deveng
Well-known member
I've just about completed my mic pres but have one issue to resolve and hope someone has a "simple" solution for my problem. The mic pre is Jensen JE-115K input, 2*5*2*0 opamp and A*P*I output transformer. The input to the opamp can be switched between mic and line with a Shadow type switch. This switch injects the line input through a blocking cap to a 100k termination resistor at the non-inverting input to ground. Now the problem. When depressing this switch, momemtarily, there is lots of crackling until the switch is fully depressed and everthing settles down. I'm sure it's caused by the changing offset at the input of the opamp. The JE-115K uses the typical termination network (150k termination resistor only). Any ideas on how to reduce this problem without re-design?
By the way, this unit sounds very good and works well (less the mic/line switching issue). The bottom end is noticeably rich. I will build 7 more units, some with Jensen output transformers and hope to have sound clips for comparisons. Once I've solved this problem I can finish the other 7 I'm building so, I am anxious to get this fixed.
Any ideas?
Thanks,
Jeff
By the way, this unit sounds very good and works well (less the mic/line switching issue). The bottom end is noticeably rich. I will build 7 more units, some with Jensen output transformers and hope to have sound clips for comparisons. Once I've solved this problem I can finish the other 7 I'm building so, I am anxious to get this fixed.
Any ideas?
Thanks,
Jeff