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 on: March 29, 2017, 01:41:36 pm 
Started by Recording Engineer - Last post by klaus
Though I now have egg on my face that does not wash off easily (my ignorant comments regarding "magnetostriction"), I am on firm ground with this part of your inquiry:

Nothing should ever rattle inside a microphone, regardless of type or brand, because such rattling is invariably transmitted to the mic's output as audible noise. 

If a transformer rattles in its installed position inside a mic, it is defective, and unsuitable to work as intended.

 on: March 29, 2017, 12:32:25 pm 
Started by Recording Engineer - Last post by boz6906
From my experience you want ZERO mechanicsl noise from any part, especially in a high-gain mic preamp.  High quality audio transformers like UTC are even 'potted' to prenent mechanical movement.

I would hesitate to say your transformer is defective, the mounting scheme may somehow clamp the transformer to prevent the rattle.

Do you have a website or product info about this transformer from the manufacturer you can share?

 on: March 29, 2017, 10:22:22 am 
Started by AusTex64 - Last post by AusTex64

Thansk for the link. I had forgotten about that discussion. I must be getting old...

I am wondering about the difference in sound between the two capsules. I have looked at the frequency response plots for KM54 and Gefell MV691 with M94. The Gefell shows a 5db lift in the high frequencies, which is clearly audible when recording stringed instruments, which is my primary use for these mics. KM54 plot is much more flat in the high frequencies. So does Neumann tame the capsule HF rise with the buffer?

I still need to do a side by side comparison with KM54 and my tube modified Gefells.

 on: March 29, 2017, 04:45:58 am 
Started by AusTex64 - Last post by panman
We did discuss that before here: http://repforums.prosoundweb.com/index.php/topic,36984.msg535981.html#msg535981

All the age/quality issues aside, the only meaningfull difference is the backplate-holes. I can only speak from the older ones, but to my knowledge the current M94-backplates are ceramic and may have other differencies too.

 on: March 28, 2017, 10:41:44 pm 
Started by AusTex64 - Last post by AusTex64
What exactly are the differences between Neumann KK54 and Gefell M94? I have not had opportunity to study both. Thanks!

 on: March 28, 2017, 06:04:24 pm 
Started by Recording Engineer - Last post by Recording Engineer
The couple of people I've shown it to have years of audio electronics experience of all-type and I made no mention of the rattling; they independently commented on their own saying their only real concern would be the microphonics-potential.

I did contact IOAudio to see if this was normal for their product or defective. He says it's the way it was designed and will go away once mounted. I'm satisfied with the response should it really go away. However, I am quite surprised I've not seen anyone else express concern anywhere. I was even more surprised to hear him mention magnetostriction (the way Neumann did) and that I've never heard anyone ever mention that anywhere either! This is why I thought it would be best to ask about it here.

If this really is so or some-other-type of "changing-process" happens once mounted and used, would it be expected that original vintage Neumann transformers wouldn't ever rattle even after being unmounted?

 on: March 28, 2017, 01:43:06 pm 
Started by Mikeyod - Last post by Mikeyod
Hi guys,
I've got an A80 2 inch 24 track Mark IV and it has begun randomly slowing down.
After about a half hour the problem is gone and it runs fine.
What I have done/checked.
Stabilizer voltages all check out fine.
All motor caps have been replaced.
All motors have been rebuilt by Athan corp. in Jan. 2017
Replaced timer IC on capstan control board
While viewing the 1600 Hz signal on a scope with frequency counter the frequency drops to around
1300-1375 Hz the second I hit the stop button the frequency comes right back up to 1600Hz.
When the freq. drops the tape tensions on both sides remain normal 300 on left 450 on right.
However if I turn the left tape tension sensor manually and lower the tension down to 100 the frequency comes back up to 1600Hz but falls off again as soon as I release it. All voltages on the stabilizer card hold steady when the machine slows down. Like I said after about half hour I can go about my business as usual and it will not slow down.
Any thoughts ? Thanks in advance.

Mike O'Donnell

 on: March 27, 2017, 10:30:25 pm 
Started by jdier - Last post by MikeZidd
Do this, it's never been known before.

 on: March 27, 2017, 05:13:26 pm 
Started by Recording Engineer - Last post by uwe ret
Transformer magnets, as used in condenser mics, are not ferromagnetic, so that phenomenon would not be encountered there.'

Practically all electrical transformers do rely on ferromagnetic core material and would be rather inefficient or non-functional without it.

 on: March 27, 2017, 05:04:01 pm 
Started by Recording Engineer - Last post by uwe ret
Actually as defined in Wikipedia:
Magnetostriction (cf. electrostriction) is a property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetization.
As noted in a previous post magnetostriction requires considerable energy, not encountered in microphones or elsewhere in conventional audio electronic equipment.
This has no relation to the rattling of transformer lamination as reported in the original post. Possibly one or more layers of the core material may be missing and/or this rattle may disappear when the transformer is properly installed, thereby affixing the ferromagnetic components.

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