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Author Topic: Is a preamp always necessary?  (Read 5138 times)

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Offline dklein

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Is a preamp always necessary?
« on: August 07, 2004, 01:05:16 PM »
Now that my recording chain is all broken into pieces, I'm wondering if the pre is always necessary.
KM184 > V2 > A62 > laptop

The emagic A62 is an audio interface that'll give full scale digital from a 0 dBv input (+2.2 dBu)
I've also run into a V2 > UA-5 for a>d and the UA-5 gives fsd from a -10 dBu input on the rear.

At a loud show, I had to dial down the V2 to 10dB of gain and turn the trim pots down (-10dB) for a total of 0 dB gain!
So is the V2 truly providing no gain here?  Or is there an additional output stage.  If the mics are in fact generating enough output at high SPLs, what if I were to just provide phantom and run straight into the a>d.  Are there impedance matching issues?  Is this one of the additional functions of a pre?

UA-5
Nominal Input Level (variable)
Input 1/2: -50 -- 0 dBu
Input 3/4: -10 dBu

Input Impedance
Input 1/2 22 k ohm
Input 2 (Hi-Z) 500 k ohm
Input 3/4 12 k ohm

A62
Input level
0 dBv, +2.2 dBu
unknown input impedance - probably standard consumer line level

V2
Input impedance 1600 ohms

Are ya out there JK?
KM 184 > V2 > R4
older recording gear: UA-5  / emagic A62 / laptop / JB3 / CSB / AD20 / Sharp MT-90 / Sony MDS-JE510
Playback: Pioneer DV-578 > Lucid DA 9624 >many funny little british boxes > Linn Isobarik PMS

Offline creekfreak

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Re: Is a preamp always necessary?
« Reply #1 on: August 07, 2004, 01:21:23 PM »
as doug oade says...the best pre-amp is no pre-amp
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Offline C.Clark

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Re: Is a preamp always necessary?
« Reply #2 on: August 08, 2004, 04:34:06 AM »
i made some nice tapes in a small room with my audio technicas powered
by a ps/2 in to an ad500e, and those tapes were nice.  and sometimes
its nice to just have one box.
Current Rig:
Mics: Neumann SKM184, Neumann SKM185, AKG C414 XLS/ST
Recorder: SD MixPre-6ii, SD MixPre-10ii
Extras: SD MixPre-D, SD USBPre2, Sony TCD-D8
-------------------------------------------------------------------------------
Former Rigs:
ADK TL --> Segue Dogstars --> SD 722
AT4051a --> Segue Dogstars --> MP-2 --> SD 722
AT4051a --> V2 --> MiniMe --> VxPocket V2 --> Laptop
AT4051a --> V2 --> MiniMe --> Sony TCD-D100
AT4051a --> V2 --> Mod SBM-1 --> Sony TCD-D100
AT4051a --> MP-2 --> AD1000 --> Sony TCD-D100
AKGC1000s --> Denecke PS/2 --> Denecke AD-20 --> Sony MiniDisc
-------------------------------------------------------------------------------
http://db.etree.org/cpclark

Offline eric.B

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Re: Is a preamp always necessary?
« Reply #3 on: August 09, 2004, 01:57:05 PM »
when possible.. give just a phantom powered unit a try running into your a/d/recording device..  if you can get decent levels that is..   you will notice an upgrade in spacial detail, but your gonna have to watch your levels..   I had GREAT results running akg568's straight into a DAP1 for acoustic amplified stuff(low levels,no percussion,no bass  etc)..   or mics>akgB18(phantom)>line in>DAP1 

another quote ...

"theres no mic preamp like no mic preamp!"

and

what we all need is that "straight wire" with gain!

eBowne


We have a system that increasingly taxes work and subsidizes nonwork.  ~Milton Friedman

Offline som

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Re: Is a preamp always necessary?
« Reply #4 on: August 10, 2004, 11:04:01 AM »
So let me get this straight....

With my simple "rig" (see my signature), as long as I get adequate levels on the D7 (going line in), there is no reason to get a preamp, and I am actually better off without one?

So why do so many people typically run a preamp? Is it because most mics are not as sensitive as the AT's and do not provide a strong enough signal? Is there that much difference in the sensitivity of the various mics? In other words, I have the D7 on, say, 4 and I'm getting good levels at a particular show. I switch to some AKGs or ADKs or Studio Projects or whatever, add a phantom power box, and I can no longer get adequate line-in levels, even turing the D7 up? That's when the pre becomes a "necessary evil"? 

