Yet another Royer Mod based Mic

bruce0

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Last Year I did this take on Royer mics.  I did 4 mics, 2 of them based upon the Royer Mod 2 (Small Diaphragm Condenser, with the tube in the mic, and the transformer is near the power supply) and two based upon the first royer mod (Large Diaphragm Condenser.)  One was using the original circuit board layout, the other was re-layed out to fit in a smaller mic.

All of them use the same power supply.  The way I did this is that I created a little "interface" box to work with the SDC versions, to contain the transformer.  It also accomplishes getting the transformer out of the Power Supply Box, which is good for the noise floor.

It was my first exposure to tubes, but I use the LDC's a lot, and really like them.


First circuit cards, hand drawn copies of the royer layout

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Later I re-layed out the mic card to fit a short mic, and the power supply to fit a small box.

Original Royer design being built

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Picture of completed Royer Mod Mic

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Traditional Royer Mod, hand copied and drawn PCB

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Second round mic, a modification of a big echoey MXL mic, that I shortened, opened the basket, and put a royer circuit in with a different card layout for size.  Also fitting the tube inside the basket.

Plastic cup works well to protect the delicate diaphragm while you re-assemble the mic.

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Shorter mic, using a mic trafo backwards for the stepdown.

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Closeup, you can see how the circuit card fits up under the plate that supports the capsule.  At this point the transformer was 4:1 stepdown, which made the mic much too hot, but later I put a 10:1 stepdown in there which works fine.


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Finished short Royer.

You can see the tube glowing in there.

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Here is the little converter box, that has the transformer in it.  In Dave Royers original design this transformer was in the power supply enclosure.  By taking it out of the enclosure, yøu can worry less about shielding, and you can use the SAME power supply for all these mics (but on the SDC mic's you need to use this little interface box.)  This works well to reduce the amount of stuff I have to carry for on location work.

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Two mics and interface boxes can fit in one case.  And they will work with the same power supplies that  feed a normal royermod mic.

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A dual power supply and a single.  I did a re-layout of the power supply card and I can fit two of them in the small box (it is tight)  too with one inverted (the caps overlap).

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I have to dig up some photo's of the guts of the power supply, and the little interfaces.  But they are really very simple.  It is Dave Royers design, but the cap, resistor and transformer are mounted in the interface box instead of the power supply.  I also re-configured the pinout so that if you accidentally plug the mic in without the interface box, you are less likely to fry something.








 

hop.sing

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Those small mxl603s work great with the tube cathode follower.
They are a little bit noisy, but that is no issue on loud sources and that is where that circuit shines, they have plenty of headroom, just use a pad in front of the micpre.
They are actually my favorite on toms in the moment, great ooouumph without beiing muddy, I like them better than our sennheiser md421s in that application.
 

bruce0

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hop.sing said:
Those small mxl603s work great with the tube cathode follower.
They are a little bit noisy, but that is no issue on loud sources and that is where that circuit shines, they have plenty of headroom, just use a pad in front of the micpre.
They are actually my favorite on toms in the moment, great ooouumph without beiing muddy, I like them better than our sennheiser md421s in that application.

I agree, I have found them to be good Drum Mic's.  I have not found them noisy I have not needed to Pad them (but I admit I am working at pretty low Sound Pressure Levels, project studio accoustic music recording)

If you are having noise, it might be the cables from the mic to the transformer are picking up noise . 

Or maybe the difference is you did the transformerless version. I know the Dave's article says you can use a circuit without a transformer, but he says that if you are going to feed "unbalanced circuits of medium to high impedance (10,000 Ohms or more)".  If you are using a mic pad, you are feeding low impedance, and that would explain your hot mic problem and possibly the noise. 

Or if the transformer is in the power supply box, you can pick up noise there.

In mine, I keep the transformer in a small box on the cable, I keep the cable from the transformer box to the mic short (after that point, the cable run is 4x lower impedance, and balanced), I shielded the balanced signal as it runs through the power supply with a scrap of MU metal foil (although I am not sure that did much good). In my setup I balance everything... the real world treats unbalanced arrangements pretty badly.
 

hop.sing

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Well, i used a 2:1 transformer as impedance converter after the tube (it works ok into every micpre we use, but of course the level is hotter than with a 4:1 tranny as recommended). Padding is necessary with a close miced and hard hit snare or tom, which seems reasonable to me. But there is no distortion from the mic itself.
I had problems with the power transformer straying 60Hz hum into the mumetal shielded 2:1 transformers, but placing the powertransformer in a seperate box solved the problem, similar like you did.
The noise I have left is typical tube hiss, its not bad at all, it is just louder than for example a km84 or my elam circuit with a telefunken ecc801s. So I would not use those mics for an acoustic guitar or so, but for those applications I have better mics anyway.
 

bruce0

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I didn't use a 4:1 stepdown, I used the Jensen MB-D, wired as a 2:1 stepdown (but that causes a 4 to 1 impedance stepdown).  Sounds like you are all over this in any case.

I will take another listen to mine, but I don't get a lot of noise/hiss that I recall.  I use them on drums, and I have used them to mic a guitar amp, but I have to say they are not my favorite mic's, I don't have the high end mic's you mention but of my set I prefer Oktava's on accoustic strings, 414's or LDC Royer Mods on vocals and Brass. If I have a hiss and I haven't noticed it yet.  Do some tubes hiss more than others?
 

bruce0

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hop.sing

I was interested in hearing that you had an ELAM circuit.

I would be interested in doing an elam circuit.  Do you have a readable schematic, or any DIY links that might get me started on that?

Thanks!
 

Rybow

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Wow! Very cool man. I might have to give that royer mod a try.

