XLR Microphone

w9kjo · May 3

Sirs,

I purchased a Flex 6400 at an SK sale. I am using a dynamic 3 pin XLR Microphone, made by ICON it is a DM-1. Using a shielded XLR Cable into and adapter cable to a 3.5mm Stereo Jack. I have Mix 31 clip on Ferrite Cores on the XLR Cable and a Ring Core at the back of the Transceiver wrapped 8 times before being plugged into the radio jack.

I have used three different Dynamic Mics and all have the same problem.

When I first plug the mic in it adjusts perfectly and the audio reports are excellent. Then after a few weeks the Mic begins to develop what appears to be carrier noise in the audio. To clear the noise for a time all I have to do is unplug the XLR Cable from the mic and plug it back in. then it will return to great audio for a short time. The duration before the carrier noise returns is intermittent.

I am running

Smart SDR v3.7.3
Windows 10 PC

Mic Connections
XLR 1 (Shield) --->   Sleeve
XLR 2 --->   Tip +
XLR 3 ---->   Ring -

Mic Settings
Bias - On
+20 DB - Enabled
DEXP - 24
Proc - Off - Sometimes PROC is On

I often run power at about 700 Watts into a 80m Slopping Delta Loop. My station is well grounded with a Ground Loop into a one point ground box.

Any help resolving this recurring problem would be greatly appreciated.

Thanks

W9KJO

Gord-VA7GP · May 3

This is very weird indeed! Because it's a dynamic mic, I wonder if you could turn off your Bias (under mic settings) - it's not needed for dynamic.

My XLR mic (Shure Beta 58A) is a bit different, and I admit I've not experienced your problem. I was on the cusp of needing / not-needing the +20dB gain, so I tend to leave that off and talk closer to my Shure. My ham room is multi-tasked, so to make room for Zoom + laptop I am unplugging and removing my mic every week. I wonder if this may have "cured" me of what you're seeing, unbeknownst to me :-O

A bit more extensive that your snap-on ferrites, I use the larger FT240-31 toroids, and manage to get about 7 turns through it with my XLR mic-cable. Initially I used just one of these on the mic-cable feeding into my Flex 6400.

And quite recently: the +20dB and Bias are now irrelevant to me: I added a mic distribution amp so I can feed my Shure mic into 3 rigs. This Aphex 120A provides me with individual-rig gain settings. I kept the one FT240-31 toroid on the mic-cable, and added another on each of my distributioh-amp outputs.

Thinking about all this - I don't think my toroids and extensive filtering will help you. You are not seeing immediate, consistent interference. I don't think asking you to reduce power will help either, again because you're experiencing progressive, non-immediate issue. You know, the only reall suggstion I have is to turn off the Bias, and see if this helps. I know it's a long test-cycle (weeks, in your case)…

HTH!

WX7Y · May 3

You can try a ground loop filter that plugs in between the MIC cable and the radio like this one.

https://www.amazon.com/Filter-Ground-Isolator-computer-Systems/dp/B07TBC6JQL

I had to use one on my ANAN radio when I had it that was plagued with Ground loop issues on the MIC circuit.

w9kjo · May 6

Thank you for your comments

VA7GP - I have turned off my bias and will see what the results are over time. If I turn off the +20db I have to turn the mic gain all the way up and still don't have full Mic.

WX7Y - I have some of these ground loop eliminators here in the shack somewhere I'll dig one out and see if it helps. I really don't think its a ground loop because it is so intermittent, but I'll try it and see.

73 W9KJO

w9kjo · May 6

Hello VA7GP

Do you operate with the distribution amp connected to all your rigs while operating or do you have to plug and unplug the rigs that are not transmitting.

I have three rigs and would like to use my one mic with all three rigs. I have the 6400, Ft-450D, and a TS-2000.

Please, if you would, provide more information on how you operate with this configuration.

Thanks, 73, W9KJO

Walter

Gord-VA7GP · May 6

Hi, Walter:

I leave all the rigs plugged-in at the same time (Kenwood, Flex, Yaesu 2m, optionally Heath). There are "mic-splitters" which are passive, and I don't think they offer any kind of isolation. My Aphex 120A distribution-amp is active. It is not often that I have more than one radio turned on, but for the occasions I have done so, everything works exactly as you'd expect.

You have to consider your antennas and PTT though, so you don't transmit into thin-air :-O I'm old-school and use a foot-switch for one rig, and a thumb-button for another - only one is within reach at any time. But as I mention above, in 20 days out of 30, I only have one radio turned-on so no mistakes are possible.

Good luck!

EDIT: for interfacing XLR to my TS-850, I bought and use the Heil CC-1-XLR-K cable, which plugs into Kenwood's round-8-pin front panel, and breaks out the PTT separately. For the Flex, Amazon provided a Tisino-brand XLR to 3.5mm cable which I had to slightly modify:

https://www.amazon.ca/gp/product/B083R482GW/ref%3Dppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

w9kjo · May 6

Thanks Gord

I may follow your Q on this and give it a try.

73 W9KJO

XLR Microphone

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