Blue Jinn
Rider of the ARPocalypse
I know I started the 2006 thread, and that project is on hold until the capsule mounts come in which is starting to look like they'll come in slightly before my ship does....
So, in my boredom, i tore apart a 2001, stripping out the transistor output stage, swapping the 2:1 transformer for a 11.5:1, replacing the cap between the two 1g reisistors with a poly 470pf cap, and replacing the coupling capacitor (now between the fet and hte transformer) with a poly 1uF/100v (nice big airy capacitor). Also swapped the 32mm capsule for a 34mm K67 clone capsule. Those will fit nicely on the same mount. The reference schematic (for the mod) is attached.
well, so far not so good. mic has output of about half a cheap dynamic, and you really have to kiss it like a cheap dynamic to get an kind of voice pickup. Mmmh I say. Well, the trafo is a bit higher turns than it should be (11.5:1 vs 9.5:1 for a T13 clone, or 10.5:1 for a Cinemag 2480 which is half as much money btw.) also, the stock FET may not really have enough gain, and is liekly not uptimally biased. (Which I honestly don't have the test equipment to do properly)
Next step however, is going to replace the FET with a 2n3819 and just swag the bias on it and perhaps get the Cinemag trafo (The 11.5:1 I have doesn't really fit in the the bell housing anyway....)
View attachment U87 FET Frontend.pdf
So, in my boredom, i tore apart a 2001, stripping out the transistor output stage, swapping the 2:1 transformer for a 11.5:1, replacing the cap between the two 1g reisistors with a poly 470pf cap, and replacing the coupling capacitor (now between the fet and hte transformer) with a poly 1uF/100v (nice big airy capacitor). Also swapped the 32mm capsule for a 34mm K67 clone capsule. Those will fit nicely on the same mount. The reference schematic (for the mod) is attached.
well, so far not so good. mic has output of about half a cheap dynamic, and you really have to kiss it like a cheap dynamic to get an kind of voice pickup. Mmmh I say. Well, the trafo is a bit higher turns than it should be (11.5:1 vs 9.5:1 for a T13 clone, or 10.5:1 for a Cinemag 2480 which is half as much money btw.) also, the stock FET may not really have enough gain, and is liekly not uptimally biased. (Which I honestly don't have the test equipment to do properly)
Next step however, is going to replace the FET with a 2n3819 and just swag the bias on it and perhaps get the Cinemag trafo (The 11.5:1 I have doesn't really fit in the the bell housing anyway....)
View attachment U87 FET Frontend.pdf
