With OPA2604AP set the trim pot to centre postion (12.5 turns) and leave it there no need to trim at all.mike wrote:So I just finally finished my first channel and it is alive and working! I am getting normal sounding audio output when I plug a mic in and it seems to be behaving as any mic preamp should.
I am having trouble with the "alignment" process though. I initially tried to do it without my IC1/IC2 plugged in. At that stage I was getting 48.1 V at TP1, then with turning the trimmer next to that, I was able to get TP3 to 24.5 V. Turning the trimmer further (no matter how many times) would not allow me to go any further down on TP3 voltage. Next I was able to turn the other trimmer enough to get the DC voltage across the volume pot down to 5 mV.
They will click over and over when they reach the end of the 25 turns.A further question regarding these trimmers: Are they infinite turn? I feel like I can turn them pretty much forever though maybe that's not actually true.
We run a wire from the 0v dc connector to the back panel of our cases and then on the bottom panel we remove the powdercoat under the countersunk screw heads with a countersink so all panels connect.I am also having trouble determining how I should ground the chassis itself. Currently, the chassis conducts well with itself (ie. from a screw on one face to another screw on another face), but there is no conductance between the chassis and the black ground terminal of the DC power jack. I tried to resolve this by grinding off a bit of powder from the bottom panel with my dremel and soldering a ground cable from the black ground terminal of the DC power jack to it, but it does not stick well to the metal of the chassis, and if I remotely bump it this lead will come free. I am debating drilling a hole and putting a bolt/nut through the bottom of the unit that I can crimp a ground wire to. I just find it peculiar though that for an otherwise comprehensive project the grounding solution for the chassis is missing. Or am I missing something?
If you bought a BA4 or BA2 rack kit this is already done. You only need to get 0vdc connector wire to one transformer bolt hole on the back panel.