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Author Topic: What's an active cable comprised of????  (Read 11537 times)

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Offline Evil Taper

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What's an active cable comprised of????
« on: January 24, 2006, 04:21:41 AM »
If one were to build their own active microphone kit, how would they build the cables?  In the photos of the JK Labs active setup for the MGs the element that connects to the capsule appears to be identical to the one on the actual microphone bodies.  What is the body at the end of the cable actually made of?  It looks like it's smaller than the capsule even so I don't think there's too much inside of it.  So what parts would you need to build a similiar set of cables?  If the cables can be figured out I have a friend who is willing to build MG active setups for the community (he's a certified electronics specialist).  Any info regarding the subject is desired and very much appreciated.  Thanks! 
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Offline Nick's Picks

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Re: What's an active cable comprised of????
« Reply #1 on: January 24, 2006, 07:39:10 AM »
I cant give specifics, as I dont know them..
but from my understanding the "active" part of an active capsule is comprised of a preamp stage that will boost the signal from the the diaphragm so that it is strong enough to run the lenth of wire between the cap and the actual preamp assembly in the mic body itself.
w/o the cable, the cap screws directly on to the preamp...which is boosting the signal to a mic level (or line level in some cases).

so,. the goal would be to build this circuitry as quiet as possible, introducing NOTHING to the signal comeing from the cap, but enough of a boost to drive the signal down 3-5m of cable.

Offline Evil Taper

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Re: What's an active cable comprised of????
« Reply #2 on: January 24, 2006, 08:20:17 AM »
oh, well that's simple enough of a problem to solve.  this stuff can't be ridiculously complicated or demanding of special machinery and such since the models out there now are just DIY projects made by electronics folks.  I'm willing to bet that you can get everything you need to make this stuff (except the actual piece that mates to the capsule) from an electronics catalog.  i'm gonna have a prototype built once this active cable stuff is figured out and i'll see how it actually sounds.  not really sure how much different the circuitry would have to be for AKG/Schoeps/Neumann caps but it's possible for sure.  the final goal is to have an active setup that's not "spitty" ... just transparent and accurate.  but first things first!
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Offline JasonSobel

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Re: What's an active cable comprised of????
« Reply #3 on: January 24, 2006, 09:09:51 AM »
well, the way that the JK Labs boxes work (and also the nbox, for that matter), is that the active cables go straight to the box, and the mic bodies get skipped altogether.  Because of that, you've also got to figure out a way to power the mic capsules.  Tim's JK Labs box for the MG's just acts as "bodies", in that, you need to feed the JK Labs box phantom power, and then the box powers the capsules.  The nbox, and some other JK Labs boxes, are battery powered, and provide power to the mic caps directly.

I know that Nick (the creator of the nbox), is working on a similar one for MG caps (and AKG, I think).  I don't know how much time he's already put in, or how much longer it'll be until we can buy MG nbox's, but just something to think about.  It certainly can be done, and I agree with you that just about all the electronic components are pretty standard stuff that one could buy from a catalog (the exception being the mounting thing that the caps actually screw onto, as you noted).

So, to sum up, in addition to providing some sort of amplification so that the signal can be sent down a wire, the box that the active cables attach to also has to be able to somehow provide the optimum voltage to the capsules.  as to what the optimum voltage is for the MG's, I'm not sure.  but it is definitely something else that must be done and considered in the design.  Please let us know how it all goes...

Offline Nick's Picks

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Re: What's an active cable comprised of????
« Reply #4 on: January 24, 2006, 09:17:43 AM »
but thats only if you intend to skip the mic body entirely.  that would be nice and all...but I have to think that the factory preamp will sound better than any DIY effort as they have many years and much resources all ready thrown at this to acquire "the sound" that they want the mics to have.

building something like the nbox requires the active cable assembly, and then a preamp as well, as Jason points out.

Offline JasonSobel

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Re: What's an active cable comprised of????
« Reply #5 on: January 24, 2006, 09:35:39 AM »
well, it's sort of interesting.  Nick, in your first post, you mention that the active cables would need a small pre-amp circuitry to boost the signal to make it suitable to send down the wire.  If you put the pre-amp circuitry in the active cable portion, than you wouldn't need a seperate pre-amp section in the seperate box.

based on my fairly limited understanding of it all, MG has stated that it's not feasable to create active cables to put between the caps and the mic bodies, unfortunately.  I have to think that if MG could reasonably do it, they would do make such a product.  I agree with you that the mic bodies would sound the better than any DIY effort, but my guess is that it would be a lot easier to create active cables that work with a seperate box than to create active cables that work between the caps and the mic bodies.  but, again, I lack the full understanding of the electronic circuits involved.

on the other hand, Tim claims to not hear any difference between the JK Labs setup that he currently runs and the MG mic bodies that he used to run.  I'd love to get a chance to run a side by side comparison with him sometime, just not sure when or if that'll ever happen.

