Telefunken Copperhead 6AK5 circuit

Have heard this mic on the Telefunken session tracks, and once briefly in person, and thought it was really cool. Interesting midrange, and a distinctly different sound than some of the usual candidates. Digging around, it looks like the tube is a pentode Telefunken 6AK5/EF95/6554, apparently the same as used in the LOMO 19A9. The output transformer is a Lundahl LL1935 DI tx, and the capsule is a single-sided K67.

Is anyone familiar with the architecture of this circuit, or could hazard a guess as to how the 6AK5 tube is used?

Dylan

As I try to answer my own question, I'm reading about cathode followers and all sorts of wonderful stuff. I've got a few tube mic projects on the bench (building a 251 circuit in an Apex, Dan's DU-67 project, etc), but I know very little about tube mic architecture. I'm sure PRR and others have some great posts on the subject that I'm missing... this seems like a good excuse to learn about tube mic circuits in general. Maybe someone could point the way to a primer on the topic?

The Lomo 19A9 schematic is here: http://www.xaudia.com/xaudia/Documents/Entries/2010/6/13_Lomo_19a9_manual.html.

Dylan

Those new Telefunkens seem really interesting to me, as well. I've managed to reverse engineer their AR-51 from internal pics on the web, but they are far too new for any real info to exist on the circuit. RecordingHacks.com may have internal pics, begging on the forums might get you somewhere, but, from my experience, it won't be easy to obtain rock solid info. I got lucky with the Fox Audio Research website's overview and internal pics of the AR-51. As someone who has walked in similar shoes as you, I wish you good luck.

-James-

Found some internal pics here http://www.telefunken-elektroakustik.com/products/show_product.php?item=36, under the "photography" tab.

Looks like a very simple circuit. 7 resistors and 4 caps. The capacitor near the capsule says "10000J," which would make it a 0.01 uf 5%? Unsure of the rating. The cap in the middle of the circuit is a 2uf 150v. The coupling cap looks like a Wima 0.022uf 400v. Could figure out the resistor codes but I'm too tired. The Lundahl transformer is a standard 1+1 : 5+5.

I don't know enough to guess how the circuit is laid out, maybe someone more knowledgable will chime in.

Dylan

A picture of the tube and point to point connections.

I got really lucky, I guess. The AR-51 pics I have show the back of the circuit board unobstructed. That tube on the Copperhead pics seems to be right in the way. The AR-51 is also a variation on a well known circuit (ELA M 251). If you have the patience, looking at the circuit pics for awhile might help with tracing out the circuit.
Then, if you're lucky, the circuit will be a variation on a documented design (schematic layouts can be tricky, as there are many ways to draw the same circuit). If you can hold the mic in your hands again, your life will be a lot easier. If that were possible, you could, in theory, just take LOTS of photos, and use those to build a copycat circuit (point-to-point might be easiest).
I hope you do not have insomnia because this kind of stuff will keep you up night.

-James-

What do ya'll say we make the Copperhead the new DIY project?

What do ya'll say we make the Copperhead the new DIY project?

Click to expand...

Since it's a currently produced product and seemingly an original design, some might feel it isn't very cool to try to reverse engineer it or clone it.
But if you do try to build one, be sure to make the headbasket out of copper!      (Nice marketing touch by tele)
Interesting to notice that the mic in the pictures (as you posted) are different than the pictures in the right side animation, which has the lundhal.

ShellShock said:

What do ya'll say we make the Copperhead the new DIY project?

Click to expand...

I agree with dmp--it's an original design in current production, and I have no intention of turning this into a "groupdiy project." Mostly curious about what's going on inside, and hoping to learn something in the process. I took a brief glance at other circuits that use the same tube (Lomo 19a9, Oktava MKL-5000).. when I have some more time I will try to draw the whole thing out.

Interesting note about the differing internals. Seems like it's the same circuit or thereabouts--maybe a revision for production, switching to a PCB mount transformer.

Dylan