Thursday, 29 September 2022



The Kenwood TS-590SG built-in tuner is pretty awesome, but it just cannot find a tune for 160 or 80M on my EFHW.  It manages fine on all other bands right up to 6M, but not at the other end of the scale. I don't use 160/80 that much but I don't like the idea of being restricted.

I connected my LDG AT-200 PRO and that could find a match anywhere but it's quite old and clunky and there's no integration with the TS-590SG.  It's also the least intuitive ATU I've ever come across! 

So, I searched for a cheap modern solution and found it in the MAT-TUNER mAT-K100 which comes as standard with a Kenwood interface. You can also buy an Icom interface which makes it a little more versatile. I think the Icom cable costs about £20.

ML&S, RadioWorld, Lamco, were asking £189 for the K100 but Moonraker had them up for sale at £149 so that was a no-brainer!  Waters & Stanton (and associated Nevada) don't appear to sell MAT tuners any more.

The parcel arrived quickly and well packed. It included the tuner, the Kenwood interface lead and the operating guide. The unit is very compact which suits my small shack perfectly. The construction quality of the mAT-K100 looked pretty darned good, with a real nice milled aluminium finish - better I'd say than any of my LDG tuners.

On the front panel are two simple LEDs and around the back you have a couple of SO-239s, a GND lug and the 4-pin interface socket. I was pleased to see that the 4 pins in the connector were quite substantial and not the usual ones which feel like they're made from "fuse-wire" :-) 

Once I'd detached the AT-200PRO and installed the mAT-K100, it was time for testing. Needless to say, the integration with the 590 was perfect. There are no buttons to press on the K100; it's all done from the radio's AT button. A simple press-hold sets off the tuner and quickly finds a match, which is then stored in one of the K100's 16,000 memories!

The K100 supports almost every Kenwood radio which is either  AT-250 or AT-300 compatible, so that includes the 570, 590, 850, 870 and the flagship 990. It also supports a few other Kenwoods like the older TS-2000 and the TS480SAT, etc, but the much older 430/440 radios are just too old to interface with this ATU.

Coverage is 1.6 to 54MHz and has a power-handling range of 0.1 to 120W (30W Digital). 

Tuning speed is impressively fast, but a full tune from scratch might take up to 5 seconds depending, of course, on how close to resonance your antenna is. All matches are stored in memory and recalled with lightning speed when needed. It pays to run through all the bands at various locations (CW area, PSK, FT8, Phone, etc) so that tuning time is minimised because you've already tuned there and it's all in memory.

A small but valuable feature is this ATU is powered from the radio, so no need to faff around connecting it to a DC supply.

The MAT-TUNER mAT-K100 looks great, works VERY well and is relatively cheap at Moonraker's price. I especially like the fact that it is so very well integrated with the Kenwood (and presumably the Icom range) which means that you can just totally forget it's there!


- 1.6-54 MHz continuous coverage

- 0.1-120 watts SSB/CW power 30 watts on PSK and digital modes.  

- 100 watts max SSB/CW above 50 MHz.

- Tuning time 0.1-5 seconds for full tune cycle.

- 16,000 frequency memories

- Impedance matching range 5 to 1500 ohms

- Dimensions  20D x 13W x 4D cm

- Weight 0.8 kg

Tuesday, 27 September 2022



When I bought my WSPRLite Flexi, it came with a Lowpass Filter Board which the previous owner had built and chucked in with the deal. It included the 15/40/80 bands which  was fine apart from 80M which I rarely use, so I decided to make a second board as a kit from SotaBeams, here in the UK.

I opted for the 20/15/10 and the kit arrived a couple of days later. It's very easy to build and it only took a couple of hours to complete. For now, I've stuck it on the reverse side of the existing board until I can find a suitable enclosure. At one time you could just nip into town and pick up an enclosure from Maplins or Radio Shack, etc, but sadly no more :-(

When I ordered the kit, I just assumed that the new PCB would be the same as the old one, but they modified it and the new V1.2 is smaller than the old one which scuppered my plans to have them back to back using the same mounting holes. 

Anyway, here's the completed kit. Note that I secure the toroids with a blob of Hot Glue. Might look a bit messy but it keeps them in place and prevents breakages.

