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Re20 hum

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Re20 hum

Postby kinglouis » Thu Jan 11, 2018 9:27 am

Hi all,

I don't use my re20 all that much but when I do, I find it needs the preamps turned up an awful lot to capture usable audio, and consequently there's often a hum in the recording - associated with having a preamp turned up too much.

Its fine for brass/percussion but for spoken word its SO quiet. With the speaker 2" from the mic facing straight at it, the gain needs to be turned to 11. Is this my poor technique? A faulty mic? I've run it through UAD, focusrite 428 and Audient pre's and its always the same.

Many thanks for help,

Alex
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Re: Re20 hum

Postby Mike Stranks » Thu Jan 11, 2018 9:37 am

Almost certainly nothing wrong with the mic. It's just that many dynamic mics need far more gain than capacitor-condenser mics - especially for spoken voice.

It's a problem I encounter all the time...

This:

https://www.soundonsound.com/reviews/martiaudio-line-preamp-booster

could well be the answer...

Or if you have cash to splash look at the products from Cloudlifter and Fethead; but in all honesty I don't think you'll need to. I use the MartiAudio preamp all the time for spoken voice. Good product; good price.
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Re: Re20 hum

Postby ef37a » Thu Jan 11, 2018 9:48 am

Hi Alex, the re20 incorporates a humbucking coil so I am surprised you get hum problems.

The sensitivity is slightly lower than an SM58 but not enough to matter I wouldn't think. Have you tried another dynamic mic in the same position? If so and that one does not hum, or has a much healthier output then you have to consider that the re20 is faulty.

If another mic shows the hum then you have something in the room putting out an usually strong hum field. Not likely to just be a cable, more likely a transformer in an amplifier or, very bad for it these, a line lump PSU.

It is often instructive to run 10 secs or so of the hum signal through an RTA? The one in Right Mark is excellent, needs a 16 bit .wav. If the signal is predominately 50Hz, got to be a radiating transformer, poor filtering in gear gives mainly 100Hz.

You have OF COURSE checked the XLR cable for continuity?!

Dave.
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Re: Re20 hum

Postby Ariosto » Thu Jan 11, 2018 10:10 am

I find that running a wire from the XLR casing (Just twisted around) and connected to a suitable earthing point on the amp or recorder, gets rid of all hum, even at full gain.
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Re: Re20 hum

Postby ef37a » Thu Jan 11, 2018 10:20 am

Ariosto wrote:I find that running a wire from the XLR casing (Just twisted around) and connected to a suitable earthing point on the amp or recorder, gets rid of all hum, even at full gain.

Ah! Likely then that you have NOT checked the 3 wires in the cable!

Dave.
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Re: Re20 hum

Postby Hugh Robjohns » Thu Jan 11, 2018 10:54 am

It is quite normal to need to run the mic preamp at maximum gain when using an RE20 for speech. Given it's sensitivity of 1.5mV/Pa, a sound level of 70dB SPL (gentle speech) at the mic will produce an output level of -78dBu, so you're going to need a lot of gain to raise that to a decent line level signal.

The hum is a more troubling issue. There are lots of possibilities, some of which have been mentioned above. I think I'd try switching equipment off to see if anything is radiating a strong hum field first. You could experiment with moving the mic cable around to see if that makes any difference too.

Some mic cables are wired with the XLR shells linked internally to pin 1, and some aren't. In theory, they should be linked but the presence or absence of that link can both cause and prevent hum problems depending on the design of the equipment the cables are plugged into, so that could be worth experimenting with as well.

And finally, it's not unusual for preamps running at very high gains to pick up mains hum from their own internal power supply...

Mike's suggestion of using an inline gain booster should help.

H
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Re: Re20 hum

Postby The Elf » Thu Jan 11, 2018 10:54 am

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Re: Re20 hum

Postby kinglouis » Thu Jan 11, 2018 11:03 am

Wow - thanks for such a helpful set of responses!

Am doing a bit of self SoS today, making some panels and moving kit about so will use the opportunity to do an A-B with an SM57 and try different cables, preamps, different positions etc. An inline gain booster seems like a no-brainer, will invest.

