Mic input Question for 6400M

Art - N4QNT

I understand on the 6400 and the M model the 1/8 TRS pseodo -balance input, but my question is what if I wire an XLR to DB15 connector utilizing pin 1 (line in) and say pin 10 (ground) to the Accy Port would this be considered a Balanced input? Or is it still picking up the pseodo circuit?

Neal Pollack, N6YFM

On a model 6400, according to page 22 of the hardware ref manual, in both cases you have an unbalanced input (one signal, and ground).     If you want the noise & hum rejection of a true balanced XLR cable, the you would need a small 600:600 ohm line/signal transformer between the XLR jack and the TRS 1/8 inch plug.

You can find many super small/cheap 600 ohm signal transformers on ebay, or if you want to spend more, your local music or Guitar Center store should have XLR to TRS adapters with the transformer built in, as does Amazon.

Cheers,

Neal

Art - N4QNT

Thanks Neal

Neal Pollack, N6YFM

Here guys.   Take a look at diagram/figure #2 in the following doc.
It shows you how to maintain a balanced XLR cable, and then convert it to unbalanced
right where it will enter the radio.

https://www.rane.com/note110.html

Cheers,

Neal

Neal Pollack, N6YFM

And another example of what you are looking for;
https://www.lundahltransformers.com/wp-content/uploads/datasheets/1584_x.pdf

Neal Pollack, N6YFM

And lastly, here is an example link on Amazon of a converter between XLR balanced and TR unbalanced, using 1:1 isolation transformers.   It includes a user manual link on the listing.
This may be worth playing with if you don't like wiring up your own using transformers from ebay.

https://www.amazon.com/PYLE-PRO-PHE400-Eliminator-2-Channel-Outputs/dp/B00BARTW42/

Good night,

Neal

W1MSG

I think the point of his question has been missed. He wants to use the Accessory connector, there isnt any info on whether that is a balanced input or not via the 15 pin Acc Port ..

Neal Pollack, N6YFM

No, it has not been missed. The accessory connector is unbalanced, since there is only one signal wire plus ground, and not a balanced differential pair plus ground

W1MSG

Sorry Neal , I missed your first reply. Sometimes it says 3 or 4 comments and I cant see anything ..

Neal Pollack, N6YFM

No worries :-)

Cheers

KC2QMA_John

Yes Art, Like Neal said if you need to go from a device that has a "Balanced" output like an external mic preamplifier to the UN-Balanced input of the 6400/M you will want to use an audio isolation transformer. You can use the one Bill recommends because it gets the job done, is low cost and is more than sufficient for ham radio. ( https://www.amazon.com/PYLE-PRO-PHE400-Eliminator-2-Channel-Outputs/dp/B00BARTW42/ )

Keep in mind some of the of the lower end boxes like these tend to use transformers that are not audiophile grade and can have a bit of low roll off at @60 down and also some attenuation in the top end at around 16khz and up. This should not matter for normal SSB but if you were more into ESSB you might want to go for the better transformers.

You could optimize even more by using higher quality transformers like Lundah or Jensen and try to match input and output impedance with equipment as much as possible for best audio fidelity.