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Fethead Phantom -can be a solution for low cost preamps?

carlo

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Hello to everybody,
Will an inline preamp like the Fethead Phantom ( it's the only available as other like Cloudlifter, Klark etc. only produce the version for dynamic mics; it draws about 1mA and passes the rest to the mic providing +18 db of gain ) could really produce a benefit with something like the Zoom H6 I own.
I understand that answers like " buy a Sound Device or a high end external preamp may have their sense, but budget matters and form factor also. As a musician I need to record on the fly when there is no time-convenience for proper setup ( i.e. just with H6 x-y capsule) or adding a couple of condensers on a stand if possible, all powered via a USB battery; for this reason a handheld is hard to beat, but you have to struggle with the -120 db EIN which adds noise with lowish sensitivity mics or recording at a distance.
Has any of you ever tested this product? I googled a lot finding that some find an improvement in S/N with cheap recorders, while others report no difference or- sometimes even worse results. The report go from "zero difference" to 7/8 db of better S/N, which is a clearly audible improvement. I've come to the conclusion that it probably depends a lot on both the type of recorder and mics involved in the chain.
I'd use these with condensers or also with a battery powered mic ( verified from the mic schematics that phantom would not touch the mic), all with sensitivities ranging from -48 to -42db; my expectation is that the boost will avoid raising the gain of the recorder, thus substituting the first 18 db with a "better preamp" ( Fethead is rated EIN -129), if it does make sense.
Any advice?
thanks
C
 

Blumlein 88

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Some inexpensive mic pres have even worse EIN specs at gains lower than 60 db. Some have about the same EIN from maybe 30 to 60 db. The EIN spec is measured at 60 db according to the standard. It's possible by using the fethead and turning down the Zoom you'll loose as much as you gain. Or if the Zoom ein holds up at lower gain you may reduce noise a few Db. Without knowing the zoom EIN at different gain settings no way to know.
 
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carlo

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Thanks,
I think it’s not easy to find measurements about Zoom‘s behaviour along the gain path....so there is no clue I guess?
Only - but I think it won’t tell anything- I can report that hiss is punctually appearing when the dial is between 5 and 6 /10 and suddenly increases, no matter what mic is plugged. Low or high sensitivity it seems that this is the limit not to go over. With higher sensitivity the level is ok, with lower sens mics the problem arises because you need more gain.
 
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Blumlein 88

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You may already know all this, but I'll go thru it so we know we are communicating effectively. So don't feel insulted if I explain it and you already know all of this. I don't know how much you've delved into these matters.

A standard impedance to test EIN is 150 ohms, and most condensers are at this or near it. Theoretical perfection with 150 ohms means there is with zero gain a noise level of -130.9 dbu. This is the thermal noise of 150 ohms impedance. When tested at 60 db gain the noise level would be -70.9 dbu because that noise has been amplified by 60 db. This would be with a gain circuit that adds zero noise of its own. So even with no added noise, if you add enough gain you'll begin to hear hiss at high gain levels. If you aren't familiar with this you'll think, "oh my mic preamps are noisy". When this actually might not be the case.

So if you are using your Zoom at 60 db gain, and it is rated for EIN of 120 dbu, then you'll have noise levels of -60 dbu. If instead you had a perfect preamp adding no noise you'd be looking at -70.9 dbu. So there no possibility to lower noise by more than 10.9 db.

Some of the best mic preamps have real EIN levels of -128 or -129 dbu. So they all add 2 or 3 db of noise.

So getting back to the Zoom, with the Fethead you could reduce gain on the Zoom to 42 db. The noise level then with the EIN of the Zoom becomes -78 dbu. You'll be adding gain with the Fethead of 18 db. If it were perfect the combined noise levels would be -60 dbu. And you didn't gain a thing vs just using the Zoom. The Fethead isn't quite perfect and you probably added a fraction of a db noise above just the Zoom. Probably less than .5 db extra noise using both devices vs just the Zoom.

If the Zoom's EIN is reduced by turning it down, then you'll have added even more noise using two devices instead of one.

