3DJ7 FET transistor

[maxwall]

Looking for a 3DJ7i FET transistor equivalent ( 3 leg gold plated, nickel TO-18 can ). Cannot find a datasheet on this Chinese made transistor online. I'm assuming its a N-Channel type as in most phantom powered mics. Found in M-Audio Solaris mic .

 

[kingkorg]

Not sure about that exact one, but most mics that use that topology, and probably come from the same manufacturer use 2sk30a.

 

[maxwall]

Yes, (2SK30AY) a good candidate. The 3DJ7 appears to have leaky junctions in question. They sure go thru the trouble to make it look pretty on the outside, gold legs and all. Don't know the mfgr on the Chinese FET , it has a circular logo with a star in the center.
Those Toshiba SK30AY are good sounding , I'm considering to use it on this repair , but was considering the J305 low noise FET as well. Some symptoms I'm having are : audio dropping in and out and intermittent high frequency artifacts. Thought it was the diaphragm , but it looks ok. Have not measured the polarization voltage yet.

 

[kingkorg]

Not sure how much you should focus on low noise aspect of it. The high impedance part seems to be a bit of a mess layout wise. Quite a lot cabling around there, pad, low cut. Not sure what the exact layout is, but there might be quite a few parasitic sources of noise and probably lowish polarization voltage.

 

[maxwall]

No schematic for this anywhere , but yeah the high imp area below the capsule is bit unrefined , however has some nice color and does sound ok for what it is when it is not acting up. Just looking to solve the reliability issue for now.

 

[maxwall]

Well the FET is ok, Turned out to be a wire going to the capsule ( bad connection ) and cold solder joint , as well cleaned the capsule . The mic sounds good now no issues. Looks like someone was in the mic soldering before I received the mic & discovered the problem. Lucky I guess.