Making a Unity / M7300 Mobile 44-pin Speaker Cable - Help

[brian86]

So I am by no means electronically inclined enough to understand exactly what I need to do to build my own speaker cable. I have 2 Front Mount Unity Radios with CH721 heads and would like to get away from the Harris Accessory Cable that is dawg gone near as bulky as the radio itself.

I purchased a 44pin breakout board to prototype and I have 44pin assemblies to make a finished product. First things first, I connected the speaker wire directly to pins 19/21 and I get nice clear audio.

I see in the schematic Below there are some loop-d-loops around Pin/Cable 19/20 & 21/22 that go to Pin7 Drain...

My question is what am I or how am I suppose to do that? Is that just shielding? I know Pin 7 is ground... I just don't want anything smoking in my shop.

Any help would be, well... very helpful. Thanks.

 

[BMDaug]

Tie 19 and 20, then tie 21 and 22. 19/20 are positive, 21/22 are negative. 7 is tied to the shield of the Harris cable assembly.

Do NOT connect 7 to positive or negative. Just bridge 19/20, then bridge 21/22, (both at the 44pin connector) and connect those two leads to the speaker. Disregard 7 and the shield.

-B

 

[brian86]

Thanks BMDaug, this is what I ended up doing... I made a pigtail that has the speaker Molex connector (19/20 & 21/22) and a RCA/Phono (14 & 1) out for connecting to a live stream (Radio Feed). So When I am out and about I can still monitor everything on the go. Seems to be working great.


I also changed the screw terminals on the rear DB44 female to Studs for this quick disconnect setup. You just have to squeeze the sides to release the connector. This makes it so much easier then trying to get a screw driver behind the radio in tight quarters.

 

[BMDaug]

That looks great! Just be careful swapping those Jack screws… they will shear off in the aluminum chassis if the threads are longer than the blind hole. Just FYI.

Also, if you are so inclined, the RCA could be wired to the FDISC output pin, which is a fixed level output so you can adjust the speaker volume independently of the stream feed. Just something for V2!!

Again, great job and much more compact than the official Harris solution!

-B

 

[brian86]

That looks great! Just be careful swapping those Jack screws… they will shear off in the aluminum chassis if the threads are longer than the blind hole. Just FYI.

Also, if you are so inclined, the RCA could be wired to the FDISC output pin, which is a fixed level output so you can adjust the speaker volume independently of the stream feed. Just something for V2!!

Again, great job and much more compact than the official Harris solution!

-B

I seen the Forum about the FDISC output but I was lost when the notes in the manual said I needed to add components and stuff. Like I said I am not a very knowledgeable Electronics Component person. I was lost after the deformed u that came after the 33 below.

Use a 33 µF / 50 V (or greater) AC-coupling
capacitor to couple to a 600-ohm load.

 

[mancow]

33 microFarad

 

[brian86]

33 microFarad

View attachment 139091

Ah... It says 50V or greater. I just ordered

Nichicon FG Capacitors 63V 33uf Audio Grade​

off of Amazon as that was all I could find close that can be here by tomorrow. Hopefully it will work.

I am sure there is a correct way and an incorrect way to wire this in, I see one prong is longer then the other.

 

[prcguy]

I seen the Forum about the FDISC output but I was lost when the notes in the manual said I needed to add components and stuff. Like I said I am not a very knowledgeable Electronics Component person. I was lost after the deformed u that came after the 33 below.

Use a 33 µF / 50 V (or greater) AC-coupling
capacitor to couple to a 600-ohm load.

A capacitor will not change impedance. If the speaker output is designed for a 4-8 ohm speaker you want to give the radio a load resistor like 10 ohms then cap or resistor couple to a 600:600 ohm line transformer.

 

[BMDaug]

Luckily, the equipment I needed to interface with already had the necessary components in place on its input stage, so I didn’t need to integrate any passives into my design.

But ya, that’ll work!

-B

 

[BMDaug]

A capacitor will not change impedance. If the speaker output is designed for a 4-8 ohm speaker you want to give the radio a load resistor like 10 ohms then cap or resistor couple to a 600:600 ohm line transformer.

You wouldn’t attach a speaker to the FDISC output though. I think his plan is speaker output to speaker, FDISC to line level.

-B

 

[brian86]

You wouldn’t attach a speaker to the FDISC output though. I think his plan is speaker output to speaker, FDISC to line level.

-B

Correct. That way the Line Level is a constant level and the speaker can be adjusted freely.

 

[prcguy]

Correct. That way the Line Level is a constant level and the speaker can be adjusted freely.

Ahh, makes sense. Its still a good idea to transformer couple when connecting something like this to a computer audio input.

 

[brian86]

Ahh, makes sense. Its still a good idea to transformer couple when connecting something like this to a computer audio input.

Recommendation on the Part I should use to accomplish this? and maybe a quick wiring explanation. If its explained in layman terms I can probably get the components and solder everything. I do thank you all for your input.

 

[prcguy]

This should work for the constant line level to a computer. Cut the center pin off of each side then solder the pins on one side to the radio cable then the pins on the other side to the cable feeding the computer. Polarity doesn't matter much in this case.

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[brian86]

This should work for the constant line level to a computer. Cut the center pin off of each side then solder the pins on one side to the radio cable then the pins on the other side to the cable feeding the computer. Polarity doesn't matter much in this case.

(4) 180 pF ±5% 500 Volts - CDE Mil-Spec Silvered Mica Capacitors * USA SELLER * | eBay

Silvered Mica Capacitors. 180 pF Silver Mica Capacitors by Cornell Dubilier. (4) 180 pF. ham radio etronic e-tronic hamtronic qba BootsParts USA boots. Datasheets are provided when available. US ZIP Codes ONLY .

www.ebay.com

I had already ordered these... Will they work?

https://www.amazon.com/gp/product/B07Q6RSWYC/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&th=1

 

[prcguy]

I had already ordered these... Will they work?

https://www.amazon.com/gp/product/B07Q6RSWYC/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&th=1

Yes

 

[mancow]

What is FDISC? I assumed it would be short for Flat DISCriminator with potentially no squelch no subaudible filtering and no deemphasis.

 

[brian86]

What is FDISC? I assumed it would be short for Flat DISCriminator with potentially no squelch no subaudible filtering and no deemphasis.

Manual Says: Buffered Filtered Discriminator Audio Output

 

[mancow]

Manual Says: Buffered Filtered Discriminator Audio Output

Ah, ok. Thanks.

 

[BMDaug]

What is FDISC? I assumed it would be short for Flat DISCriminator with potentially no squelch no subaudible filtering and no deemphasis.

“Buffered Filtered Discriminator Audio Output (typically not used). A fixed-level audio output with DC bias. Approximately 200 mV rms into a 600-ohm load at rated deviation. Does not contain signaling (e.g., CTCSS). Mutes when speaker mutes. Use a 33μF/50V (or greater) AC-coupling capacitor to couple to a 600-ohm load. Use P4 pin 12 for ground.”

From the manual.

-B