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Gear / Technical Help => Microphones & Setup => Topic started by: igene on February 09, 2011, 06:07:41 PM

Title: NAK 700 circuit questions (PLEASE HELP)
Post by: igene on February 09, 2011, 06:07:41 PM

I'm repairing the mess someone created in one of my 700's.
(could be a mess right from the original build @ Nak)
I can't tell whether they ran out of components or had really poor building skills.
It's even put together wrong.  They're soldered together correctly though.
The circuit path is the same.

1 is fine and looks clean and correct, the other is WTF.
I need to replace all the components, but Mouser says the transistor is obsolete.
Anyone know what to replace it with ?  (I'll do both if I have to so they match)
also, I'm not sure of the value of the BROWN resistor. It seems to be missing a band.

the abortion circuit >

(http://i188.photobucket.com/albums/z48/igene_01/100_3826.jpg)
 

all shots of the good circuit featuring each component separately >

(http://i188.photobucket.com/albums/z48/igene_01/resistor1.jpg)
(http://i188.photobucket.com/albums/z48/igene_01/resistor2.jpg)
(http://i188.photobucket.com/albums/z48/igene_01/transistor-1.jpg)
(http://i188.photobucket.com/albums/z48/igene_01/cap.jpg)

THANKS !!!

Title: Re: NAK 700 circuit questions (PLEASE HELP)
Post by: Roger Gustavsson on February 10, 2011, 12:07:37 PM

(http://i188.photobucket.com/albums/z48/igene_01/resistor2.jpg)
The brown resistor should be a high-ohmic one, 1 GOhm or even more. They are expensive. Not sure if this one will fit, Digi-Key Part Number, MOX300F-1000ME-ND.

I am no good in reading resistor values from the colour bands. 1.2 kOhm is my reading. At least they seems to have the same value. They could stay, they are just mounted differently. The one flat with the PCB takes up less of the space.

The ceramic capacitor could stay.

The JFET is a Toshiba 2SK118-O (not zero!) is what is in there and it is doing fine but it is hard to find.
http://www.cen-fr.net/find.php?ref=2SK118O
www.n-tronics.com/english/stock/New-rfq-Stock02.xls
www.hwh-electronic.com/stocklist.xls

Roger

Title: Re: NAK 700 circuit questions (PLEASE HELP)
Post by: igene on February 10, 2011, 01:08:11 PM

I was talking about fixing this circuit >
http://i188.photobucket.com/albums/z48/igene_01/100_3826.jpg

The other one is fine.
I want to make the messed up one look like the good one.
They both work, it's just the one is a MESS.

I'll look into the links you gave me.

Thanks.

(I spent a lot of time on a bench building circuits, and can't stand looking at that disaster when I know I can fix it)

Title: Re: NAK 700 circuit questions (PLEASE HELP)
Post by: Roger Gustavsson on February 10, 2011, 01:29:12 PM

Just remember these highimpedance circuitries are very sensitive! A fingerprint in the wrong spot could upset the whole thing.


Roger

Title: Re: NAK 700 circuit questions (PLEASE HELP)
Post by: igene on February 10, 2011, 02:06:07 PM

are you saying I shouldn't mess w/ it ?

Title: Re: NAK 700 circuit questions (PLEASE HELP)
Post by: Chuck on February 10, 2011, 02:19:56 PM

Just be careful and clean. You can swab the circuit board with some de-natured alcohol to remove flux and grease after you are done working on it.

Title: Re: NAK 700 circuit questions (PLEASE HELP)
Post by: igene on February 10, 2011, 02:27:07 PM

I didn't think it was THAT sensitive.

I'm all apart and ready to start... >

(http://i188.photobucket.com/albums/z48/igene_01/nak700sapart.jpg)

I always clean up after. I leave the jobs neat and clean.
I'm concerned now with what you mean by 'very sensitive'.