So what things can cause "thuddy" pick attack?

[wizard333]

What I'm describing is a big bassy thump that underlies the notes and occurs on pick attack, sort of like mixing in a kick drum when the pick hits the string. This is on a gain channel. Turning the bass all the way down helps it, but not quite. It isn't the sort of "push too much bass through the gain and get muddy flub" thing either; chords are tight and fat, its just the 'thud' on the pick attack on single notes. The higher the note, the more it comes out, but that is due to the disparity between the pitch of the "thump" and the fundamental of the note. I've used this circuit before and not had the issue, so I'm trying to figure out, why this time.

Things that CAN cause this, but I know it isn't:
1) bad tubes
2) Over filtering

Ideas?

[potatofarmer]

Is the thump always the same frequency, say around 120Hz?

[wizard333]

It's very hard to ID the frequency exactly, but it sounds lower than that. It's not really a pitch per se, at least, not one that can be easily ID'd like 120hz.

I checked for leaking coupling caps btw if that's where you were going, no coupling caps are leaking. DC on the non-hot side of the caps is in the few mv or sub mv range.

[loudthud]

Please tell us a little more about you amp. Transformers, choke(?), filter caps, output tubes, what style music you play, and speakers you are using. What about your guitar, anything special or different?

Things that CAN cause this, but I know it isn't:
1) bad tubes
2) Over filtering

Under filtering might cause it.

[pdf64]

'Under filtering might cause it'
Yes, there may only be marginal stability.
Also you may have used that pre-amp scheme previously without this happening but is the VB+ and B+ arrangement the same.
Pete

[J M Fahey]

Or simply you have too much bass in your signal chain.
There's a reason all those high gain amps usually cut bass to avoid mud.