Mic Bias

Greg

Can someone tell me how much voltage is applied when the mic bias is turned on? And.... Is it applied to both the front and rear mic inputs or is it just on the foster plug connection on the front panel? Thanks Greg AB7R

Dudley-WA5QPZ

Greg, Quote from Gerald, Bias is only available on the front panel microphone connector. The XLR/TRS does NOT have any bias connection. There are two sources for Bias on the 8-pin Foster connector: There is an always on 5V sourced through a 560 Ohm resistor to pin-2 as shown below. You can also turn on the Mic Bias in the GUI that turns on a 2.97V source that is applied to pin-8, which is the microphone hot lead. Hope that helps

Greg

Thanks Dudley. I was looking at one of these to go with my Bose Quiet phones but their website says they run on 9V (which I thought was strange). www.iflymike.com Radio shipped this morning...you should probably see it on Wednesday. Tnx Greg

W4YXU

Electret mic bias voltage stated as 5v ( 15.9 voice tab - Smartsdr software manual). I only measure 2.77 (3 different meters!) OK - I see you answer that it is 2.97. Close enough. With due thanks to my daughter-in-law my son gave me a Telex aircraft headset. The specs call for 9-15v for the mic. It works fairly well down to 5 and or 3.3 but below 3v it just becomes nasty. I understand that the pin2 5v line is fed through 560 ohm. Am I correct and can I jumper pin2 to pin 5 in the connector? A sketch of the equivalent input circuit like in IC datasheets would be very useful.

Tim - W4TME

"Am I correct and can I jumper pin2 to pin 5 in the connector? " - You need to connect pin 2 (+5 bias) to pin 8 (mic +) and turn off the BIAS in Radio Setup->Voice tab to get +5 VDC to the mic element.

W4YXU

As expected and thanks. I don't know why I typed 5 instead of 8. I DID solder correctly! Pin 5 would have been a bit useless! I would still like to know what the input looks like (Like could I go closer to the mike specified voltage? What is the safe DC voltage limit there? etc.)

Tim - W4TME

Pin 2 is an output voltage so I would expect the limiting factor would be your mic element.

W4YXU

Agreed. However my concerns are for the input pin 8 if external power is provided for the mic. BTW the 5v from pin 2 does indeed appear to be behind 560 ohm.

Tim - W4TME

Got it. I would not put more than +5 VDC on the mic+ (pin 8) as the radio was not designed for a greater voltage.

Greg

I picked up a headset buddy electret mic for my Bose Quiet phones. I first tested it on my K3 and it works great. I built an adapter for the front panel mic connector with audio+ on pin 8 along with a jumper from pin 2 to pin 8. Mic- goes to pin 7. Bias is turned on in SSDR and mic selection changed to MIC. Not getting any mic output with this configuration but it seems correct. Any ideas what I may have wrong? Thanks 73 Greg

Tim - W4TME

If you are using pin 2 (+5 VDC) jumpered to pin 8 (Mic+) you do not need to enable the BIAS in the Radio Setup. That is only for enabling low voltage (~2.5VDC on Pin 8 (MIC+)

SV1RXI

Hi ,is anyone connect a heil icm mic to the flex 1500 radio? i see the pic pinout 5v and the heil i think needs 8 .Do i need turn on the bias?

Mike-VA3MW

Yes, just wire your Heil like a Yaesu microphone and it will work on a 1500.