Sorry for the stupid newbie questions!
AT ES943/C's > Church Audio ST-9100 > iRiver H100 (Rockboxed)

Offline Tim

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Re: Is a preamp always necessary?
« Reply #5 on: August 10, 2004, 11:14:15 AM »
some people run a preamp because they like the way it sounds, like the m148 or psp2 which have a nice amount of low end colour
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Offline eric.B

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Re: Is a preamp always necessary?
« Reply #6 on: August 10, 2004, 12:37:39 PM »
With a preamp(besides the colour, but i run a v2 with little to no colour), you have more versatility when it comes to the varying levels at shows..  along with that.. each mic has it's own "sensitivity" which can hurt/help in the many many taping situations..  example:
I used to run a pair of akg's that had a sensitivity # at 11, which meant that with a phantom unit running line in to a DAP1, the show had to be real loud(or i had to be real close) to get decent levels..  for large venues(arenas, sheds etc), I would use a pair of trransformers for each channel to get a tiny boost of gain to get levels of say -5db ..    which was acceptable..  but small clubs/bars situations where i was close to the sound source, i could use just the phantom and be safe, or like i said, with amplified acoustic stuff i could run Mic-in to the DAP1 and get good results(more clarity/dynamic range).. 
 
If you can get good levels, and like the way your mics sound on their own, use phantom line-in(with or without transformers) into the deck when you can, but in some situations, it will not be your best choice..   
all i can say is experiment..  it's what i did..  but then again i make crappy tapes..   ::)
follow some examples of other tapers, but dont take what they say at being pure truth..  trust YOUR ears..
with the equiptment you have.. id try runing phantom>line in    in a few situations where you'll think youll get levels adequate enough, then get a pair of tranformers when you need just a touch more gain.. 

I was trying to find a thread from years past on the oade board..   but couldnt..  this might help a bit, and would require a bit of research on your part..

Subject:  Re: Is is possible? PS2>M1, no mic pre
Date:  Wed, 26 Feb 2003 14:09:16 - (EST)
From:  Doug Oade <doug@oade.com> 


Hello!
 Yes, but it depends on the mics. The AKG480s will do that and sound
great. EW mics need a transformer. You need to know two thing to
know if your mics will run line in without a transformer. One, they
must be able to be unbalanced with a cable and two, they need to have
13mv/Pa sensitivity rating or higher to work for most PA taping.
I hope this helps..Doug



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Offline som

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Re: Is a preamp always necessary?
« Reply #7 on: August 10, 2004, 01:34:46 PM »
Thanks for the reply and info!

Quote
One, they must be able to be unbalanced with a cable

I'm not sure what this means. Anyone care to take a layman's stab at the whole balanced/unbalanced thing?  :)

I did find this on the web:

Quote
What makes a balanced connection work, is some electronic trickery that makes the noise on the line phase cancel itself out of existence. (Remember our feature on Phase?) Here's how it happens. A balanced connection first runs through a differential amplifier which splits the hot signal into two and flips one half 180 degrees out of phase. This travels along the cable as plus and minus along with the ground on three separate conductors (on an XLR, pin 2 is hot, pin 3 is cold and pin 1 is ground). Along the way, the usual noise is encountered and picked up by the line. At the other end of the connection, the minus is flipped back into phase and you end up with a plus and a ground again, just as it was when you started. The difference is, that now the noise is out of phase with itself and cancels completely.

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Offline jk labs

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Re: Is a preamp always necessary?
« Reply #8 on: August 17, 2004, 09:27:11 AM »
So let me get this straight....

With my simple "rig" (see my signature), as long as I get adequate levels on the D7 (going line in), there is no reason to get a preamp, and I am actually better off without one?

So why do so many people typically run a preamp? Is it because most mics are not as sensitive as the AT's and do not provide a strong enough signal? Is there that much difference in the sensitivity of the various mics? In other words, I have the D7 on, say, 4 and I'm getting good levels at a particular show. I switch to some AKGs or ADKs or Studio Projects or whatever, add a phantom power box, and I can no longer get adequate line-in levels, even turing the D7 up? That's when the pre becomes a "necessary evil"? 

Sorry for the stupid newbie questions!



An external pre-amp adds degrees of freedom.  I.e. it gives you more choice in configuring
the recording chain. 

The possibility of adjusting the signal levels (gain & attenuating pads) is only one of many features but admittedly
it might be the most important one especially with low-output mics.   

