Low End Rumble in Mic

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4tracker

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Hey guys. I got my first tube mic today. The 1050 Joly mod. It sounds great, imo. But I am picking up low end rumble. Any idea what this is?

In this test clip I didn't put on a high pass filter and you can really hear it.
https://soundcloud.com/4-tracker-1/video-games-no-eq

And in this test clip I tried to remove the low end rumble with a high pass filter at 100hz. You can hear it's better, but it still seems to come in and out.
https://soundcloud.com/4-tracker-1/video-games-eq-low-end-removed

The mic is on a shock mount. We record in an apartment. Any ideas on (a) what this is and (b) how to fix it?
 
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4tracker, it could be grounded, but if its poorly done it will make noise.

Can you check the plug connection? I've had the same problem with my mic and I had to re-solder the ground. Now its working perfectly.
 
Is it possible it's a noisy preamp? I am using a Scarlett 18i8.
The reason I ask is I just did another take and turned the gain down on the preamp, and there is much less rumble. The problem with that is the vocal is now so low it's probably not unusable (-30db).
 
4tracker said:
Is it possible it's a noisy preamp? I am using a Scarlett 18i8.
The reason I ask is I just did another take and turned the gain down on the preamp, and there is much less rumble. The problem with that is the vocal is now so low it's probably not unusable (-30db).
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Try plugin another mic. If it persist, the preamp is fucked. If it aint, its the mic.
 
Good call.

I tested a SDC and it's quiet, no rumble. I wrote MJ to ask what's up; we'll see what he says.
Any other ideas would be appreciated, though.
 
Well the source is certainly the mains Ac, but I'm not certain it's a ground loop, but that's one possible cause, the other simple a fault power supply. The easy solution is to disconnect pin 1 on the cable from the psu to the audio preamp, and see if remains or changes. If it remains with no change then the psu is faulty, if it goes or changes in level or harmonic content, then it's a ground issue. . If it goes completely, use the cable that has no ground. In the UK we never lift the ground on a mains powered device, even though that often suers a ground loop, it also removes the protection!
 
rob aylestone said:
Well the source is certainly the mains Ac, but I'm not certain it's a ground loop, but that's one possible cause, the other simple a fault power supply. The easy solution is to disconnect pin 1 on the cable from the psu to the audio preamp, and see if remains or changes. If it remains with no change then the psu is faulty, if it goes or changes in level or harmonic content, then it's a ground issue. . If it goes completely, use the cable that has no ground. In the UK we never lift the ground on a mains powered device, even though that often suers a ground loop, it also removes the protection!
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Okay, this is a 7 pin mic cable, though for a tube mic. I'm not such which is pin 1 or the ground on it. The way it is setup is the psu has a mic in that is a 7 pin male, a mic out that is 3 pin female. That mic out goes into the audio interface (3 pin male).
 
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DO NOT MESS WITH THAT MIC, ITS CABLE OR THE PSU!

Lethal voltages in all. The spectrum attached* shows a massive, fundamental hum at precisely 60Hz and a decent bit of 2nd harmonic at 120Hz. The former has to be caused by a missing earth/ground connection or (and I had an ignoble mate, sorry!) a ground loop between the mic PSU and some other mains powered, earthed device, computer, active monitors or other.

If the hum was just 120Hz it could be bad filtering in the PSU but that would not throw up 60Hz.

I have never read or heard of a valve cap' mic supply causing a hum loop and I would have thought any maker worth his salt would know of the possibility and design it accordingly?

*Had a bit of a job isolating a section with the hum (kept saying to self "that's nice girl but FCS shut up for ten seconds!") Peeps, if sending in samples for noise diagnosis, ten secs of waffle for level then twenty where you STFU please?

Bottom line: Faulty mic IMHO.

Dave.
 

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Not the 7 pin cable - try lifting ground between the PSU and the preamp/mic input. There are some hefty HT voltages inside the PSU, which hurt - lots!

As an aside - the UK version sounds quite different - the difference between 50 and 60 Hz is pretty pronounced.
 
Just a +1 for what ecc83 said. Unless you know exactly what you're doing and have lots of electronics experience, don't mess with the mic, cable or PSU. The voltages floating around in there are potentially lethal.
 
rob aylestone said:
Not the 7 pin cable - try lifting ground between the PSU and the preamp/mic input. There are some hefty HT voltages inside the PSU, which hurt - lots!

As an aside - the UK version sounds quite different - the difference between 50 and 60 Hz is pretty pronounced.
Click to expand...

Does the UK model hum as well then Rob??? Heh! And yes, 60Hz is an unfortunate mains frequency! Many small monitors are "tuned" about there but LF output falls sharply below it.

Cheers Bobbs. I have never looked at any valve mic PSU schematics but I would have though a floating, balanced output would have been pretty vital with a CR anti-loop network in the screen?

Dave.
 
ecc83, you are the man. thanks for doing that.
I'm not technical enough to know exactly what it means, but i get the general idea.
 
Ha! trouble is that 60Hz is more of a real note, and the first harmonic helps turn it into something more than what happens here - where it's more an annoying hum, and not a proper 'tone'. seriously, though, there's a big capacitor on the rectified HT side, and back in the 'good old days', when these failed, the nasty ripple on the anode made a quite distinctive hum - I've never heard the 60Hz version, but in a new mic, it's a send it back job, once you rule out the ground loop.
 
that is disturbing if it failed after 1 use.
 
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rob aylestone said:
Ha! trouble is that 60Hz is more of a real note, and the first harmonic helps turn it into something more than what happens here - where it's more an annoying hum, and not a proper 'tone'. seriously, though, there's a big capacitor on the rectified HT side, and back in the 'good old days', when these failed, the nasty ripple on the anode made a quite distinctive hum - I've never heard the 60Hz version, but in a new mic, it's a send it back job, once you rule out the ground loop.
Click to expand...

Should not cause a ground loop problem anyway IMHO Rob!
Valve cap' mics used to be the preserve of the very rich and famous and would invariably have been used with an earthed mixing desk so plainly the possibility of a ground loop would have been addressed at the design stage and eliminated (to get technical again 4T!) by the use of a floating transformer balanced output.

Now "they" make valve mics that can be afforded by U.T.C and all, they have probably cheaped out on the design?

Fort occurs! It could be that the XLR 3 output cable has pin One* strapped to the shell lug? This means that even if the PSU makers have done right you would be undoing their good works by tying pin 1 to casing...WHICH I sincerely hope is securely bonded to mains earth!

A quick test with a Digital MultiMeter (which ALL good little Home Recordists should have!) will quickly tell all.

*Yeah! The "Pin One issue" whether or not to bond it to the shell has raged since the XLR (nee' Cannon) was invented. My view has always been don't.

Dave.
 
4tracker said:
Good call.

I tested a SDC and it's quiet, no rumble. I wrote MJ to ask what's up; we'll see what he says.
Any other ideas would be appreciated, though.
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We had a chat here not long ago re a condenser with main's hum that lead to poor sheild connection to the grill.
Try am ohm meter between the grill and case..
 
MJ wrote me and said I am operating the mic too close to a source of AC interference and said to move it around the room. I'm in a small apartment so I don't have many options. What are the most common sources of AC interference?
 
What!?
Um, that would be along the lines of 'get your mic more than two feet from a CRT tv!
He know his stuff ..better than me ok, but...

Got ohm meter' BTW..?
 
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