Topic: Experimental 'umbilical cable' for C460 to CKxx capsules

[groovon]

This might be an off-the-wall idea, but I've collected and/or made the parts to make 'umbilicals' for a couple of my C460s, as an experiment. (And of course without irreversably changing my beloved mics.)

But will it work?

And if so, how long a cable do you think I can get away with? It will of course be carrying a super low-level, unbalanced signal. Shielded, but will probably be quite high in capacitance, as it will be of small diameter. I'm thinking three, maybe four feet might be OK.

Whaddya reckon?

Dave

[groovon]

Right, of course. I will not go too small dia., or too long. Even a couple of feet extension would be useful.

[groovon]

CATV coax? Yeah, but try hiding a length of that in your hat!!

You're probably right though, I'm already thinking that even a foot or so would probably play havoc with the freq response.

Well, even a few inches of flexible extension gives the possibility of mounting the caps at an angle to the bodies, and I'm still interested in it as an experiment. (I've actually got a pair of A61 angle adaptors, but they're in storage at the moment and not accessible.)

Dave

[groovon]

Sorry to say (but as I might have guessed), this experiment was a dead loss. S/n ratio went out the window even with a short length of RG-58 RF cable. The small amount of cable capacitance was enough to suck the life out of the cap's output.

I have to put a hold on this project until I have time to make buffers or preamps and find suitable hardware. Maybe it exists somewhere. I know I'm not the only AGKer with this fantasy.

I'd welcome any other ideas, or anything you find relating to this topic. Especially of the DIY sort. Please post links(!)

PS - Ha-ha! I wrote this before I ever heard of the 'AKG Active Project'. All I can say is, Good Luck y'all!

Cheers
Dave

[Walstib62]

What parts did you get? Are you using threaded tubing to attach to the caps?

[groovon]

No, apart from the 1mm gold-plated pins it's all pretty makeshift so far. First experiment I tried 2 feet of RG-58 coax through ground-down plastic wine corks, the shield sandwiched against the cap threads by the corks. Lost most of the cap's signal through cable capacitance! Verdict: naked mic capsules need a buffer/impedance converter to drive a cable. But we already knew that, right? 

Dave

[Walstib62]

Yep. Gotta have the FET circuit right there at the cap. Theoretically, any condensor mic could have this type of cable.

[groovon]

Yes, 'theoretically'!

There is much wishful thinking going on on this subject! "Just stick an FET in there and Bob's yer uncle!"

Right. 'Easy' to make a CK6x cap sound like a $20 Radio Shack lapel mic.

Schoeps, AKG spend millions on R & D and have reputations to consider. They don't allow anything out that will sound like crap. So maybe there's a reason why AKG C460B/ULS system mics are the way they are, without 'active (true condenser) caps'. I'm just sayin'.

The reality is, even from a skilled amateur's workbench, it will not happen without some loss of signal-to-noise ratio and degradation or change in quality. Even the high-end R&D'd-up-the-wazoo remote/active caps can't be as good or as quiet as the same company's best all-of-a-piece studio mics.

It's fun trying, though... long as the wishful thinking lasts(!)

Dave  8>)

[Walstib62]

Yes, 'theoretically'!

There is much wishful thinking going on on this subject! "Just stick an FET in there and Bob's yer uncle!"

Right. 'Easy' to make a CK6x cap sound like a $20 Radio Shack lapel mic.

Schoeps, AKG spend millions on R & D and have reputations to consider. They don't allow anything out that will sound like crap. So maybe there's a reason why AKG C460B/ULS system mics are the way they are, without 'active (true condenser) caps'. I'm just sayin'.

The reality is, even from a skilled amateur's workbench, it will not happen without some loss of signal-to-noise ratio and degradation or change in quality. Even the high-end R&D'd-up-the-wazoo remote/active caps can't be as good or as quiet as the same company's best all-of-a-piece studio mics.

It's fun trying, though... long as the wishful thinking lasts(!)

Dave  8>)

I'm not sure that is totally accurate. Why would a properly designed and built active cable be inferior to a stock mic?

[Colin Liston]

Why not just buy these?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=330445464761

AKG – 2 mk46 cables and 2 ck1x cardioid capsules

[groovon]

I have already detailed the potential limitations of such a system in the other thread, so for a person who four days ago didn't understand the effect of cable capacitance on a condenser microphone capsule to lecture me as a "skilled amateur" is, to say the least, rather insulting 

Good for you. But no need to get your panties in a knot.

