Setup for the Icom 756 Pro III

Background

Most of the audio guys and gals are Kenwood bigots. That is to say that they started using Kenwood gear and some of that gear will go a little wider than Icom stuff stock, so they feel that the audio coming from Icom transceivers is in every way inferior to Kenwood audio. 

Kenwood audio is very good and I like using my TS-850 and DSP-100 combination very much, but I would not go so far to say that Icom radios can not sound very good in their own right. There is at the time I am writing this part of my page, a pretty sever limitation on the Pro series bandbass. There are always roomers that the folks at Icom are about to extend the bandpass of their radios, but as of now we are pretty well stuck to 100Hz to 2.9Khz or a total bandpass of 2.8Khz. The magic point of fine audio has been established by many audiophiles as being at least 3Khz. So you can see that the pro series, is just a little short in bandpass. The radio can be extended down by 20 or 30Hz by putting the audio into the back accessory jack, but still the radios are bandpass challenged.

By going in the back to what many call the balanced modulator, by the way this is miss-information, that you really are not going to the BM of this DSP radio, but you are bypassing the first microphone amplifier with some roll off that it does on the bottom end. So by going in the back, your low end will be extended a little and it will sound much smoother. When you do the wiring for the accessory port there are other things to be considered and I will describe them latter in this part of the page. 

My Environment

Please note the following environmental conditions of my shack, goals and assumptions when considering how to use the information presented here in this part of the page. 

1. I am not a long time Icom user with knowledge of all the ins and outs of the Pro series rigs.

2. I want to get the best sounding Enhanced Audio (EA) I can with a bandpass under 3Khz.

3. I have all my radios and rack gear in a commercial relay rack for easy access and maintenance. Rack panels can be ordered from   novexcomm

4. I want to control most of my radios functions via a computer interfaces using Ham Radio Deluxe.

5. I want to use the same equipment for EA and have the ability to  switch over to a DX or contesting mode very quickly and easily. 

6. I am using all Behringer gear consisting of a MX1604A mixer, 2496 Ultra-Curve Pro, and 1024P Virtualizer going to the radio via a W2IHY I-Box used for isolation only. No step down is needed when going into the back of the Pro III. 

7. The microphone used on the Pro III will be exclusively the Heil PR-40 with the Electrovoce 309A shock mount and the VAC-RE20 Popless filter. 

8. This page is a reference for the Icom Pro series only. Please do not call or write me asking questions about other Icom transceivers or other audio equipment I do not reference here on this part of the page. I have no idea how to open up a 746 Pro to go out to 20Khz which seems to be the rage in Europe and South America. 

So lets get one thing straight, you will not be setting up this radio under the current definition of ESSB as defined by John NU9N.  ( www.nu9n.com )The bandpass of these radios is not great enough to fit into the lo-fi definition of ESSB, but they will work just fine into my definition of EA or Enhanced Audio. Please keep both modes fixed into your mind as you go forward in SSB audio. 

Hardware Considerations

You are going to be using the Pro III for audio work so you should consider a couple of things when setting up the radio. When you have any radio in a shack these days there seems to be many many cables and cords strung around the room. Putting them there willy-nilly may work for other types of operation, but in EA, you most pay closer attention or you will be suffering the consequences for a long time. In every shack there is RF. RF is good, RFI is bad. If you do not pay attention to how you set up your hardware, you will have our old nemeses RFI come by and bite you right in the butt.  Do not run audio patch cables in parallel with signal coax or AC/DC power cords. Try to keep all types of cords or cables as far away from each other as possible. Put split beads mix 31 on all audio cables as they go into other boxes. Use a Radio Works T-4 line isolator or equivalent between the Pro III and any linier you may be using. I use an Astron RM-35M power supply. In any case keep the DC power cables as short as possible and bunch any extra left over and tie with a plastic tie strap to keep it from coming in contact with coax, patch cords or AC lines. If you use an after market power source like the one I use, remember to tighten the lugs onto the power supply very tightly. Check them regularly and make sure they are tight. Use a lock washer. Lose connections will give you fits and many a rig has gone to Icom for repair after appearing flakey because of this oversight by owners. 

Keep it cool. Your rig may look so neat tucked there inside that computer cabinet. But consider that all those little surface mount components must be kept cool. There are vents on the top and back of the Pro III used to suck and push air through the cabinet. If these are blocked or the air flow is restricted, well, I hope you like packing the radio to the service department. Also when you are working in audio, you will find yourself continually pulling cables off the back of the radio to make changes. If you have to pull the radio out of a tight space this just makes it harder. This is just one of the many reasons, I have always used racks for my audio gear and lately, have used them for my rigs as well. It really makes life easier. 

When connecting your Pro III to an linier amplifier check the voltage and rating of the switching circuit of the amp. Some of the older amps put way to much voltage to the Pro III. If you find that the amp you are using exceeds 16 V DC at 0.5 A, you will have to purchase an external amp switcher. These devices can be acquired from Ameritron or The Heathkit shop www.theheathkitshop.com Both will do a good job and much cheaper than a trip to Bellevue for repair. There may be other places to get this type of switch that I am not aware of, but of course you could build one yourself. Oh Oh I said something nasty didn't I?

Connections on the back of the Pro III

This is the back of the Pro III for reference below. From left to right: Ground strap, Coax to Linier, Power connector, Din plug to provide audio, and push to talk and fixed audio, 1/8 inch connection from computer, external speaker, and amp control cable.

I have provided the simple pictures above so that you can see what it looks like and I can reference the connections here in this part of the page. The grounding strap here is the braded type with a plastic coating on the outside. That connection and the coax and power connections probably do not need further reference or comments. The next cable is the DIN plug. My eyesight is too bad and my hands are not stable enough to solder onto those little little pins anymore. I buy my cables from W2IHY. He does a great job on them and gets them to you at a reasonable price and very quickly. www.w2ihy.com . You will want to select the pins to provide audio from your rack to go into the radio here. Also if you want to do any recording off the air, this plug can also be wired to pick off the fixed audio from the rig. You will also want to activate the push to talk circuit here as there is not PTT port on the back of the Pro III. Silly of Icom not to include that in the design. The next port, the silver looking plug into it, is the connection from the computer. You can purchase an Icom CT-17 level converter to go here or do as I did and get a ZLP Electronics cable  and pay about $35 for it instead of $130 from Icom. The next black plug is for the external speaker, and the last red plug goes to the amp control. The is the one you have to make sure that you do not have to much voltage going to and may need a amp switch for. 

The pin break out for the DIN plug are as follows:

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