Real simple tube mic w/ 6AK5 (Royerish)

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Blue Jinn

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I bought another broken MXL microphone (V89MBP) to just use the body. It was pretty cheap. If I am correct the 5840 and the 6AK5 are pretty close in specs. So I thought: why not the basic Royermod with a 6AK5? Granted, I am not breaking any new ground here, but thought I'd share it anyway, and post for criticisms. Except for the body, I just used (cheap) parts I already had.

KCM transformer and a capsule I got from a mini group buy. (Factory second?)

Here is the mic:

finin_a.jpeg


finin_c.jpeg


finin_e.jpeg


It passed the smoke test and the brief hello world check. So at least it works. How it sounds will be determined.



Here is the schematic: (Except I didn't have a 1uF that would fit, so I used a 2.2uF)
 

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That is such a hard core DIY Mad Max microphone that I want to build one myself just looking at the pictures!  8)

REALLY hope it sounds great; let us know when you find out!

Best,
Michael
 
Very cool build. Did you check the bias point or use the 750r as a starting point (since that was Royer used in the original design)?
Edge-terminated or center-terminated capsule from the china gb? I've been using both in mic builds, and think the edge is awesome, and not sure yet on the center.
 
trans4funks1 said:
I enjoy seeing/learning how you mounted the tube socket. That's a nice move.

Thanks for sharing.

Some of it was dumb luck having parts laying around.

First located a chassis mount socket in the stash of parts.  There wasn't enough clearance between the switch board and the bottom of the headbasket plate to drill holes for the tube leads so I eyeballed where to place a socket to clear the switch PCB with enough room to solder the tube leads, clear the mic circuit board and give ample room between the tube and the body sleeve.

Then I lined up the tube socket in that location and marked the switch PCB with a sharpie to drill the mounting holes. I wasn't able to match screws with the standoffs I had on hand. So I found some other screws that were just long enough. They were a perfect fit  and basically "threaded" thru the socket holes, so I could do without the standoffs as the socket would not move up and down the screw, and I had lock washers for the nuts on the switch board.

I also bent the tube leads, but left the metal piece in the center of the socket, which pushes against hte switch PCB and provides some tension.

Here is a closer up:

finin_f.jpeg

 
dmp said:
Very cool build. Did you check the bias point or use the 750r as a starting point (since that was Royer used in the original design)?
Edge-terminated or center-terminated capsule from the china gb? I've been using both in mic builds, and think the edge is awesome, and not sure yet on the center.

Honest, I just went straight with the Royer values.  :-[ I plotted the plate curve way down in the weeds and didn't worry too much about it and the curves are almost exactly the same.

Capsule is the center terminated 47 clone. I put one of the edge terminated ones in an MXL 2006 and took out the coupling cap. I like it too, found it to be "creamy."
 
Also, I added the grid resistor. BigUgly's mod uses the same values as the Royer, but adds the 1G for Rg. I didn't have a 1G with long enough leads so used a 2G instead.

My eyes glazed over at at "ionization" but I think the 2G is OK, although I did handle. I didn't seem to get any buzz or hum though without cleaning anything:

http://www.neumann.com/forums/view.php?bn=neumann_archive&key=993770179&v=f
 
Great, I just cleared my benches off and now you go and inspire me to strew parts everywhere all over again! 8>]

Good job - love the experimental 'odd tube' aspect, and the spontaneity!

I'm curious what you're using for a power supply(?)

Dave (shaggy)
 
shaggy said:
Great, I just cleared my benches off and now you go and inspire me to strew parts everywhere all over again! 8>]

Good job - love the experimental 'odd tube' aspect, and the spontaneity!

I'm curious what you're using for a power supply(?)

Dave (shaggy)

Hi,

Sorry I missed this post. I am using the PSU I built for my other Royer mod, which uses the BigUgly PSU boards. (I just leave out hte pattern switching part.) I need to replace the transformers in that, as I'm only getting 70v under load. I have located a transformer (in the big box under the bench.....) that works. 

I can post some pics if you want.

 
Thanks for the info. Actually I have the perfect regulated supply for that project, when I get around to it. So many things to build, so little time! 8>]
BTW, how's it sound?

Dave (shaggy)
 

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