Topic: AKG Active Project part 3

[illconditioned]

Hey there.  I've got a "vintage" set of Beyerdynamic actives.  They have:
  CV750 (body) ---- cable ---- AV750 (collette) + CK703 (capsule)
It is a three wire cable with: 1=polarization, 2=ground, 3=signal.

Well, I just took an AKG CK63 capsule and put it on the end (with about 1" of tubing, and some layers of (tin foil!) tape to make the ends mate).  And it worked!

Here is a schematic of the AV750 adapter, see below.

Comments: It gets 48V (dropped a bit) from the CV750 bodies).  Note also that this draws a fair bit of current at 48V.  Another circuit would run a very low current polarization voltage, and run a lower voltage to the FET.  But, yes, this does work.  A real-world system waiting for someone to build.  Oh yeah, the FET is 2SK67A-J7.  This is a "self biased" fet, used for electret mics.  It is a SOT-23 package.  The J7 refers to the Idss current of the FET.  The J504 is a JFET with only two wires, it acts as a constant current source.  Enjoy...

[Chuck]

1984... There are probably some better FET's out there now, too.

[illconditioned]

1984... There are probably some better FET's out there now, too.

I don't think FETs are the limiting factor.  Also note that a "self biased" fet avoids the problem of biasing (and tuning) the FET.  This is a real simple circuit that works great!

  Richard

[illconditioned]

^^^ Hey.  Is anyone out there?

I'm going to build this circuit behind an AKG CK63 capsule.  The circuit will be "hard wired" in a small tube behind the CK63 capsule.  (Proposed method is to find a brass tube that just fits the CK63 thread.  I'm using a 1" segment from an old NAK/TEAC body.  Then fill the gap with a layer of thin brass mesh, and twist the threads into it.  This is a one time connection, it will not harm the threads, but will make a solid connection.)

Following the Beyerdynamic wiring convention, I'll use a three pin connector on the back of the capsule.  Beyerdynamic uses "Binder" connectors, series 711.  Visit "binder-usa.com".  These are great connectors.  They are small, easy to solder, and have nice screw lugs that secure the cable connectors.

  Richard

[darby]

Richard,
I think most of us are patiently waiting for something solid before getting too excited about anything
considering this project has been going on for how many years?

please keep us posted though and possibly Jon can use your idea for his AKG active setup he's going to be working on

[illconditioned]

^^ All I'm saying is when I plugged in my CK63 cap it worked.  Sounded great, no hum or buzz or other problems.

And posting a schematic of a *working* product may be helpful.  I'm going to build this myself, hardwired to the CK63 capsules.  Hopefully Jon or someone else comes out with a version for sale.

  Richard

[F.O.Bean]

That circuit will work well; that FET seems fine so long as noise is reasonable (couldn't find that spec quickly).  My circuit is not a lot different other than the need to bias the FET which adds a few parts.  I also have a cascoded FET, which is a common feature in these circuits.

The electronics have never been the difficult part of this project, it's the machine work that is critical.  Unfortunately the way things are going, I won't have time to get to that for at least another month.  I think I just answered six prospective preamp purchase emails today and I've had a record two months for preamp sales already.  There is essentially no design work going on right now, if the economy keeps up it might have to wait for the summer doldrums!

Richard, if you like you can borrow my tap for your tubing.

2 months from time of purchase to delivery DAMN, I'm SO GLAD I ordered mine when I did

[Chuck]

No, in the last two months I've sold a record number of preamps.

That is great news Jon!

[newplanet7]

No, in the last two months I've sold a record number of preamps.

That is great news Jon!

x2.
Congrats.

[Dkrogh]

If I get this job that I have been interviewing for the past 2 weeks I will be picking up where I left off on the 'colettes'.  I had been working on a design with a machinist but things have been on hold since I have been strapped for cash lately.

[newplanet7]

Richard, excellent find man.
How long have you had those Beyers??
Also wondering if you still have the Beyers bodies in the chain?

[igene]

I have a question... (and possibly an offer)

I have these CK1X caps stored away, not being used.
(As well as an extra single cable)
They are mismatched spares.

Quest.#1. what's the difference between them. Other than the body.
 They sound identical. They actually sound great.

Quest.# 2. If I was to sell such a pair of mis-matched bodies, what should I ask for them.

Again, they sound great with no issues.
They've been around a bit (as you can imagine).
The bodies are in 'B' condition.
The body is also inscribed with a rental company's name.
 I was told they were bought as used equipment.
I got them in a trade as a back up set, in case of repair issues on my main set.
I'd need to get something else, so I'm thinning out all my extra gear.

Please help. I figure you guys know your stuff...

thanks in advance.

[newplanet7]

What do you mean by mis matched bodies?
The only thing I can think of is one is the three switch version and the other is the one switch version.

[igene]

that's what I mean.
You can't clip the one into the same type mic mount as the other...thus mismatched.

Otherwise - Yes - they are both CK1's.

any suggestions ?

[ts]

What do you mean by mis matched bodies?
The only thing I can think of is one is the three switch version and the other is the one switch version.

I don't think he has any 460 bodies with this stuff.

Only thing I see is two different style caps and one MK46 cable.

Looks like a tough sale. Maybe you would have some luck on ebay. Sell one cap and cable and the other cap by itself. The caps go for around 125 each and the cable with one cap might get 250.