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Mic attenuator idea - someone should make this! Single-Channel Preamps
Old 22nd December 2010
  #1
Mic attenuator idea - someone should make this!

I use vintage mic pres (like RCA OP-6 and Ampex 350) which have so much gain that pads are often required between the mic and the pre. I've tried several inline pads and they all degrade the sound somewhat, each in it's own way.

I'm told that ideally a pad should be built to match the specific impedances of the mic and pre being used.

So what I want is a high quality passive mic attenuator box with XLR I/O, selectable input and output impedances, and selectable amounts of attenuation. [edit] and a phase reverse switch as suggested by indecline.

Is there such a thing already in existence? If yes, I haven't been able to find it. If no, can someone please invent it?

.
Old 22nd December 2010
  #2
Registered User
That sounds like a brilliant idea ... it would be nice if it could work at Mic or Line level too ...

I imagine a small passive stompbox with XLR's and some switches ...

Alternatively, some mics put out close to line level and don't really need a preamp. A quality phantom power box might allow you to go direct to your A/D ...
Old 23rd December 2010
  #3
And a phase reverse button!!
Old 23rd December 2010
  #4
Quote:
Originally Posted by indecline View Post
And a phase reverse button!!
Yes! Those old pre's don't have 'em.

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Old 23rd December 2010
  #5
Gear Addict
 

Wow, my sincere and unabashed compliments on the pedigree of your large rack (did that come out right?)

Your idea sounds great. I'd buy a 2 channel or higher version. Are there patchbays out there with all these features? One would think so if it's possible to change loading, input levels and phase passively. Is it?
Old 24th December 2010
  #6
OK, assuming from the lack of responses that no such box exists, does anyone have any suggestions as to who could custom-build me one?

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Old 24th December 2010
  #7
Gear Nut
 
John Nonjohn's Avatar
 

A-Designs ATTY?
Old 24th December 2010
  #8
Quote:
Originally Posted by John Nonjohn View Post
A-Designs ATTY?
Thanks, but ATTY goes after the mic pre. I need something before the pre. Maybe A-Designs can build me something...

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Old 24th December 2010
  #9
Old 24th December 2010
  #10
Lives for gear
 
Daedalus77's Avatar
Am I missing something? If the mic-pre is the source of the inordinate gain—rather than the mic having too much gain for the preamp (which would be odd)—I'm confused as to why you want to attenuate the signal going into the preamp. Is this not so much a gain issue as an impedance-matching issue? Do you have this issue with all manner of microphones—dynamics and ribbons (lower-output microphones) and condenser (independently-powered) mics?
Old 24th December 2010
  #11
Quote:
Originally Posted by GYMusic View Post
Thanks. I might have to make several pads for different mic/pre combos...

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Old 24th December 2010
  #12
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emrr's Avatar
You need some advanced tech skills and test gear on hand to sort out an ideal pad for a given mic AND a given pre. Otherwise it's an average guess. I think we're splitting hairs; if it's too hot, you need a pad OR a different pre. That's the only practical observation.

Phase reverse at mic level is stupid. If you have a balanced output, why on earth would you do it at low level on the input side?
Old 24th December 2010
  #13
Quote:
Originally Posted by Daedalus77 View Post
Am I missing something? If the mic-pre is the source of the inordinate gain—rather than the mic having too much gain for the preamp (which would be odd)—I'm confused as to why you want to attenuate the signal going into the preamp. Is this not so much a gain issue as an impedance-matching issue? Do you have this issue with all manner of microphones—dynamics and ribbons (lower-output microphones) and condenser (independently-powered) mics?
Take my RCA OP-6 pre for example -

Rebuilt RCA OP-6 Ribbon Mic Preamp All Tube 1930s RARE - eBay (item 110626277009 end time Dec-28-10 12:16:20 PST) (this one's not mine BTW)

- it was built in the 1940s for broadcast use. It's likely optimized for RCA ribbon mics and does sound amazing with my AEA R44CE. It has 90dB of gain and even on it's lowest setting it is too hot for recording a vocal with my U67. Even a passive ribbon mic on a loud amp is too hot for it. But the preamp sounds so good that I want to be able to use it. All the inline pads so far have diminished the sound. So I need a quality, flexible mic level attenuator with variable impedance so I can use various mics with it and my other vintage pres. I have similar problems with my Ampex 350 and Ampex 400 pres.

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Old 24th December 2010
  #14
Quote:
Originally Posted by emrr View Post

Phase reverse at mic level is stupid. If you have a balanced output, why on earth would you do it at low level on the input side?
Maybe so. It would be convenient because my ancient preamps have no phase reverse switches, but I can work around that in other ways...

.
Old 24th December 2010
  #15
Gear Guru
 
u b k's Avatar
 

Quote:
Originally Posted by Trakworx View Post
OK, assuming from the lack of responses that no such box exists, does anyone have any suggestions as to who could custom-build me one?

I could recommend at least one or two guys in nyc but you're on the left coast, not sure if that's an issue.

There are more than a few killer techs on the geekslutz forum, Brian Roth comes to mind. I imagine a post on that forum would get you what you need.


Gregory Scott - ubk
Old 24th December 2010
  #16
Lives for gear
 
Ruudman's Avatar
 

You could call Magneto Audio Labs and ask them about a customized version of VariOhm
Old 24th December 2010
  #17
Quote:
Originally Posted by u b k View Post
I could recommend at least one or two guys in nyc but you're on the left coast, not sure if that's an issue.

There are more than a few killer techs on the geekslutz forum, Brian Roth comes to mind. I imagine a post on that forum would get you what you need.


Gregory Scott - ubk
Thanks Greg,

Great minds think alike! heh

I already posted in Geekslutz and I PMed Brian. Haven't heard from him yet, but am making some progress. thumbsup

Mic attenuator idea - someone should make this!

Thanks everybody!.
Old 24th December 2010
  #18
Quote:
Originally Posted by Ruudman View Post
You could call Magneto Audio Labs and ask them about a customized version of VariOhm
Ooh, that looks promising! Thanks!

.
Old 27th June 2011
  #19
Lives for gear
 
DONNX's Avatar
 

I run across those problems as well. My tech makes a custom box.

Very useful tool to have around the studio.

Crane Song Avocet does all this, even though its a monitor controller by heart.

Best W
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