It might help a little if turning down gain on your Zoom improves the EIN. That isn't likely though I've seen a couple mic preamps that might pickup 2 or 3 db less noise turning them down a little. The place it could help is if even at max gain on the Zoom a microphone doesn't have enough output. Adding the Fethead can push the signal above the noise floor of the Zoom so low level details are heard, even though it didn't improve EIN. That really is where the Fethead works. When you need the extra gain, and it will provide while adding very little noise.
 
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carlo

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You may already know all this, but I'll go thru it so we know we are communicating effectively. So don't feel insulted if I explain it and you already know all of this. I don't know how much you've delved into these matters.

A standard impedance to test EIN is 150 ohms, and most condensers are at this or near it. Theoretical perfection with 150 ohms means there is with zero gain a noise level of -130.9 dbu. This is the thermal noise of 150 ohms impedance. When tested at 60 db gain the noise level would be -70.9 dbu because that noise has been amplified by 60 db. This would be with a gain circuit that adds zero noise of its own. So even with no added noise, if you add enough gain you'll begin to hear hiss at high gain levels. If you aren't familiar with this you'll think, "oh my mic preamps are noisy". When this actually might not be the case.

So if you are using your Zoom at 60 db gain, and it is rated for EIN of 120 dbu, then you'll have noise levels of -60 dbu. If instead you had a perfect preamp adding no noise you'd be looking at -70.9 dbu. So there no possibility to lower noise by more than 10.9 db.

Some of the best mic preamps have real EIN levels of -128 or -129 dbu. So they all add 2 or 3 db of noise.

So getting back to the Zoom, with the Fethead you could reduce gain on the Zoom to 42 db. The noise level then with the EIN of the Zoom becomes -78 dbu. You'll be adding gain with the Fethead of 18 db. If it were perfect the combined noise levels would be -60 dbu. And you didn't gain a thing vs just using the Zoom. The Fethead isn't quite perfect and you probably added a fraction of a db noise above just the Zoom. Probably less than .5 db extra noise using both devices vs just the Zoom.

If the Zoom's EIN is reduced by turning it down, then you'll have added even more noise using two devices instead of one.

It might help a little if turning down gain on your Zoom improves the EIN. That isn't likely though I've seen a couple mic preamps that might pickup 2 or 3 db less noise turning them down a little. The place it could help is if even at max gain on the Zoom a microphone doesn't have enough output. Adding the Fethead can push the signal above the noise floor of the Zoom so low level details are heard, even though it didn't improve EIN. That really is where the Fethead works. When you need the extra gain, and it will provide while adding very little noise.

Thank you very much for your competent and very kind answer. I'm not an expert and by no means I feel offended! On the contrary, I like very much to learn something. I followed your explanation and I have to say it makes 100% sense.
Still, what I'm trying to figure out if it is possible to match the technical and undoubtable point of yours with the practical experience that some people report. I.e. Curtis Judd, a video guy who's making a lot of videos about gear, measured the noise floor of a recording with and without a fethead phantom coupled with a rode microphone and plugged in a Zoom H4n, reporting a difference of almost 6 db which was clearly audible in the video he posted. There are other similar positive experiences while there are cases in which no improvement has been noticed, as you could expect. The superficial assertion is: "if you have a poor preamp and low sensitivity mics, adding an inline device means sharing the preamp work between your recorder and a better preamp, so you get an improvement".
Another more commonly shared experience between tapers is the use of a very good portable preamp ( like Sound Devices preamp etc.) with a low end recorder like I have; still not bypassing the recorders' preamp - there is not a line in but just a padded input - they claim to achieve a dead quiet recording compared to that without the external preamp. Isn't it just about the same as adding an inline preamp?
Something I can report about my Zoom is that as the gain knob is turned beyond 5/6 on 10 suddenly hiss shows up, regardless the mics I'm using; with some omni capsules which are -30 db sensitive I have to stop raising my gain because the level is just ok while with a -48db microphone the output is still low but the noise becomes evident. This led me to think that the noise I'm hearing is probably from the preamp more then the mic's self noise and the ingenious idea was that an inline preamp could just act like having a hotter mic.
 

