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Author Topic: M49: Does it look authentic? Does it Matter?  (Read 14761 times)

Offline soapfoot

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Re: M49: Does it look authentic? Does it Matter?
« Reply #60 on: January 20, 2014, 07:50:20 am »
...and that would physically fit, of course!

Thanks, Klaus.

Offline Kai

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Re: M49: Does it look authentic? Does it Matter?
« Reply #61 on: January 20, 2014, 10:07:11 am »
All I can tell you is that my story is not about bypassing bad caps, but very good caps
It's good you made this clear.
My imagination was you could have left the original cap (in a vintage, historic mic) in place to guarantee reversibility of the mod, and add a bypass.
Seems you not.

Today we have more, better (and sometimes only cheaper) choices then in those days.
So it should be possible to find a single cap that sounds good in a certain application.

Still I find the mentioned articles interesting, specially the part where you can see that higher voltage caps in general (not only electrolytics) perform better.

Regards
Kai

Offline Jim Williams

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Re: M49: Does it look authentic? Does it Matter?
« Reply #62 on: January 20, 2014, 11:14:06 am »
I would consider any electrolytic cap formulation to be a poor choice for quality audio. None of them can approach the sonics of a quality film cap. A quality film cap cannot approach the sonics of using no cap at all.

Unfortunately, single ended power supply designed audio circuits must use a cap to block DC. If one designs with bipolar power supplies, you can design out those caps. Nearly all tube mic and 48 volt powered mics forbid those choices. You would need to scrap the 48 volt single ended powering designs for a bipolar power design, that would take more then the 3 wires in an XLR cable.

There are plenty of undiscovered audio designs that could be tried out in microphones. Unfortunately, most are content with the current offerings and 2014 marketing forces will not reward such advanced designs. They remain oddities and reside in private collections. Larger manufacturers will not upset their apple carts as most are satisfied with the current state of microphone design, as long as they keep selling.

Offline boz6906

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Re: M49: Does it look authentic? Does it Matter?
« Reply #63 on: January 20, 2014, 11:54:07 am »
Fascinating discussion, thanks guys!

Question:

"You would need to scrap the 48 volt single ended powering designs for a bipolar power design, that would take more then the 3 wires in an XLR cable."

The Neumann KM1xx series uses the 48Vdc to power a 60Vdc bi-polar supply.  Would it be possible to run a sub-mini tube with that?

Offline Jim Williams

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Re: M49: Does it look authentic? Does it Matter?
« Reply #64 on: January 21, 2014, 11:18:08 am »
Not likely with 10 ma of available current and no heater voltage available. That is the reason tube mics have several wires in their cables, high voltage, heaters, ground and differential audio.

A bipolar powered transistor mic would require a + voltage, - voltage, ground and polarization voltages. The advantages are no current limiting, no single ended audio paths and capacitors, higher headroom and lower noise. Remote control of patterns would also be possible.

20 years ago there might have been some excitement and buyers for such designs, but with a busted recording biz there are no takers.

Offline boz6906

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Re: M49: Does it look authentic? Does it Matter?
« Reply #65 on: January 21, 2014, 12:45:43 pm »
AT makes a tube mic that can run on 48Vdc at 3mA, the AT3060:

"This is the first tube mic I've encountered that doesn't need a separate power supply it runs from regular 48V phantom power and draws only 3mA of current. This seems impossible when you consider that conventional tubes require high plate voltages and high heater currents, but the AT3060 uses no conventional tube. It doesn't even use a miniature military-grade Nuvistor tube. Instead it uses a miniature low-current tube developed for use in hearing aids, the aim being to achieve tube warmth at a lower UK price point and without the need for bulky power supplies."

http://www.soundonsound.com/sos/jul03/articles/audiotechnica3060.asp

Heater should be no problem, there are tab-type switching dc-dc chips that can output 6-12 Vdc from 48Vdc.

I've actually seen the tube-type hearing aids, shirt pocket size with an earphone, they ran on 15 Vdc batteries.

Hmmm, maybe we should start buying up the NOS Raytheon CK series peanut tubes...

Offline soapfoot

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Re: M49: Does it look authentic? Does it Matter?
« Reply #66 on: January 21, 2014, 05:20:42 pm »
With heaters, it's not usually the voltage required that's difficult, but rather the current drawn.

Offline boz6906

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Re: M49: Does it look authentic? Does it Matter?
« Reply #67 on: January 22, 2014, 11:56:03 am »
Right, but a 6148 heater only needs 10mA at 1.25V and plate at 15Vdc, no problem from standard 48Vdc/10mA phantom.