U87 Jfet question

[Greenie]

Hi. I am trying to finish my D-87 build, lying aound for years. Bought a Maiku capsule and a T13 transformer. I am wondering if the middle leg of the jFet have to be done like in the pic?

 

[Drosselmeier]

Hi, what is the name of the transistor? they can be in the same body but have different connections, you need to look at the datasheet

 

[Greenie]

2N3819 PBFree?

 

[Drosselmeier]

it is better to read on the transistor itself

 

[RuudNL]

If it is a 'real' 2N3819, the gate is in the center.
(By the way: you can reverse drain and source without any problems!)

 

[Greenie]

Are there any other JFets that are better to use?

 

[oscarhuang]

Hi. I am trying to finish my D-87 build, lying aound for years. Bought a Maiku capsule and a T13 transformer. I am wondering if the middle leg of the jFet have to be done like in the pic?

Maiku k87 will be very dark if you put it in U 87 circuit.

 

[RuudNL]

I agree. The Maiku K87 is almost 'flat'. You have to reduce the value of the de-emphasis capacitor, of leave it out completely. (Personally I find it strange that this capsule is advertized as a 'K87'. It suggests that you can use it as a replacement for another K87, but you can't without changes.)

 

[RuudNL]

The 2SK30a will also work in a U87. (Pin compatible.)

 

[Ricardus]

Hi. I am trying to finish my D-87 build, lying aound for years. Bought a Maiku capsule and a T13 transformer. I am wondering if the middle leg of the jFet have to be done like in the pic?

Yes. That is correct. Just make sure you get a good solder joint from the leg of the transistor to the post.

 

[shabtek]

the insulated turret/post is not mandatory if you dont have one, floating in mid-air will work too, be careful not to bend/stress the middle lead

 

[oscarhuang]

I agree. The Maiku K87 is almost 'flat'. You have to reduce the value of the de-emphasis capacitor, of leave it out completely. (Personally I find it strange that this capsule is advertized as a 'K87'. It suggests that you can use it as a replacement for another K87, but you can't without changes.)

I installed Maiku k87 in my diy u87 circuit and so disappointed. I didn’t know Maiku is a flat capsule at that time. Then I bought MP RK87 that is a correct capsule for u87 circuit. I never tried other company K87 style capsule yet. Any better capsule than RK 87 for recommend? Thanks.

 

[Khron]

I installed Maiku k87 in my diy u87 circuit and so disappointed. I didn’t know Maiku is a flat capsule at that time. Then I bought MP RK87 that is a correct capsule for u87 circuit. I never tried other company K87 style capsule yet. Any better capsule than RK 87 for recommend? Thanks.

... Or you could have just disconnected the frequency-correcting feedback, with the flatter capsule...

 

[oscarhuang]

... Or you could have just disconnected the frequency-correcting feedback, with the flatter capsule...

Yes, I did. But still doesn’t sounds good in that circuit. IMO Maiku sound better in the KM84 circuit with AMI T8 transformer.

 

[kingkorg]

If you use darker capsule and disable feedback you defeat the whole point of u87. Also you don't get the same curve in the end. Remember bright capsule + deemphasis network are meant to work as dolby NR, and reduce noise of the mic. U87, especially vintage one with lower pol.voltage, has pretty lousy noise specs. Remove deemphasis you make the mic almost unusable as a professional tool.

It actually makes more sense to use as bright as possible capsule, and use higher value filter cap.

 

[oscarhuang]

If you use darker capsule and disable feedback you defeat the whole point of u87. Also you don't get the same curve in the end. Remember bright capsule + deemphasis network are meant to work as dolby NR, and reduce noise of the mic. U87, especially vintage one with lower pol.voltage, has pretty lousy noise specs. Remove deemphasis you make the mic almost unusable as a professional tool.

It actually makes more sense to use as bright as possible capsule, and use higher value filter cap.

Totally agree. I putted M7 capsule in u87 circuit and removed the 220pf cap. Guess what, I heard the hizz and very muddy bass. It didn’t sound like a good mic should be.

 

[Drosselmeier]

Totally agree. I putted M7 capsule in u87 circuit and removed the 220pf cap. Guess what, I heard the hizz and very muddy bass. It didn’t sound like a good mic should be.

you had to connect the capsule to ground and not remove the capacitor

 

[Greenie]

I need on teflon turret D87 build, anyone? It seems hard to get, been searching all over?

 

[LevinGuitar]

If it is a 'real' 2N3819, the gate is in the center.
(By the way: you can reverse drain and source without any problems!)

it's really the same or just can work with reversed drain and source?

 

[RuudNL]

For the 2N3819 it makes no difference if you reverse drain/source.
(On a lot of FETs you can exchange the drain/source connections, without any problems or performance loss.)

https://www.quora.com/Is-MOSFET-a-b...device-What-is-a-clear-explanation-about-this