Re: HAO Sole Pressure
Posted by induction on Jan 15, 2015; 10:32am
URL: http://guitar-fx-layouts.238.s1.nabble.com/HAO-Sole-Pressure-tp5725p16588.html
A few corrections are needed here.
The switch does not select the output cap. The output cap is the 10u attached to the op-amp output (pin 1). The caps on the switch form a low pass filter with the 100k resistor. So the result is a little different to how you described it: In the center ('bright') position, there is no cap to ground, and therefore no low-pass filter, and the sound will be brighter rather than darker. You are right though, that increasing the size of those caps will make the sound darker, but this is not because it cuts less bass, but rather because it cuts more treble, in other words, moves the corner frequency of the hi-pass filter to lower frequencies.
Rockett is correct that anything you do to increase treble in 'bright' mode, will change the response in the warm and normal modes. But you can experiment.
As Rockett points out, you can decrease the input cap, but this will change the frequencies that get affected by the distortion, so instead of tone shaping, you will be reshaping the distortion, and you may end up with a very different sounding unit. The general rule is this: EQ before (or during) distortion changes the distortion flavor, and EQ after distortion acts like normal frequency shaping. So if you like the sound but just want more treble, I wouldn't mess with the input cap.
The simplest solution would be to reduce the 10u output cap. This will make all three modes brighter. Try 1u and then go up or down from there until the 'bright' mode gives you what you want. Then increase the 1nF and 2n2 caps on the switch until the 'normal' and 'warm' modes are dialled in.
However, in this case, most if not all of the clipping is coming from the leds, which are actually after the output cap, so you may still end up changing the distortion characteristics if you reduce the 10u output cap. So another idea is to leave the circuit stock, but use a DPDT on/off/on for the mode control. Then you could use the second pole to cut some bass in bright mode. This could be done by inserting a smaller cap between the diodes and the treble attenuator caps, or by adding a resistor in parallel with the 100k output resistor (the one between the output cap and the level pot). You'll have to play with the values to see what works for you.
Your best bet would be to build two versions of the circuit on the breadboard, with a switch to select between them. Make sure they sound identical, then start modifying one of them to improve the 'bright' sound. That way you have a reference to compare your mods to.
Jared: The pins are labeled incorrectly in the schematic (pins 2 and 3 should be swapped, and pin 7 should really be pin 8, check the pinout on a datasheet to see what I mean). Trust john's layout and ignore the numbering on the schematic.