Mod tube power supply to work with Rode K2

[Pat Maki]

Hey all, I'm looking at purchasing a Rode K2 with no power supply. Would love to repurpose one of my extra Chinese tube power supplies (Nady, CAD, MXL.aka Alctron). Anyone ever attempted this?

 

[Khron]

I don't see why it wouldn't work.

http://www.coutant.org/rodek2/

Looks pretty "standard" to me. Just make sure the connector pinouts in that power supply match what they should be.

https://groupdiy.com/index.php?topic=30971.0

 

[Gus]

I would check if the microphone is stolen if it does not have a power supply(PS).

Look closer at the pinout and other things you can find doing searches about the NTK and K2.

 

[Pat Maki]

Thanks Kron and Gus for your replies. Not sure how i missed them until now. I did call Rode and they checked the SN and the mic hadn't been registered...so no way to to know. Ended up getting an NTK w PSU as well and while it only has a cardiod polar pattern...works fine with the K2. I think modding a stock Chinese PSU to work with this mic would be a fun challenge though (-;

 

[Gus]

Check the voltages to ground
do a web search you should find information

 

[Pat Maki]

Thanks again Gus, noted.

 

[Ricardus]

Just an FYI. The PCBs in the NTK and K2 are identical in  both the mic and PSU. I had an NTK and a friend modded it with a new 2-sided capsule and added the pattern pot to the PSU (the hole is there for the pot, it's just covered up) and suddenly I had a K2.

I had gotten the NTK for free so I figured some mods would be fun.

I laser cut a pattern bezel for it, and ended up putting a different knob on than this one.

 

[Ricardus]

You can actually see on my "NTK" mic PCB that it says K2 right on it.

 

[Sredna]

Im following this with great interest as I got my hands on a NTK with a damaged capsule an no PSU.
As I had a NT2000 capsule laying around I popped it in there and applied the necessary voltages,
cardioid and omni works very well but figure eight doesnt sound right.
The backside sounds much duller than the front, and yes, Im aware of the phase differences between back and front.

The pinout for Rode K2:
1 - Gnd
2 - Signal Hot
3 - Signal Cold
4 - Gnd
5 - Filament (-5.8 V)
6 - HT (-125 V)
7 - Pattern control

Notice that its a positive ground circuit.

Does anyone here with a K2 PSU have the possibility to check the pattern control voltages?
Or even pop the hood and take some pics?
Does both LEDs (in the mic) shine with same intensity?

Thanks in advance, Anders

 

[Pat Maki]

Ricardus, that's a great discovery.

Anders, regarding your questions about the K2 PSU, I gave this a go tonight, but this is the first time I've checked voltages on a tube mic power supply, so I will likely need some guidance on this because i was unsuccessful at getting a reading on Pin 7 (pattern). The method I used was to stick a wire into the pin 4 slot of the female jack on the PSU. This being a positive ground, I touched the red probe tip from my multi-meter to it. Then stuck another wire into the Pin 7 hole (pattern), and touched that the black probe tip from the multi-meter. The meter is set a 10VDC....but no needle doesn't move. I also took off the lid and did some testing (very carefully of course), but didn't have better. Let me know if you can suggest the right way to test this? Below is a pic of the backside of the XLR's...happy to snap others...just lemme know what you want to see.

Pat

 

[Sredna]

Thanks Pat!

Great to have the voltages (-125V & -5.8V) confirmed (they are written on the PCB).

Is this the NTK PSU?
If yes, then there shouldn´t be any voltage on pin 7.
On the K2 PSU pin 7 should measure between 0 to -125V  relative to ground depending of the position of the pattern knob.

You should probably set your volt meter to at least 200VDC. ;-)

Thanks again, Anders

 

[Pat Maki]

Hi Andreas, So the -125V and -5.8V on the board read as they should...actually the -125V was more like -120V...but I did use an analog meter, so...However, still no voltage reading off 7 pin. This unit is relatively new to me and I hadn't even listened to the mic through this PSU yet. So with getting no reading on pin 7, I plugged in the PSU to a preamp to do a listening test and see if the pattern knob had any affect. Low and behold, turning the pattern knob did NOT affect the mics pickup behavior. Then to rule out the potential of the mic itself being the source of the issue, I plugged in my other K2 and the result was the same. So..it's starting too look like my amateurish understanding of electronics may not be the biggest problem with this PSU! (-;.

 

[blindjohnny]

@Sisu MT: Hope that you fixed your power supply.

I also have a K2 without psu (NOT stolen and an NTK with the psu. I would like to mod it so I can also use it with the K2. Apparently there is an extra circuit board on the K2 psu with a relay and some resistors(?). Would be nice to have a schematic. What multi-pot is used?

Also would like to know the voltages on pin 7 for changing the pattern: 0 to 120 volts?

Don't think those microphones use a lot of current. Wouldn't it be possible to turn it into a dual psu?

Thanks!

 

[Khron]

I would think your main limitation might be providing enough heater current for both, rather than enough current on the high voltage rail.

Don't think those microphones use a lot of current. Wouldn't it be possible to turn it into a dual psu?

Thanks!

 

[blindjohnny]

You're probably right, Khron. Maybe a seperate heater supply would work?

For now I would be happy just to be able to switch between cardioid and figure-of-8 on the power supply.

Anybody checked the voltages on pin 7?

 

[blindjohnny]

This was a bit confusing, but it looks like Pat has a very old K2 psu where they added an "outboard" to the existing NTK psu. Seems like my NTK psu has the circuitry for the pattern change already on board, in which case, like Ricardus stated, it's just a matter of installing a pot.

 

[blindjohnny]

...but going back to the original topic of this thread:
Wouldn't the fact that the Rode NTK/K2 require a positive ground psu complicate things a little bit? All the cheap Chinese psu's have a negative ground, tied to chassis ground. It would definitely require more than just changing out some zeners...

Anybody more knowlegeable on the subject of tube microphone psu's could shed some light on this?

Thanks!

 

[evil grill]

...but going back to the original topic of this thread:
Wouldn't the fact that the Rode NTK/K2 require a positive ground psu complicate things a little bit? All the cheap Chinese psu's have a negative ground, tied to chassis ground. It would definitely require more than just changing out some zeners...

Anybody more knowlegeable on the subject of tube microphone psu's could shed some light on this?

Thanks!

Shouldn't be hard. Basically reverse diodes and capacitors + switch out stabs. I've changed the heater this way in a t.bone Retro Tube II supply.

 

[blindjohnny]

Yes that would be doable, but why not make it float and just change polarity?
Might be better to start from scratch...

 

[blindjohnny]

Concerning the mod to the NTK psu: There is a 100k (bleeder?) resistor across terminals 1 (common) and 3 (-125v) where the pot should go. Maybe that has to be removed?

As a schematic is not available, anybody could shoot some photos of the pcb of a later version (mine says Iss4, dated 2007) of the K2 psu? That would be very helpful.

Thanks!