Tube Mic Royer Mod Build Thread

[dmp]

Did the buzz go away when you lifted the PCB ground from the earth ground? What happens if you lift the IEC ground?

I haven't tried this but I have experimented with the grounds a bit, as well as drawing it out to make sure I wasn't doing something stupid. I think it is the shared ground plane on the psu pcb.

Is this a 120Hz or a 60Hz buzz?  It sounds like maybe something is NOT grounded...  Have you tried connecting various spots with a piece of insulated wire?
Does it change when you get your hands near the PCB?
Or, is it perhaps the layout of your PCB?
David

I think it is harmonics of 60 Hz - it sounds much higher than 120Hz. A noise reducer plugin with a 60 Hz setting (which cuts harmonics also) removes the buzz.
I also thought it seemed like a ground problem, because I've had similar buzz in preamps when I didn't have a ground connection or something, but the fact that a different PSU does not buzz means the mic is OK, and I now have changed the grounds on the pcb by running wires and have one psu buzz free. So I think I am on the right track.
FWIW, it is a really low level buzz.

Does it change when you get your hands near the PCB?

Haven't tried this and not going to. I take precautions with tube equipment by maintaining good habits - like keeping my hands away.
The buzz does not change though, not when the mic is moved etc... so I don't think it is that type of buzz

 

[dmp]

I have both power supplies finished now with no buzz. I think there were many things contributing to the problems I had. The orientation of the transformers, the ground scheme, and the grounding on the psu pcb.
Even with the grounding changed on the psu to connect the filter caps and rectifiers first, then to the ground plane, I put the second psu together without a good ground connection to chassis mistakenly and had a similar low level buzz.

Note that the mic pcb has a ground plane that extends to the holes for the mounting screws. Unless an insulating washer is used, the audio ground is connected to the mic chassis through the screw. I found that either way was quiet in the end.

 

[bigugly]

sorry 'bout the grounding problems guys. this was designed very early in my electronics hobby and it was also my first foray into tube circuits. if I remember correctly I also had issues getting the ground right on my first mic but once I figured it out I built each additional PSU identically. I just wish I still had some of those mics so I could share some pics.

I am glad that everyone is working out the problem. If there are any suggestion for a re-design of the PSU I'd be happy to.

cheers,
James

 

[dmp]

No apologies necessary at all! Thanks for making the boards and offering them to the group.

I'm just been experimenting with different output caps on the mic. I tried 2.2uf, 1uf, and 0.47 in Mallory 150s - the 1uf has more bass than the 2.2uf (with a Beyer 10:1 output transformer). Going to 0.47 loses bass and lacks a full sound. Definitely going to use 1uf - a clear winner.
Then I tried 1uf in PIO and preferred the Mallory. Had a little more real sound, though the differences were subtle. It might be hard to say there was a difference in a blind test.
I'd suggest trying a few sizes with whatever output cap one's using and pick the voicing you're going for.

 

[tchgtr]

Dang! 
Let that be a lesson to me. There's a reason that Royer originally set the  output cap at 1uf. It's been the fashion to increase the size of these, and I thought of going back to the 1uf just for space concerns, but I managed to cram 2.2 into the space available in the donor mic I'm using for this.
Ah well, I'll leave it as is.
  Thanks also to Big Ugly for the project, and dmp for working thru the noise problem. I was glad to find a multi-pattern version of the Royer circuit. I'm just doing the head amp now, and will get to the PSU in a while.

 

[dmp]

Royer originally used a Jensen DI transformer as well, which is very different from the transformer I am using. By reading and searching here I've read that the capacitor interacts with the inductance of the transformer to define the sound, and it is not a simple correlation of higher or lower uF values.

As such, I went out and exercised, came back, and listened to the samples again (of 2.2uf, 1uf, 0.47uf). After giving my ears a break, I much preferred the 2.2uf! It does have less bass, but the voice of the guitar, particularly the mid-highs, sounded much better. The 1uf had a weird ringing frequency hyped. And I don't need these mics to have strong bass at all.
So, I'd suggest trying different caps with your transformer and see what you like best. 

 

[bigugly]

I used a 2.2uF Panasonic in conjunction with a Cinemag CM-2480 for every build I did.(about 7 mics total) I always liked the sound I got with that combo.

