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Old November 30th, 2005, 05:32 AM   #1
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Looking for a good mic preamp

I've done a bit of research and I'm kind of amazed at the paucity of real specs, so far all I read about is 'warm' or 'tube' or some might even suggest 'low noise' but no actual figures. The only ones putting numbers to the hype are Sound Devices, are they the only ones trying?

What I'm looking for is something that comes close to the theoretical limits, from memory around -128dBV equivalent, with enough gain to make that usable, I remember 30 years ago high end preamps were coming in around -110 dBV, hopefully they've improved a little since then.
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Old November 30th, 2005, 08:31 AM   #2
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Sound Devices mic preamps will get you -128dBV noise at 66dB gain.
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Old November 30th, 2005, 09:50 AM   #3
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The theoretical limit for a 50 Ohm input impedance would be -144 dBv (assuming a source noise temperature of 293 Kelvins and 20KHz bandwidth). For a 1K input impedance it would be - 130 dBv and for 4K input impedance -126 dBV. Modern amplifiers in the audio range have noise figures of at worst a couple of dB so a good preamp should offer noise levels a couple of dB higher than the numbers I just gave (e.g. -128 dBV for 1 K input impedance).
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Old November 30th, 2005, 10:49 AM   #4
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Not to be discouraging, because specs can be very helpful, but, to quote Count Basie: "If it sounds good, it IS good!"

I'd rather have 100db and good sound than 110 and....

A tube preamp is used to warm things up a little, ie. to add noise! Pleasant sounding noise, but you're adding something the mic isn't hearing. (which can be a good thing).

Manufacturers' specs can be a little misleading. They might just cover the preamp stage and not include the tube stage, for example, because if they did they wouldn't look so good. Some manufacturers don't publish certain specs because there are no industry standards in how to measure them. Others do their best, others narrow down the measurements until they find something they can brag about.

IMHO as your search narrows you should be out there listening to these preamps.
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Old November 30th, 2005, 02:54 PM   #5
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If I was close micing instruments or voice then yes, I might be interested in a 'warm' sound however that's not the application in this case although it seems to be the market that most manufacturers are targeting.
In this case the preamp is being used for recording distant / faint sounds so S/N is the most critcal factor. Obviously add to that the sensitvity of the mic itself!
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Old November 30th, 2005, 03:48 PM   #6
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Bob, have you looked at any of the PSC stuff? I've heard
they make high-quality components.

http://www.professionalsound.com/Cat...Promix%201.htm
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Old November 30th, 2005, 06:24 PM   #7
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Bob, thanks for the clarification - unusual app? Whatever.

Of course you're probably also concerned with low self-noise in mics.

I think Mr. Largent is on the right track - I'd check out some of the higher-end location mixers such as Sound Devices, Shure, etc. Also, there are the Zaxcom, HHB, and Sound Devices hard disc recorders that include mic preamps.

I think it's probably a strikeout for most standalone preamps, almost all either include a tube stage or are designed to get multiple tracks to line level.

Have you looked at the apogee digital converters that include preamps?
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Old November 30th, 2005, 10:18 PM   #8
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What recording device will you be using, Bob?
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Old December 1st, 2005, 04:15 AM   #9
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I'm using an Edirol R4 which for my money is a pretty decent effort however I've been trying to help out another R4 user who's finding he's hitting the noise floor in the mic preamps. He's recording orchestral works from some distance and the solo quiet instruments are his problem. Not being helped at all by using low sensitivity mics which is the first thing I'd have looked to address.
For myself so far I've only got one mic that gets used for just about everything, a Rode NT1A which is about as quiet as a mic can get at 5 dBA and I'd like to be able to make full use of its noise performance. Maybe I'm the odd man out these days but noise is the one thing that I really don't like, drives me nuts listening to a lot of movie soundtracks when I can hear the gates and compressors working because the noise gives the game away
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Old December 1st, 2005, 05:12 AM   #10
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None of the really high-quality pres are cheap.
About the cheapest really good ones seem to
be the Sound Devices.
If you're just using the one mic (i.e. not two
mics) I'd suggest the Sound Devices MP-1.

What's the S/N ratio on your Edirol R4, both line-in
and mic-in. I have read somewhere that the S/N
on the R1 for line-in is actually not that great.
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Old December 1st, 2005, 09:21 AM   #11
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Quote:
Originally Posted by Bob Grant
He's recording orchestral works from some distance and the solo quiet instruments are his problem.
Seems to me mic *placment* is the real problem here...nothing technical about that...my .02
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Old December 1st, 2005, 03:00 PM   #12
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Quote:
Originally Posted by Dave Largent
None of the really high-quality pres are cheap.
About the cheapest really good ones seem to
be the Sound Devices.
If you're just using the one mic (i.e. not two
mics) I'd suggest the Sound Devices MP-1.

What's the S/N ratio on your Edirol R4, both line-in
and mic-in. I have read somewhere that the S/N
on the R1 for line-in is actually not that great.
My only gripe with the R4s line inputs are they're too sensitive, feeding them +4 I'm having to use 10dB external pads, I guess better too much gain than too little. At that setting coming off 1/4" tape from a Dolby SR decoder my meters read -90dB from blank tape, stop the transport and they read nothing, no complaints there. I know that's not a definative test but more real world with leads connected etc.

Sure mic placement is the answer but sometimes that just isn't possible, or even desirable. Ever tried to put a lav on a tiger to record the sound of it panting.
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Old December 1st, 2005, 05:53 PM   #13
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Quote:
Originally Posted by Bob Grant
My only gripe with the R4s line inputs are they're too sensitive, feeding them +4 I'm having to use 10dB external pads

That's the same problem they're saying about the
MicroTrack. Actually, I think MT can't even handle
+2!
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Old December 2nd, 2005, 07:53 AM   #14
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I should clarify that comment in fairness to Edirol, they'll handle +4dBM, probably quite a bit more before you overload the front end, it's just that I end up with the gain set way down which makes it hard to set to reference, the pads just give me a bit more ease of use. Probably would have been nice if Edirol added switchable pads but then again it is built to a price!
Provision for an external battery would have been a nice feature too but one I can easily add. Seeing as how I picked this unit up on the last day of NAB for USD 1200, I'm sure not complaining, it's got 95% of all things I wanted in such a unit and none of the annoyances of the competition.
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Old December 3rd, 2005, 06:21 AM   #15
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Did I miss where the mics being used for the orchestra were mentioned?

The NT1-a are low noise, but the NT2-a have a more flatter top end.

Regards,

Ty Ford
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