Apex 460

[PhilGood]

There's 2 ways of dealing with it. You can put a small capacitor (preferably a polystyrene, 2pF to 100pF from the anode to grid, or you can replace the capsule to a K47 style as Michael suggests. Relieves all the sibilance problems and sounds very silky and fat.

I happen to have access to a good supply of very good sounding K47 style capsules That I will sell for $150 each. $200 installed. They are just like Peluso's, but without the sales BS. So far I have installed 8 of them in my own mics and others and feel the sound is phenomenal! Supply is limited in quantity, but the sound improvement is out of this world.

PM me for more info.

 

[MichaelJoly]

The stock headbasket has issues that can be dealt with also. The top ring, side bars and capsule baseplate create coloration due to reflection between these parts, the capsule diaphragm and the headbasket mesh.

I've been working toward a solution by modifying the headbasket and capsule mount. In the pic below you can see the new 10mm taller "Floating Dome" headbasket without side bars to reduce reflection coloration and MJE-K47 capsule sitting in a saddle 6mm lower than stock. Not visible is a conical diffuser installed below the capsule.

 

[PhilGood]

I like the more open grill mesh!

 

[MichaelJoly]

Me too! But here's a kicker - this is the first mic I've come across that needs a second layer of mesh to sheild from AC hum. I've yet to get my head around the electromagnetic gobbledygook to explain why. All I know is a very open, single layer grille (like the C12 below) in the Apex 460 is very postition-sensitive regarding AC line hum.

 

[PhilGood]

I just pulled out the inner 2 laters and left the stock screen.

Maybe it would help to put a few beads of conductive silver epoxy between the grill and body, or are you soldering it?

 

[MichaelJoly]

The issue is not the electrical contact between the mesh and frame - I use silver epoxy for conductivity and five minute epoxy for strength - measures 0 Ohms between the grille and frame. What are you using for a capsule in your mic with the single layer grille? What happens when you bring the mic near a source of AC field like a power cord, transformer or house wiring?

 

[PhilGood]

I have a Peluso CEK12 style in one and an AKG Teflon in the other. I'll have to test later and see if I get the same problem.

Wait, isn't the other floating dome mode you do for the Oktava 319, or are there others? Doesn't the Oktava have some kind of a plastic backplate with sheet metal? I know the CK12 is like 4 inner plates. I wonder if such a thick solid brass backplate has anything to do with it?

 

[MichaelJoly]

I do floating dome, single layer grilles in a number of cardioid-only and mulitipatern mics - Oktava, MXL, CAD, Nady...all of them dead quiet with regard to AC hum pickup. I've been doing a lot of CAD GXL-3000 FET mics with my MJE-K47 capsule - perfectly hum free with a single layer grille.

Gotta love a curveball thrown once in a while.

 

[PhilGood]

He batta batta batta su-WING batta!

 

[MichaelJoly]

LOL. yeah, how 'bout that Mark Buehrle

 

[dgatwood]

Is it possible that they didn't ground the frame? I mean, it should be a Faraday cage at 60 Hz for all practical purposes, but it's nowhere near a single skin depth in thickness, so if it isn't grounded, it's not doing much. Worth a shot. Maybe they assumed the mic cable would jumper pin 1 to the ground tab/case. Oh, wait, this is a tube mic. Maybe they just screwed up.

 

[MichaelJoly]

The grille and frame are well-grounded.

Just had a thought regarding AC hum pickup with the new headbasket - to make a new, taller headbasket I used some heavy gauge wire mesh I have on hand. This stuff has a very high open area percentage - more open than the wire mesh in the stock mic. Its entirely possible that pulling out the two inner layers of wire mesh from the stock headbasket and leaving the outer layer intact will provide adequate AC shielding (I never tried this, just immediately rebuilt the headbasket using the new taller grille mesh).

I'm pretty sure this is the answer because I used some of this same wire mesh during the early development of my Ultimate SDC Mod and found it did not provide adequate AC shielding. In that mod I switched to a slighter tighter grille mesh with a smaller open area percentage to achieve excellent AC shielding.

Another case of engineering tradeoffs at work.

 

[dgatwood]

I'm having a hard time accepting the size of the holes being a problem. I have an SDC where I accidentally shredded a third of the mesh while modding the capsule. It now has no mesh with a 1/2" aperture and only a little over 1/8" of tubing sticking out beyond the diaphragm. I still don't get any AC hum....

The wavelength of 60 Hz is measured in miles, so you should be able to literally rip the entire end cap off, and if the sizes of the mesh extend past the capsule, you should get no hum. So what you're describing seems way beyond weird to me.

Are you sure this outer mesh isn't plastic or fiberglass with conductive paint?

 

[MichaelJoly]

The diaphragm of an SDC mic is at ground potential so it shields the high impedance backplate. I've got some SDCs I run without any grille mesh for maximum openness - but the diaphragm is completely unprotected from damage. This is not acceptable as a commercial mod, but it does illustrate the point you've made that an SDC really doesn't need any grille mesh for RF or AC hum reasons - only for protection.

 

[PhilGood]

I'm building another mic using an MXL 960. I'm going a different route this time and ripped out the inner mesh and I'm going to replace it, but I'm borrowing on David Bock's idea he used on the e49. The thinner mesh is in the shape of the flat surface of the m49, u67, u87 etc, inside a cylinder. The sound is pretty open that way and also causes reflection to arrive staggered so there are no standing waves. Also better off axis response.

 

[MichaelJoly]

Yeah that's good idea - keeps the shielding advantage of two layers but offers a more complex acoustical signature. Probably is more effective at reducing plosives too with the air gap between layers.

 

[dgatwood]

The diaphragm of an SDC mic is at ground potential so it shields the high impedance backplate.

Makes sense.

 

[BudgetMC]

Hmmmm... I've pulled the inner two layers of mesh out of my TMC1200s, but haven't had any hum problems. Maybe I'm just in fairly quiet space...

 

[MichaelJoly]

That's good to hear.

I'm convinced the heavy guage mesh I used to make the taller headbasket has greater open area percentage than the stock grille. I've added a very fine mesh on the inside and its dead quiet now.

Your results suggest it should be possible to make a taller headbasket with same-as-stock grille mesh guage and not have hum. But the downside of using the stock guage is that its not quite stiff enough to support an extended headbasket without undesirable flex.

I'll probably stick with the very open, heavier gauge grille for strength and use an high open area fine mesh on the inside.

 

[dainja]

I ordered a Cinemag 2480 transformer, Mundorf MKP 1 uf/250V cap, Black Gate 100uf / 16V cap and Electro Harmonix 12AY7/6072A tube.

Hopefully that gets me started. If this yields a considerable difference in sound, I will buy a CEK12 capsule and possibly mod some other capacitors/power supply.


*excited*