I'm currently not building mics and I don't have a need to do so but I'll help out when I can. So, here's a link to a suitable power transformer.
http://www.antekinc.com/pdf/AS-05T120.pdf

Also, I reworked the mic and PSU PCBs. I have them with isolated and elevated heaters and the mic PCB traces were slightly reworked for a neater layout. If anyone wants the schematics and gerbers I have them in a zip file.

 

[tchgtr]

All good. I'll most likely be using the Cinemag 2480 also. This is what is in my Royer cardioid build, and it sounds great.
Also appreciate the link to the PSU transformer. I was wondering if folks were just bringing in raw 120v.
Will most likely leave the 2.2 in there. If that's what's called for in the Cinemag transformer notes, I'm fine with that.
Here's a shot of the head mic PCB, recycled from the original donor mic board.

 

[dmp]

So, here's a link to a suitable power transformer. http://www.antekinc.com/pdf/AS-05T120.pdf

I would use that one in the future - cheap and should have less chances of creating nasty fields.
It would be hard to drop it to 100v however with the current psu design.
Perhaps use a power supply that can regulate the B+. For instance, a zener diode to ground after the CRC, followed by another RCRC.
Mouser has 5w zeners for 80v, 100v, 120v, etc... to pick from.

 

[Blue Jinn]

All good. I'll most likely be using the Cinemag 2480 also. This is what is in my Royer cardioid build, and it sounds great.
Also appreciate the link to the PSU transformer. I was wondering if folks were just bringing in raw 120v.
Will most likely leave the 2.2 in there. If that's what's called for in the Cinemag transformer notes, I'm fine with that.
Here's a shot of the head mic PCB, recycled from the original donor mic board.

Not sure what you mean by "raw 120v" You should always have at least an isolation transformer. You could e.g. (if you have the right power ratings) use a dual primary transformer for your 120v winding (see the PRR Varimu PSU) That transformer price is pretty good that BigUgly posted.

Private email sent for the re-worked files. 

FWIW's I don't have a problem with buzz on my first build of this (grounds float and my transformers are under spec'd somehow, but don't get hot.)

 

[dmp]

FWIW's I don't have a problem with buzz on my first build of this (grounds float and my transformers are under spec'd somehow, but don't get hot.)

Are you sure that your audio ground is not connected to the chassis? Checked with a multimeter? I ask because I tried this last weekend and it buzzed like mad.
The mic pcb will connect audio ground to the mic body unless you used insulating washers / screws.

 

[dmp]

Will most likely leave the 2.2 in there. If that's what's called for in the Cinemag transformer notes, I'm fine with that.

Cinemag recommends a 2.2uf cap? Don't see that in the datasheet.

 

[sr1200]

DMP, did you ever get those sockets? (and if so, any chance i can buy one from you?)

 

[dmp]

DMP, did you ever get those sockets? (and if so, any chance i can buy one from you?)

Nope. I didn't win the auction

 

[sr1200]

bummer, 
im probably going to buy a lot of 10 of the tubes (if anyone is interested) and i have a possible source for the sockets if you can let me know what the foot print is for the socket (im at work don't have the board in front of me at the moment)

 

[sr1200]

Think this would work?

**edit Theres nothing to suspend the socket from... but theyre 11/32" which i think should be small enough no?

 

[Blue Jinn]

FWIW's I don't have a problem with buzz on my first build of this (grounds float and my transformers are under spec'd somehow, but don't get hot.)

Are you sure that your audio ground is not connected to the chassis? Checked with a multimeter? I ask because I tried this last weekend and it buzzed like mad.
The mic pcb will connect audio ground to the mic body unless you used insulating washers / screws.

I didn't isolate the board from the mic body. So I"ll talke a look tonight and report back.

 

[dmp]

Think this would work?

I think so - you won't be able to mount them to the mic pcb unless you are going to have the tube stick out from the mic body.
Look at my pic on page 1 - I put wires on the socket to the board. I used a wirewrapping tool, which worked great.

 

[sr1200]

yeah i saw that after i posted, totally forgot about that, but, if the pins were long enough, might have been possible to mount it by bending the pins.  Those sockets are going for $8/USD. I will contact them tomorrow to see if any are in stock.  Also, i have REALLY tiny eyelet screws that could go into the plastic for suspension if needed.

edited was USD not CAN$

 

[dmp]

I've got some extra 6 pin male switchcraft connector thingies if any of you guys need them from your builds. These fit in most mic bodies, mxl 2001, etc...
Free if you pay the shipping. PM me.