DIY M50 capsule

[aazaa]

Which circuit did you use for this?

DC/DC converter is a modified Schoeps circuit.

Amplifier is a self-designed circuit with BC550C on top of a BF256B fet.
Collector of the BC550C is connected to the UTM transformer with 1 µF.

I have built this circuit several times in a 107 body with correction for a C12 capsule.

 

[k brown]

I just discovered that the backplate holes don't need to be sealed with epoxy, or other, to convert to omni.

Once the center terminal is unscrewed and the rear backplate and main backplate are separated, just remove the small washer/spacer, then put the two backplates together such that their holes don't line up; there is one position where none of the rear plate's holes will align with those in the main plate.

Thus, the holes in the rear backlate don't need to be glued shut, and if the washer is retained, the capsule can be harmlessly returned to cardioid, if so desired.

 

[k brown]

Here is a Takstar CM-60 capsule with grille cut off, leaving only about a 1/16" lip for retaining; filed smooth. I trimmed just enough off the edge of the mesh disc that it could be re-installed.

Shown mounted on a CM-63.

Gotta say, it's kinda sounding better than my Rode NT-45O (they have slightly less top-lift), which unlike the capsule on the Rode TF-5, is not constructed like these Takstars; it is in fact the same basic design as the Behringer B-5 capsule, except for having the honeycomb plate in front of the diaphragm that the Behringers lack. This could explain why the B-5 omni capsule sounds so much better than the cardioid; the more sophisticated backplate design of the Takstar and TF-5 capsules is important for a good-sounding cardioid; being much simpler, omnis don't require this.

The backplate change is probably one of the main things Tony Faulkner suggested for the TF-5.

Thanks yet again to @kingkorg for discovering what wonderful omnis these make.

Got a couple of 40mm hardwood APEs I can slip onto these when I need to go "M 50" with 'em.

 

[k brown]

A bit of an aside - I had a couple of Rode NT-45O go bad on me (still a bit of a mystery there), so I put their honeycomb-fronted diaphragms into a couple of Behringer B-5 capsules.

Upgrade!

 

[kingkorg]

I still use couple of those first capsules with black balls, they are great sounding mics. I highly recommend trying this out. Awesome stuff @k brown

 

[thomasdf]

@kingkorg I am curious about these black balls, because I've been thinking of using such a gizmo on my DIY 84s, in order to make them omni, or at least experiment with this. The link is dead : were these just regular rubber balls, or already drilled ?

 

[Murdock]

@kingkorg I am curious about these black balls, because I've been thinking of using such a gizmo on my DIY 84s, in order to make them omni, or at least experiment with this. The link is dead : were these just regular rubber balls, or already drilled ?

I’m not kingkorg, but I don’t think it will sound any good. You can’t turn cardioid mics in to Omni by just blocking the rear vents. I mean technically it kinda works but it probably will sound really weird.
If you would block the holes right at the backplate it maybe sound kinda decent but I would imagine that the cavity behind it makes a mess with frequency response.
Also as an APE you normally want a hard surface, not a soft rubber ball although it seems to work for Kingkorg. Would be interesting how different it sounds.
If you know someone with a 3d printer this should be fairly easy to print.

 

[thomasdf]

Yeah, I've even considered making it from plexiglass with a CNC, easy for sure. Plus it looks cool haha
True about the freq response, it actually makes sense.

 

[molke]

You can’t turn cardioid mics in to Omni by just blocking the rear vents. I mean technically it kinda works but it probably will sound really weird.

If I compare this with the later type KK50, described here (and already mentioned at the beginning of the thread), I don’t see much difference. I’d be more concerned about the higher diaphragm tension that is usually required for omnis.

If you would block the holes right at the backplate it maybe sound kinda decent but I would imagine that the cavity behind it makes a mess with frequency response.

Maybe I’m missing something, but what kind of cavity would result by blocking the holes (just rotating the secondary backplate appropriately)?

