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Lundahl Transformer for the Apex 210: Mods and Upgrades Pt. 3

So we have a new ribbon.

Now let's install the fabulous and justly famous Lundahl LL2912 microphone transformer!

This is one of the two most popular transformers for the Apex ribbons. The other transformer being the Cinemag CM-9888.

We just need to remove the stock transformer and put the new one in its place. However it's critical that the new transformer is wired correctly so that proper polarity is observed.

I followed a couple of guides I found on the interwebs as to the polarity of the ribbon. Usually a red lead is positive, but in this case, it's negative.

You can see the primary and secondary leads identified in the photo on the right.

It's easy to figure out the secondary connections by tracing them to the XLR connector. I marked my PC board to make it easier to identify when I connected the new transformer.

The stock transformer is mounted in a steel can which shields it from RFI.

Desolder the leads and unscrew the can from the chassis frame.

Note that the cable shield ground was soldered to the tab on the chassis - you will need to get all of the solder off to remove the can.

This is a shot showing the color coding on the stock transformer for reference.

Primary positive is white, negative is red.

Secondary positive (to pin 2 of the XLR) is green. Cold (pin 3) is black. And pin 1, ground goes to the tab on the right.

There are two small screws on the sides of the can that need to be removed.

Then the transformer can be removed. In my case, the cover 'lid' of the transformer didn't want to budge, so I threaded the nuts back on and used them to leverage the cover off.

Here's the stock transformer removed from the case.

Plunk it in your parts bin.

Here's our new Lundahl transformer along with the schematic. The heavy black leads are the primary and the thin black and white leads are the secondary.

I put some green shrink tubing on the primary lead so I didn't get confused when connecting it.

I had to drill out one of the holes in the can cover so I could pass both primary leads through it.

The new transformer is more compact than the stock one, so it will easily fit in the can.

Just pass the leads through the holes. I used a piece of copper shielding tape to hold the transformer in place. Any kind of tape would be fine I think.

Then solder the leads in the proper places. Shouldn't be hard to figure out.

Slip the can onto the cover and fasten the screws.

I confess that I did this after I soldered the transformer connections. It seemed more logical, but I had less room to maneuver the screws. It worked fine though.

I replaced the stock cable with Mogami low noise cable. And I decided to run the output cable up under the pc board. So I had to remove the mounting screws, run the leads up, and then solder them and remount the board.

The board helps clamp down the leads.

Note the cable screen now soldered to the ground.

Turns out that keeping the ribbon leads parallel to the ribbon, in the same plane will result in the lowest noise.

Here's how I routed the leads - right along the edge of the ribbon motor assembly, held in place with wire ties.

Be very careful threading the wire ties near the ribbon so you don't tear it!

Then you can put the motor back on the chassis and solder the primary leads to the appropriate places on the board.

The other low noise hint I learned is to twist the respective positive and negative leads from the ribbon together. Meaning, the red lead on the left side of the motor with the blue on the left and the same on the right. The idea being that they will cancel out RFI.

I got maybe 2 twists on each, so I'm not sure how much it helps, but I did it, so there!

Remember, though that BOTH of the red leads (negative) still go together to the same terminal on the board, and likewise for the blue (positive). You can see this on the larger version of the image.

You can also see how I used a small piece of shrink tubing to hold both red leads together and the same for the blue leads.

Then the two reds go to the old "red" terminal and the blues to the "blue" terminal we marked earlier.

The body of the mic needs damping. If you tap it with your finger, it rings like a bell! Even worse than the Oktava MK-219.

So I put some CLD tile material inside the body, and stuffed it with speaker stuffing to fill the open space. Now it's totally dead.

See also how I ran the cable through the body - I reused the factory cable sleeve and put a new cable clamp on (broke the old one taking it apart!).

Put a new Neutrik XLR connector on the Mogami cable.

You may recall I left the screens off the ribbon.

There is a second headbasket mesh screen and a fabric windscreen in the basket - I decided to leave them in for now. The ribbon does need some sort of protection.

Now we just put the headbasket back on the body.

And reattach the mounting screws.

And test it out.


Compared back-to-back with a stock Apex 210, it's a night and day difference. Amazing!

The stock one sounds small, boxy, boomy and not a lot of high end.

The modded one is much more open, less boomy, and has much more high end. It's pretty amazing.

The difference is like having earplugs in (stock) and taking them out (modded).

And it's dead silent.

I'm running the mic through a Cloudlifter Z and I find I can use the low (12dB) setting if I wish. Plenty of gain after the Cloudlifter boost.

I think all this improvement is a combination of the thinner ribbon and the transformer. I want to convert another one and use a Cinemag transfomer to see if there is a difference. But for now, I'm super pleased with this one.


Post a Comment 2 comments:

  • kylelundy said...
    January 14, 2017 at 6:36 PM
    this is awesome! definitely going to have to try it out... where did you source your parts?
  • Yr Fthfl Blggr said...
    January 15, 2017 at 10:57 AM
    Thanks. I got the ribbon and the transformer from Geistnote:

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