How did you make boards like that? I am looking to experiment with some simple circuits, and I would love to make them the way you have. My girlfriend isn't allowing me to have an etching tank in the house.
 

zebra50

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bruce0 said:
Do you have a readable schematic, or any DIY links that might get me started on that?

http://www.xaudia.com/xaudia/Schematics/Pages/AKG,_ELAM.html

;)
 

hop.sing

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Hi

Look at that:
http://www.sdiy.org/oid/mics.html

It is with a ac701 tube but you get the idea, a simple circuit with a twist.

http://www.sdiy.org/oid/mics.html

This thread shows the biasing of the 6072 tube:
http://www.groupdiy.com/index.php?topic=15418.0

I biased the ecc801s the same way and it sounds fine.
The interesting thing about the elam is the capsule which has a high end lift build in, the ck12. (I used the mbho copy, but the tim campbell version should be great, too.)
To counteract the highendlift there is a 100pF cap from plate to ground acting as a lowpass filter. I played with the value a bit and ended with 220 pF, which tames the highend quite a bit, I guess 4dB down at 15k (maybe even more). I liked it that way best, sounds very balanced and still crisp.
As for the transformer, you can get a t14/1 from Haufe for not very much money, and it sounds good to me.
By the way I tried the c12 biasing scheme in that micophone, too and found there is not really to much sound difference between the two. At least while testing with my voice. But the elam is easier to implement.
The Originalschematics shows a gridresistor of 8Mohms, which seems unbelievable low, I used 100Mohms and that works very well, good bass response and low noise.
The housing is the one ioaudio sold a few years ago, seems not be in the way of the sound of the mic, and easy to work with.
Microphones are great fun to build, you can tailor them the way you want, experiment with biasing schemes and capacitors, capsules and transformers, but in the end I would say that 90% of the sound is definitly in the capsule and the electronics simply should not be in the way.
Best Tobias
 

bruce0

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Insomniaclown said:
Wow! Very cool man. I might have to give that royer mod a try.

How did you make boards like that? I am looking to experiment with some simple circuits, and I would love to make them the way you have. My girlfriend isn't allowing me to have an etching tank in the house.

How did I make the boards?  I drew them in Sharpie on copper, and etched them in ferric chloride.  The round board I made in Eagle, and then I peeled the labels off a laser print label sheet, and printed on the coated backing.  Then I ironed the backing onto the copper and etched that with ferric chloride, I did it two sided, but it would be easier one sided.

Sounds like a very sensible girl. The stuff is a mess.  I use a tupperware tray with a sealable top, and when it wears out I put it in a bottle for the recycling center (it is full of copper and very bad for pipes (the ferric chloride) and the environment (the copper));

You can point to point it.  I can post the eagle schematic for the boards I did, if you want to etch them.  They are from the Dave Royer articles I don't think I changed much except the position and layout.

The Small Diaphragm Condenser ones (SDC) are point to pointed (all they have in the mic is a tube and the capsule, so that's easy.  The little impedance converter has a 2:1 stepdown in it, and a cap and a resistor.  The power supply can be point to pointed too.

For the LDC (which I find to be a more useful mic) you need to get a 8:1 to 12:1 stepdown (Jensen makes a nice one which fits in the MXL2000 which is what Mr. Royer did in his article if you get it without the mu-metal can, it fits right in)... I used a mic input transformer backwards (secondary as primary) for the little mic, the shielding can't hurt, and it fills the resonant chamber of the mic.  I put the tube up in the basket (where it keeps the high impedence capsule lead as short as possible) and you could point to point it but it would be harder.

The only part that you will have trouble getting is some insulation for the tube leads (i had to buy a 100 foot roll of teflon spaghetti, but you can strip some teflon coated wire, you only need about 6 inches of it.).  Other than that there are a few caps and resistors.

It really depends upon which chinese mic you are starting with (unscrew the bottom, and look to see what the board is shaped like.  Mine had a V shaped board and a little round board, and I just shortened it and used the little round board.  But the MXL-9000 (I think that is what it was) that I converted just had the V shaped board, so I did that, and you can point to point that but it is a little tighter.  They are big mic's and have plenty of room (which is one of the problems with them, the empty space resonates, so I filled it and made it smaller).

What mic are you starting with?
 

Rybow

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Ok. I guess I have officially asked the stupidest question on prodigy pro. It looked kind of like you just drew them with solder or something like that, but I guess that's from tinning the traces? Anyways, I guess I can't get by etching. Although a small tupperware container would be easy enough to keep hidden.

The mic I am working with is an Apex 435. I think the body is too small for the royer mod. The reason I was asking about the boards is that I was going to try out a KM 84 type circuit or something like that. For the time being, I am changing the capsule, upgrading the caps, and then I will try out a dorsey circuit. I will probably try some P2P work. I don't have much practice with that.

Thanks for all the info! I am going to investigate the royer mod more fully. Would love to have a tube mic!
 

bruce0

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I did the Dorsey circuit (which I think is what you are speaking of - modeled after the schoeps circuit with a fet as a phase splitter).  The result worked fine, but I did side by side listening tests, and the difference was very small... It might have been better, it wasn't worse, and I think it was just as likely to be the capsule basket change, (I opened the mesh up).  But of course it matters what the existing circuit is (some of the chinese mics already have schoeps like phase splitter circuits in them).

The Royer LDC Tube I really liked, and was substantially different in side by side listening tests.  And in actual use, Tubes are very forgiving (of levels and such).

I point to pointed the Dorsey circuit on Radio Shack proto board.

I think there is room in the APEX 435 case for either.

Yes, my early etching was pretty bad.  I burned the board tinning it with solder paste... I am a little better at it now.

 

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