First test

Friday, 23 September 2022


Tru Bling!

I work with stainless-steel everyday and so it was pretty inevitable that I should ask the CAD Department if they could copy the plastic lid, personalise it and make a couple of replacement lids for my (tr)uSDX radios.

They won't really serve much purpose other than stroking my vanity and generally looking great on the radios. I also took advantage of the opportunity to reduce the screen aperture size by 1mm all around - now it looks much more 'fitted'. Previsouly, there had been a tiny gap around the screen and it bugged the hell out of me.  Additionally, I fitted a stand to each radio. They cost £4 each from Amazon and come with self-adhesive backing. LINK HERE.

And before you ask, no I am not able to make any more. Sorry, but I had to pull some strings to get these two done. I intend to replace the black screws with stainless-steel hex heads. Here's some pix...

Modified with new screws

Thanks for popping by!

(tr)uSDX Review here

Tuesday, 13 September 2022


Back To Base

14 September 2022 
After getting our new holiday home in the Forest Of Bowland, I decided that I had no need for a Base Station at home, since I'd be going away every single weekend. I hardly spent any time in the shack to begin with, since most of my radio-time is spent outdoors with one of my QRP rigs. So I sold my  beautiful (but expensive) IC-7610 and put the money toward the new caravan.

At the caravan I setup my radio gear and pretty much leave it there. I also setup a telescopic mast for quick installation of a wire, so everything's pretty much sewn up and ready to go within a few short minutes.  But that leaves the shack at home pretty bare. In fact, we recently decided not to have a weekend at the caravan, but instead stay at home - and it was at that point that I realised I was 'HF deficient

At home I still have an FTM300D and an IC-705 (2M/70cm, DSTAR & C4FM) but no HF other than a tiny (tr)uSDX, so it was time to look for a cheap base station. To be honest, my very first thought was a used Yaesu FT-DX3000 because I think they're one of the most underrated HF rigs out there! I have very fond memories of the one I used to own and before I knew it, I'd found one on HamRadioDeals. The only thing that stopped me from buying it, was that it looked really grubby.

Soon after I spotted a MINT, 1yr old Kenwood TS-590SG for £875. These are currently £1500 new, so that represented the sort of bargain I go for. When buying a radio, I do my utmost to buy cheap and hopefully sell high - or at least break even. So with that in mind, I put in a cheeky cash offer but he took too long responding so I bought another minter within minutes!
When it arrived, I was really very pleased with the condition of the radio. The radio is surprisingly compact and fitted perfectly into the shack next to my Yaesu speaker (a remnant from my FT-DX101D ownership).

I've never had a Kenwood base station before - in fact the only Kenwoods I've ever bought were a TH-F7 and a TH-D74💖(both handhelds).  I'm very aware that Kenwoods are generally considered to be the kings of audio and the TS-590 has been on the periphery of my vision for a long time, but I've just never got around to trying one before.

Before I bought this, I studied the spec and general opinions of existing owners. It seemed that no one had a bad word to say - quite the opposite in fact! The vast majority of owners absolutely loved their 590 and the newer "SG" model just put icing on top of an already excellent cake with...

.... much improved receive performance and TX-spike performance (close to TS-990), CW Decoder, ANT Out, Improved Multi-Knob, 10 LCD Screen Colours and better styling.

The TS-590SG is a good old fashioned SuperHet so there's no fancy scopes or waterfalls, just a very clear and straightforward LCD screen with an option to adjust the background colour. After owning some of the most advanced transceivers on the market, it felt like going back to basics - but in a very good way. 

The TS-590SG hit the UK shelves in 2015 and is still very relevant in 2022 with its 32bit DSP, USB connector, built-in SoundCard and Remote Control capability, but it still has that old school feel about it and it's so nice to have all those buttons, knobs and dials. Kenwood is not a company for changing its product lines every two minutes - they make a radio, they make it well and it keeps on selling.

The "SG" update has turned a great radio into a superb radio thanks to technology borrowed from the mighty flagship TS-990S including some sharp roofing filters (with a first IF of 11.374MHz) and an IF AGC. In addition, Kenwood has improved the reciprocal mixer dynamic range, almost matching it with the SDR competition.  After testing the radio, Rob Sherwood said it offered the best bang for the buck on the market!

