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Author Topic: KM84 Electronics- Too Colorful?  (Read 4757 times)

Boy Griffioen

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KM84 Electronics- Too Colorful?
« on: July 23, 2014, 11:23:21 am »

Dear All, I have some KM84's that get not enough use from me because i think the electronics are too colourfull  ;)

I would like to try to upgrade the internals with a totally new circuit, i think will use them a lot more because i like their sound a lot. I'm searching around but can't find good designs to start with. For tube mics there is a boatload of info but for the small mics not so much. Could you point me in the direction of a few good designs?
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Kai

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Re: Looking for buffer designs to upgrade KM84
« Reply #1 on: July 23, 2014, 01:17:35 pm »

Dear All, I have some KM84's that get not enough use from me because i think the electronics are too colourfull  ;)
Sell them to me, use the money to buy something that fits your taste.

I'm not completely joking!

Regards
Kai
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klaus

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Re: Looking for buffer designs to upgrade KM84
« Reply #2 on: July 23, 2014, 02:08:18 pm »

...maybe not completely, but here is a critical, and hopefully constructive, interpretation of your post:

You want a mic that, in my opinion, no mic (and no audio processor, in general) can do. "Colorful" vs. "neutral" (I inserted the term neutral here, but am sure, that's what you had in mind) in audio is one of those terms that are conceptually sound and logical, but ultimately undefined and unattainable in practice:

There is no audio device, especially no active, amplifying, audio processing device that is not impinging its own alteration or color on the audio which entered it. Lack of color, at best, is an illusion, and it usually connotes a desire raised by an advertising strategy, rather than attainable as an engineering feat.

You may not like the tonality or timbre of the KM84 (you are indeed a rare exception, considering the enormous popularity of this mic, even in comparison to its successors from the same company), and you can find mics with a noticeably different color from the KM84 (a Schoeps CMC-series, or a B&K 4000 series mic, for example), but they, too, will alter the original audio entering these mics considerably. Often, the terms of that alteration or modification of the incoming sound by the mic are nebulous, but in the end, your personal attraction to the music counts.  An attraction that unconsciously tunes out the device that brought the music to yoru ears and lets you enjoy it.

There are fortunately, or unfortunately, depending on your mindset, no other arbiters of good taste in mics than your intuitive connection or disconnection to the music when using a particular mic. Any graphic or numerical representation of audio events, especially complex audio wave forms, are still woefully under-developed at this time.

P.S.: Could there maybe something wrong with your KM84 that you came to your conclusion.
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Klaus Heyne
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Boy Griffioen

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Re: Looking for buffer designs to upgrade KM84
« Reply #3 on: July 23, 2014, 04:48:24 pm »

Thank you for the respose, The km84 are in good shape. But i think they can be better (to my taste) The basic sound of the capsule i like. But in the low frequency range happen some things in the amplifier that are not nice for me. I can confirm this because i have heard the capsules a lot on other amplifiers. But those amplifiers are not for sale and the design is not public. The sound of those can be heard on multiple releases of Polyhymnia (former Philips Classics) So my goal is to get closer to that sound. And that is why i'm fishing for inspiration.



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klaus

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Re: Looking for buffer designs to upgrade KM84
« Reply #4 on: July 23, 2014, 05:41:32 pm »

You write "the design (of the mic amp modifications you mentioned) is not public". Have you heard these mics independently, or only on recordings that were supposedly made with these mics?

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Klaus Heyne
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Boy Griffioen

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Re: KM84 Electronics- Too Colorful?
« Reply #5 on: July 24, 2014, 02:28:23 am »

Yes i heard these microphones independent because i work with them on a regular basis. I freelance for Polyhymnia.



I even know one or two things about the design. But they are hard to produce because they have on PCB printed resistors of 8 gigaohm.

These microphones render the Cb in a more transparant way and with omni capsules they are also superb for AB orchestral recording. I can't say this about the stock microphones. They sound nice but not nice enough. I know they can be made the way i want. Just not that easy. No problem i work harder.

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klaus

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Re: KM84 Electronics- Too Colorful?
« Reply #6 on: July 24, 2014, 03:49:12 am »

Can you be more specific, how and where an 8 Gig Ohm resistor (with its inherent noise issues) would be implemented in a condenser mic amp?
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Klaus Heyne
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Boy Griffioen

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Re: KM84 Electronics- Too Colorful?
« Reply #7 on: July 24, 2014, 07:25:49 am »

I try to clarify some things.

Here is a picture of the buffer i'm talking about.

http://i4.photobucket.com/albums/y141/raytheapostle/MICROPHONE_ELECTRONICS_2.jpg
This was on their site previously but not on the new page.

When I asked about it and they told me it was made with on pcb printed resistors of thick ceramic film Of 8G. This would explain the wide bars on the pcb traces. But my goal is not so much as to copy this topology. I want to make the same sound. This could be described as very transparant as with 83 capsules FFF orchestra passages all instruments (especially in in the low freq region) are easy to seperate in the stereo image. And the same goes as stereo 84 spots on Cb or Tuba. There is also less of the smoothing sauce in the high freq range. This sound is what i remember from Haufe Trafo splitters. So i think the trafo causes this. Also noise is lower but that is not a huge problem. As solo instrument mic i would like this sound sometimes but with orchestral work or bigger ensembles and distant micing not so much. And i know it is not the capsule to blame for this.



