5F2A build sounds fizzy

[Groover]

Built a 5F2A into Musicmaster Bass chassis. Stock except for a)larger filter caps (22mfd subbed for 16mfd, 20mfd subbed for 8mfd) b)volume pot 250 K instead of 1meg, and c)I have not put in negative feedback. PT is a Mercury Vibro-Champ PT, OT is stock Fender VC OT.

Everything seems to be working. It cranks great but has a "fizzy" sounding high end that I would like to smooth out. Any ideas?

I am also planning on adding a switch disconnect the tone control, for Champ sound.

[JHow]

Could it be lack of NFB? You could try switching it in or out. Another thought, it could be some blocking distortion on the 6v6? I added 1500 ohm resistor onto pin 5 (grid) of the 6v6 of my otherwise normal 5f2a weber kit and that cleaned up some unwanted noise.

[ThermionicScott]

Could it be lack of NFB? You could try switching it in or out. Another thought, it could be some blocking distortion on the 6v6? I added 1500 ohm resistor onto pin 5 (grid) of the 6v6 of my otherwise normal 5f2a weber kit and that cleaned up some unwanted noise.

I've done some of those tweaks with my 5F2A build... I'm running it without the NFB and apart from sounding a little "richer" at lower volumes, I don't hear any fizziness. I tried a 1.5K grid-stopper and it didn't make an audible difference.

I'm wondering if it's that volume pot -- a 250K will interact differently with the tone caps than a 1 Meg.

- Scott