An update to the box for going places

I’m still working on the headset interface box to allow use of inexpensive plantronics wired headsets with common amateur radios.

My original post looking into this

The problem with straight wiring the plantronics to the radio is the higher impedance (~150 ohms) which does not mesh well with the common 8 ohm output of a radio speaker output. Ideally, a higher output impedance amplifier would handle matching, so an appropriate volume can be achieved… without that, cranking the 8 ohm output pretty high is required to drive a single headset.

To work through this, I’ve built an ugly (but working) prototype based on an NE5532 dual op-amp. The NE5532 is well suited for this, as it’s designed for a higher output impedance, and is a copy of the JRC5532, which was designed for just a purpose like this. I have a PCB designed to fit in a convenient enclosure that will also fit a 9V battery for instances where the radio does not have 8V available at the microphone port.

That’s not what this post is about, though… that will come later, if I finish it.

While researching the plantronics headsets, I came across this website:

On this site, K5PA not only presented a lot of basic information about the plantronics headsets, but specifically talked about the WO2 base, and what it could do. What really caught my attention was the conference call capability. In this mode, multiple wireless headsets can connect to the same base unit, and listen or talk on the call. Off to eBay. These things were $50-$100 in 2022, and they’re a lot cheaper now. I picked up a lot of 5 headsets and bases for under $50 total.

So, using K5PA’s site, I wired up a quick proof-of-concept breakout cable, manually shorted the PTT line to ground, and proved that the WO2 easily matched the audio from the radio to the headset(s) connected. What’s more, I played with the conference call capability, and found that one headset could be muted, and the other still talk on the call – allowing one headset to be the main operator, and the other a “logger”. The operators can even talk to one-another using the headsets in higher noise environments, or both can mute themselves when not talking on the radio.

The real beauty of this system is not only the cost, but the fact that the interface cabling is all passive – no need for external active circuitry, though the base still needs power. This got me thinking – I could easily wire application-specific cables, like K5PA does on his site (https://www.k5pa.com/catalog.pdf)… I had planned on building 2 or 3 cables right off the bat for some upcoming events, and then I had another idea.

Amazon sells a 4-keystone jack surface mount box. This was perfect – it would allow a small interface board for connecting things as needed, and provide openings for the following four jacks:

• Speaker audio from radio to system (1/8″ audio jack keystone insert)
• RJ45 to the radio’s microphone port. For radios like there Icom 2820H, this is a straight ethernet cable. For radios like the Yaesu FT-7800, an RJ11 telephone cable will do fine.
• RJ45 to the WO2 base “device” input. This is a straight ethernet cable, though only pins 1 – 4 will be used (1: Mic +, 2: Speaker -, 3: Speaker +, 4: Mic -)
• RCA keystone insert for PTT. Some users prefer a 1/4″ mono jack… I had to use this, as it was actually available, and interfaced directly with the same connections I use for my HF station and foot pedal. I’m sure there are RCA-M to 1/4″-F adaptor cables out there.

Inside, all four connectors go to a small PCB with headers, so that the system can be reconfigured easily (and on-site, if need be). This prototype is a LITTLE ugly, but it works flawlessly.

one cool thing about the Icom IC-2820H (pictured in the featured image) is the fact that the remote head attaches to things with a couple magnets. I epoxied a few black steel washers to the plantronics base – which makes for a very clean setup. I can put the box under a table, and only have the plantronics headset, interface, and control head up in front of the user!

(Update 19 June 2026)

Not one to leave things be… I did forget that the headset needs POWER. To address this, it’s easy enough to include the wall wart power supply in the box – but then what if I only have ONE outlet? I thought about putting an outlet inside the box, and plugging the wall wart in to it.

If you recall the original post, the box is configured to run off AC or DC, depending on what cord is plugged in. If I was running off DC, the wall wart idea wouldn’t work. For that reason, I decided that I needed some sort of power supply was needed to convert 12V to the 9V that the plantronics system required.

Enter this from Amazon (Link):

I mounted this to the side of the white keystone jack box, and then ran 12V power leads along the bundle (with the audio, control head and mic audio) into the fuse block in the box. Now the system can easily run from either 115VAC or 12VDC. Granted, the headset is advertised to only have a 10 hour talk time, so this isn’t a system that’s going to be used for days on end without recharging the headsets… still a cleaner setup at the end of the day.

22 June 26: On an unrelated note – the Plantronics WO2 will pair very well over bluetooth with the Icom 705 – there’s no push to talk functionality, but the receive audio is great, and even VOX for transmit seems to work well in a quiet-ish room. I couldn’t find an anti-vox setting, but that’s not something I would normally be using anyway. More to come on that, as I tinker with things. Too bad the 7300 doesn’t have bluetooth natively for audio!