Sennheiser MKH800 / MKH80 capsule (ks80)

[rogs]

@rogs
Update. Today i received the right gauge wire, just like in Spectrum ones. I got best results with 2X13 turns on primary, and 5 turns on secondary. This got me inductor range of 5uH to 15uH. It was extremely easy to dial in the inductors and i got even better snr with this one compared to previous DIY coil.

I've started to try out a couple of transformers using Aliexpress formers and 0.1mm wire.... (c.38 AWG )
The 1st was a direct copy of the Spectrum coil, and turned out to be very similar..... Those formers seem to be almost identical
to the Spectrum ones.....

I tried out 2 x 12 for a tapped secondary, and 6 turns for a primary (to try and create a slighlty higher input impedance primary, to allow for better matching to the oscillator output.
I can only really do comparisons with the actual Spectrum coils, but first tests suggested a 'central slug' inductance of around 11uH -- which was a little bit higher than I was expecting from just a couple of extra turns?....

Now we have the options to vary both primary and secondary turns, a whole new world of 'optimisation' opens up ...... Certainly when using capsules with smaller capacitiances for example...
It may also allow more experiments with 8Mhz oscillators...... In theory, that type of former should have it's highest 'Q' settings at around 7 or 8MHz.

With the right conditions and a 'following wind' you can get pretty good results with Spectrum coils .
This new option to create virtually a whole selection of different inductors - with various turns ratios and inductor values - may open up options for even better results?......

 

[kingkorg]

Wow Tim,

that looks awesome! I've been really into the symmetrical capsule design lately and have been trying to make one myself but my progress is pretty slow, with lots of hiccups along the way. How thick are the backplates you made there, if you don't mind me asking?

Best
Jannis

@rogs @jarvis i managed to mod this typical Ali edge terminated into push-pull, f8, undamped symmetrical capsule. I made a video as well, it's in the editing stage.

I guess the images explain most of it. I widened the "through holes" sandwiched the diaphragm in-between. I got the typical sad face curve response, countered it with a plugin in the daw and it sounds like this. This is just a rough setup, not optimal circuit so there is some noise.
View attachment Push pull capsule.mp3

 

[jarvis]

Hey Kingkorg,

really nice effort, looking forward to seeing your video! And also a good idea terminating the diaphragm at the side there! Did you use the original spacers in between the backplates and the diaphragm? What circuit did you test it in?

Best
Jannis

 

[kingkorg]

Hey Kingkorg,

really nice effort, looking forward to seeing your video! And also a good idea terminating the diaphragm at the side there! Did you use the original spacers in between the backplates and the diaphragm? What circuit did you test it in?

Best
Jannis

Yes, stock diaphragm to backplate spacers. Just a regular Schoeps circuit for the test.

 

[Tubetec]

Rogs ,
Remember in an inductor if you double the number of turns the inductance is 4 times the value .
I did a test wind on a pot core earlier , 10 turns got me 350uH , adding an extra five turns got it upto around 1000uH or 1mH .

That looks good Kingkorg ,
so each diaphragm has both a front and back plate ,but the frontplates are backplates from another capsule .

 

[rogs]

Rogs ,
Remember in an inductor if you double the number of turns the inductance is 4 times the value .
I did a test wind on a pot core earlier , 10 turns got me 350uH , adding an extra five turns got it upto around 1000uH or 1mH .

The notes I linked to in this post: DIY RF Condenser Mics have produced some quite useful results....

 

[ccaudle]

push-pull, f8

Wow, that is a real fig-8, the attenuation at 90 deg was really good. I assume that was not an anechoic room, so I doubt you can get more attenuation than that in a normal room.

 

[kingkorg]

Wow, that is a real fig-8, the attenuation at 90 deg was really good. I assume that was not an anechoic room, so I doubt you can get more attenuation than that in a normal room.

No, just my living room. The attenuation at 90° is insane. What you hear are pretty much just reflections.

 

[kingkorg]

I am pretty much done with this one. I ended up using 10Mhz crystal as the other values didn't give me better results. Custom wound T1 as described before.

The capsule is gently overdriving the fet at higher SPL but only in the midrange where it puts out a lot of signal as the curve is sad face shaped. That gives me very unique, musical saturation which i actually really like. Nothing like clipping, just some nice harmonics, very, very tube like. I did try tinkering with R2 value but it has to be lowered a lot in order to reduce the capsule output, and then it throws off the current of the whole circuit too much. So i left it alone.
I correct the sad face curve later in the chain with an EQ.

