"MK84" or KM84 in an Oktava MK-012 body

[OneRoomStudio]

I always wondered if it would be possible, so I took some measurements of an MK-012 and drew up a pcb to see if everything would fit. It looks like it would. This is using one of Moby's Bv.107 transformers. I had to use MLCC caps instead of tantalums due to the lack of space, but I don't think that's a big deal. Thoughts? Would folks be interested in these boards?

 

[Ricardus]

Are large value MLCCs really going to save space?

 

[Ricardus]

I have a pair of MK-012s but I wouldn't sacrifice those mics to do this conversion. I did do Graeme's conversion of MXL bodies to KM84s though and love them.

 

[OneRoomStudio]

Are large value MLCCs really going to save space?

Just enough to fit, yes. The box-MLCCs are 5mmx3mm, whereas the tantalums at 5mm diameter. That 2mm saving in width makes a difference across 4 caps!

I have a pair of MK-012s but I wouldn't sacrifice those mics to do this conversion. I did do Graeme's conversion of MXL bodies to KM84s though and love them.

Fair enough. old/broken MK-012 bodies are cheap enough though, and the capsules are very good. Adding a little transformer coloration seems like a fun option.

 

[OneRoomStudio]

Waiting on a Bv.107 from Moby, but so far, everything fits.

 

[mrgrooves666]

Would be nice to compare both, the stock oktava can also be a little noisy too. Although this could be also due to the lower polarization voltage, wich I guess will remain similar after this conversion? could you share a comparison once you finish?

 

[McIrish]

Very cool project. The MK-012 is a favorite of mine on acoustic guitars

 

[OneRoomStudio]

Just another update. The transformer has arrived and fits perfectly. Plus, the circuit works as intended and sounds very good upon first power-up (before even messing with the fet bias!). I want to do another board revision though, to optimize the high-z connections and make it a little easier to assemble. More to come...


...And when I am satisfied with the final version, I will record some A/B comparisons with the original circuit.

 

[mrgrooves666]

Looks great

 

[kingkorg]

Just another update. The transformer has arrived and fits perfectly. Plus, the circuit works as intended and sounds very good upon first power-up (before even messing with the fet bias!). I want to do another board revision though, to optimize the high-z connections and make it a little easier to assemble. More to come...


...And when I am satisfied with the final version, I will record some A/B comparisons with the original circuit.

Make sure you push them with some level, some low end rich material, the difference should be more clear.

 

[emrr]

There are a couple different MK-012 body lengths to account for in any replacement PCB. I haven’t seen anyone address that.

 

[OneRoomStudio]

There are a couple different MK-012 body lengths to account for in any replacement PCB. I haven’t seen anyone address that.

I wasn’t aware of that. All of the Russian MK-012’s I’ve seen (as opposed to the Chinese-made “MC-012’s”) have been the same dimensions. Maybe there was a recent change? All the ones I’ve seen are at least 10-15 years old.

 

[ostrol]

bumping because... I'm very interested!

 

[Ricardus]

I wasn’t aware of that. All of the Russian MK-012’s I’ve seen (as opposed to the Chinese-made “MC-012’s”) have been the same dimensions. Maybe there was a recent change? All the ones I’ve seen are at least 10-15 years old.

I bought a set a few months ago. I can measure mine if you like.

 

[OneRoomStudio]

I bought a set a few months ago. I can measure mine if you like.

That would be great. The ones I have seen have body tubes that are 73mm long with an inner diameter of about 18.5mm. If you could also measure the PCB, that would ensure a good fit. All the ones I have access to have PCBs that are 61mm long from the rear mounting tabs to the front (with additional 4mm mounting tabs for the capsule pin holder, so 65mm total), and are 19mm wide.

 

[Ricardus]

I don't wanna take them apart, so I can't do the PCB. But I can get you in the ballpark with external dimensions.

 

[OneRoomStudio]

The new revision boards have arrived and work well (with some careful assembly). Built-up and biased and sounding good! I'll try to do some direct comparisons with a stock MK-012 soon.

 

[ostrol]

The new revision boards have arrived and work well (with some careful assembly). Built-up and biased and sounding good! I'll try to do some direct comparisons with a stock MK-012 soon.

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looking forward! they look gorgeous

 

[OneRoomStudio]

I’ve been sick so I haven’t had a chance to edit and upload the recordings I’ve made yet, but the differences are not subtle. The “MK84” has more output overall (~3.5dB more broad-spectrum), and quite a bit more low end (on the recording I made of electric bass through and Ampeg amp, it was over 6dB hotter than the stock Oktava). I’m going to level-match the clips and upload them soon.

 

[OneRoomStudio]

Ok, here are some clips. I had intended to record some more, but the flu hit me. I'll share which mic was which in a few days. Caveat - I'm a rusty musician and was coming down with the flu on top of that, so please forgive the performances (in hindsight, the flu may have been the reason I picked such a slow tempo, haha).
As for process - I taped the to mics together to get the capsules as close as possible and set them up around 12" from the source to minimize differences between what the capsules would pick up. I then ran them through the (digitally-stepped gain) preamps on my MOTU interface, level matched them, and normalized them. No other processing whatsoever.

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