5f6a Bassman?

[chuckb]

Hey guys, I want to add more noticable treble to the normal channel of my 5f6a bassman build.Can anyone here point me in the right direction. And also There isn't a whole lot of range on the presence control either. Any help here would also be apreciated as well?

Chuck.

[Gibsonman63]

Can you really add treble? Unless I have this backwards, you should be able to cut some bass by decreasing the coupling capacitor size or increasing the cathode bypass capacitor size.

[chuckb]

Yes your right,that's exactly what i want to do,reduce the base. I'll give your suggestions a try and see what results I get.

thanks,
Chuck.

[jlatrace]

Go to YouTube and compare your tone stack to the originals shown there. THe schematics floating around the web are different from these originals in one respect, the tone stack. Fender apparently changed the tone stack very shortly after issuing the 5F6A schemtic to match its 100K slope (verse 56K) and .1UF bass cap (verses .02uf). Making this change makes a BIG difference in the amp (clean & sparkles with treble), verse woofy and dark. Ofcourse if you like dark and gritty try a JTM45, solves the woofy and remains mid-range/dark.

[Enzo]

All things are relative, but yes you can add treble - look at any bright switch.

[Hella1hella]

If you did not really want to modify the circuit, (it wouldent lower the bass) but you could just get a treble boost pedal, there are a couple pretty good ones out these days.

[Chuck H]

Can you really add treble? Unless I have this backwards, you should be able to cut some bass by decreasing the coupling capacitor size or increasing the cathode bypass capacitor size.

You would decrease the coupling cap and/or decrease the bypass cap.

In the case of the 5f6a the bypass cap is 250uf. That's really large, bypassing frequencies well below the useful range of the amp. You would have to reduce that size to around 3.3uf before you'll hear any difference so try values like 3.3uf, 2.2uf and 1uf. Note that there will be some interaction between the two input stages with the smaller bypass cap unless you seperate the cathodes. If you are cranking the amp and don't mind some added gain try a 2.2uf on the first AND second preamp stages (second stage currently not bypassed) this will reduce bass and actually increase mids for a thick tone that's not boomy or farty. If you want less mids change the second stage bypass cap to 1uf.

Chuck

[Hella1hella]

I would listen to Chuck H he knows his stuff...

[tubeswell]

There isn't a whole lot of range on the presence control either. Any help here would also be apreciated as well?

Hiya chuck

The strength of the presence control is affected by the PR:Sec impedance ratio of the OT, and the voltage divider in the NFB loop. Therefore if your presence control hasn't got much range, it may be because you are using a 'non-standard' OT, in which case you could try increasing or decreasing the NFB resistor accordingly. (try doubling or halving as the case may be)

[Chuck H]

Tubeswell is on the right track. I must have read past the presence issue. FWIW I would diagnose the presence range problem before changing resistors in attempt to get more range on the control.

Chuck, is there anything different about your amp, ie: impedance, selectable impedance, OT primary impedance, any component values within the NFB loop or any kind of post PI master volume???

Chuck