Building the long discontinued sought after Ampeg© Scrambler
last update: May 14, 2010
This unit is not subject to modding - at least not in the author´s experience. It is beautifully weird as is.
I used the tonepad layout, what they call the Revolcador. This is a bit crammed for my taste, but at least there is provision made for evaluating diverse transistors on the PCB. Also, most caps are electrolytics, which very often use the same footprint for various working voltages, unlike film caps. So most of the caps that rumble around your drawer will fit.
Before I realized that I had already ordered a set of MPSA14, I made homebrew piggy-back darlingtons out of garden variety silicon transistors which worked fine. In fact, they sounded a little sweeter than the MPSA14, but I did not use them after all in because they were a bit bulky in the crammed layout.
If I were to rebuild the board, I would use the board mictester had done for this very purpose.
One thing I noticed, when I was sweeping the balance knob (which is a mixer between dry and effect), the volume dropped somewhat towards clean - meaning I have too much gain. This is contrary to what somebody else has experienced, who had too little gain. This must be subject to the transistors used.
Fortunately, this is very easy to remedy. One could modify the collector resistor of Q4 in analogy to the method shown by the previously mentioned builder. But dropping the value of this resistor may change things in an unwanted way besides increasing the current draw slightly. I decided to leave the overall value intact but splitting the collector load and tapping the output signal from the split point instead. It turned out, that a half/half split works fine (470 Ohms). The balance control now sweeps smoothly from clean to distorted. I think it is clear what I have done, so there is no need for a schematic.
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I did not make any sound samples because there are plenty of them around and mine does not sound any different . Also, there there is no tweaking.
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