Balanced microphone on 8400 ?

Mike W9OJ

The photo of the rear panel of the 8400 clearly shows a TRS balanced microphone connector.

https://edge.flexradio.com/www/offload/20240507150519/Flex-8400_Back.png

Just received my 8400 and there is NO balanced microphone connector. This was one of the reasons why I decided to buy this radio.

Oh well…

Mike W9OJ

Neil D Friedman N3DF

Not sure at what photo you are looking. The “400” series has always had a pseudo-balanced mic input while the “600” has always had, in addition, a balanced mic input.

Neil D Friedman N3DF

Mike W9OJ

https://edge.flexradio.com/www/offload/20240507150519/Flex-8400_Back.png

Mike-VA3MW

There is no Balanced connector on the 8400. There are a few images floating around that do show that, but they are in error.

If you found one, please send me the link of the actual page (not the link to the image). Thanks

Mike W9OJ

https://www.flexradio.com/products/flex-8400-signature-series-sdr-transceiver-1/

Third picture on the right hand side of the page.

Trucker

Whoever setup the photos for the 8400 used the wrong photo. The one in the photo is the back of the 8600. ( web master alert!)

James

WD5GWY

KD0RC

I believe that it is a pre-production photo of an 8400 - there is only one RX port and one XVTR port. The 8600 has two of each (one for each SCU).

Mike-VA3MW

Thanks James

That radio doesn't even exist, or I guess we had 1 for pictures.

I'll get it replaced.

Mike-VA3MW

Mike W9OJ

My 8400 has a hole with a black plastic plug in it labeled BAL-IN above the PWR SPKR jack.

It also has two larger holes below the accessory jack with black plastic plugs in them. The top one is labeled RXB IN.The bottom one is labeled XVTR-B

Mike W9OJ

KD0RC

Hi Mike, it sounds like you got an 8600 rear panel. Since everything but those three holes are in common with the 8400, I am guessing that they chose to plug the holes rather than make you wait for the next batch of 8400 panels.

Mike-VA3MW

As a signifcant cost saving, we are using the same back panel for all radios. The 8400 series has the BAL IN, RXb, XVTrb covered (2nd SCU).

David DeVos KF8QL

So how do those of us who purchased an 8400 connect our balanced microphones (PR 781 here) to our radio? I could hack together a cable with an inline transformer, but what is Flex recommending?

I understand the significant cost savings of using a common back panel, but I don't understand taking away the balanced input. I'm an audio engineer, and running unbalanced microphones in an RF environment can be a recipe for noise in the transmitted audio.

Neil D Friedman N3DF

Why would a transformer be needed to convert the 781 to the 8400’s pseudo-balanced mic input?

Gord-VA7GP

Why a transformer… ? I use an XLR-to-XLR isolation transformer with my 6400 and it sounds like my problem / solution may also apply to the 8000-series. But to support Neil N3DF: I cannot see why a 781 would need a transfomer.

Here is my longwinded explanation why I needed isolation transfomers; it may help someone else (but not if they use a Heil 781 by itself):

The problem (IMHO) lies with Flex terminolgy: "pseudo-balanced". Flex says they equalized and treated the two mic-input traces carefully, but in the end (when they hit the ADC and digitize) one side of the mic is grounded.

This is OK if you use a dynamic mic, by itself. It's a coil, right, and is quite happy if one end (or the other) is grounded, and there's signal on the opposite side.

My problem arose when I added active devices: may you add an XLR equalizer… in my case, I added a distribution-amp to feed one dynamic mic to several radios. It is key to understand that active outputs don't like being grounded 😯😫

My distribution amp uses + and - voltage-rails internally, and (with servo-feedback) outputs the bi-polar, differential driven signals directly. without coupling. Shorting one side of these active-outputs to ground inside my Flex was deeply unhappy (buzz, hum, but no damage). Simply adding a coupling transformer made for the job (ART DTI was my choice) resolved all problems - active outputs are happy driving the "floating" input-side of the isolation transformer, and Flex is happy grounding one end of the output-side.

Summary: in my mind, the use of the word "balanced" means something different than how Flex used that word. And (again, IMHO) if there is to be a "balanced input" capable of accepting active-device inputs, then it must not be grounded! A transformer will do that nicely. Even using XLR, one must understand the signal-flow, connections, and intervening devices.