjustments. I think the first thing you need to consider is that the tone stack, per se, is not the real problem. Afterall, it is what it is, and is pretty standard fare. The 'problem' (although many think the circuit perfect in its stock form and not a problem at all) is perhaps more about how it gets to the power tubes and what happens there.

Eh, if you are into amps then you are constantly tweeking things it seems. I think this is true. So if this is you, read Merlin's book. It might give you some ideas that might solve your issues. ...Er, differently than what you have already come up with maybe.

[nee]

Hey Rooster. You're so absolutely right. I have Merlin's book - required reading! I'm playing my 'Wreck homage thru one 12", so I'm not going to get the wall of oomph that Glen K does. Another mod I've made is the one Jackie Treehorn suggests: changing the PI resistors to 39K/1K. This gives it a majorly throatier sound, so much so that - after having a chance to really let the amp rip today - I think I'll be changing the slope resistor back to stock - there's certainly plenty of oomph for one 12" now.

But half the fun is in the tinkering and tweaking! My only thing with the bass control was trying to get the adjustment up into guitar territory rather than bass guitar territory.

IanG