I don't know you from a bar of soap, and my comments weren't directed at you personally, anyway.

I've designed and built stuff from mic preamps to tube guitar amps for damn near 40 years. I doubt you could teach me much I don't/didn't already know about high-impedance circuits (unless I've forgotten it!)

Good luck
Dave (proud 'skilled amateur' audio tech for 40 years)

[groovon]

Why not just buy these?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=330445464761

AKG – 2 mk46 cables and 2 ck1x cardioid capsules

Colin - $800? Too steep for me. Aren't they electrets? Powered off the 13.5V on the contact ring in the 460 preamp, I think. I'm happy enough for now with my 460s and A61 swivels. Thanks, though.

Dave

[groovon]

No, you suggested why the experiment might not work (shunt capacitance of the cable), which I was quite well aware of else I wouldn't have been restricting the cable length to a mere ONE OR TWO FEET(!) 

Cheers!

[groovon]

Yes, 'theoretically'!

There is much wishful thinking going on on this subject! "Just stick an FET in there and Bob's yer uncle!"

Right. 'Easy' to make a CK6x cap sound like a $20 Radio Shack lapel mic.

Schoeps, AKG spend millions on R & D and have reputations to consider. They don't allow anything out that will sound like crap. So maybe there's a reason why AKG C460B/ULS system mics are the way they are, without 'active (true condenser) caps'. I'm just sayin'.

The reality is, even from a skilled amateur's workbench, it will not happen without some loss of signal-to-noise ratio and degradation or change in quality. Even the high-end R&D'd-up-the-wazoo remote/active caps can't be as good or as quiet as the same company's best all-of-a-piece studio mics.

It's fun trying, though... long as the wishful thinking lasts(!)

Dave  8>)

I'm not sure that is totally accurate. Why would a properly designed and built active cable be inferior to a stock mic?

I just meant that, all other things being equal, the best performance will be with the cap and amp as close together as possible. Schoeps himself says exactly that in his patent papers, but then adds, "in the recording of sound, it is frequently necessary to keep the use of the microphone as inconspicuous as possible", thus his remote cap idea (link below). It isn't to increase audio fidelity that we want this, it's purely for convenience. Not that it isn't worthwhile to try and get the best performance you can from this setup, just that it won't be as easy as some might think.

http://www.wikipatents.com/US-Patent-4002859/multi-mode-electrostatic-microphone-construction/Page-5

(thanks to mshilarious, I believe, for the link.)

Cheers
Dave

[groovon]

You're still telling me what I more or less already knew, and insisting I didn't know it. One can know things in theory, and still wonder what would happen in practice, perhaps bending the rules. Or maybe you're above that. The experiment was casual at best - RG-58 was what I had on hand, and another type of cable wouldn't have made the experiment 'successful'.

Please don't insult me, I'm well aware of the theory and importance of impedance matching, and have been since I was about 16 years old. This particular case is an extreme one though, and quite possibly you have more experience with Gigohm-range circuits than I've had. There you go, happy now?

Good luck with the project

(BTW, I did not 'forecast doom and gloom' on the project, I just noted that a lot of people posting on it had too-simplistic ideas about how easy it would be to accomplish.)

Dave

[Todd R]

I would only ask that if you know as much about all this that you say, that you share your wealth of information.  That and that you acknowledge that others have tried to be helpful and that it would be nice to appreciative and not antagonistic.

I've been here long enough to know that it is hard to find someone like mshilarious, a professional microphone and mic preamp builder, impart their knowledge freely and openly.  And as is gets harder and harder for them to keep with their open exchange when over time people challenge and attack them, they eventually stop posting as much or not at all.

Not saying you're doing all this groovon, just saying it is nice to create an atmosphere that encourages an open exchange of ideas.

And to jon -- much appreciation for your willingness to share your wealth of knowledge!

[groovon]

Appreciate your input, Todd. I can only say that I never attacked or challenged anyone here, and certainly not mshilarious, either personally or professionally.
I don't know why what I wrote was taken personally.
I was merely making an observation that I thought the project would probably not be as easy to accomplish as some appear to think, especially given that, presumably, AKG itself had not thought it either worthwhile or, perhaps, achievable to an acceptable standard.