Now it's my understanding that the older 590's had a TX overshoot problem, but this has been eliminated in the new SG. As far as I know, there are no other known issues with the radio. It appears to be a rock solid workhorse which is admired by rag-chewers and contesters alike. 

As usual though, there are people who are always looking for problems so that they can be the ones to come up with a solution - an example of this is the all too common belief that a radio is not outputting full power because of an over-aggressive ALC - this is a particularly common myth in the Icom User circles. It appears that there are also some Kenwood Users who see fit to delve into the guts of their 590 to cut a resistor and get "the full 130W" available. Well I certainly shan't be doing any of that nonsense - and not just because I can't operate at more than 10W - but because I don't believe there's anything actually wrong in the first place. And this radio is built to operate at a maximum of 100W anyway.

Having been a big user of SDR radios, I am pretty used to having a panadapter and so I was pleased to see that the TS-590SG has a phono output for an external receiver, which means that you can easily connect a cheap (eg. SDRPLAY RSP1A ) receiver and share whatever antennas you have connected to the 590. 


The rear panel of the TS-590SG is well laid out and has decent spacing between connectors. There are two SO-239's for antennas A and B and a phono socket (RCA) for the RX-Only antenna. There's a second RCA connector for DRV (external receiver or transvertor).

Accessory wise, there's a few bits and bobs that can be added to the radio such as a very high-accuracy TCXO and a Voice Recorder, but the latter is of no interest to me personally. The frequency on the other hand drifts off by 7Hz. That’s a tiny amount, I know, but it drives me potty,  so I’ve ordered an SO-3 TCXO. 

There's also a range of microphones but the last three years has taught me that the stock fist-mic is usually the best sounding mic you can plug into the connector. Boy, I've wasted some money going down that road! 

I'd just like to point out that the Kenwood feels superbly well made! I mean the whole thing feels slick and all the buttons and dials are solidly fitted with very little lateral movement or "slack". This is better than I've found on transceivers costing three times as much!

My home QTH isn't the quietest place (electrically speaking), so it's not really fair to talk about the radio's noise-floor, although it certainly doesn't seem any worse than any of my previous radios. It does, however, have a gorgeous rich sound to the audio and is less tiring to listen to on SSB. Those fabulous roofing filters no doubt contribute to the great sound of the Kenwood, as does the Noise Reduction system.

The radio has a buit-in equaliser for both TX & RX and there's some useful presets plus a custom user-defined setting. The trouble is with these things is that you can get carried away with them and end up with a setting that is excessively biased one way - way too thin or too thick and heavy. I think I'll end up assigning the RX Eq to one of the PF buttons for quick access.

The TX audio is equally impressive according to those who were good enough to help me with tests. I've not bothered altering the TX-Eq and probably won't.

Tuning around with that velvety smooth dial is a pleasure and when you com across a signal, rest assured that you've got the tools to improve it, no matter how poor it is. Using the RF Gain, Noise Reduction and the Filter Shift & Width you will pull out all but the very faintest signals. The Beat Cancel button (1&2) works amazingly well to get rid of annoying  whistles and beeps on your frequency, without degrading the desired signal too much. I really like that feature and use it quite a lot.

The ATU : WOW! Normally I don't even discuss built-in ATU's except on Elecrafts, because they're always pretty "average" but I have to give credit where credit is due. The TS-590SG has a superb ATU and it's super fast too. If you have something like a 40-6M EFHW, you won't need an external atu - simple as that - it'll tune all bands without an issue. Brilliant!!

Unsurprisingly, the Kenwood ATU won't find a match on my EFHW for 80 and 160M, so I might look out for a cheap external ATU like the MAT-TUNER K100.

Finally I'd like to mention how very easy it is to work Digital modes - this thing is a breeze to work with on FT8, WSPR, etc. Just follow this super simple guide. It makes you wonder why some other manufacturers make it so damned difficult! 😡

So, there you have it. I managed to find a cheap marvel and I'm super happy with it. Even though I've previously had some high-end radios in the shack, I don't feel I'm losing out massively by using a TS-590SG.  Sure, if I did a lot of work from my shack, I'd have kept the 7610, but I'm an occasional user at home, so I reckon I've done pretty good choosing this rig. 




