Re: jet city 20 watt combo
I did find the bass flubby when I first got mine. There are four things you can do to fix it, and I'll list them in order of difficulty.
1. Swap out the PI tube with a 12AU7. This increases the headroom and tightens the bass significantly. It also clarifies the string-to-string definition.
2. Use different speakers. I'm not a big fan of the Jet City combo speaker. I'm running with a Governor and a Wizard, and I think that combination is much, much better than the cheap speaker that comes with the combo. Mine's a head, by the way.
3. Add a choke. This is a relatively simple mod that cleans up the power supply a bit. It tightens up the bass a bit by cleaning up the power supply.
4. Add a depth control. This was by far the most difficult step to take, and it was the most apparent in the tone. There is a lot of powerful bass available in the power section that is damped with the default setup. This reduces the negative feedback in the power section and tightens things up. It's a mod to the amp, but it makes it much more awesome.