You can even try combining such an asymmetric clipping gain stage to the existing symmetric clipping circuit.ĪFAIK the real problems of that amp, desperately and actually needing some modifications, were the tremolo optocoupler and the power amp IC. Zener diodes fitted to earlier gain stage also sound like a bright idea. What might be great feat of such board though is that it could house a JFET switch one could then patch to the channel switching circuit enabling overdrive enables the clipping diodes, disabling disables them, or something in that manner. Basically, routing some flyby wires to a small breadboard from the LED send point and their ground return would allow building pretty much any type of shunting soft limiter circuit in place of the LEDs, even weird stuff like tube diodes a la Fender ROC PRO amps personally I just think the differences gained from the "diode tasting" -type stuff aren't really all that drastic unless there are really big differences in the forward voltages of the different types of diodes fitted there. Series resistor or other series diodes might also be reasonable mods if higher headroom was needed, this would retain the soft clipping scheme but just move the forward voltage of it somewhat higher. Rather than removing the LEDs I'd simply a switch to enable or disable them. It's now a very portable and usefull SS amp, and it sounds pretty good, really! Other change was regarding power IC, power supply and the transformer for a more comfortable overall volume playing with a band. I tried an Eminence 875 on it and it sounded better, more bass content, eventhough you can't expect a 12"speaker performance out of an 8", but it's a bit dangerous as this speaker has a 4 Ohm impedance. It does not turn the Pathfinder a good valve amp, but now it sounds better than a bad one.
I added a pair of Zener diodes (5.1 and 9.6 volts) in anti-series at the negative feedback chain. I get a nice crunch out of it, not unlike the Tech21 early pedals.Īnyway I was tempted to try a soft clipping on the gain OpAmp, the stage after the input buffer.
It's pretty decent if you use IC's with FET inputs like TL072. But I must disagree with you as it is terrible. With the hard clipping section out of the circuit what we get basically is the IC's distortion when the gain is cranked up. I've tried a lot of associations, but it would need some kind of re-EQ the signal to get a "tubish" sound. I just did some mods in my Vox Pathfinder and the first was about trying to fix the clipping LED's section.
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