Again, I made no personal attack, and I certainly wish anyone working on the AKG active cap project the best.

Cheers
Dave

[Todd R]

Right on Dave, thanks.  Just hoping to keep the good ideas flowing!

[groovon]

No problem!

[Chuck]

I'm just happy that there is some interest in the AKG Actives project again. 

[Walstib62]

A buddy of mine in Tampa had a set for his AKG's that sounded great. I don't remember what model mics/caps they were. But I'm reasonably sure the actives were made by the Oades, but this was 16 yrs. ago. If Doug Oade has made them, but does not now, perhaps he could be persuadd to part with the info.(?)

[Walstib62]

Small-diameter cable is often ~100pF/ft, which will be not good for an unbuffered capsule.

So...Jon, is this something you would be interested in tackling?

[Chuck]

Awesome

[groovon]

If it will help, later today I can try to set up a CK61 cap on a surface plate and get you the depth measurements. Distance from top of pin to bottom of male threads I think is what you need, right? PS - and length of threaded section too, from shoulder to edge. (I think dia. is 19mm x pitch 0.75mm.)

Do you think if you do the CAD and find a machinist who can do these in brass, that they will eventually be available for us to buy in pairs to experiment with?

Looking good. I like the idea of compact built-in connector.

Cheers
Dave

[illconditioned]

Price for the coupling with mini-XLR jack and single PFA terminated in mini-XLR plug would be about $100.

I would be happy to see you take this on.

By the way, even if you built just the board and battery box (with polarization), I would purchase a setup for my capsules (by hard wiring them).

  Richard

[johnw]

This might be a minor point, but instead of a mini-xlr, would it be possible to hard wire the cable to the PCB in the housing? The reason being that MBHO has a similar design and the stiff mini_XLR sticks out so far that it makes these harder to stealth compared to Schoeps or Neumann. The hard wired cable more like the Schoeps KC connector or CMR is softer and easier to work with. Also, if you machined the connector to have a collar the same size as the schoeps KC connector or CMR, it would work with already existing accessories.

[groovon]

If it will help, later today I can try to set up a CK61 cap on a surface plate and get you the depth measurements. Distance from top of pin to bottom of male threads I think is what you need, right? PS - and length of threaded section too, from shoulder to edge. (I think dia. is 19mm x pitch 0.75mm.)

For any machinists, here's the dimensions from one of my CK61 caps, relevant to mounting it in a threaded adaptor:

Length of the threaded portion, from shoulder to bottom edge, is 0.143"

Inside depth, from surface of plastic spacer (effectively level with the base of the center pin) to bottom edge, is 0.195"

Tip of center pin protrudes from bottom edge by 0.012"

Thread appears to be nominally 19mm x 0.75mm pitch. Actual O.D. measures 18.85mm.

(Measurements are from CK61 cap serial no. 8158. Other caps may vary slightly.)

[groovon]

PCB design, I still might need to cram a couple more components on the head amp (round PCB), but the goal there is to keep stuff away from the input so as to avoid stray capacitance . . . I'll be testing the head amp circuit later today, see if I can dial in the right gain/current/noise/distortion sweet spot.

Somebody wanna measure a capsule's capacitance for me    I'm going with 22pF, should be close enough.

Hi ms - I would be happy to, but don't have the setup for it at the moment as most of my test gear is in storage. It's probably in AKG specs somewhere.
 
BTW, I measured 13.55 volts (w/ Fluke 8050A) on the bias ring with the mic body powered from a DA-P1, if that helps any.

PCBs looking good.

Cheers

[Chuck]

I can donate a malfunctioning AKG CK-61 capsule if needed.

[NOLAfishwater]

I can contact the machine shop I dealt with in the past regarding making the connectors out of brass. Once you get all the measurements for the threading, I think tonedeaf made a cad drawing of housing with no threads.

[Todd R]

Great to see this moving along like this.

Don't mean to derail the work on the AKG front so I hate to ask -- but is there any chance this can also be done for the Gefell m20/m21 capsules?  Looks like the circuitry is meant to be universal, any thoughts on how much of a market is needed to do the machining for the company-specific capsules?