Final result is nothing like MKH mic should be, not the quietest one, nor THD free, but i got a vary interesting microphone i'm very satisfied with. And when i leave out the technical quirks i really like how it sounds. Recording vocals, the bleed from the headphones is way higher than the noise, so for the purpose i will be using it mostly this is more than good enough.

Some of the components are on the other side of the PCB.

 

[rogs]

........ The capsule is gently overdriving the fet at higher SPL but only in the midrange where it puts out a lot of signal as the curve is sad face shaped ...........

I'm intrigued to know how you are measuring this?...... In this configuration the JFET is used as an infinite impedance detector - an RF demodulator - so is essentially being turned on and off at every clock cycle.... How are you determining the linearity of the modulation? ...

 

[kingkorg]

I'm intrigued to know how you are measuring this?...... In this configuration the JFET is used as an infinite impedance detector - an RF demodulator - so is essentially being turned on and off at every clock cycle.... How are you determining the linearity of the modulation? ...

Oh, i measured it with REW, just regular audio sweeps, and it was very audible when i recorded some high spl vocals.

However, now that you ask, i have no idea if it's coming from the JFET, i just made the assumption. Could there be another source of distortion? Obviously following bipolars, but other than that?

 

[emrr]

I have an 800 Twin. If we can arrive at some comparative sample types, maybe we can compare.

 

[ricardo]

I had a lot of correspondence with Beiss maybe 10+ yrs ago on inductors. I've lost all that and my notes via several HD crashes ... including my list of all available RF inductors & pot cores at that time.
IIRC, both the cores he used and what I used for GG Baxandall's circuit circa 1980 are now Unobtainium. But we figured certain RM potcores might still be suitable.

One tip was that the primary (main RF) winding would probably be only 1 or 2 turns with the core to give your required inductance.

The wire you use also affects the Q. He found wirewrap wire even better than traditional Linz wire (which I'd used.)

Hope this helps widen the range of possible inductors & hence capsules.

My hat is off to kingkorg & rogs from a beach bum in Oz

 

[ricardo]

The wire you use also affects the Q. He found wirewrap wire even better than traditional Linz wire (which I'd used.)

Du..uh! That should be Litz wire

 

[LuckyNat]

I have an 800 Twin. If we can arrive at some comparative sample types, maybe we can compare.

I bought a KS80 capsule again from the guy in romania and also found a Twin chassis with PCB on ebay at the same time.

Happy to take any photos.

I've put them together and finding some issues - poor performance on one side, none on other when both receiving phantom, one side sounding great when powered seperately and the other very quiet (or silent - cant remember) . *could* be an issue with phantom on my AA-battery powered field mixer and I forgot to swap inputs when testing .. I'd guess that the chassis I bought could have been a repair swap-out sold in a job-lot of parts, then sold on ebay - judging by the sellers other items.

Are there any schematics about for the Twin?

 

[Gerard]

I've started to try out a couple of transformers using Aliexpress formers and 0.1mm wire.... (c.38 AWG )
The 1st was a direct copy of the Spectrum coil, and turned out to be very similar..... Those formers seem to be almost identical
to the Spectrum ones.....

I tried out 2 x 12 for a tapped secondary, and 6 turns for a primary (to try and create a slighlty higher input impedance primary, to allow for better matching to the oscillator output.
I can only really do comparisons with the actual Spectrum coils, but first tests suggested a 'central slug' inductance of around 11uH -- which was a little bit higher than I was expecting from just a couple of extra turns?....

Now we have the options to vary both primary and secondary turns, a whole new world of 'optimisation' opens up ...... Certainly when using capsules with smaller capacitiances for example...
It may also allow more experiments with 8Mhz oscillators...... In theory, that type of former should have it's highest 'Q' settings at around 7 or 8MHz.

With the right conditions and a 'following wind' you can get pretty good results with Spectrum coils .
This new option to create virtually a whole selection of different inductors - with various turns ratios and inductor values - may open up options for even better results?......

Wow! This is exciting news for DIY RF condenser mics. It got me thinking about designing coils, something I tried as a teenager when pot cores were easily bought.

I did some browsing instead of work this morning and found the following which might be of interest. In no particular order...
https://www.rfcafe.com/references/radio-craft/if-coil-design-april-1932-radio-craft.htmhttp://arrl.org/files/file/Technology/tis/info/pdf/8504028.pdf (I seem to recall the annual ARRL Handbooks were the source of my info back in the day)
https://www.qsl.net/w/wa3mej/Articles/Transformer & Baluns/Winding your own coils.pdfhttps://www.angelfire.com/electronic/funwithtubes/IF_Can-1.html
This also might be of interest, in a slightly hair shirt sort of way: DIY IF CANS FOR VALVES

Forgive me if this is all teaching your grandmother to suck eggs