Difference between J309 and 2SK170?
« on: June 23, 2020, 02:06:50 AM »
Could someone please explain to me the difference between these 2 Jfets?

I am currently working on a u87 clone build and I am unsure which one I should use. I understand that the 2sk170 is considered a medium gain fet, but what about the J309? Would the J309 be more similar to a 2n3819 (high gain fet) or the 2sk170 (medium gain fet)?

I'm not getting enough gain out of the 2n3819 so I want to swap it with a different fet and I have both a J309 and 2sk170. I have to max out my mic gain before I can even get a decent mic signal. 

Also, would anyone recommend swapping out the 1:8:1 trans for a T13? Dave from Advanced Audio recommended I stick with the stock 1:8:1 but I see a lot of people building u87 clones and using the T13.


Khron

Re: Difference between J309 and 2SK170?
« Reply #1 on: June 23, 2020, 04:36:43 AM »
Are you 100% sure the JFET is indeed the (actual) problem? Are your DC voltages ok? And what about the JFET  bias?
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RuudNL

Re: Difference between J309 and 2SK170?
« Reply #2 on: June 23, 2020, 08:49:42 AM »
There should be no reason that the 2N3819 is producing a low signal level.
Even the non-AI versions of the U87 produce ample level.
There is a solution for every problem!

http://www.vansteenisaudio.nl

Gus

Re: Difference between J309 and 2SK170?
« Reply #3 on: June 23, 2020, 09:09:06 AM »
Did you buy the 2N3819 from a distributor or off ebay etc.?

Test it out of circuit maybe you bought a counterfeit one.
The JFET specs are easily found on the web with a search

Check the Vgs and IDSS a web search should find simple test circuits, check if the measurements fit the graphs, this will remove the JFET being the problem

read Khron's post

You did not post voltages or pictures so any answers you get are guesses
So many things can be wrong
dirty capsule
Flux on the board around the gate etc.
wired wrong
transformer wired wrong or built wrong
wrong value parts used
etc.




Ricardus

Re: Difference between J309 and 2SK170?
« Reply #4 on: June 23, 2020, 11:41:42 AM »
I can vouch for the fact that every 2N3819 on eBay is a phony. But last time I checked, one of the big manufacturers was making them again and Mouser was stocking them.
Audio mastering for hire..

Re: Difference between J309 and 2SK170?
« Reply #5 on: June 23, 2020, 12:28:50 PM »
I got the jfet feom mouser. I need to test voltages obviously. Sorry guys this is my first build and I'm not experienced in this at all. I just bought a kit and watched a 4 part video on youtube not realizing theres much more to this than soldering alone. Maybe you all can assist me here and tell me where to put the probes from the multimeter and what those voltage readings mean? It is an Aurycle a460 circuit (not apex), i believe it shares the same design as the original 414. I'll post a pic once I get to my computer. Still learning to use this site as well. ....i have another recent post that contains the schematic here: https://groupdiy.com/index.php?topic=75429.0

Thanks everyone. Sorry for all of the inexperienced questions...i suppose if I never ask I'll never know though.

Khron

Re: Difference between J309 and 2SK170?
« Reply #6 on: June 23, 2020, 12:32:20 PM »
More like, the U87. Or rather, AKG Perception 200/220, iSK BM600 etc.

It is an Aurycle a460 circuit (not apex), i believe it shares the same design as the original 414. I'll post a pic once I get to my computer.

Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Re: Difference between J309 and 2SK170?
« Reply #7 on: June 23, 2020, 01:09:55 PM »
More like, the U87. Or rather, AKG Perception 200/220, iSK BM600 etc.

Mxl v67 and mxl 2001 are almost identical. I was told by Dave from Advanced Microphones this circuit matches the original c414 from the early 70s

Re: Difference between J309 and 2SK170?
« Reply #8 on: June 23, 2020, 01:13:39 PM »
Here's a pic of the schematics and parts I used.

Re: Difference between J309 and 2SK170?
« Reply #9 on: June 23, 2020, 01:30:43 PM »
Here's a pic of the schematics and parts I used.

EDIT!::: R10 uses a 6.8k 1% resistor. I was told to use this value instead of 7.5k .... "With 6.8K feeding the output transistor there will be another db or two of output level before clipping.
"


Khron

Re: Difference between J309 and 2SK170?
« Reply #10 on: June 23, 2020, 03:03:33 PM »
Close, but not quite - the old C414 uses the JFET as a follower (no drain resistor, unity-gain), and has an NPN driving the transformer, but has no "tone shaping".



Mxl v67 and mxl 2001 are almost identical. I was told by Dave from Advanced Microphones this circuit matches the original c414 from the early 70s
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans


 

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