Attempt to upload MXL2001 mod pictures

[Blue Jinn]

The uploader I've determined is completely arbitrary. E.g. upload the 2001 schematic = fail. Save as a GIF, OK. Whatever Now I can't manipulate the order of the pictures.... OK, here goes again:
Unmodded board:



Modded board:
Note, I didn't route the transformer wires the original way. Also, lifted a solder pad while undoing the stock transformer, (brute force desoldering iron...) so had to move the new one to a new place. Once you've removed the pnp follower section, there are a lot of free spots to solder. R7 is the second resistor in from the right. R6 and R7 form a voltage divider for the FET. There is a thread on Groupdiy regarding the Aurycle FET mics (same circuit) and installing a trimmer at R6. I'm going to look into doing that, as I replace the FET next.





The new transformer is a little too big for the bell housing, which is basically flapping in the breeze at the moment. I used the same ones on a Royer I did, which required some drilling to the base of the mic to make it fit, (basicallly just making four notches for the transformer.) The Cinemag will fit, and I'm tempted to get one, but going to see the impact a new FET has first.

The original 2001 schematic



The u87 View attachment 72747View attachment 72747-which won't upload with the WYSIWIG editor: even though it's a jpeg....



Except this version will.

OK and the pdf of the front end mod.

 

[kip4]

Thanks for sharing Jinn
nice work mate

 

[Blue Jinn]

Thanks, except it ain't working... I'm going to swap out the FET next, also the orig U87 schematic has different values for a couple of resistors, I may try that as well.

 

[moresound]

Doesn't work!

 

[Blue Jinn]

Doesn't work!

Which part? (I.e. I'm open to suggestions....)

 

[Blue Jinn]

Update: I noticed I had left R6 and R7 in place, where the mod schematic calls for a ~3k resistor alone, with the 1g and capacitor all sharing a common ground at that point. So I removed R6 and replaced with a jumper (only pathway to ground on the pcb) and changed R7 to a 5k pot, set initially at 3k. At 3k, got 24v. Not sure if that is in the ballpark for a 2sk170, but now it sounds even worse... the sound actually is weak, distorted, and ripply, if description makes sense.

Damn, I thought this was going to be an easy one... Now however, I am pretty sure the circuit looks like the pdf file.

 

[Blue Jinn]

Update:

I found my error, I had C8 installed on the wrong side of R8. Must have followed the wrong trace at some point. Moved to hte correct place (the junction of R8 and the former C6) problem solved. Mic is not very sensitive (which I expected) also, not sure what kind of headroom it has. Want to try out on a few things and see how it sounds. Not as bright/harsh/hot as the 2006 I was comparing it too in the initial optests.

 

[Blue Jinn]

Update: I don't have a 'scope, but came across a discussion at groupdiy about several MXL 2001's with varying drain voltages from about 8 to 17v. The lower values having more headroom then the higher. So I dialed back the voltage to about 10. The mic sounds fine now. I just did a quick side by side with the unmodified 2006 I have. Any description is bound to be subjective and also probably influenced by my expectations. But the modded 2001 sounds a bit more refined then the 2006 which has a sharper more metallic quality to it. I have some spoken voice recordings of hte 2001 unmodified, I'm going to do a comparison to next.

To summarize the changes:

Replaced the capsule with an OEM 34mm K67 style capsule ( from my own source)
Replaced C2 with a 470pF mylar
Remove R9, R10, and C6, and Q2 (labeled D2 on the board)
Replaced C8 with a 1uF poly
Replace R7 with a 5k pot and R6 with a jumper.
Replaced T1 with a 11.5:1 ratio. I happened to have a bunch of these. Probably a 10:1 would work, e.g. an AMI T13 or a Cinemag 2480.
Adjusted R7 for 10vdc measured between drain and ground. I haven't measured the value of R7 now though..

Note that with a unidirectional mic like this, R4 and C2 could be eliminated, wonder how that would sound?

NOte also that hte mod schematic and hte orig have different part numbers. I had to go through and edit the mod schematic to be consistent with the board.

I have a set of 2001 boards from a Royer mod I did, and I have some J305 FET's. I may do this mod on those, with a different FET and eliminate the coupling cap. I need to get new teflon posts first.