Sunday, November 24, 2013

Revoicing a middle seventies Fender Bass Amp

Back in the early seventies Fender produced a number of eminently forgettable amps based on Super Reverb architecture. The Bassman 10 is one of them, and the Bantam Bass is another-which is the subject of our disquisition.

The original CFA 7003 Bantam came from Fender with, of all things, a trapezoidal shaped Yamaha speker with a styrofoam cone.  Think I'm kidding? That was the day that the crack truck collided with the LSD wagon and both overturned outside the Fender factory no doubt.

To say the Bantam in its 35w configuration was not a commercial success may qualify as the understatement of the twentieth century. The speakers lasted a week or so.

However we're not here to second guess what some marketing mavens cooked up out of spare Super Reverb cabinets and chasses. Yes, Virginia that is the plural of chassis.

The one I have came to me with a Jensen P15L speaker installed and a Fender Twin Reverb output transformer, which made it into a passable amp for guitar with more volume. Kinda like the Fender Pro they never built.

The P15L was not a great speaker although being well able to soak up the extra 20w or so of power being generated. Gerald Dishon, my accomplice, produced a JBL for me from only he knows where, and that put the thoughts of crossover networks to rest.

I hauled it out yesterday for some noise and I said "This just has to sound better." I had revised the normal channel of a friend's Bassman 10 to look like standard AB763 a/k/a Super Reverb.

On my own Bantam which is the subject here I went a little farther. After routine maintenance I gutted the normal and bass channels and built them to look like an AB763 Super Reverb on both sides. The easiest way to do this is to just remove all the old stuff, nobody'll miss it and it only takes a few minutes. Then following the AB763 layout you can duplicate all the tonal stuff as you wish.

One thing I've been puzzling over is whether, since I have plenty of room for expansion as the real estate boys say, if I should incorporate a second gain stage or a vibrato circuit stage before the phase inverter gets involved. I'll mull it over tonight.

Film at 11 as they say.

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