and, also, just one more thing I'd like to add, you're friend who is a "certified electronics specialist", I'm sure is able to put the circuitry together.  but because this is for high-end audio, it'll probably take a lot of trial and error to determine which components sound the best.  sure, you could put something together that works, but maybe this op-amp sounds better than that op-amp, maybe this capacitor sounds better than that capacitor.  Once you have a circuit that works, I think you should spend a good amount of time refining it and getting it to sound as best as you can. :)


Offline Evil Taper

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Re: What's an active cable comprised of????
« Reply #6 on: January 24, 2006, 09:58:27 AM »
that makes sense to me.  i was wondering where the battery plugged into the DVC thing.  so, you have to run:

Caps>actives>DVC>pre>recorder

So you'd need something like the mp2 or other stealthy phantom boxes.  You could probably actually build the phantom power into the DVC box itself, like the PPG box JK Labs made for the AT853s.  FWIW my friend said that the wiring in the DVC is sloppy and could be miniaturized with an etched circuit board to like 1/4 of the size it is now for relatively cheap.  That being done would leave plenty of room to build a small phantom powering circuit into the same size box as the current DVC.

To be fair and honest, the prices are ridiculous on the active kits selling now.  That's why I wanted to pursue other options.  I can't even post what the cost on the DVC box is because the owners would be ANGRY.  That is all.


edit:  the parts would be identical to the DVC that Tim has if it were just a replica of that piece.  The parts are identifiable via the photos even.  He was just unsure how the cables worked and what they were made with.  I wasn't even thinking of getting the mic bodies involved, just the cables>dvc>??>recorder.

and on another footnote - MG are in developement of an active kit for their mics.  The source said that they have no estimated street date (and knowing MG it's going to carry a shockingly high price tag also).
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Offline Nick's Picks

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Re: What's an active cable comprised of????
« Reply #7 on: January 24, 2006, 10:46:10 AM »
well, it's sort of interesting.  Nick, in your first post, you mention that the active cables would need a small pre-amp circuitry to boost the signal to make it suitable to send down the wire.  If you put the pre-amp circuitry in the active cable portion, than you wouldn't need a seperate pre-amp section in the seperate box.

well...yes and no..to an extent.
schoeps, neumann and MBHO all have both the "active" cable and the mic preamp at the other end.  the bost given by the active cable does not render a mic level signal.  its less than that, I would guess, or there would be no need of the mic body at all (unless of course it is needed for flavor, and poweing the capsule).  That is another step in the active cable, not only must it act as a little preamp, but it also carries power from the phantom supplied to the mic body itself.
the schoeps model that is bodyless, and DPA all have miniaturized preamp assemblies in the capsule itself.  far more complex.  and that signal is much hotter (mic level "lowZ" I believe) than the "active" signal in a standard lc3 cable for example.
That is what something like the Nbox does.  only instead of mounting it all in the end of the cable where the capsule screws on, its "downstream" in a little box.
Thats my best guess understanding any way.
fwiw...
« Last Edit: January 24, 2006, 10:48:01 AM by Nick's Picks »

Offline it-goes-to-eleven

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Re: What's an active cable comprised of????
« Reply #8 on: January 24, 2006, 01:18:20 PM »
To be fair and honest, the prices are ridiculous on the active kits selling now.  That's why I wanted to pursue other options.

I disagree.   If they were so overpriced, we'd have many more alternatives to choose from. I am a little surprised we haven't seen cheap knockoffs out of china.  They may exist but we just haven't seen them.

First question: Do you want to make recordings or make active parts?

At first glance, it seems like the cord that connects the cap to the body should be so simple and inexpensive..  I think we have all had that thought.

The amount of engineering and testing time necessary to refine the sound is significant (but is easier for some mics than others). You also need good hearing.  The people capable of doing that work can probably make quite a bit of money in their chosen field.  Copying someone else's R&D is easier but still very difficult and time consuming (and highly unethical).  At some point, you have to put a price on your time.  Sourcing the components takes a lot of time and you will likely not find the exact same components.  So you have to test what you can get and determine whether there is an impact on the sound.

Electronics aside, I have a lathe and a mill. My fab and machining skills are pretty good.  I could machine shells to match any of these caps and bodies.  Definitely not worth my time.  It only becomes worthwhile if you're going into biz on a fairly decent scale. Then you pony up the bucks and have a bunch of them made.  At that point, you only have the shells. You still don't even have the connectors or the mounts for the connectors or the electronics..

It is a simple thing to sell a product.  Supporting that product is another matter. Nick, for example, does both with the nbox.  An nbox without that support is not much of a solution. What he charges for the nbox, for example, is very fair.

But, seriously, good luck.  These are good questions. We all want cheap actives!

Offline JasonR

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Re: What's an active cable comprised of????
« Reply #9 on: January 24, 2006, 01:42:41 PM »
When I had my Schoeps KC5 active cables modified (basically cut and added 3-pin LEMO connectors) to work with the Sonosax SX-M2/LS, Bill Drucklieb at Cinemasonics did some research and drew up a rough schematic of the Schoeps cables.  His comment when delivering these to me was that he was surprised that there's "really nothing active about them", which I took to mean that there's no amplifying of signal whatsoever.  Perhaps someone with an EE can better read what this diagram means and take that comment in the proper perspective.