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Kai

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Re: KM84 Electronics- Too Colorful?
« Reply #8 on: July 24, 2014, 05:40:08 pm »

Analysing the picture without digging too deep into it, it's a symetrical transformerless design.
The heart of the circuit is the Op-Amp.
I guess the two FETs to the right are inside the feedback loop of the OP-Amp (I would need to see the back for further analysing this, but the 8 GOhms resistors (if they are) would make sense then.

These type of circuits tend to be very "linear" (in a technical sense), closer to the "piece of wire with amplifcation" idea then the classic designs with one FET + Transformer.

There is a commercial solution that might help you: DPA / Bruel&Kjaer offer transformerless replacement amps as upgrade for their 4000-series mics to "TL".

I guess they dont fit into a KM84 housing, but if you are a good handcrafted guy you might work around that.

Anyway I would strongly suggest not to alter the original KM84's, but build something that can take the capsules.
It's not too complicated, basicly a piece of tube with a thread on one side and an XLR connector on the other.

Regards
Kai
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klaus

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Re: KM84 Electronics- Too Colorful?
« Reply #9 on: July 24, 2014, 06:30:12 pm »

(...) These type of circuits tend to be very "linear" (in a technical sense), closer to the "piece of wire with amplifcation" idea than the classic designs with one FET + Transformer.

I question that this type of circuit design truly brings the mic closer to the music, as in "just a piece of wire with amplification".
I never found the B & K approach (or any TLM circuit, for that matter) especially when recording classical music, appealing to the senses. It always struck me as a bit surgical, clinical, cerebral in its representation.  Kind of like listening with your brain, but never able to go deeper...

Comments?

P.S.: Good catch, Kai! I had just responded with the same recommendation (and also added some Schoeps models to the list) but, due to my Luddite approach to forum hosting, that post went into cyber netherlands.
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Klaus Heyne
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boz6906

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Re: KM84 Electronics- Too Colorful?
« Reply #10 on: July 24, 2014, 06:36:35 pm »

That's an interesting photo of the KM84 preamp mod.

It's also posted on this 2006 Gearslutz page:

http://www.gearslutz.com/board/remote-possibilities-acoustic-music-location-recording/89696-mics-decca-tree-2.html
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Boy Griffioen

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Re: KM84 Electronics- Too Colorful?
« Reply #11 on: July 25, 2014, 04:50:28 am »

Thanks!

That should be my approach also just to use the capsule and build te rest in a tube.
This Photo has been on the Polyhymnia website for years so probably it ended up on Gearslutz also ;)

As for brain vs emotion if there is something in the way between musician and listener it is unwanted in my point of view. So if emotional load is reduced this is not good information is lost. But this also goes for technical aspects as noise and distortion, information is lost. It should not be one OR the other. Both can be improved.

But, i would appreciate some schematics of circuits 8).
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underblu

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Re: KM84 Electronics- Too Colorful?
« Reply #12 on: July 25, 2014, 09:16:48 am »

I have to agree.  I think the engineers at Neumann in trying to design a more accurate, noise free, linear design have allowed measurements to take precedence over listening.
While their transformerless TLM series is certainly successful, none of those mics can so effortlessly capture the weight, impact and texture of a source as vividly as a u67, u47 or m49.  And yes there are colorations inherent in these mics but ultimately, to my ears, they do a far better job of capturing the essence of the source better than anything "more neutral"

The Telefunken USA elam 251 ac701 is the first mic I've used that on several sources actually sounded like the un amplified source in the room.   I was actually shocked at the lack of electronic glare and the complete absence of any sort of mechanical presence.  The naturalness of that mic was revelatory to me.  And this is a mic is based on an over 60 year old vacuum tube design.  Far from the text book measurement of straight wire with gain.

My suggestion to the OP is to get a mic that is more suitable to your goals and delivers the results you are searching for rather than modding a perfectly good Neumann km84.  While not as rare as the similarly discontinued km54 or km56, it still seems unnecessary to mod one when there are so many other SDCs available that may meet your needs. 


on that this type of circuit design truly brings the mic closer to the music, as in "just a piece of wire with amplification".
I never found the B & K approach (or any TLM circuit, for that matter) especially when recording classical music, appealing to the senses. It always struck me as a bit surgical, clinical, cerebral in its representation.  Kind of like listening with your brain, but never able to go deeper...

Comments?

P.S.: Good catch, Kai! I had just responded with the same recommendation (and also added some Schoeps models to the list) but, due to my Luddite approach to forum hosting, that post went into cyber netherlands.
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Kai

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Re: KM84 Electronics- Too Colorful?
« Reply #13 on: July 25, 2014, 01:39:40 pm »

But, i would appreciate some schematics of circuits 8).
Here's one I developed.
It does not need any extreme high Ohm resistors and has very low distortion and noise.
The FET is powered by an adjustable constant voltage, which makes it posible to linearize it in combination with the Drain to Gate FB through R1, R2, R3, C3.
Therefore the circuit has exeptional high dynamics.

Regards
Kai

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J. Mike Perkins

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Re: KM84 Electronics- Too Colorful?
« Reply #14 on: July 28, 2014, 12:22:41 pm »

You should consider trying a vintage Neumann KM74 if you can find one.  They have the same capsule as the KM84 but a different amp which is T Powered and transformerless.  While the sound is certainly related to the KM84, they are not identical.  I think the KM74 is slightly less colored (mainly in the low mids), a little more open sounding on the high end, and their sound MIGHT be what you are looking for.  I have a pair of them and generally speaking, I prefer them to the KM84 (but both are great and classic mics, just  slightly different).     
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