I guess the biggest competition for this radio would be the ICOM IC-7300 and if you 're specifically looking for an SDR, then that would be the natural choice, especially with Icom's super intuitive operating systems - it's certainly the cheapest option! I've had a 7300 myself and for the money it's a fabulous entry point into SDR radio. I could have got a used one for less money than the 590, but I decided I wanted to go back to a more 'traditional' rig and I personally feel that the 590 actually performs better than the 7300 IN THE SHACK! 

I say 'in the shack' because outdoors (say on a Field Day), the 7300's scope and waterfall could be considered a massive advantage in quickly locating band activity. But back in the shack, that advantage has been lost. Why?? Because back in the shack, you always (or I do anyway) end up connecting the radio to a computer and more often than not, to an SDR Receiver like the SDRPLAY RSPdx...

I've done it on almost every radio I've had - including the heavyweights IC-7610 and the FT-DX101D! 

The TS-590SG's external-receiver connector (DRV) is a great feature! You should bear in mind though, that this is an antenna-splitter and not an IF-Out, so you're not hearing the 590's output - you're simply sharing the 590's antenna and splitting antennas between two receivers has the obvious detrimental effect of a slight signal loss on both pathways (about 1 S-point).

Some people might have hoped for an IF-Out but the advantage of feeding your RSPdx with an antenna is that you get to hear the difference between the two receivers instead of hearing the same. There'll be some circumstances where perhaps the RSPdx processes the signal in a way that makes it more readable than your 590. Certainly, if you're monitoring LW, the RSPdx does a fabulous job!

It's nice to see that you can switch off the sharing by the simple press of a button, if  for example, you wanted to focus on a particularly weak signal momentarily. This built-in splitter is infinitely more convenient say, than using a clunky MFJ-1708B (not to mention cheaper, lol)

It doesn't matter how good your radio's SDR screen is, you can't beat having the flexibility and rich feature-set of software like SDR UNO, SDR CONSOLE or HDSDR and being able to control everything on the computer screen.

SDR UNO (with OminRig installed) can operate your radio flawlessly and provide you with a staggering range of information and options all on one big screen. You can even have multiple receivers open. And if you spin the physical dial on the radio (or press any buttons), it changes on the computer too. UNO is also constantly being modified and updated with an amazing array of features. I believe they're currently writing a completely new multi-platform version called SDR CONNECT which should be released at the back end of 2022.

Kenwood also supply some free software (ARCP-590) which allows you to control the radio but it obviously doesn't provide any panadapter features. It does, however, give you access to all the controls and menus in a nice, easy to access way. Please note from the screenshot below that you must download the correct version for your 590S or 590SG. Installing the wrong one (as I did 😁) will result in an error.

So apart from being cheap, the IC-7300 just doesn't compare to the TS-590SG (in my humble opinion). The 7300 only has one antenna connector, whereas the 590 has 2 TX and 3 RX connectors. The 590 has an output for an external receiver - the 7300 doesn’t. The 7300 ATU is like most other manufacturer's - average. Basically, the 7300 is a low-cost, entry-level SDR transceiver for people who are perhaps new to radio or for those who just want something very simple - it's a fabulous choice. The TS-590SG is more of an ‘experimenter’s’ radio.

I've never had an FT-DX10 so I can't really comment on it, but I have had its bigger brother the 101D (which I dumped in favour of the fabulous IC-7610).

73, Tom, M7MCQ.

If you have any comments or questions, then please post in the comment section below or email me directly on and remember, this post is just my own personal ramblings - I'm not an expert, but I have at least bought and tried the equipment that I talk about :-) 

Wednesday, 27 July 2022

(tr)uSDX Review


The (tr)uSDX is something of a marvel! Okay, so it's no KX3, but neither is it £1500. It's a supremely affordable QRP transceiver which can be purchased pre-built or (if you're into diy), can be ordered as a simple, easy to build kit. Because I'm tight-fisted 😂 I bought mine second-hand from YouTube's  TechMinds.

Everything about the (tr)uSDX looks cheap - it's encased in a 3D printed enclosure with all the associated crude detailing and tacky colours. The VFO encoder knob is also 3D printed. The case is held together with bulky screws and it has those stick-on rubber feet that you can buy from the £Shop.

