XLR Microphone

w9kjo

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

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

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

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

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

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

Thanks Gord

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

73 W9KJO