A friend of mine called and asked me to optimize (mod) his Fender Concert Amp, which he used for his rhodes and wurlitzer piano for recording. He stated, that the Sound lacks some mids in the upper mid register. To be honest, I really had to hear it first until I knew what to do.

Some Information about the amp:
The Concert is an amp of the 80s, while Paul Rivera was working at the amp department of Fender’s. He produced amps in Point2Point manner, so modifiying is an easy task. It has one 12″ Speaker which sounds good. It’s basically a fenderesque preamp with some special circuit tricks and a poweramp design roughly derived from the 5F6-A Tweedbassman cicuit.

My first ideas were to bring the poweramp back to the original specs by inceasing the poweramp entry cap from 0.010uF to 0.022uF and then increasing the caps to the powertubes from 0.010uF up to 0.1uF.
The preamp is based on the idea of a first gain stage feeding two Fender TMB Tonestacks at the same time. My Client liked the clean channel, so we improved that particular channel by increasing the mids by increasing the High-Cap from 220pF.

Because my Client is recording Artist, he recorded each step while modding the amp to where it is now. Here’s the results, what we did at last:

1. Increased the TrebleCap in the EQ from 220pF to about 550pF to increase mid response
2. Increased the PI-Entrance Cap from 0.010 to 0.022uF to open up the overall Sound
3. Increased the coupling caps to the power tubes from 0.010uF to 0.033uF to fill up the Sound with more bass

My friend was impressed about the result, which to me was to bring the amp more in the original direction of one of the mothertones, that of the Tweed Bassman. Our ears know that sound.