The potential for using truly dedicated circuitry within the mic-pre, resulting in cleaner
sound, lower noise floor, deeper bass, less low end rolloff (phase delay) etc is there but
the purchase price of those mic-pres quickly get pretty dedicated too.   

Then there are issues of transformer/non-transformer, solid state, tube, large geometry
discrete devices, no-global feedback, voltage feedback, current feedback etc etc ad infinitum...

The possibility of tailoring the sound with bass rolloff filters, high boost filters exist but now we start
to get into issues that are very mic dependent. 

The next level would probably be to optimize the sound of a mic & mic-pre combo where the mic-pre 
"compensates", "corrects" or "adds/subtracts" to the sound of the mic. A condensor mic is after all a highly complex
acoustic-mechanical-electrical transducer where the designer needs to wrestle with a slew of competing
issues.  (Look at actually measured non-averaged frequency responces as a function of incident angle for a few
directional mics and you start to see why this topic contains way more surprices than any episode of temptation
island... )


Benefits:
The benefits of a mic-pre is self-evident if the levels need to be boosted
or the quality of the external mic-pre is such that the overall sonic result is improved.
An external mic-pre is also beneficial if the higher signal levels allow use of a cleaner, higher quality signal path
downstream (in the recorder all the way up to the ADC itself).

In consumer gear the mic-input is often a highly compromised port with little headroom,
poor linearity and scads of self-noise.  On the other hand,  if the line-input on the ADC is
of compromised quality then an external mic-pre will not be able to improve much on the overall
signal path because you can't wire around that weak link.       

Drawbacks:
All else being _equal_ a mic-pre will add noise, coloration, bulk, power needs etc etc ...  Some also present
rather low impedances to the mic bodies (or active heads) which then must work hard to drive the mic-pre
input.   

To conclude:
The pre / no-pre issue really becomes an exercise in carefully evaluating the benefits of a mic-pre 
up against the drawbacks. A mic-pre shouldn't be necessary if the mic is a perfect match to an already
existing high quality gain/line/buffer/ADC stage. 


Regards
Jon
« Last Edit: August 17, 2004, 10:01:41 AM by jk labs »

Offline jk labs

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Re: Is a preamp always necessary?
« Reply #9 on: August 17, 2004, 09:57:18 AM »
Thanks for the reply and info!

Quote
One, they must be able to be unbalanced with a cable

I'm not sure what this means. Anyone care to take a layman's stab at the whole balanced/unbalanced thing?  :)

I did find this on the web:

Quote
What makes a balanced connection work, is some electronic trickery that makes the noise on the line phase cancel itself out of existence. (Remember our feature on Phase?) Here's how it happens. A balanced connection first runs through a differential amplifier which splits the hot signal into two and flips one half 180 degrees out of phase. This travels along the cable as plus and minus along with the ground on three separate conductors (on an XLR, pin 2 is hot, pin 3 is cold and pin 1 is ground). Along the way, the usual noise is encountered and picked up by the line. At the other end of the connection, the minus is flipped back into phase and you end up with a plus and a ground again, just as it was when you started. The difference is, that now the noise is out of phase with itself and cancels completely.

The balanced connection between a balanced transmitter and a balanced receiver, IF DONE RIGHT, is quite effective at suppressing all common mode noise picked up equally by the two closely spaced conductors within the cable carrying the balanced signal from the source, through a noisy environment  (electromagnetic fields from power lines, lighting, lightning, transfomers, RF towers, cellulars etc etc) and to the receiver.

Imagine a long clothesline hanging out in the storm. The wind perturbs it violently with noise. Any gentle tapping by a friend at the far side of the clothesline would be lost in noise. 
Now hang a second one right next to the first. Hang it so close that the second line picks up the exact SAME noise. Do not apply any tapping to the second line.
Now amplify the DIFFERENCE in signals received from your end of the two lines and voila, the tapping at the far end of the first line is fully recovered.
(uhhrmmm This demonstrates that you can get the full benefit of balanced-line common mode noise suppression capability without a balanced transmitter :-) )


As for your first question:
For short interconnects, a fair distance away from mains cables etc, the problem with pick-up of EMC noise is typically way smaller than your inherent nosiefloor. 
To connect a mic with balanced output directly to an unbalanced line-input will require either a) some work or b) no work depending on how the mic is powered and how it's output is wired.   

Regards
Jon
« Last Edit: August 18, 2004, 08:31:32 AM by jk labs »

Offline MattD

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Re: Is a preamp always necessary?
« Reply #10 on: August 17, 2004, 10:41:14 AM »
To connect a mic with balanced output directly to an unbalanced line-input will require either a) some work or b) no work depending on how the mic is powered and how it's output is wired.   

