From: steven.rousse~mail.amdahl.com Date: Friday, 8 September 1995 12:50 ET Subject: Crystal mics and mega ohm inputs.
I use a Blues bullet crystal mic through a blackface Fender bassman. The input impedance on the input jacks is 1 mega ohm. After reading how crystal mics sound better with 5 mega ohm impedance I decided to try it out last weekend.
input jack ()------------> to tube | 1meg | ground
I simply replaced the 1 meg resistance on the input jack with a 1/2 watt metal film 5 meg resistor. I only modified the normal channel. Result... much more gain since less of the signal coming from the mic is making its way to ground. I did not notice much difference in tone. I did notice the amp would feedback A LOT more easily and I could not drive amp into the distortion range anymore. Needless to say the 5 meg resistor is out and the 1 meg back in. What I did do to improve tone 10 fold was to replace the 6L6/5881 power tubes with 6V6 tubes. The bassman sounds more like a tweed deluxe which is my favorite harp amp. I had to rebias the amp to keep the tube's anodes in the 440 Volt range with 38 milli amps idle current. Really pushing the 6V6's 360 Volt limit BUT it sounds great, hope they last a few months...
