Just picked up a used FR-12 at a decent price. Unfortunately, it was one of the hissy serial numbers. I popped it open and unfortunately it didn't have the updated board in it. I've had a TMP since it was released, but have either used it via the home audio system or a powered PA speaker (with reasonable results)
At stage volume, the hiss from the FR-12 isn't really a problem. However, in the house, at practice volume especially with a backing track playing, the hiss is quite annoying.
I ordered the same op-amps that Fender did their mod with, and I have the SOIC-DIP boards in my stash of parts anyway. Figured it was the cheapest, simplest way to update it.
Very interesting, informative thread. Lots of good tech info. I'm leaning towards the V3 board, just waiting to see how I like it.
I meandered a bit with the board of the FR12 and drew out bits of the circuit. Honestly, I can't figure out what they were trying to do, other than to use up what must be an enormous stock TL084. Hard to fathom how they even managed to squeeze 16 gain stages into something that would work better with 1/2 or even 1/4 of that. Truly puzzling. Also - why a "high cut" like a Vox, where the treble goes down as the knob turns up? Fender traditionally used "presence" for that function which increases high frequency with the normal CW rotation.
On the board, I don't think Fender was trying to make it repairable. That one-sided through-hole circuit board is how they tend to build everything. I think they probably own a plant in Mexico with through-hole single-side production capability and design everything they possibly can to run through that process, even if it gets made in China. Most of their current run of tube amps are built with exactly the same layout practices and board designs. I wouldn't even be surprised if the boards were made in Mexico and shipped to China for stuffing and final assembly into the amp.
That circuit is a head scratcher though. I'm an EE, but mostly been writing software for the last 30+ years. But it is puzzling to build it like that. TMB tone and a high-cut and a volume control ain't all that hard. Not building XLR defensively against phantom power is also - puzzling.
It's all it needs to be.
