Blue Jinn

23 May 2020

6AK5 Microphone build thread

I'm not a professional blogger, doing some organizing posts here. I think maybe somebody might find this helpful.

MXL V89MBP donor body for RoyerMod/BigUgly/G7'sh mic update 21-July

Picked up one of these that was not working on battery. Had the hole already cut and a switch so thought to make cardioid/omni version of the Schoeps circuit. (I am not interested in doing any metal work) Upon a brief inspection, some of the circuitry is on the main board on a smd circuit board, and some on the board containing the switch. Seemed too complicated now.

But there is about the same amount of space as found in the MXL 9000/76t; so I thought I could just gut the thing and do a point to point SELA/Royer'sh with a 6AK5 instead of a 5840 and a dual sided capsule. I have some generic K47 clones so will use that. Will post some pics of the internals soon. One more project on the table. This should be relatively simple though.

Have taken apart mic partially, removed XLR plug (which was in pretty tight) remembered this time that the screw is threaded counter-clockwise and tight is up not down. The switchcraft I have will go in much easier. Need to solder the wires to it next. I've sketched out a schematic and a parts placement guide. Plan to leave the switch board in place as it already is lined up, and just remove all the other parts on it. Here is my schematic, the circuit is pretty much the Royer/SELA with an added grid resistor (I have a 2G to try out, with longer leads than the 1G's from the original mic) also an omni/card pattern switch. I want to keep my PSU's consistent (for no good reason, I'm not going to have that many....) so will use the 100/60 voltage divider as in the Royer rather than the 120/60.

Here is my proposed layout, basically following the schematic:

The transformers are noname appr 11.5:1 or so. I used one in my other RoyerMod 2001, and in the "U87 Front End" mod I did to another 2001. I got several of these off Ebay and in a trade.

Single sided G7 build

Single sided G7 build.Schematic found here: (xaudia blog)

Mic started out as a MXL9000 which I got a sweet deal on. Didn't have the PSU, and I had to take the capsule out for a MXL 2001 "BigUgly" so repurposed for a G7. I accidentally damaged the transformer I had (a Bv8 from Dave Thomas) so I used a 3U Audio 6.5:1 transformer, http://www.3uaudio.com/cp.asp?id=668

The "bottom" resistor on the voltage divider is changed from 470k to 270k to get about 50v at the capsule. I also couldn't fit the 2u2 capacitors I have, so had to go with a 1uF Russian I had on hand. Soviet 6Ж32П Tube. Capsule is Chinese manufacture, originally from WGT, edge terminated C12 clone. Mic is nice and quiet, a little bright, sensitive. Going to try it out soon!

UPDATE: 26 April '20: Found a cheap MXL V76t PSU. Changed the two zeners out for 75v, for 150vdc B+ Total build cost is about US$200 including everything, body, capsule, PSU, cable, etc.