KM84 revisited

[joulupukki]

Nice! That’s gonna be fun to build. That stash rivals mine and then some. I need to clean house and convince my band mates or someone to buy a couple from me. I don’t think I need so many!

 

[jp8]

Thanks for the heads up, @museric! Of course, I'm just as excited as @joulupukki and I hope you manage to build some great microphones. And that you also enjoy building them!

Did you already decide on which transformers to use?

Cheers

Jan

 

[micolas]

If you have been following this and this thread of @joulupukki , you know that I have made two SMT variants of the KM84 circuit with several improvements compared to the classic KM84 circuit. For convenience, I have called these circuits KM84+ and KM84++. They are described in detail on my website, which I have now launched. You will find the links below. The KM84+/KM84+ article texts are not completely finished yet, but I plan to finish them during the Christmas holidays. I hope you'll enjoy reading the articles on my website and find them useful!

I will make KM84+/++ PCBs available for the Takstar CM-60 and CM-63 and Alctron T-02A on PCBWay, but at the moment of writing, I have only finished the building instructions for the KM84+, suitable for the CM-60 microphone.

Links to KM84 and KM84+/++ articles on my website:

KM84 circuit description: https://modimications.com/km84-style-charge-amplifier-circuit/

KM84+ and KM84++ description: https://modimications.com/km84-and-km84-head-amp-circuits/

Takstar CM-60 and CM-63 description and mods: https://modimications.com/takstar-cm-60-and-cm-63/

Available PCBs (at the moment only one, but you get an idea of what I'm working on: https://modimications.com/all-orderable-pcbs/

When more KM84+/++ PCB variants become available, I'll keep you informed via this thread.

Note: unfortunately, my website does not display correctly on mobile devices. I'll have to work on that.

Happy reading and Merry Xmas to all!

Great! @jp8 , you're tempting me to build a pair of these beauties too!

 

[museric]

Thanks for the heads up, @museric! Of course, I'm just as excited as @joulupukki and I hope you manage to build some great microphones. And that you also enjoy building them!

Did you already decide on which transformers to use?

Cheers

Jan

Yes, I did get the AliExpress transformers this time around (just a pair for the first build of the KM84+.) I think I’ll try the 3U transformers for the next pair, and grab those same time as the capsules. Yay!

Now - I’ve noticed that one component is out of stock vs. the rest of the parts purchase. I’m looking at alternatives to that Wima 1uF cap, and discovering that everyone seems to be out of the 5% tolerance for that size and value. The wait may be awhile according to both Mouser and Digikey - March or April. Ugh.

 

[Khron]

I’m looking at alternatives to that Wima 1uF cap, and discovering that everyone seems to be out of the 5% tolerance for that size and value.

Get some other 1uF film cap. Wimas aren't sprinkled with magic fairy dust, and the transformers will have more loose tolerances than the film caps.

Keep a realistic perspective, is all I'm saying / advocating...

 

[museric]

Get some other 1uF film cap. Wimas aren't sprinkled with magic fairy dust, and the transformers will have more loose tolerances than the film caps.

Keep a realistic perspective, is all I'm saying / advocating...

Good, yes, I was wondering about just getting another brand or a looser, and more available, tolerance. Thx!

 

[jp8]

On the KM84+, you can either place a 1uF film capacitor (C4a), or electrolytic cap (C4). Whatever you like... Some people have very specific preferences regarding capacitors. I am not one of them, but I thought a red Wima capacitor looked nice on the black PCB. But I do believe that the value is important and that 1uF is the ideal value in my opinion. This is explained on my website.

The components that some people like to swap out and experiment with, are mostly through-hole technology parts, which many find easier to swap out than SMT parts. This is one of the reasons why I chose THT parts in some cases, instead of SMT to make the design more DIY-friendly. To this end, I also added a GND and Bias testpoint to facilitate bias adjustment and fault finding.

Jan