ART M-Four microphone parts upgrade

[ln76d]

For example no resistor in series in audio path?
I like simple things, usual it sounds better
Ok, ok, ok
I don't see the point to use grid stopper in microphone circuit.
It can be used, or not.
Like in other tube equipments, in some is installed in some not.
Ok, ok, ok again
Sorry Guys, but am writing here between doing many things, so am trying write as quick as possible.
One important thing which i missed.
In my opinion 10k is only here for lpf, that's why for the first time i see it in microphone CCDA circuit, as also 220pF for lpf.
I don't believe it was used for "stability" or anything related to grid stoppers.
Without 220pF cap it will form lpf with miller capacitance.
For lpf, cap from plate to ground is sufficient like in plate followers before output cap.

 

[Gus]

Look up stability in followers.  It is worth the time.
Followers(emitter, source and cathode)  have traps for the new players

 

[ln76d]

Look up stability in followers.  It is worth the time.
Followers(emitter, source and cathode)  have traps for the new players

Yeah, yeah, maybe someday.

 

[The Sugar Lion]

I fixed the annoying hum today by firmly twisting the top portion of microphone slightly! ttp://groupdiy.com/Smileys/default/shocked.gif

Would like to move forward on this but ideally would do it in stages. Start with the "more advanced mod" for example.
I know that all the information is clearly laid out on the schematic but it is hard for me to translate that with confidence.

From what I can tell these are the steps I need to take.....

1. Remove C4
2. Add a Cap with the value 470pF/250V that stays connected to #2 on the tube on one side but now connects to C5/R9 on the other
3. Move the ground from microphone to #2 on the tube

This make sense?

 

[ln76d]

No, not exactly 

1. Yes
2. i will try mark it on the photo
3. ground, is gorund, you are not moving it anywhere Only front diaphragm connection wire directlyto the tube grid.

Here's updated schematic for your needs.

Both 470pF 200V-250V rated. Polypropylene (Philips/BC orange caps are good here) or styroflex/polystyrene.
Note that, you also need add extra resistor Rx, which you cn get from R5, then R5 replace with 33M (easiest to buy from high-ohm resistors, if you will find higher value, then use it).

 

[ln76d]

One thing!

Are you able to resolder two pins on XLR?
If so!

Bottom of the PCB:
Point 5 two black wires, Point 6 two green wires, desolder it.
Then green wire from the transformer solder instead black on xlr, and black from transformer to the place of green wire.
It's needed.

 

[ln76d]

After that you have free point 5 and 6.
At the pic i marked connections.
You need move blue wire from point 3 to point 6.
At the the points above point 5 and point 6 (free after removed C9/C10 caps) you need to install 51M resistor (taken from R5).
Then from point 5 to point 3  install wire (this isn't marked on the pic).
Cap C5 solder as marked - you need to change position of one leg.
After all of that back diaphragm connection is ok.
You don't have to desolder back diaphragm wire, it's in proper place.

After all of these, will be easier