 

[Mihobro]

Your experiments are interesting. The years I spent on the scoring stage bring to mind a few things.
First, Neumann made a FET version of the M50, it was called the TLM150 and we used them on the boy's chorus in "An Interveiw with a Vampire" among others as a M50 substitute but, we preferred to use one of the maybe two sets of M50 tubes that were available for hire in Manhattan during the 90's.. But most M50's were tube electronics only.
Except....
I remember when Decca came in. (I think it was John Locke at the helm) Their engineers had grown tired of servicing the tubes, so they had converted (some say butchered) their famous M50s' by swapping out the tubes for FET circuits and still made many fine orchestral recordings, (I think this was in the 90's) and including some of the early 24bit 192K recordings.
M50's used a nickel plated capsule, not gold, as well a perspex (something like lucite) plastic sphere.
When coupled with an appropriate preamp, like an Avalon M5, a good acoustic space, and the best studio musicians, it was an integral part of a very sweet, familiar orchestral sound that was so warm and pleasing, Which everyone grew up with in film and orchestral recordings. Ben Hur, Lawrence of Arabia, Raiders of the Lost Ark, Star Wars. etc warm, very warm compared to the cold sterile first generation digital recordings.

 

[Murdock]

If I compare this with the later type KK50, described here (and already mentioned at the beginning of the thread), I don’t see much difference. I’d be more concerned about the higher diaphragm tension that is usually required for omnis.

Maybe I’m missing something, but what kind of cavity would result by blocking the holes (just rotating the secondary backplate appropriately)?

About what capsule are we talking? If about an original kk84 I would be hesitant to disassemble the capsule. It’s notoriously hard to get it back together “correctly”. So "just" turning the secondary backplate is not really an option in my opinion.
My train of thought is that the air cavity between the capsule and the mic body (without modifying the backplate but just blocking the side vents with the sphere) would mess with the compliance and damping of the capsule. But maybe I'm wrong. Happend a lot of times already

I think there are more differences between an Omni and cardioid capsule than just diaphragm tension.

But forget all I said. Experimenting is the best way to gain experience. So keep us updated how it sounds!

 

[k brown]

About what capsule are we talking? If about an original kk84 I would be hesitant to disassemble the capsule. It’s notoriously hard to get it back together “correctly”. So "just" turning the secondary backplate is not really an option in my opinion.
My train of thought is that the air cavity between the capsule and the mic body (without modifying the backplate but just blocking the side vents with the sphere) would mess with the compliance and damping of the capsule. But maybe I'm wrong. Happend a lot of times already

I think there are more differences between an Omni and cardioid capsule than just diaphragm tension.

But forget all I said. Experimenting is the best way to gain experience. So keep us updated how it sounds!

When here and on other threads we speak of blocking the rear vents, it's only the actual capsule's backplate holes that are blocked; just covering up all the capsule housing's side slots never works since it creates a resonant volume of trapped air behind the diaphragm. With many cardioid SDCs, what can work is taping over a small percentage of the side slots which will open the pattern to subcardioid or 'open cardioid'.

A quote from Classical engineer Tony Faulkner: "I use Rode NT6's from time to time and I stick some insulating tape around the bottommost opening of the back chamber of the capsule. This is the sort of thing I would hesitate to publish on Gearslutz because the world and his wife would give me a hard time, but it is worth trying. The Schoeps MK5 capsule is switchable mechanically between cardioid and omni and this is achieved by shutting off the rear chamber when you want omni - I figured you could try something similar with sticky tape to achieve an intermediate pattern."

A very famous example of a capsule that successfully shifts from cardioid to omni by simply closing it's rear vents (and obviously not changing diaphragm tension) is the Sony C-37A. Another is the Schoeps MK 5, though it's construction is much more complex, but part of that is not altering the diaphragm's tension. It works so well in omni that famed Classical engineer Marc Aubort based his entire carreer on it's predecessor, the M 221B in omni mode.

 

[k brown]

Yeah, I've even considered making it from plexiglass with a CNC, easy for sure. Plus it looks cool haha
True about the freq response, it actually makes sense.

The first mic made (1950) with with an SDC omni capsule mounted in a small sphere was the Neumann M 50 referred to in this thread, and used exactly that material.

 

[Murdock]

When here and on other threads we speak of blocking the rear vents, it's only the actual capsule's backplate holes that are blocked; just covering up the capsule housing's side slots never works since it creates a resonant volume of trapped air behind the diaphragm. With many cardioid SDCs, what can work is taping over a small percentage of the side slots which will open the pattern to subcardioid or 'open cardioid'.

