Hum on latest 2 ribbon mics I've tried

Petimar · 01-19-2019, 05:12 PM

I use ribbon mics a lot in my home studio recording acoustic stringed instruments. I currently own or have owned in the past

RCA44bx
AEA 92 and 84
Royer R121, R122 and SF12
Beyer M500 and M 160
SE VR1 Voodoo
Shinybox I can't remember model #

Used all of these with no problems, mostly with an AEA TRP.

I've heard a few of the recent ribbons designed to have less of the high end rolled off and so ordered and tied
Samar VL37
AEA KU5A

I REALLY liked the sound of both of these, BUT they hummed enough to be noticeable in quiet passages, so I returned them as I can't use them with that much noise. VL37 was passive, KU5A was active (John Hardy M1 pre for that one).

Any one know why I might have noticeable hum on these 2 and never any other ribbon mic?

citizenkeith · 01-19-2019, 06:03 PM

AEA has fantastic customer service... have you contacted them?

cyrano · 01-20-2019, 04:59 AM

The AEA TRP has an unusually high input impedance (63 kohm). That would make any mild ground loop stand out. Maybe it's time to check your cables. If these show no broken grounds, check your setup, most importantly from you audio interface to your computer. Is the USB cable well seated? All stuff on the same electrical circuit? Is the mains ground OK?

Supposing you're in the Northern hemisphere, it's winter. Very dry air. Maybe the earth where the ground pin is located is sandy and dried out completely, in which case you have no ground connection?

DVDdoug · 01-20-2019, 08:43 AM

Quote:

VL37 was passive, KU5A was active (John Hardy M1 pre for that one).

Before you "blame" the mic a valid experiment would require measuring (or recording or listening to) the hum with different mics in the exact-same setup with the mics in the same location at the same gain settings.

...Now, as a practical matter that's not important... You're interested in the signal-to-noise ratio and with a hotter mic you can turn-down the gain to turn-down the hum, so it doesn't matter where the hum is coming from, but it may not be coming from the mic.

bolgwrad · 01-21-2019, 05:23 AM

This may or may not help, but I had a Headway pickup fitted to a guitar and it hummed like billy-o. Last string change, I wrapped a bit of air-conditioning installation tape (the metal self-adhesive stuff) around the battery cable, etc. Hum is gone.

Petimar · 01-21-2019, 02:42 PM

Thanks for all the answers, appreciated.

No other mics (ribbons, condensers, dynamics) hum in same locations and same pres as these two mics.

AEA couldnt help. Especially when I told them an 84 was quiet and the KU5A was not.

JamesPeters · 01-21-2019, 02:48 PM

Perhaps the mounting of these microphones is a bit different, more conducive to ground loop issues if they're present. If the ground of the mic is set up a certain way, and the mic stand grounds when it shouldn't, you can get a ground loop. It'll depend on your entire system (mic, stand, cable, preamp, computer, your headphones and you if you're touching any part of the system). But if you can at least try removing the mics from the stand and isolating them (lay them on something which isn't conductive), see if that helps. If it does, you might need to mount them to the stand differently or choose a stand which insulates differently (larger rubber feet, some kind of isolating mic mount, etc.)

Also, when you rotate the mics does the noise increase or decrease? Single-ribbon mics are more prone to interference than dual-ribbon mics (which are effectively wired up as "humbuckers"). If a mic is more prone to picking up noise, you can possibly choose to orient it such that it doesn't pick up the noise (then move the source relative to the mic as needed).

Icchan · 01-21-2019, 03:44 PM

Cyrano is right, that setup has very high input impedance, low signal level and probably very high gain such that any degradations in the signal path or ground or shield will make themselves heard.

Even professional microphones can have all kinds of issues regarding shielding and grounding. And if the mic cable isn't of very high quality with very well braided shield and good soldering etc. it can cause problems really easily.

Read about "pin 1 problem" for example which is very common and might only show itself when having very high impedance, low signal level and high gain circuits like your ribbon setup:

https://www.prosoundweb.com/channels...n_1_revisited/

and yeah... that pin1 problem can easily be caused by badly made microphone cable or sub standard xlr-connector etc..

Check them through!