I'm stuck. I hope somebody of the gurus here could chime in and give some kind of explanation.
What happened was this. I decided to measure my clone for frequency response, thd, imd etc. The thing measured really good but...
When in bypass, if I turn the threshold knob all the way clockwise, thd is around 0,004% which is pretty cool. Now, when I turn it fully counter-clockwise, thd grows up to 0,37% (92 times!). I'm using Spectralab for measuring, the fft graph shows only odd harmonics in cw position, and odd (but greater amplitude) and even harmonics in ccw position.
I'm usung 2181LAs all the way through. And I've done all the mods and calibration suggested by martie-08 (I can't find the link right now).
Oh, and the unit is trimmed for minimum thd (which is actually 2nd harmonic only).
Actually that's not all. I've measured the second gssl which is identical to the first one but doesn't have the mods and hasn't been calibrated yet. In cw position it measures slightly worse, 0.007% thd. And the threshold behaves the same except it has max thd in the middle position (I think that's because I don't have 47k resistor soldered to the threshold pot - look at marties site for more info). And it acts kinda like thd "blender": in cw it has only odd harmonics, in ccw - mostly even, and in the middle it has both.
I have no idea if this behavior is normal or if I did something wrong (though I'm pretty sure I haven't screwed anything). Looking at schematic I can't tell if this is the right thing or wrong.
Maybe somebody can measure their clones as well to see how it reacts.
P. S. I'm using RME FireFace 800 as a reference audio interface.
What happened was this. I decided to measure my clone for frequency response, thd, imd etc. The thing measured really good but...
When in bypass, if I turn the threshold knob all the way clockwise, thd is around 0,004% which is pretty cool. Now, when I turn it fully counter-clockwise, thd grows up to 0,37% (92 times!). I'm using Spectralab for measuring, the fft graph shows only odd harmonics in cw position, and odd (but greater amplitude) and even harmonics in ccw position.
I'm usung 2181LAs all the way through. And I've done all the mods and calibration suggested by martie-08 (I can't find the link right now).
Oh, and the unit is trimmed for minimum thd (which is actually 2nd harmonic only).
Actually that's not all. I've measured the second gssl which is identical to the first one but doesn't have the mods and hasn't been calibrated yet. In cw position it measures slightly worse, 0.007% thd. And the threshold behaves the same except it has max thd in the middle position (I think that's because I don't have 47k resistor soldered to the threshold pot - look at marties site for more info). And it acts kinda like thd "blender": in cw it has only odd harmonics, in ccw - mostly even, and in the middle it has both.
I have no idea if this behavior is normal or if I did something wrong (though I'm pretty sure I haven't screwed anything). Looking at schematic I can't tell if this is the right thing or wrong.
Maybe somebody can measure their clones as well to see how it reacts.
P. S. I'm using RME FireFace 800 as a reference audio interface.
