I finally finished the tube mic I've been working on for a while. It's a plate load circuit plagiarized from the G7 circuit, with a 5840 tube, 100K plate and 850 ohm cathode resistors (EDIT: B+ 130V, heater 6.5V). Capsule is a Thiercsh red line and the trafo OEP 1:6.45 backwards. Whole thing is built in a t.bone SCT700 (TCM 1050 type) body and PSU is stock, slightly modified. There's nothing beautiful in the looks of it. I even had to use pliers to get the pattern selector to fit in the PSU, so no pictures attached!
I have a switch in the mic to choose between 100uF, 100nF bypass capacitors or unbypassed cathode resistor. 100nF was supposed to act as a kind of treble boost but I find it quite unusable. Maybe a little lower value for a "air boost" or a higher value for "anti-proximity effect" could be more usable. The other two choices are nice to have. I kind of like the sound of the unbypassed cathode resistor more, but the S/N ratio is not suitable for quiet sources without the bypass cap. The gain difference seems to be almost 10 dbs, which I find a little odd..
I made some experiments with the head basket, and am now settled for a two layer grill. It seems to emphasize the mid's a bit compared to one layer grill. I lowered the the plate where the capsule is mounted from the stock height and gained some extra air above 10khz or so. The rubber mount is the shortest one Thiersch offers. I'm still not sure if there actually was some useful sibilance rejection when the capsule was higher behind the ring, maybe gonna take a look at it sometimes. .
The sound is nice. I have only compared it to 414 XLII and Rode NT1a and it kicks their both a** big time, at least with my voice. Rode is brighter but smaller sounding, 414 is muddier and more nasal. Haven't had chance to test it yet with other than my own voice and room mic for drums but I have no doubts that it is going to be a very usable mic.
TO EVERYBODY WHO HELPED ME ALONG THE WAY AND HAD PATIENCE TO ANSWER EVEN THE STUPIDEST QUESTIONS, THANK YOU VERY MUCH!
I have a switch in the mic to choose between 100uF, 100nF bypass capacitors or unbypassed cathode resistor. 100nF was supposed to act as a kind of treble boost but I find it quite unusable. Maybe a little lower value for a "air boost" or a higher value for "anti-proximity effect" could be more usable. The other two choices are nice to have. I kind of like the sound of the unbypassed cathode resistor more, but the S/N ratio is not suitable for quiet sources without the bypass cap. The gain difference seems to be almost 10 dbs, which I find a little odd..
I made some experiments with the head basket, and am now settled for a two layer grill. It seems to emphasize the mid's a bit compared to one layer grill. I lowered the the plate where the capsule is mounted from the stock height and gained some extra air above 10khz or so. The rubber mount is the shortest one Thiersch offers. I'm still not sure if there actually was some useful sibilance rejection when the capsule was higher behind the ring, maybe gonna take a look at it sometimes. .
The sound is nice. I have only compared it to 414 XLII and Rode NT1a and it kicks their both a** big time, at least with my voice. Rode is brighter but smaller sounding, 414 is muddier and more nasal. Haven't had chance to test it yet with other than my own voice and room mic for drums but I have no doubts that it is going to be a very usable mic.
TO EVERYBODY WHO HELPED ME ALONG THE WAY AND HAD PATIENCE TO ANSWER EVEN THE STUPIDEST QUESTIONS, THANK YOU VERY MUCH!
