0dbfs said:I noticed the photo's from above have what appear to be different zoebel values. Any additional info there on the cap value? I don't have a cap decade box but could order parts to make one to do the tests. If you have the info on the zoebel it would be much appreciated.
Steve Hogan email said:There are two networks on the mic transformer. There is 470pF + 12K1 in the position where the Factory put 1000pF and zero Ohms.
That damps the response quite nicely on the low gain ranges. However, the high gain range has some fairly severe ringing with that same network. I added a second damping network across the input to the first stage so that at high gain settings both networks are loading the transformer. The damping network required to kill the ringing in the high gain mode was really severe. It had considerably less bandwidth than the results on the low gain range. I tried lots of combinations to try to get close to the same bandwidth as the low gain range, but was at first unsuccessful. You could have either extended bandwidth with ringing or reduced bandwidth and no ringing. Somehow I stumbled upon the idea of using a 2nd capacitor in parallel with the resistor and low and behold! The bandwith came back without the ringing!! In this case I was able to eat my cake and still have it. The network across the input to the first stage is 2200pF in series with the parallel combination of 1000pF and 3K01. The bandwidth is very similar to that of the low-gain range.