Topic: The AKG Active Project - 2

[Church-Audio]

Let me see if i have this right,

the schoeps cables have a buffer in the line to boost the signal to make up for the loss that the cable creates, while the akg actives that i have and all of the jklabs/nbox solutions use no circuitry in the line to boost the signal. 

my cables use no extra circuitry whatsoever to form the bridge between cap and body, while jklabs/nbox contains some extra circuitry not present in the body that it is replacing. 

It seems as though the 480s don't need any extra circuitry judging from what is inside the A61 swivel at least for a very short run, do we know if the goosenecks have any circuitry inside them? 

Not quite -- the neumann km100 series (eg, km140s), the schoeps, and the jklabs "active" solution for the ck6x caps (480 caps) all use active electronics in the head of the active cables where the capsules attach to.  The nbox solution, which uses the schoeps active cables, therefore also contains active electronics.  The active electronics act as a buffer, but do not really "boost" the signal.

The jklabs box (as opposed to the jklabs active cables) and the nbox both include electronics that replace the electronics in the mic bodies.

Your "active" cables for the akg blueline series are not true active cables in the sense that they do not contain active electronics.  These cables do not require active electronics because the blueline series are pre-polarized (aka electret) mics -- they are not true condensor mics that require external biasing.

The AKG gooseneck for the 460/480s, which doesn't contain active electronics, does not necessarily mean that you can have "active" cables without electronics since the distances involved are so short.

I think that summarizes everything.

The main stumbling block is the capacitance of the cable. It causes a capacitive load on the capsule that reduces its bass response and output and increases the noise floor. We need to find super high quality super low capacitance cable and then runs of up to 3 feet "might" be possible.. Even with good cable there might be some loss of low frequency and of output possibly resulting in a increased signal to noise ratio and loss of low end. But until someone sends me a microphone with a swivel I cant test my theory....

The reason why there is active circuitry is simple. They use a FET to isolate the capsule from the wire and eliminate the problems associated with directly loading a true capacitor microphone and reducing its performance. That's not to say it cant be done because we know AKG has made 3 foot extension wands with no circuitry in them, there is a huge possibility that it can be done.. I think it can be done but with out a mic to test and try I cant help you guys.. I have the test equipment to show if there are any differences between the cable and the direct mic/body mount.


Chris

[Nick's Picks]

i'll have those mics w/swivels come mid month.  then we'll move forward

[Thomas]

i'll have those mics w/swivels come mid month.  then we'll move forward

Are you looking at building cables, or are you trying to immitate the schoeps ortf bar?

I think the ortf bar would be a much better option than building passive cables of a very short length.  It wouldn't be too hard to mount the electronics from the inside of the 480s inside a tube, then wire the xlrs from the bodies to a 5 pin xlr socket.



As far as making active cables, does the buffer circuit function to keep the bias accross the cap at a constant value?  and how do the other brands of active cables power this circuit?, do they pull power from the signal?  every analog circuit we ever talked about in school had an external power supply.

[poorlyconditioned]

i'll have those mics w/swivels come mid month.  then we'll move forward

Are you looking at building cables, or are you trying to immitate the schoeps ortf bar?

I think the ortf bar would be a much better option than building passive cables of a very short length.  It wouldn't be too hard to mount the electronics from the inside of the 480s inside a tube, then wire the xlrs from the bodies to a 5 pin xlr socket.



As far as making active cables, does the buffer circuit function to keep the bias accross the cap at a constant value?  and how do the other brands of active cables power this circuit?, do they pull power from the signal?  every analog circuit we ever talked about in school had an external power supply.

The "active" cables have a FET (field effect transistor) in the collette, right behind the capsule.  This is necessary to buffer the *very* low current signal from the mic element.  You may get a few feet without the FET, but it is then highly dependent of the extension cable.

So, the proper circuit will have a FET very close to the capsule.  You will need two additional signals: a low voltage (eg., 5-10V) source to power the FET, and a high voltage (eg., 50-60V) to polarize the capsule.  The polarization voltage is high, but very low current (theoretically zero current in fact).  So you can make this out of a bunch of alkaline batteries in series.  A voltage invertor could be used (that is what is in the 480 body), but is more complex and IMO not needed, at least in the first version.

I've built these circuits on my workbench (look for photos in the previous Actives thread), but have not yet built a prototype.  The reason is a *mechanical* one.  I need "collettes" to screw the capsules into, to connect to the center pin reliably, and to shield the small circuit (a FET and a few resistors).

My offer is the following: if someone is willing to send me (to keep!) a set of machined collettes, or a set of swivels, or anything else that will solve the mechanical problems, I will build a prototype and disclose all information I discover and allow anyone to copy/build/sell the design to others.  If I succeed, I will keep the system.  If I fail, I will return the parts to the donor.  I have already bought the capsules (a pair of CK63) and they are sitting idle on my bench, so I have contributed enough money, I don't want to buy more parts.

In the meantime, I have since decided to buy a set of Beyerdynamic actives (see the Team Beyer thread), but I am still willing to contribute to this project *in exchange for gear*.  If anyone wants to step up and donate their parts, the project will move forward.  I am also happy to help anyone else who actually builds something on their own.

No offense to others, but we don't need any more questions about this topic.  We need someone to either donate parts, or to build something.

Thanks for listening folks...

  Richard

[Thomas]

Thanks everyone for helping me out with the info, I know all of this stuff has already been discussed, and I am stumbling in here at the end of the conversation. 

