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August 08, 2022, 06:52:18 PM

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Vox Pathfinder 10 as a modding platform

Started by dimkasta, May 09, 2021, 05:52:05 PM

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dimkasta

Slow day at work today, so I had some time to experiment.

There are two interesting parts in the first gain stage.

The first is the capacitor C5 and how it interacts with the gain pot. At first glance it looks like a coupling cap. But it's in the feedback loop, and interacts with the pot. As the gain increases, the upper part of the pot divider decreases, and the cut off frequency of the high pass filter is increased (less bass passes the filter). But because the filter is in the negative feedback loop, this means that low frequencies are increased at the output. This works exactly like a resonance control. But the problem is that bass increases with gain. Which is quite counter intuitive, especially at higher gains, unless you like fuzzy distortion. Removing C5 removes that weird interaction and high gain sounds tighter.

The second area is C4, R4, R5 and the switch. The switch acts exactly like turning up a presence control at high gain. R4 sets a minimum resistance so that things do not go too far. Ideally, we would replace R5 with a 100K or 50K pot wired as a variable resistor, and then remove this pole of the switch so that we have full control both at high and low gain. This would give us a very versatile presence-like control.