Blumlein 88

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Some of the quietest condenser microphones have a self noise of about -118 dbu. So usually, pretty much always, higher self noise microphones will be the limiting factor rather than the preamp EIN. I looked at the Curtis Judd video. He mentions normalizing the result to an output level standard. I don't know the steps involved, but that could be part of the reason. I don't see how a device even if it adds no noise, can lower the noise with extra gain when running in series with another preamp circuit. These devices are talked about for lowering noise all the time, but they shouldn't do this by more than a db or so under certain circumstances.

So I'm not saying Mr. Curtis is wrong, but there is an extra step or two we don't know what it was. He shows a 5 db increase. Okay, but that is rather large to expect. The Fethead may be a better input impedance for the microphone which can help it some too.

Mainly if you just need more gain for the Zoom, then the Fethead would help you.
 
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carlo

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Thank you again, really appreciate your help. I don't really need more gain, but my idea was to reduce the noise floor of a recording. I've read this document: https://www.ranecommercial.com/legacy/note148.html . Table 3 - assuming that what's written there is true, which is questionable- helps to calculate the noise output of a given mic according to its sensitivity and self noise values. After it is indicate that a preamp won't add noise to a given mic if the preamp EIN is better by at least 6 db.
As I've written in a previous post, both my lower sensitive mic and the hotter I own show up noise after applying the same gain on my Zoom ( that's what I had identified as the " noise issue" starting point), but since with the hotter one I just need less gain my recording sounds noise free ( peaking -6 db or so), while I need to raise up the gain with the other mic in order to get the same level. In either conditions noise doesn't disappear but it's just not so audible with a stronger signal fed into the recorder. According to the chart I linked it seems that the self noise of my sensitive mic stays far below of the -120 EIN of the preamp, while the other mics I own don't match similar requirements.
My probable mistake has been in thinking that adding the fethead phantom to a -48 db mic could someway transform it ( by adding 18 db) in a hotter -30 db microphone, thus needing less gain to achieve the same recording level without reaching the perceived "noise zone".
It seems to be true for dynamic mics, which seems really to benefit from a fethead or cloudlifter, but I understand that with condenser will be a different thing...
Thank you very much for your advice
C
 

Blumlein 88

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That page is one of the best sources of info on microphone preamps you will find. I was going to link to it earlier, but they had moved it. So I'm glad you found it, and now I can bookmark it again.

I think you just aren't able to get there from here without some noise in your set of conditions.

And I know I'm repeating myself, but with enough gain you'll eventually get noise. It is unavoidable and is what those charts in that document from Rane are showing you. I had a mic preamp with 75 db of gain. I have one of the two or three quietest microphone available in a Shure KSM44a. It has 4 db self noise and a low 50 ohm impedance. But if you cranked the pre gain up to 60 or more db you'll hear noise. It is thermal noise from the resistance and noise from motion of the air even were I to have it in an anechoic chamber. You can't have 75 db of gain and not have audible noise. The physics of everything puts limits on it.
 
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carlo

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Of course noise is unavoidable, I totally agree. I wanted to point out another fact that lead to my first question. Given two mics placed at the same distance from the source, with equal self noise but different sensitivity, I.e. -48 and -32 we may assume that if the goal is bringing both at -6 db I’ll need to apply 42db to the first and 26 to the second. A very good preamp will apply both 42 and 26 dB without ruining the recording: even if in the first scenario the noise floor will be higher, the listener will not hear a hissy recording.
With a worst preamp which makes hiss very prominent after 25 dB of gain the noise will be still there from the beginning but probably the hotter mic has already reached the required -6 dB level so there is no need to raise further and we have an audibly clean recording ( what I experienced with a hotter mic or with a less sensitive one in closer miking). Should I need to apply all 42 required dbs to reach the desired -6 level we’ll end up with unwanted noise.
My dumb question was wether in this latter case the inline preamp, being quieter, would reduce the “ bad influence “ of the weak recorder’s preamp. You explained that it will not introduce any benefit, so I understand.
Thank you really very much for your time and attention
C
 

Pluto

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Does your Zoom recorder have a genuine line input i.e. no gain, no noise and ability to handle about +20dBU (without a pad) should the need arise? If so, I would not use an uncertain ‘combination’ of gain from both an external mic. amp. and the internal input stage, the latter typically trying to be all things to all men and not doing any of it particularly well.

