Need advice on replacing JFET for mic - Page 1
Forum section: electronics / repair

author: Cjoooooooo
author_rank: Newbie
timestamp: May 31, 2024, 11:50:57 pm
content: Hi guys! I'm looking for some advice on replacing what I believe to be an FET that was externally fitted to an old-ish USB mic.Quick summary of it's life.Purhased it for gaming a good while back, found it too quiet so I ripped the microphone out and directly wired it to a jack. Switched it out for a headset mic.Fine for a couple of years but then I think i had some grounding issue.Behind the mic was a small pcb about 1.5 by 1 cm with a small 3 pin component on it, which i believe was the FET.While cleaning up the soldering the copper came away from the pcb and broke one of the legs to this component.The mic itself is fine I just need to figure out what the replacement part is.Unfortunately there's no readible numbers on the component.I've included a picture of the mic, A drawing of the component and a link to the actual original microphone.https://www.worthpoint.com/worthopedia/prosound-a99jb-usb-0-hq-podcast-vocal-523124932Any help would be grately appreciated.Chris

author: Greybeard
author_rank: Frequent Contributor
timestamp: June 03, 2024, 08:29:39 am
content: You can try this JFET:2SK1109https://www.firstpr.com.au/rwi/mics/2009-09-b/2SK1109-datasheet.pdfMore Info:https://www.firstpr.com.au/rwi/mics/2009-09-b/

author: floobydust
author_rank: Super Contributor
timestamp: June 03, 2024, 09:25:26 pm
content: Welcome to the forumsThe JFET is typically built inside the mic capsule due to the high impedance involved. So I wonder if the part knocked off is down stream? You can measure resistance across the capsule pins to figure that out. Another electret mic JFET part is 2SK596S in a different package.Some ideas if the capsule is kaput:https://www.cuidevices.com/catalog/audio/microphones/electret-condenser-microphones

author: Cjoooooooo
author_rank: Newbie
timestamp: June 04, 2024, 06:45:35 am
content: So I've done a drawing of how it was setup.Because i had the mic mounted on a headset in replace of a much worse mic I didnt really need the high levels of amplification. Just adjusting the volume slider on the computer was enough given it's close proximity to my voice. My voice sounded rich and full through it.Bare in mind this was a capsule I pulled out of a device that's probably over 10 years old so it won't be as tidy as the modern day ones.I believe the little retangular component was the jfet. No markings on it. I suspect it was a fet with built in bias (resistor) which is why it worked seperate from the pre amp. Could be wrong as I am a noobie.It's tough understanding all of the technical jargonIt doesnt have to be an exact replacement. If someone could explain what i have to do if i just bought a standard jfet or better yet, a better one.I've seen an ebay listing of this 2SK170 BL which apparently is real low noise. Whether it's genuine or not is another thing.I looked at the JFE150 but the daft postage cost makes it all dumb. I'm sure there's a reason for it.I know i could just by a new headset but that's boringPlus I already have some nice headphones that doesn't have a mic.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 04, 2024, 07:00:43 am
content: A suitable replacement depends on the circuit and resistor / current values. There is likely no need to go for super low noise JFET types, as the microphone has it's own noise and the super low noise types also have higher input capacitance, that can be an issue. The normal electrete capsules don't need extra amplification and they have a JFET already inside. I could also be an option to just replece the whole capsule to a different type.

author: Greybeard
author_rank: Frequent Contributor
timestamp: June 04, 2024, 07:49:32 am
content: Why don't you just replace your mic by a new electret mic for 1 buck?https://www.mouser.de/c/?q=electret%20microphoneIf you're interested in electret mic basics:https://en.wikipedia.org/wiki/Electret_microphonehttps://www.hobby-hour.com/electronics/computer_microphone.php