Are there any other options? :P

Just giving you a hard time ... you know way more about most of this stuff than I do! +T for all of your useful posts.
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Offline som

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Re: Is a preamp always necessary?
« Reply #11 on: August 17, 2004, 11:50:36 AM »
Thanks for the posts! The clothesline explanation really helps.



I have a lot to learn.....nice that there are places like this to pick up information!

+T


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Offline jk labs

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Re: Is a preamp always necessary?
« Reply #12 on: August 18, 2004, 08:34:43 AM »
To connect a mic with balanced output directly to an unbalanced line-input will require either a) some work or b) no work depending on how the mic is powered and how it's output is wired.   

Are there any other options? :P

Just giving you a hard time ... you know way more about most of this stuff than I do! +T for all of your useful posts.

Options? How does a chilled bottle of homebrew sound? :-)

 

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Re: Is a preamp always necessary?
« Reply #13 on: August 18, 2004, 02:27:25 PM »
This is all Len Moskowitz's fault... :)

I think this all got started back when folks started noticing clipping when using the D7s mic pre...even at the low sensitivity setting. The soloution was to use the Line In instead...At very loud shows, folks were able to get enough gain off their microphones to drive the Line In. I think the Core Sound crowd were the first to make this asertion.

yes you may get "adequate" levels - but you are probably always risking under-recording...Unless you are sure you are clipping in mic pre...I see no reason not to use it...

and yes there are impedence issues - but I'm still foggy as to what the effects of mismatched impedence...?

Most folks who use externals just want a higher quality piece of equipment for that task...the idea being to deliver the signal to the recorder at line level...Line level is a bit more of a standard and has fewer varialbles compared to mic level...

Offline dnsacks

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Re: Is a preamp always necessary?
« Reply #14 on: August 18, 2004, 04:15:52 PM »
if, running mic in (or line in, I believe) on a d7/d8, you need to turn your level knob below 5 in order to not have digital overs, the mic pre IS going to clip/brickwall unless it's been modified (oade mod, etc.) to get past this problem. 

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Re: Is a preamp always necessary?
« Reply #15 on: August 20, 2004, 05:43:34 PM »
if, running mic in (or line in, I believe) on a d7/d8, you need to turn your level knob below 5 in order to not have digital overs, the mic pre IS going to clip/brickwall unless it's been modified (oade mod, etc.) to get past this problem. 

Huh? Whether you get digital overs has really nothing to do with where the level knob is...


and digital overs really have nothing to do with Mic Preamp headroom - any mic pre can be brickwalled...modded or not...brickwalling is an analog issue...

Are you saying the D7/8 pre is going to brickwall with any signal?

Offline dnsacks

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Re: Is a preamp always necessary?
« Reply #16 on: August 20, 2004, 06:35:33 PM »
yep -- my understanding is that if the signal being fed to a d7/d8 (mic in or line in) is hot enough to require you to turn the volume knob below 4 (threw in 5 to be safe), to avoid digital overs, it's too hot for the d7/d8's analog circuitry to handle and will cause the analog circutry to brickwall.

This was the reason that the oades started modding d7/d8 analog inputs.

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Re: Is a preamp always necessary?
« Reply #17 on: August 20, 2004, 07:07:25 PM »
I think the Oade mod is for the Sony Mic Pre (mic in) only...


From Oade

Here is a little information on a problem with Sony D7/8/100/PCM-M1's known as "brickwalling" . Many of you know that to record thru the D7/8/100/M-1 mic inputs and go over the -6 level on the level meter is bad news. Here is why, the mic preamp overloads. It is NOT possible to fully utilize the dynamic range of these digital recorders thru the mic inputs. The stock D7/8 mic preamp overloads with a -15 db input level when set on the low sensitivity setting. They overload at -35 db when set on the high sensitivity setting. The D100/M1 mic input overloads at -20db with the pad on and -40db with it off (i.e. set to 0 db). No matter which mics you use or what the signal source is, this is true. It takes a -10 db input signal to get to 0 db on the D7/8's meter using the line level inputs even with the record level knob at its highest setting. It takes a -5db input signal to get to 0db on the D100/M1. As you can see there is a 5 to 15db "hole" in the gain structure of this design. The upgrade rebuilds the mic preamplifier completely in the D7/8 and the D100/M-1.

 

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