[poorlyconditioned]

Thanks everyone for helping me out with the info, I know all of this stuff has already been discussed, and I am stumbling in here at the end of the conversation. 

No worries.  I'm just reminding people how we will make progress.

I think both Chris Church and I have offerred our services.  But I don't think either of us will be spending (any more!) of our own money on this.
You may not be aware of it, but *someone* (besides myself) has actually machined collettes too.  (Mine were aluminum, and I gave up partway though),  I'm not sure their status, or whether they are willing to donate.

As I said, I'm willing to help with any aspect but buying more gear.  I've hit my limit there...

  Richard

[Church-Audio]

Thanks everyone for helping me out with the info, I know all of this stuff has already been discussed, and I am stumbling in here at the end of the conversation. 

No worries.  I'm just reminding people how we will make progress.

I think both Chris Church and I have offerred our services.  But I don't think either of us will be spending (any more!) of our own money on this.
You may not be aware of it, but *someone* (besides myself) has actually machined collettes too.  (Mine were aluminum, and I gave up partway though),  I'm not sure their status, or whether they are willing to donate.

As I said, I'm willing to help with any aspect but buying more gear.  I've hit my limit there...

  Richard

I did not spend any money/time on this not like Richard has... That's for sure.. I think Richard is right about the buffer you need a way to get over the cables capacitance. But the experimenter in me would still like to try 3 feet. I mean if the AKG wand was three feet the only difference is a 100% shield we can get dam close to that with a good braided shield/foil. I think like Spark'ie says if you can find some very high end Teflon wire that will give you the super low capacitance that is needed in order to MAYBE make this work with out a buffer. But I dont know.

Chris

[Nick's Picks]

my intentions are to dissect the swivels when they arrive and  see whats what w/some simple experimentation of lengthening the distance via a better single conductor shielded cable between the assembly and the capsule.

I do want to keep and utilize the swivels for my own use, and am not ready to throw away a pair of them for research...but I'll pass them around for sure so people can poke around on them as well, should I fail.
I'm also not opposed to donating a single one for the greater good.  I'd buy a replacement for myself.
we'll see.

fwiw, i'm not interested in an ortf bar for the capsules, so probably will not go very far w/that.

[kskreider]

So, Nick, done dissecting?  I'm not really interested per se, but this thread was always a fun read.  I hoped that as a ts.com community everyone would bang their heads together and have some SKG 480 actives fall out.   

[Nick's Picks]

funny this comes up.
I had my swivel on the bench the other day to see whats what inside.

now, i'm talking w/my cable sources to see if I can come up with a cable that is:

1 thin
2 sheilded
3 very low capasitence

once I get a hold of what I think will work, i'll try myself.
and if that doest' work, then I'll send a swivel to Chris or Richard.

If two swivels are needed...absolutely...
then I will offer up mine for the chopping block, and ask that the peeps involved with this thread and those w/any interest make a small paypal donation to me.  After all...its $400 odd in parts.  I think it will be fair if we can all work with the "greater good" in mind.

[Nick's Picks]

ok fellas...

how low is low enough?  will 50ohm coax work?
http://tinyurl.com/2gyx43

or maybe these people can help:  http://www.quabbin.com/tech_briefs/tech3.html

[landshark]

Hi Nick -

Count me in for $50 of the cost if you go this route.  I'd love to go active with my 460's!!

Mike

[Nick's Picks]

I was thinking more like 10...but 50 is good.


dont sweat it though, i'll let the group know when i'm ready to roll forward.
probably august as I have a bunch of shows right now, and like the swivels.

[esteyes]

hello all, neil in san marcos here. i have inhouse CK8X's as well as CK1X's, CK63's, and CK61's. i have 451's 451E's and 451EB's as well as 460's. i ran the 460/CK8X combo after the dead's europe tour. jeez, was it that long ago??? anyway, the MK46 cable was always somewhat fragile - we were always careful to hold the MK46 and spin the 460 or the cap when attaching the parts. nevertheless, the cables became unreliable. so i rebuilt them with a heavier cable (i _may_ be able to find the spec sheet akg sent me on the original cable - will dig). i do remember searching hard for the same spec cable in terms of impedance as well as other factors. the mk46 cable is triaxial. my mk46 schematics show that the center cable is "hot", the inner cable is "ground" and the outer cable is "screen". if you meter the connections at the 460 body, the screen is common with the body which is common with XLR pin1. so the outer cable acts like the tube in the A15 to prevent inteference - rfi, emi, etc - getting into the signal... i still have original AKG cable as well as the replacement cable not used in the repair. likely i can find the cable info for the stuff i used as replacement. never noticed any degredation of SQ after replacement, btw... so maybe this will assist in providing a quiet link between the cap and body....

to poorlyconditioned... i have not looked at a schematic in many years for the CKxX caps. i assume that it is a fact that there is a FET in the cap? (can't remember from the previous thread and i have been absent from this forum for a few months, so please forgive the dumbness of my question). just thinking, cause there are only 2 connections for the CKx series and 3 for the CKxX series...

i think the idea of the A51 as a basis for investigating the soundness of seperating the cap from the body is a great idea. i really think the potential noise issue needs to be looked into very carefully.

as a side note, sent my 8x caps in as one diaphram is bad. akg did not even have ONE MK46 available to test my capsule with - i had to ship my eq to them. best part? they charged me boo-coo bucks and never even repaired them, then denied the claim when asked to warranty them.

neil in san marcos
glad to help in any way i can...

[willndmb]

+t