Modifying the input on a vintage fender

[BassGuy97x]

So....i've been having a bit of a dilemma. on my '79 twin(which is no longer a guitar head, and has not been used as such for years ) ive been having some distortion issues at low volume. from what i have found out, my Ibanez ATK805E, being a higher gain active bass, has been causing it. so my question is, what resistor level is implemented on active channel bass amps to get the -6 or -10 db? being that my budget is relatively small, i cant just buy a pre-amp with an active channel, and i can do this input mod myself. thanks for the help

 

[BassmanPaul]

Old Fender amps have two input sockets connected together by a passive mixer consisting of two 68KΩ resistors and a 1MΩ resistor.

If you plug into input one, your signal "sees" the 1MΩ to ground and the two 68KΩ in parallel to the grid of the first tube. This is the high gain input.

Input two cuts your signal in half with a 68KΩ to ground and a 68KΩ to the grid. This is the input you should use with an active bass.

 

[wcriley]

Or just turn the volume knob down some on the instrument if its output is too hot.

 

[BassmanPaul]

Or just turn the volume knob down some on the instrument if its output is too hot.

I would have thought that this was obvious however it's a good point to mention.

 

[BassGuy97x]

I would have thought that this was obvious however it's a good point to mention.

yea...lol....i've been doing that for a while, but it compromises the tone that i'm looking for....couldn't tell you why... but anyway, thanks a bunch for the help, gonna go try'er out

 

[dhsierra1]

could swap a 12AY7 in there to give you more headroom. Doing that to my blackface Showman shortly.

 

[BassGuy97x]

could swap a 12AY7 in there to give you more headroom. Doing that to my blackface Showman shortly.

ill keep that in mind. after you do the switch, let me know what transpires.