- Jason
Schoeps MK21,MK4,MK41,MK41V,MK8 > CMC5/Naiant Tinybox/PFAs > Sound Devices 744T, Sony PCM-M10
DPA 4060 (CS HEB) > SD 744T, M10

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Re: What's an active cable comprised of????
« Reply #10 on: January 24, 2006, 01:56:00 PM »
I Pmd spark E and Graeme. those two are definitely qualified to read that schematic.

Offline JasonR

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Re: What's an active cable comprised of????
« Reply #11 on: January 24, 2006, 02:07:49 PM »
+T Teddy!  I'm still hoping someone can come up with a simpler/smaller alternative to the SX-M2/LS that will just power the caps (no preamp necessary).  I'd love to keep my caps and cables, but not have to run bulky bodies or a preamp into the 722.  JK Labs clearly had something but...   ???

- Jason
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Offline poorlyconditioned

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Re: What's an active cable comprised of????
« Reply #12 on: January 24, 2006, 02:20:26 PM »
When I had my Schoeps KC5 active cables modified (basically cut and added 3-pin LEMO connectors) to work with the Sonosax SX-M2/LS, Bill Drucklieb at Cinemasonics did some research and drew up a rough schematic of the Schoeps cables.  His comment when delivering these to me was that he was surprised that there's "really nothing active about them", which I took to mean that there's no amplifying of signal whatsoever.  Perhaps someone with an EE can better read what this diagram means and take that comment in the proper perspective.

- Jason

I think I replied to this before.  Anyway, I think you need a machined case/connector + a FET (the "MK Capsule end") to connect to the mic capsule, a four conductor cable, and a box with a 62V power source and a standard mic body circuit (balanced low impedance cable driver).  I'm tinkering with 62V circuits for AKG CK61 caps, but I'm sure others will get there before me.

  Richard
Mics: Sennheiser MKE2002 (dummy head), Studio Projects C4, AT825 (unmodded), AT822 franken mic (x2), AT853(hc,c,sc,o), Senn. MKE2, Senn MKE40, Shure MX183/5, CA Cards, homebrew Panasonic and Transsound capsules.
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Offline JasonR

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Re: What's an active cable comprised of????
« Reply #13 on: January 24, 2006, 02:55:47 PM »
I think I replied to this before.  Anyway, I think you need a machined case/connector + a FET (the "MK Capsule end") to connect to the mic capsule, a four conductor cable, and a box with a 62V power source and a standard mic body circuit (balanced low impedance cable driver).  I'm tinkering with 62V circuits for AKG CK61 caps, but I'm sure others will get there before me.
Thanks, Richard.  Since I already have the MK capsule end and the cable (currently terminating with 3-pin LEMO connectors), then "all" I'd need is everything else.  ;)  If as someone asserted previously the Sonsoax only powers the caps with 48 volts, I wonder how much simpler it would be to build a box that's powered via 48V phantom and runs the caps at 'only' 48v, along with whatever circuitry is needed to accomplish that.  Or even just running them off of 9 volt batteries would be fine.

- Jason
Schoeps MK21,MK4,MK41,MK41V,MK8 > CMC5/Naiant Tinybox/PFAs > Sound Devices 744T, Sony PCM-M10
DPA 4060 (CS HEB) > SD 744T, M10

Offline SparkE!

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Re: What's an active cable comprised of????
« Reply #14 on: January 24, 2006, 02:57:26 PM »
When I had my Schoeps KC5 active cables modified (basically cut and added 3-pin LEMO connectors) to work with the Sonosax SX-M2/LS, Bill Drucklieb at Cinemasonics did some research and drew up a rough schematic of the Schoeps cables.  His comment when delivering these to me was that he was surprised that there's "really nothing active about them", which I took to mean that there's no amplifying of signal whatsoever.  Perhaps someone with an EE can better read what this diagram means and take that comment in the proper perspective.

- Jason

Jason, it appears that there's a JFET amp in the capsule, so my guess is that you provide a low DC voltage bias to the capsule through the cable from the CMC pre end of the cable.  That way, you provide phantom power to the CMC module and it regulates it down to something that's usable by the JFET amp.  It appears that the capsule's diaphragm is polarized by a voltage that comes across on Lemo pin 2 and I'd guess that it's a much higher voltage.  Of course, I'm guessing on all of this because I can't see what's on the other side of the interface to the CMC box.

I will say that it appears to me that R3 should be connected on the left side of C2 instead of the right side.  If the drawing shown is actually correct, then the stuff I said in the previous paragraph is wrong.

Anyway, Bill's comment about the cable not being active is correct.   The cable contains no active or passive components other than the cable itself.  The reason it's called active is that the adapter that goes on the MK capsule end contains a JFET amp that's not normally there when you attach the MK capsule directly to the CMC end.  It's the same type of amp structure that's normally used in  back electret mics.  So, it becomes an active cable only by virtue of the fact that the MK capsule adapter has some active circuitry in it.
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