I'm building the 2 microamp board at tonepad, and i want to turn microamp 1 into a distortion by adding clipping diodes, then use #2 as a switchable boost on the output. i have a question about diode placement, though.
So, i just want to make sure that i am placing them correctly. if i read the schem right, then i would need to place opposing diodes to ground from the positive side of the 15uF electro on the output. is this correct? i'm operating on the assumption that the diodes need to be before the cap so that the cap can block dc to the output. someone with more knowledge, is this correct?
If you are stringing back to back diodes directly off the op amp output then they must connect to vb (half rail voltage). If you connect them after the 15uf capacitor, then they can go to ground. Either method will work okay for you.
cheers
bajaman
If you're placing clipping diodes at the output of an opamp, you typically need some kind of impedance between the output of the opamp and the diodes to keep the current out of the opamp from banging the opamp into current limiting all the time. This is why all of the opamp-plus-diodes-to-ground pedals you see have something like a 10K between the opamp and the diodes.
Baja is right about the voltages. If you have them after the opamp, you either need to return them to Vref if they are DC coupled, or separated by a capacitor to block the DC level if they go to ground. It's generally simpler to use a big electro cap for blocking and then take them to ground. Otherwise your Vref needs to be able to handle the extra diode current without any movement. The movement would be routed back to your noninverting input as an unexpected form of feedback, possibly giving you oscillation or other unwanted and unexpected effects.
Okay, I'm a little confused. I was operating under the assumption (apparently a faulty one) that the cap generally comes after the diodes, so you guys are saying i either need to place some sort of resistance between the opamp and the diodes, or move the diodes to after the capacitor, correct? I'm doing the diodes to ground, so i just need to move them to the other side of the 15uF from where i originally was going to, correct?
hmm, i had inferred from his post that the series resistance wasn't necessary if the diodes were to ground and came after the cap. is that not right? not questioning, just trying to learn
alright then, when i get home i will add a 10k after the diodes, which i will add after the cap. i'll reoprt my results, but it should be almost exactly like a dist+ into a microamp, correct?
