I need a simple non tube large membrane mic schemo

Can someone point me in the direction of a simple cardoid large membrane circuit.
NO tube, no bassrollof, no pad.
Less components is easier for me , maybe the chinese way?? :green:

Andre,

Check this:

http://www.pfarrell.com/music/shanghaimic.html

I really like the no-nonsense of the Neumann KM84-type circuit:

http://www.gyraf.dk/schematics/Neumann_KM83-84-85.GIF

Jakob E.

:thumb:

Are 2N3819's still in production?


Is that 1 gigOhms or 16 ohms? Got to be 1 gig, surely?

Are 2N3819's still in production?

Click to expand...

Don't know if there are still being made, but Farnell in Australia has 2n3819s stock, (stock number 352299 or 434759).

I assume there are still being made as there are two different manufacturers in stock.

tim

That's 1G.
I think the FET is still available.

[quote author="gyraf"]I think the FET is still available.[/quote]
It is:
http://www.fairchildsemi.com/pf/2N%2F2N3819.html

Best regards,

Mikkel C. Simonsen

I've never looked inside one, but does anyone know how close the Marshall 603 mics are to a real KM84 component-wise? I'm sure they cheaped out all over the place but I wonder if they could be upgraded? At least the size of the body is close...

603s are nice with a few caps upgraded. so nice I can't get my pair back from a studio. The 603 are transformerless the km84 is a transformer 1 fet circuit. Look in the meta for a simple version of the KM84 circuit I put in a MXL V67 body. I could remove some parts because the capsule in not grounded in the V67.

You could also build the MC012 circuit That sound nice with good caps. There is a schematic and pictures. Check Zebra's site.

I bought 1000 2n3819s from mouser you need to select the fet for the neumann circuit to work at its best. I use a 24 V supply and the parts in the drain leg and use a source R of 3.9K I also use a 22 meg gate to ground.

You want both 10V at the drain and about .95V at the source. This sets the drain for good signal swing and the gate for input level. Take a good look at all the tube a fet circuits you can find note the bias voltage.

So far I get about 4 per 100 but at $.06 each not a big deal. I think I paid $60.00 for the 1000.

The SD circuit is nice with good caps.

Yes, I know - that schematic isn't the full one. There is also a zener diode for stabilisation - the mic runs off P48.

I have a rev-eng. schematic somevhere that I drew up at an emergency repair sometime. I'll post it when I find it..

Jakob E.

A mic I'd like to build would be a clone of a Neumann Fet47. Does anyone have a schematic of it? I'd imagine it wouldn't be much different than a KM84. It should be a great project to build into a Marshall mic.
Kelley

The fet 47 is at the neuamnn site go to info pool, old products, manuals Last page of the 47fet PDF has a schematic. If you look in the book "Microphones" in the info pool section two simple schematics are the KM84 and 47 fet. Page 40 and 41.

It's a inverting follower charge amp, feedback cap/ capsule cap ~= gain. The KM84 is a drain follower charge amp in the same type of way less openloop gain (a 2n3819 has a gain of about 60). The u87 controls it gain via modulation of the capsule voltage supply the cap from the drain move the capsules supply voltage around because the supply voltage has an output resistance of ~= 330k. One side of the r is not bypassed to ground.

The KM84 is a clever circuit a fet does not have the linear gain of a triode. So I am guessing neumann designer(s) controlled the gain and linearized it via the feedback network

The Nt1000 seems to use a charge amp setup like the fet47 without the transformer. I need to get my 1000 back to finish the schematic and take pictures of the mod I did to it.

I think this is the link

http://www.neumann.com/infopool/history/produkte.php?ProdID=u47fet


The PDFs seem to be down?

Yeah, I get, "Connection Refused".

[quote author="hairyandy"]I've never looked inside one, but does anyone know how close the Marshall 603 mics are to a real KM84 component-wise? I'm sure they cheaped out all over the place but I wonder if they could be upgraded? At least the size of the body is close...[/quote]

Andy,

Audio part of 603 has almost the same schematics as that of Scott Dorsey (Schoeps circuit). Thre is also a simple DC-DC converter.

the full Neumann KM83/KM84/KM85/SM84 Schematic:
http://www.silentarts.de/lab/Mikrophone/neumann/KM83-84-85-SM84_Schematic.pdf

[quote author="[silent:arts]"]the full Neumann KM83/KM84/KM85/SM84 Schematic:
http://www.silentarts.de/lab/Mikrophone/neumann/KM83-84-85-SM84_Schematic.pdf[/quote]

The link showes 404 error. I tried copy and paste--the same.

[quote author="Marik"][quote author="[silent:arts]"]the full Neumann KM83/KM84/KM85/SM84 Schematic:
http://www.silentarts.de/lab/Mikrophone/neumann/KM83-84-85-SM84_Schematic.pdf[/quote]

The link showes 404 error. I tried copy and paste--the same.[/quote]

sorry - I forgot to upload ...
the link works now :grin:

Thank you - again - [silent:arts]!

Much appreciated!

:razz:

Jakob E.

Here is for Neumann KM88:

http://home.comcast.net/~markfuksman/Neumann_KM88i.gif