If the answer to the above is yes, I would seek out a proper professional portable mic. amp. This will probably cost more than the recorder itself but will be a transformative experience!
 
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carlo

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Unfortunately no true line input.... just balanced xlr/ trs with an option of a -20 dB pad....no way to bypass the preamps. There is almost never a true line in on handhelds. Neither Sound Devices mix-pre has one, but its pres are solid good so no need. H6 is versatile and gives me options from just hit recording with the attached capsule which is not bad for archival purpose, to have 4 more inputs with phantom power; the drawback is preamp quality as you move from close miking.
 

tlathbury

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You may already know all this, but I'll go thru it so we know we are communicating effectively. So don't feel insulted if I explain it and you already know all of this. I don't know how much you've delved into these matters.

A standard impedance to test EIN is 150 ohms, and most condensers are at this or near it. Theoretical perfection with 150 ohms means there is with zero gain a noise level of -130.9 dbu. This is the thermal noise of 150 ohms impedance. When tested at 60 db gain the noise level would be -70.9 dbu because that noise has been amplified by 60 db. This would be with a gain circuit that adds zero noise of its own. So even with no added noise, if you add enough gain you'll begin to hear hiss at high gain levels. If you aren't familiar with this you'll think, "oh my mic preamps are noisy". When this actually might not be the case.

So if you are using your Zoom at 60 db gain, and it is rated for EIN of 120 dbu, then you'll have noise levels of -60 dbu. If instead you had a perfect preamp adding no noise you'd be looking at -70.9 dbu. So there no possibility to lower noise by more than 10.9 db.

Some of the best mic preamps have real EIN levels of -128 or -129 dbu. So they all add 2 or 3 db of noise.

So getting back to the Zoom, with the Fethead you could reduce gain on the Zoom to 42 db. The noise level then with the EIN of the Zoom becomes -78 dbu. You'll be adding gain with the Fethead of 18 db. If it were perfect the combined noise levels would be -60 dbu. And you didn't gain a thing vs just using the Zoom. The Fethead isn't quite perfect and you probably added a fraction of a db noise above just the Zoom. Probably less than .5 db extra noise using both devices vs just the Zoom.

If the Zoom's EIN is reduced by turning it down, then you'll have added even more noise using two devices instead of one.

It might help a little if turning down gain on your Zoom improves the EIN. That isn't likely though I've seen a couple mic preamps that might pickup 2 or 3 db less noise turning them down a little. The place it could help is if even at max gain on the Zoom a microphone doesn't have enough output. Adding the Fethead can push the signal above the noise floor of the Zoom so low level details are heard, even though it didn't improve EIN. That really is where the Fethead works. When you need the extra gain, and it will provide while adding very little noise.
Hello very interested in this topic. I saw a review / test by Julian Krause on YouTube suggesting that the Fethead could improve noise performance on a device like the Zoom. The sound examples sounded pretty convincing. Is his method incorrect ?

Here is the link:
 

tlathbury

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He demonstrates Fethead noise improvement in another video as well, where he reviews the UR22C, right around the 9:37 mark:

 

Pennyless Audiophile

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You guys should stop speaking about thermal noise if you don't want to launch the new Audiophile hi-end fashion of the moment, electronics refrigeration.
;)
 

macleod

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Hello everyone

FYI, and much cheaper than the one from Tritonaudio,
the Fet-Head V2 from ProAudio G.C. ... 27dB of gain ... clean and perfect on any dynamic microphone !


fet-head-v2-booster-micro-dynamique.png
 
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