Royer MXL Tube Mod, Is there any way to do this nowadays?

comstock · Post by **comstock** » Wed Apr 06, 2011 11:45 am

thanks!

comstock · Post by **comstock** » Thu Apr 07, 2011 3:33 pm

holy crap. i don't know how it sounds yet, but i just plugged her in for the first time (just finished my cable..) and i'm getting +6.3V at pin 5 and +99.8V at pin 4. HELL YES.

this is the first diy audio project i've ever undertaken, and i'm completely amazed that i've managed not to destroy anything expensive or put myself in the hospital. i came close with my transformer wiring (followed the color code for jensen when i have a cinemag), but thanks to double-checking and the TOMB i think we're ok.

now to see if it actually works for real and then maybe post some pics or something. my power supply has a real, "i didn't know what i was doing when i started this, and i still kind of don't, but i didn't hurt myself," look to it...

comstock · Post by **comstock** » Fri Apr 08, 2011 11:10 am

i may have spoken too soon. this thing ain't workin...

i'm getting the correct voltages at the correct pins, both at the power supply and at the mic (6.3V at pin 5, 100V at pin 4), but all i hear is crackling and distortion. when i speak into the mic it has no appreciable impact on the microphone's output--just noise like i've got my ear up to a seashell.

when i first tested the mxl (prior to any modification) it was behaving like there was humidity in the capsule. at least, that's what i determined after some searching on the web--at first it was all ocean sounds, then ocean sounds with a little interruption from my voice, and then after being plugged in for about a half hour it sounded fine.

i'm wondering if my issue is my capsule. the behavior prior to modification would lead me to believe so, but at the same time i don't really know how i would verify that. the tube itself seems good--it glows orange and doesn't look any differently than it did when i bought it--but i have no way to verify this, either.

one thing that worries me is that when i first hooked it all up and started checking for voltages, my shaky, too-much-coffee hands let the positive lead from my DMM brush past and very briefly short pins 4 and 5 (just long enough to make a spark). i'm hoping this little mistake isn't enough to screw me, but if it is i'd like to know.

any thoughts?

and thanks again for anyone interested in this.

Nate Dort · Post by **Nate Dort** » Sat Apr 09, 2011 4:42 am

one thing you can do to eliminate the capsule from the equation is get a very low value capacitor (something like 100pF with a 100V rating would work) and substitute the capsule with it. If the noise is still there with the cap in place of the capsule, then it's in your circuit. If the noise is gone, it's your capsule.

phantom power · Post by **phantom power** » Sun Apr 10, 2011 3:59 pm

Comstock,

Same thing happened to me. Ocean sounds and all.

After a bunch of fussing, I finally changed the capsule with one from an ADK and sure enough, she's be doing great for a couple of years now.

I may have another one of those capsules laying around. I'll check and then report back here.

-AE

comstock · Post by **comstock** » Sun Apr 10, 2011 4:15 pm

thanks to you both for the replies. i'll try testing with a capacitor in place of the capsule like Nate said here in a little bit and see what i get...

honkyjonk · Post by **honkyjonk** » Sun Apr 10, 2011 5:30 pm

I wired my Cinemag color code the same as the Jensen and it works.

comstock · Post by **comstock** » Sun Apr 10, 2011 5:54 pm

honkyjonk wrote:I wired my Cinemag color code the same as the Jensen and it works.

hmm. this worries me because i wired my Cinemag 2480 opposite the color code of the Jensen--red and brown to the circuit, yellow and orange to the connector--as per the PDFs available online. to think i might be putting one of the expensive pieces of this project at risk is kind of unsettling.

but i did try swapping a small capacitor for the capsule, and i did not hear any ocean sounds or crackling (just the noise floor from cranking my crappy mbox pres all the way up), so that's a start. i bit the bullet and snagged another 2001 off ebay, so that will be here in a few days and i can try using the capsule from it to test my circuit (and probably use its original circuit to test my old capsule, just because).

i looked at the capsule i'm currently working with, and it sort of looks like shit. it's got particles all over it and a cracked saddle. i'm pretty sure part of the saddle is basically being held together by the pressure from the screws passing through it to the capsule--like if i were to take them out it would disintegrate. i'm getting the feeling this mic may have been dropped on its head at some point...

one thing i'm curious about is whether or not the tube should be acting microphonically. with the pre cranked way up, i can barely hear myself tapping (pretty hard with my fingernails) on the mic body, and that's the closest thing to "acting like a microphone" that this thing does. this works whether or not the capsule is connected, but i don't know what it means.

Nate Dort · Post by **Nate Dort** » Mon Apr 11, 2011 5:24 am

honkyjonk wrote:I wired my Cinemag color code the same as the Jensen and it works.

it will work, but the output will be extremely low and you'll get some frequency response weirdness. The cinemag needs to be wired opposite the Jensen because it's physically wound in a way opposite the jensen. Using the Jensen direct-box transformer in reverse was a workaround at the time Royer wrote the article. The cinemag was actually designed to be a tube mic output transformer.

comstock · Post by **comstock** » Wed Apr 13, 2011 4:14 pm

so i got my other 2001 in the mail today, swapped capsules, and still nothing. i put my old capsule in the new mic and it works. so now i'm assuming the problem is in the circuit. my tube glows orange and has a smell when it's on. i don't know much about what a tube is or isn't supposed to look or smell like, so that may be a point of interest. the tube i'm using was sold as a NOS Mullard 5840, but when i got it the box said CV465. a little research led me to believe they're interchangeable, but i don't know. i have a Phillips JAN 6205 on its way, so i suppose trading out tubes will be my next step.

anybody know what color a tube like this is or is not supposed to glow?

comstock · Post by **comstock** » Fri Apr 22, 2011 4:40 pm

sorry to keep bumping this old thread, but i got my new tube in the mail last week, swapped it out, and still got nothing. i got some time yesterday to just breadboard the thing to make sure i'm not crazy/stupid, and it worked (albeit with about the worst hum imaginable). luckily i ordered several of each of the cheap components at the beginning, so i had enough to build a circuit point-to-point, and BINGO. IT WORKS.

so i'm assuming the problem was my shitty PCB all along. what i etched for the PSU worked fine, but no dice on the mic circuit.

anywho, thanks to everyone who's made it possible to keep doing this mod long after the kits have gone away. i have a new mic to play with...

cossda · Post by **cossda** » Tue Jun 07, 2011 10:31 pm

Also sorry to keep bumping an old thread.

I did this mod about half a year ago and it was working great until last week when the filament on my tube blew up. I took some measurement and I was getting 38V on the filament line...far cry from 6V and obvious reason why it blew up.. The thing is it had been fine for half a year and, presumably, at the correct voltage.

I was going to pull up the schems and make sure I had everything wired in correctly, but apparently I don't have them anymore and the ONLY site that I could find them at previously (diyfactory) seems to be gone. Does anyone have the schems still?

cossda · Post by **cossda** » Thu Jun 09, 2011 7:30 pm

Actually it doesnt matter if anyone has the schematics or not. All I really need to know is how much current is drawn by the mic on the 100V line. And if theres any sort of regulation in the mic circuit or if thats all done on the PSU. If not, as long as I know the load current I can build my own power supply.

I know the filament draws 150mA. So I'm halfway there. Would anyone mind taking a measurement for me?

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Royer MXL Tube Mod, Is there any way to do this nowadays?

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