AFT Preamp (EQD BOWS)

MichaelW

Well-known member
Slowly whittling down all the "boost" boards I have on my shelf.

I've been sitting on this one a while because I can't remember why I ordered it:)
It was probably one of those mentions in a thread and back when I was loading up on easy builds.

I wasn't quite sure what to expect as I have not seen any video's of this but given my limited bench time this weekend I figured it would be a fun project
to do in a couple of short sessions.

Well, I guess what I get for "thinking" it was easy peasy and not paying enough attention, been a while since I boogered up an enclosure drill like this.
I "eyeballed" where I wanted the one knob to land and found that I did not allow myself enough room for the footswitch. So it took a little bit of jiggering with the holes to make it all work but it "hid" pretty well behind the washers.

Oh and my center punch slid off punching the top jacks and I have a nice neat center punched hole in the web of my thumb......fun.....:)

I also thought I would be clever and instead of putting a fixed resistor for the Ge emitter I put in a 1k trimmer. So here's the weird thing, that trimmer makes zero difference in the sound. The output of this pedal (the volume pot) actually adjusts the bias of the transistor voltage of collector, so I guess the emitter bias doesn't make a difference? I dunno, maybe @BuddytheReow can 'splain me why this is. HOWEVER, it sounds pretty darn good as is. I have the trimmer turned up to 1k.

I used an MP35 with an Hfe of 41. Good thing it sounds so good since it was the only NPN I had in my box:)

I thought that this would be more of a "boost" with a bit of Ge flavor as opposed to a full on Rangemaster style drive that it turned out to be. Sounds pretty decent on it's own but it really shines pushing another overdrive pedal or a dirty amp. I would not say it's quite as "honky" as true treble booster but it definitely nods in that direction.

In the "fat" mode it can give an overdrive pedal a bit of fuzz flavor or make it really sing. In the "treble mode" it tends towards harshness so pairing it with the right amp/guitar/drive/eq is important. I like the FAT mode a lot more than the Treble mode. Really sweet vocal quality to it. Glad to add another flavor to the arsenal.

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You're putting me on the spot now, huh? Crap. Based on my limited self-learning experience I CAN say that the bypass cap will control the gain (C3 in the schematic). Chuck wrote a pretty good article in the boneyard about biasing transistors and gain. Why your trimmer is doing squat I have no idea....
 
I built one of those for much the same reasons, and I prefer it by far to the earlier Rangemaster I built.
 
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