The new MKH8000 series has a couple of disc shaped PCBs, that are sandwiched together with the capsule in front of them. You can roughly make them out in the drawing that Sennheiser publishes on their service page.
Best
Jannis
Best
Jannis
Spectrum coils received today, as well as the coils from Aliexpress.Sadly, I'm no academic when it comes to designing inductors...... quite a lot of variables I'm not sure how to resolve effeciently!
In simplistic terms - when used with a 10MHz oscillator - I would guess you need to use a transformer with an inductance of around 12.5uH .....
I don't think Spectrum has anything suitable in their published range, and - outside the UK - their shipping costs have now made their inductors pretty costly anyway.
I've sent away for a pack of these: https://www.aliexpress.com/item/1005003604363316.html ( not yet arrived)
It may be possible to experiment using those formers, and perhaps the internal structure of the Spectrum coils as a template for some alternative - and cheaper! - options ?
The first step would probably be to just try and copy a Spectrum coil as a starting point?
As always thanks for invaluable information. Awesome part is that there aren't so many turns involved, and these Ali cans seem to be a great platform. I'm sure we'll get there. I can't let this capsule just collect dust.My Aliexpress cores have arrived, but I'm still waiting on the enamelled copper wire. I think I shall try and just copy a Spectrum coil initially (center tapped secondary wired on two adjacent spools -- primary on top of top spool ) and see how close I am.
When it comes to the best ways of creating alternative values, I'm thinking it may well be partly a 'suck it and see' approach....
The Spectrum coil lists near the top of THIS PAGE may give some idea of the number of turns needed for alternative values?
What is more difficult is to know exactly in which direction the turns ratios need to be varied, for optimising results.
The fact that T2 primary is fitted across the bridge makes calculating the total load on T1 rather complex, and the tuning of T2 core is dependent to some extent on the tuning of T1 -- and vice versa.
I would think it maybe possible to derive better options, to suit different capsule values? .....
As I have said on several occasions, my theoretical knowledge is simply not up being able to offer any 'best approach' ideas.
The Spectum coils worked out far better than I ever thought they would -- especially for capsules above 70pF in value --- but I am the first to confess my good results were pure luck, when it came to inductor design details.....
My understanding is that there are a number of variables that make calculations around the whole inductor assembly difficult to simulate .... so it looks as if good old fashioned experiments with 'actual parts' may be necessary, to try and understand better exactly what is the best way to optimise things, for any given capsule.....
I believe the difference is in the capsule construction.Looking at the Sennehiser MKH service schematics, I'm having trouble trying to read how they derive different polar patterns.
The circuitry looks very similar for all versions?.......
Quote from this document:You might get some useful snippets from John Willett's paper here:
Properly or previously wrongly wired it measured the same. Just a giant, smooth sad face curve. Just as described in the documents and in the first post of this thread. Compensated with eq for flat response i really liked it. Very good rear rejection.How did the capsule sound and measure when wired properly?
Wow Tim,I did that with this capsule. The plate in front of the membrane is +, the membrane is ground and the backplate is - times 2.
I will try to explain my thought process behind modding standard china RK12 type.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
I will try to explain my thought process behind modding standard china RK12 type.
Disassemble, drill through all the blind and through-holes, polish the backplates, then sandwich tensioned diaphragm between the halves using stock i presume 40uM spacers to separate the diaphragm from both backplates. Find a way to make connection to the diaphragm. You get + and - from backplates, and 0 from the diaphragm. And it will off course be F8 undamped capsule. Or even use a lathe to render backplates thinner.
I hope it gives you some ideas.
It could be possible to use additional (3rd) half of the stock backplate and put it behind one of the modified backplates to create cardioid. But i have no idea what kind of FR you would get. In that case it would be probably best to leave one of the modified halves - unmodified.
Or if you think the other way about it, use stock capsule, and then use third, drilled through the all holes backplate in front of it, which would hold the diaphragm in place instead of the tensioning ring. And be the "frontplate"
The HF cut off frequency is determined by the low pass filters created by R4/C9 and R10/C13. With the values selected for V.5 the cutoff frquncy is 15.9KHz............. There's some HF roll-off in the RF variant, which i believe has to do with the circuit itself........
Awesome. Will try.The HF cut off frequency is determined by the low pass filters created by R4/C9 and R10/C13. With the values selected for V.5 the cutoff frquncy is 15.9KHz.
Yuo should be able to increase that by reducung the size of C9 and C13. You could of course change the values of R4 nd R10 as well/ instead of, but that will affect the cicuit DC current drain, and thus sytem DC levels. Probably easiset to start by reducing the vlaues of C9 and C13 .
In theoey, making then 470pF instead should increase the cut off to 33.8KHz .. so possibly a value like 680pF or 820pF might prove more suitable?......
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