Question: "True Unity Gain" vs " Inherint Gain"..?

[Snatchman]

Hi all. As I've seen these terms quite often, what are the pros and cons between the two in a mic pre-amp? Which one perform better or, in what senario should one be chosen over the other? Thanks!......

[Snatchman]

Originally Posted by Snatchman

Hi all. As I've seen these terms quite often, what are the pros and cons between the two in a mic pre-amp? Which one perform better or, in what senario should one be chosen over the other? Thanks!......

Ahummmmm....!...

[Rick Sutton]

I've know of "gain". I know about "unity gain". The other terms sound suspiciously of "marketing speak" but since I've never run into them it's hard to say(although inherent gain sounds to be the amount of gain supplied "inherently", you know, level out less level in equals inherent gain, but that's just a tiny piece of the technical specs). As to what they could possibly have to do with differentiating between mic preamps is a real mystery to me. Sorry to be of no help but I think you might be barking up the wrong semantic tree.
Or are these some new buzz terms (sorry Tim) that I haven't had the fortune of experiencing yet?

[EveAnna Manley]

If something (a box, a circuit) has "unity gain" then the level coming out of it will equal what went into it.

"Inherent Gain" I dunno exactly what you mean either, but I would guess that it would be something like Joe Blow EQ has a passive EQ with a 20dB insertion loss and then it has a 20dB makeup gain amplifier to bring the box back up to "unity gain".

[tINY]

Could be "voltage gain" from an input transformer....



-tINY

[T.RayBullard]

inherent gain is simply the exisiting gain of a unit...nothing fancy there. They just threw a word in there to make it sound cool.

[T.RayBullard]

Originally Posted by tINY

Could be "voltage gain" from an input transformer....



-tINY

just curious man...why do you use that font? sometimes if you type a lot it is difficult to read...just curious.

[tINY]

I use it for just about everything, kinda like a signature, I guess. In email I bump the size up to 11 point.

Maybe I should make it bigger here too...


-tINY

[Snatchman]

Hey...thanks for the replies all. Maybe I'm asking something I'm not sure how to ask...!.. ..But...sometimes a mic pre boast " 25 to 60 db gain" ( inherent gain), then one mic pre may boast " 0 to 60 db" true unity gain.. This is what I'm trying to differentiate!So....do the " 25 to 60 db" gain mean, there is already 25 db of gain applied before turning up the gain, or am I 'ciphering this wrong?..

[EveAnna Manley]

First off "GAIN" is defined as the amount of amplification a given circuit (or complete box, if you want) has, usually expressed in dB's. The word "inherent" that you read somewhere is a bit superfluous, I agree.

To give an example:
In my micpreamps, there is a switch called "GAIN" that changes the amount of negative feedback and makes the tube amplifier amplify things more or less in 5dB steps. So this switch changes the GAIN of the preamp circuit, (how much it is amplifying) in my case from 40 to 60dB's.

There is also an input attenuator which allows how "much" tunes you let into the unit.

Thus it would be possible to make the preamp produce "unity gain" with any of the gain settings by allowing only the amount of input signal into the unit which would result in the same amount of level coming out of the unit. Because true to its name, the input ATTENUATOR would be reducing the signal before it got amplified by the tube stage.

Thus if you had a 0 dBv signal, knocked it down by 40dB on the input attenuator, then reamplified it with the tubes producing 40dB of gain, you would then have a "unity gain" situation.

Or if you had a -10 dBv signal, knocked it down by 30dB on the input attenuator, then reamplified it with the tubes producing 60dB of gain, you would then have a resulting signal that is 30dB's more than what you went in with, or an overall gain of 30dB from the whole box at those settings and your signal would be at sitting at +20dBv on yer meters.

***dBv,m,V,WTF,etc....... that's another subject, and one that's been done on a cool r.a.p. tshirt...

[Drifter]

I'll give you guys a hint. Research communication antenna systems.

There is definitely an answer to this question!

[ulysses]

Okay, moving right along.

I *think* what the OP is asking is whether a preamp that goes all the way down to unity gain has any advantages or disadvantages compared to one whose available gain range is higher, such that the minimum gain is still greater than unity. Of course the obvious answer is that when you have a signal that needs less gain than the lowest setting on your preamp, you find yourself wishing it had a lower gain setting. If you actually need unity gain, the even more obvious question is why you think you need a preamp at all.

When using a preamp that doesn't have a gain setting low enough for your needs, an input attenuator or pad can be used, as Ms. Manley explained, to scale your input signal to the amplifer so you don't hit your head on any low-hanging limbs along the way. In purely technical terms, this could be considered an inferior method of dealing with the situation because the amplifer with "too much" gain will then impart "too much" distortion and noise, as compared to a preamp with less gain that didn't require input attenuation. Or so the theory goes.

Which brings us back to the reason why you're running your signal through a preamplifier even though you only need about zero decibels of gain: Because you like the sound of it. The Manley preamp makes your signal sound sweet as hell, and you want to have that sound even though you don't happen to need the 40-60dB of gain because you used a high-output microphone on a loud source. For example. So you pad the input about 50dB, and then you get those 50dB right back from the amplifier. There's a bit more noise, but you don't care because it's rock and roll. Or because it's very quiet chamber music, but the noise floor of the performance hall is higher than the resulting noise from the preamp. Or even because wideband noise at moderate levels is actually not objectionable. Whatever. You also end up with a bit higher distortion as a result of the "unnecessary" amplification stage, but you're okay with that because it's the reason you bought that particular preamp in the first place. It sounds good.

