Heil PR40 to Icom 746pro

[N4NYY]

A fellow ham is bringing me his Heil PR40 to connect to his Icom 746pro. Before I smoke something on his $300 mic, I want to make sure I have the pinouts correct.

XLR - negative and shield to pin 1, audio pin 2
radio - audio pin 8, shield pin 7, momentary keyer to pins 5 and 6.

 

[KC2OUC]

Checkout the following web site.  The Heil site links to it from the "pinout" menu link on http://www.heilsound.com/amateur/

http://homepage.ntlworld.com/rg4wpw/date.html

[N4NYY]

That is the website I used. I wanted to make sure. I am nervous about a $300 mic and a $1,500 rig. If this is a $100 CB, I don't ask.

[VA7CPC]

PMFJI --

Many Icom rigs (I don't know about the IC-746 Pro) put a +8 volt bias voltage on the "MIC +" or "Mic In" line.

You _must_ block that voltage from the PR-40 with a series capacitor -- 10uF or 20uF should do the job..

There's an extensive section on Heil's website describing the interface between Heil's dynamic mics (e.g. PR-40) and Icom rigs:

http://heilsound.com/amateur/tips/earlyicom.php

I believe Heil's suggested mic adapter has the capacitor built-in.

The PR-40 has a lot of low-bass response, much more than any "ham" microphone.  I don't know what that will do to the IC-746 Pro's mic preamp, or compressor.   A lot of people (based on reviews here) find that using an outboard equalizer to reduce the bass response (actually, raise the bass cutoff frequency) gives really nice results.

Report back -- more data is always useful.

          Charles

[KB5ZSM]

A 1 microfarad cap on the audio line should work. Make sure to have the plus side of the cap to the microphone cable and use a tantalum type rated for at least 16 volts. it may even fit inside the mic plug.
My main concern is if you will have enough audio from the mic to drive the radio. You may need a preamp (or as one person said, an equalizer).

[VA7CPC]

There _is_ bias voltage on pin 1 (IC-746Pro manual, pg. 12).

I think a 1 uF capacitor will cut the bass by 6 dB at 270 Hz, and 6 dB per octave below that frequency.  It's a good choice for taming the bass response of the PR-40.  But it loses the bottom 2 octaves of the mic's response.   The IC-746Pro has a transmit EQ control, and a TX bandwidth control.  Some high frequency boost might be useful for DX work.

This is ham radio; you're entitled to experiment.

         Charles

[N4NYY]

I am having him buy the jumper for $40. I had no idea there was 8V on the audio line. I would have smoked his $300 mic. The reality is he tried to save a few buck, but purchased a XLR mic cable from a music store, Heil connectors from HRA, and was already out $30. It just made no sense. In addition, I did not have anything bigger than a .1uf cap.

So, thanks for the responses. He will buy the jumper.

[M6GOM]

A fellow ham is bringing me his Heil PR40 to connect to his Icom 746pro. Before I smoke something on his $300 mic, I want to make sure I have the pinouts correct.

XLR - negative and shield to pin 1, audio pin 2
radio - audio pin 8, shield pin 7, momentary keyer to pins 5 and 6.

 

Far better solution.

Buy a Behringer Xenyx 802 mixer - about $45. Connect the mike to the mixer - it has balanced mic inputs. From the output of the mixer (left channel jack) go into the ACC2 socket on the back of the radio. On the channel you plug the mic into, set the pan to left. You now have an audio source with equalisation that bypasses the mic-preamp stages and all the interference that they introduce. You can also come out of the ACC2 socket into the mixer and run an external speaker with equalisation on that as well.

More here - watch from about 42 minutes:
http://twit.tv/show/ham-nation/36