The Gefells are also a 21mm diameter mic, so hopefully besides the threading and specific dimensions on the connector, the circuitry could fit in similar-dimension collette.

[Roger Gustavsson]

And why not one suitable for the Primo EM-21 and EM-23 electret capsules? Same dia, 21 mm. Low noise with a suitable output circuit, not the one shown in the document.

http://www.twin-x.com/groupdiy/albums/userpics/EM21.pdf
http://www.twin-x.com/groupdiy/albums/userpics/EM23~0.pdf


Roger

[Roger Gustavsson]

This might be a minor point, but instead of a mini-xlr, would it be possible to hard wire the cable to the PCB in the housing? The reason being that MBHO has a similar design and the stiff mini_XLR sticks out so far that it makes these harder to stealth compared to Schoeps or Neumann. The hard wired cable more like the Schoeps KC connector or CMR is softer and easier to work with. Also, if you machined the connector to have a collar the same size as the schoeps KC connector or CMR, it would work with already existing accessories.

You can use one of these.

[johnw]

What are those?

[groovon]

The second one looks like a stainless steel weatherproof cable gland, the first one is a plastic bushing. (I don't know the brands, if that's what you meant.)
 
I think a rubber grommet/boot or or other kind of flexible strain relief would work better.

[johnw]

I see.

What I was suggesting is to machine the back end of the capsule connector down to a small diameter collar that a fixed cable would exit from. You could put a rubber heat shrink sleeve over the cable to protect it and isolate it at the solder points and it would also provide some strain relief. That is what the Schoeps KC cables do/look like. If I recall, that is also what the JKlabs cables looked like. The point is, if the brass/aluminum housing for the electronics is machined down to the same diameter as the Schoeps, you could use these with the accessories that are made by Schoeps.

You can kind of see what I'm talking about on the far right side of the screen here


If you instead use a mini-xlr female adapter inside the housing, the male mini-xlr cable sticks out almost the same length as the housing. The length of the housing plus the rigid mini-xlr makes these harder to stealth with. This is the same problem (IMO) with the MBHO mics.

Either way, it's nice to see this getting some movement.

[Roger Gustavsson]

The pictures above show some cable glands available from Conrad in Europe. The one on top have 10 mm thread and accepts cables with dia 5-6.8 mm. The weatherproof type have threads of M6 (2-3 mm dia cable) or M8 (3.5-5.5 mm dia cable).

The Neutrik nanoCON connectors are shorter than mini-XLR (or tiny-XLR).



Here some more strain relief products:







http://www.heyco.com/products/thumb_03.html

http://www.sealcon.net/str_domflex_ny_metric.htm

[Roger Gustavsson]

What I was suggesting is to machine the back end of the capsule connector down to a small diameter collar that a fixed cable would exit from. You could put a rubber heat shrink sleeve over the cable to protect it and isolate it at the solder points and it would also provide some strain relief. That is what the Schoeps KC cables do/look like. If I recall, that is also what the JKlabs cables looked like. The point is, if the brass/aluminum housing for the electronics is machined down to the same diameter as the Schoeps, you could use these with the accessories that are made by Schoeps.

We all know the pricing of stuff with Schoeps written on it....

[Colin Liston]

Another set here:

http://taperssection.com/index.php?topic=94757.0

[NOLAfishwater]

What I was suggesting is to machine the back end of the capsule connector down to a small diameter collar that a fixed cable would exit from. You could put a rubber heat shrink sleeve over the cable to protect it and isolate it at the solder points and it would also provide some strain relief. That is what the Schoeps KC cables do/look like. If I recall, that is also what the JKlabs cables looked like. The point is, if the brass/aluminum housing for the electronics is machined down to the same diameter as the Schoeps, you could use these with the accessories that are made by Schoeps.

We all know the pricing of stuff with Schoeps written on it....

I think he was referring to mounts like I make which are much more affordable than the actual schoeps branded accessories. However you could also use the rycote invision mounts with them as well. he was suggesting that they the new connectors be compatible with currently offered mounting solutions.

[johnw]

^ Exactly

$50 for a bar that will hold the mics firmly in a fixed pattern and eliminate the guesswork is a pretty popular choice around here. Plus the Schoeps SG clips are only $20 each or so. Now the SGM ones are a bit pricey...