Except sometimes it doesn't. Sometimes, the sweet sound of the preamp with a minimum of 40dB of gain doesn't make you wet. Sometimes you already have exactly the sounds you're looking for, and you just need to make it nine decibels louder. So you wish you had a preamp with a knob that went all the way down to, well, less than 40. Less than 10. I guess zero would be okay.

So which preamp is better? Is that your question?

[EveAnna Manley]

Rats... I forgot we score about 20dB of gain in the input tranny before the attenuator, but no matter for general illustration.

What Ulysses says is correct:

Use whatever you like if you like the "sound" of it and it's not too noisy, enough to bother you. It's not like you are going to break anything or burn something up by using too much gain (except yer speakers or your ears, but you'll hear that coming on...)

Or look into the concept of proper gain scaling using the right amount of gain to get you to the next device and pick gear that does this to your sonic preferences/delight...

[paully]

Originally Posted by ulysses

... Which brings us back to the reason why you're running your signal through a preamplifier...

>>>>>>>>>>>>>>>>>>
It's a lot easier than hooking up a bunch of batteries if all you want is phantom!

Paul

[Snatchman]

Hey.....Ulysses, that's it...! That's what I was trying to ask.... .. I'm not savvy enough to put it in words... ... EveAnna, you you hit the nail head also! Thanks, that's why you all are good at what you do..!....

[Drifter]

I personally have not seen the real explanation or definition of "Inherent" gain yet.

Anybody?

[tINY]

Voltage out = voltage in (for unity voltage gain)

There are other ways of figuring gain, though. That passive input transformer that scores 20dB gain for Eve_A has near-unity power gain (a slight loss). So it has curent loss and votage gain.

The apparent gain you hint at is due to antenae that don't radiate uniformly into free space (like a 5/8 lambda) that gets more power to your receiver than a simple 1/2 lambda dipole would at the same distance. Horn-loaded speakers work the same way.

(no, I didn't look that up)



-tINY

[Drifter]

Inherent gain has to do with source impedance (Microphone), velocity factor of the conductor (Cable) that drives a load ( input of mic pre) and the phase and amplitude relationship of the original signal and the final output of the device driven by the source.

These example devices like mic and a pre can be many different things.
Like pre and power amp, transmitter and antenna and so on.

[Drifter]

Oh and if you dealing with unbalanced equipment then surge impedance is a factor as well. Surge impedance is the "Ohm" rating of any given type of coax like a guitar cable and what not.

[Rick Sutton]

Originally Posted by Drifter

Inherent gain has to do with source impedance (Microphone), velocity factor of the conductor (Cable) that drives a load ( input of mic pre) and the phase and amplitude relationship of the original signal and the final output of the device driven by the source.

Or for us technically challenged working stiffs:

What you get from the goesouta jack depends on what 'ya put into the goesinta thingy divided by all the crap that happens to it on the way. It is either affected positively or negatively depending on how much money you squandered on the device in question that could have been spent on your kid's college education so they could explain it to you using all the fancy terms.

[Drifter]

LOL

[tINY]

Velocity factor has nothing to do with gain. In fact, audio frequencies are so low that you can ignore the time delay on a cable unless you are the telephone company.

Besides, what does that have to do with mic preamp specs?



-tINY

[Drifter]

Frequency has nothing to do with velocity factor, well it does but not like you are thinking. Velocity factor is the percentage of the speed of light electricity travels through a conductor.

[ulysses]

None of this has anything to do with what they guy was asking. Sure, he pulled some terminology out of his ass, but we can see what he means, even if it's completely different from the usage you guys know.

An "API style" mike preamp, for example, has an input transformer with a 1:8 ratio; a non-inverting amplifer incapable of less than unity gain; and a 1:2 output transformer. So his term "inherent gain" is referring to the 24dB (23.45dB into a 600-ohm load) that you get out of such a circuit no matter what you do. In typical cases, the gain control installed will limit the amplifer's bottom to a gain of 1.8 (20k feedback resistor and 25k reverse-log gain pot) so the "inherent gain" would be about 29dB. That number can be increased by cranking up the gain pot, but it can only be decreased by using an attenuator before or after the preamp circuit.

I think the reason this is important to understand can be illustrated by looking at the mike and line inputs on a typical console. On many consoles, the line input is simply routed through a resistive pad before being fed into the mike preamp. Thus, if you don't like the sound of the onboard preamps, using an outboard preamp isn't going to help you avoid them (unless you avoid the console entirely). The "inherent gain" of the channel inputs will contribute to the "inherent sound" of the console. This is almost always the case in cheaper mixers, but it's even true for my Amek BCII.

[Drifter]

Originally Posted by ulysses

None of this has anything to do with what they guy was asking. Sure, he pulled some terminology out of his ass, but we can see what he means, even if it's completely different from the usage you guys know.

You know it seems you don't like it when someone other than you has the correct answer. There is no need to belittle a poster because they came up with a definition that is correct, but obscure.

tutt

[Snatchman]

.....sho nuff' now..!..............................................