MXL 2001 U87 front end mod capacitor question

While I wait for parts for a 2006 mod (capsule mount specifically) I looked at stripping a 2001 and doing (is it Marik's?) U87 front end mod. The question I have is the coupling capacitor. On the original 2001 this is a 4.7uF tantalum. On the U87, AFAIK it is a 1uF presumably also tantalum. On the mod schematic it is still a 4.7uF.

I'm inclined to go with the original U87 schematic, which is 1uF, and a Cinemag 2480 not a T13 for cost considerations. But would like opinions on the capacitor value.

The mod schematic is attached. C7 is the capacitor.

I am also going to replace the 32mm capsule with a 34mm K67 style.

Here is some info I've saved from other posts. Unfortunately, I don't know who to quote (Gus maybe?).

"The front end of this circuit is basically a copy of the U87. If you take some of the values Neumann used this may be a better option.

C2 470p Styroflex
C3 820p Styroflex
C8 1uf Film

C2 Most people us a 1000pf here however the 470pf gives you more of a vintage sound
C8 is one of the most important caps in the circuit you can use a BIG cap here. Solen, Wima, Axon, Mundorf @ 250v this will give you a great tone.

Neumann also used Tantalum capacitors in in their U87 mics. This is also part of the tone of the mic."

I hope this helps.

-James-

I used a big 22uF Nichicon bipolar electrolytic in one build.

That cap couples to the output transformer, so you want it big enough to move the RLC response of the output section as close to DC as possible (at least in theory).  However it all comes down to taste:  smaller caps have less bass response which may be what you want!

I would try values from 0.47uF up to as big as you can shoehorn in there and see what sounds best to you.

Thanks, that's exactly the kind of info I was looking for.


BTW, how do you estimate the cutoff frequency? Do you use the dcr of the output transformer or the estimated reflected impedance? Or???

Went to the junk store today (which is closing  :'( among other things, he was all out of 47uF/450v and 2gig resistors and about half the shelves were empty....) but bought some nice 470pf and various 1uf caps. I need ot order a 2480 transformer. I have some 12:1 for Royer mods. I'll use one of those first while I wait for the Cinemag.

Going to put the mic back together real quick for a short recording of a few sounds for a rough before/after.

Great thread!

I’m working on an SE 2000 mic, basically like an Mxl v67 but with low cut and pad switches.
I’m trying this front end mod this week.
I wonder about transformers, I’m not sure what values/poles I’m looking for, I’ve even considered winding some myself.
Alas but I’m not sure how.

any advice?