Thank you, will post results!

Alex
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Re: Re20 hum

Postby blinddrew » Thu Jan 11, 2018 11:08 am

They frequently come up on sale as well. :)
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Re: Re20 hum

Postby The Elf » Thu Jan 11, 2018 11:19 am

blinddrew wrote:
They frequently come up on sale as well. :)
They do. I'd blush to admit how much I got mine for - I bought two of 'em!
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Re: Re20 hum

Postby Wonks » Thu Jan 11, 2018 11:37 am

But what if you've only got penultimate cables? How do you test those? ;)
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Re: Re20 hum

Postby Hugh Robjohns » Thu Jan 11, 2018 11:53 am

kinglouis wrote:Am doing a bit of self SoS today, making some panels and moving kit about so will use the opportunity to do an A-B with an SM57 and try different cables, preamps, different positions etc.

I once helped someone solve 'a hum problem' when using a low-output mic. It turned out to be caused by a radiating magnetic field from the mains transformer in a valve compressor mounted directly below the mic preamp in the rack. Swapping a few things around in the rack, and leaving a 1U gap between the valve compressor and other things cured the problem...

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Re: Re20 hum

Postby ef37a » Thu Jan 11, 2018 11:59 am

Do note that an external 'booster' will only fix the hum/noise if it originates in the AI.
An external hum field will be boosted along with the mic signal!

I have a 30 Ohm Reslo ribbon and that hums because the ribbon leadouts are not of the hum bucking form. I have it running into a 40 quid Sowter 1: 4 traff but the ~12dB boost make no difference to the hum! (in the garden it is booootiful!)

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Re: Re20 hum

Postby Tuseth » Sun Jan 14, 2018 12:20 am

better off using that mic for snares or any loud peak sound source... ;)
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Re: Re20 hum

Postby Ariosto » Sun Jan 14, 2018 6:46 am

ef37a wrote:
Ariosto wrote:I find that running a wire from the XLR casing (Just twisted around) and connected to a suitable earthing point on the amp or recorder, gets rid of all hum, even at full gain.

Ah! Likely then that you have NOT checked the 3 wires in the cable!

Dave.
Thanks Dave, but my XLR leads are short and pretty new and Van Dam so they should be OK.

I have a new multimeter now (the old one was over 50 years old!) so I might check. Pin 1 to shell?

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Re: Re20 hum

Postby ef37a » Sun Jan 14, 2018 8:33 am

Ariosto wrote:
ef37a wrote:
Ariosto wrote:I find that running a wire from the XLR casing (Just twisted around) and connected to a suitable earthing point on the amp or recorder, gets rid of all hum, even at full gain.

Ah! Likely then that you have NOT checked the 3 wires in the cable!

Dave.
Thanks Dave, but my XLR leads are short and pretty new and Van Dam so they should be OK.

I have a new multimeter now (the old one was over 50 years old!) so I might check. Pin 1 to shell?

Ariosto
No, pin 1 to pin 1 first of all then check pin 1 connects to the mic body. It is not usual AFAIK for pin 1 to be connected to shell in cables but the debate is as old as Cannon plugs!
https://www.gearslutz.com/board/attachm ... ircuit.jpg


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Re: Re20 hum

Postby kinglouis » Mon Jan 15, 2018 5:35 pm

Well having pushed some cables about in a thorough and scientific manner, I recorded some double bass today with the gain turned up to 55dB on the Re20 and it was clean as whistle. AND recorded the bass in a musical and very usable way which I have always found quite hard.

So I think the upshot was the cable need untangling or changing - which will have been done in the studio reshuffle.

Thank you again for all the help, I suspect both the Martiaudio and cable checker will be on my next birthday wish list.

Alex
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Re: Re20 hum

Postby Hugh Robjohns » Mon Jan 15, 2018 5:46 pm

Good to hear it's sorted.

And a salient lesson for all on how important it is to keep audio cables away from mains leads, mains transformers and SMPS power supplies....

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