A very famous example of a capsule that successfully shifs from cardioid to omni by simply closing it's rear vents (and obviously not changing diaphragm tension) is the Sony C-37A. Another is the Schoeps M221B, though it's construction is much more complex, but part of that is not altering the diaphragm's tension. It worked so well in omni that famed Classical engineer Marc Aubort based his entire carreer on the 221B in omni mode.

Maybe there is a missunderstanding but that's exactly what I meant when I said I wouldn't recommend it.
I just replied to Thomasdf post where he mentioned using APEs to turn a KM84 style mic into omni...

@kingkorg I am curious about these black balls, because I've been thinking of using such a gizmo on my DIY 84s, in order to make them omni, or at least experiment with this. The link is dead : were these just regular rubber balls, or already drilled ?

 

[k brown]

As to materials for making the spheres (DPA calls them APE, for Acoustic Pressure Equalizer), they need be nothing more exotic or hard to work with than hardwood.

I made mine with unfinished wood drawer pulls from a crafts store https://www.joann.com/1.5in-ball-wood-knobs-8pk-by-park-lane/16910713.html (also available on Amazon https://www.amazon.com/Pinehurst-Crafts-Unfinished-Furniture-Crafting/dp/B09R6X3YK2/ref=sr_1_11?crid=2GZ8G249IXCCP&dib=eyJ2IjoiMSJ9.x876MA-8SwtSZIypJAcRj9cvA-FoGTb_cjWdLQDTH21GllUsobMsTdsFn8rGadjtw05hQOHJxap9OrEtPgG3Tk-h_zxzhN3OTPJrbkBy10uybZ3v0MYVLuavrj8UAqv6gGOq_Z0sF1rVmM8_9F3PMDQD70UWfVCKVG9ViwTNQ-8IB1b2u8nur1KjShj-yT7Tcq1Aic0vXhbJzk9xWLZLMh1XDkJlHoNN7o0Mml494XC69Uk-7x97NJXWcLw-CM1b2D4ZKAPeL28AsKoLXrFlNcoWhmppFsOrAjtv8Oa1Jxo.X4_KpcdDNCT5DY1XIDn1sqN3YNYMruIGKmMAVKrRhfo&dib_tag=se&keywords=wood+cabinet+ball+knobs&qid=1723136515&sprefix=wood+cabinet+ball+knobs,aps,182&sr=8-11); after drilling, sanded smooth and painted. Indeed Josephson Engineering used to make APEs for use with their SDCs, and used hardwood.

Mine are made to slip fit over any 20mm SDC mic body. Drilled with Forstner bit, then lined with 1/16" closed-cell craft foam for snug friction fit.

These are 1 1/2" knobs, so 37.5mm, not 40mm, but the difference is nearly impossible to hear; just means the boost starts a very slightly higher freq. You can see below how small the difference is going all the way down to 30mm.

The exact frequency effects of APEs are of secondary importance; their main function is to cause a slowly increasing directionality starting about 1.5kHz, becoming approximately supercardioid in the top octave. It's this frequency-dependent directionality that allows the Decca Tree to work it's magic.

________

Not surprisingly, my username on Gearspace is "M50k".

 

[k brown]

Maybe there is a missunderstanding but that's exactly what I meant when I said I wouldn't recommend it.
I just replied to Thomasdf post where he mentioned using APEs to turn a KM84 style mic into omni...

Wasn't 'correcting' you, just verifying and fleshing out why that doesn't work.

 

[kingkorg]

@kingkorg I am curious about these black balls, because I've been thinking of using such a gizmo on my DIY 84s, in order to make them omni, or at least experiment with this. The link is dead : were these just regular rubber balls, or already drilled ?

I'll try to dig up the link, the it can be whatever type of solid plastic, or rubber. However it you want to do it with regular SDC you need omni capsules, if you just put it on cardioid , you are left with resonant cavity behind the capsule and it will sound really bad, and not work as intended.

 

[kingkorg]

Here it is:

https://www.amazon.com/Qtqgoitem-Plastic-Round-Lever-Black/dp/B0BHRTSM7G

 

[k brown]

Here it is:

https://www.amazon.com/Qtqgoitem-Plastic-Round-Lever-Black/dp/B0BHRTSM7G

Unfortunately showing as currently unavailable.

 

[Murdock]

I don’t know about elsewhere but here in Germany these have a dedicated DIN norm (DIN 319) so you can get them in a lot of places also with different diameter.