The sound from the built-in speaker is pretty shocking and the audio is generally poor. The receiver isn't particularly sensitive and when sat next to my beautiful little BELKA DX receiver, you feel like maybe you've made a mistake purchasing the (tr)uSDX.

But that's where the negativity ends! The (tr)uSDX (usually pronounced True SDX) is a fabulously cheap little transceiver which is not much bigger than a pack of cigarettes and weighs next to nothing. It has a small but clear OLED screen which provides an amazing amount of information. The screen is not easy to read in direct sunlight, so be prepared to shade it with your hand.

This is a 5-Band radio (mine is configured for 80-60-40-30-20 (but other configurations are available)) providing up to 6W output and CW/LSB/USB/AM/FM modes. There's a convenient built-in microphone and PTT-switch (which can even double up as an emergency CW key), making the radio pretty self-contained. Needless to say, you'd be better using an external mic and speaker, but at least they're there as a backup for those occasional days when you reach your SOTA Summit and realise you've left the mic at home! The radio has a socket for a CW Key (straight or paddles).

The receiver's noise floor is fairly high, but again, you have to remember the price point of this radio and accept the fact that it's not your DX base station - it's your "stick it in your pocket" radio, your "pop it in the glovebox" radio. And when you're sat on the beach or on top of a hillside with a bit of wire, you'll be pulling in plenty of signals strong and loud enough to be able to have some fantastic QSO's in any mode you like!

A couple of minutes Audio of my (tr)uSDX

As soon as my (tr)uSDX dropped through the letterbox, I quickly connected it to a 9V supply and an EFHW and tuned around 40M. On 7.144 I found PA0PIW and although he was in a mini-pileup, I thought I'd shout into the built-in mic and see if he could hear me. He almost instantly read back my callsign and gave me a good signal report! That was very pleasing and I look forward to taking this little beauty up to my local Sota point to see just how far I can get. My second attempt got me a 55 from F4HEC in France (he’s the one featured in the recording above).

Navigating around the (tr)uSDX's operating system is fairly straight-forward. The primary function of the rotary encoder is (as you'd expect) to control the frequency of the VFO, but if you push it down and turn, it controls the volume. Single pushes of the knob alters the tuning rate and a double-push changes bands. Single-clicking the Enter Key changes modes, while double-clicking changes filter width and a long push brings up the RIT function. Nice!

The rest of the radio's functions lay in the Menu and it's all surprisingly intuitive - no doubt thanks to the software skills of DL2MAN's partner - PE1NNZ who's done a fabulous job. When you first get hold of your (tr)uSDX you can put it into 'Practise Mode' so that the PA is shut down while you learn your way around the radio. Speaking of PA, there is a connector on the side of the radio to allow you to connect to an External Amplifier.

 DL2MAN's website is a great place to learn more about the (tr)uSDX and its heritage; there's lot's of great tutorial videos there too. Manuel seems like a real nice character and his videos make for easy watching. His command of the English language is pretty good too. There's also a very useful FORUM.

The (tr)uSDX can be run on a wide range of voltages using the small DC connector port and can even be powered from a 5V USB power pack. At 5V the TX power is limited to 500mW but even that is a great feature for those wishing to play at the lower end of QRP levels. This USB port can also be used for CAT Control and Programming.

As I mentioned earlier, the OLED screen provides lots of info and can be tailored to suit your personal preferences. You have the frequency, the VFO indicator, S-Meter, Filter Width, Rx/Tx indicator, Mode, Tuning-Step and even your CallSign.  Things like the S-Meter can be altered to show reflected power, forward power, swr, watts, efficiency and more, but the latter can only be done in CW mode. 

Another great feature of the (tr)uSDX is the built-in CW Decoder! Again, just think about the price of this tiny transceiver and ask yourself would you really expect a CW Decoder to be included?? I wouldn't! 

And it works really well too. I usually set the CW Speed to 20wpm and it pretty much decodes everything I can hear as long as the signal is strong. Occasionally I have to drop the speed down when I know the sender is particularly slow, but otherwise, it does a great job.  The radio can also SEND an automated CW Message from memory which can be a great assistance when calling CQ or running an RBN test.

 Note that I fitted an SMA to BNC adapter but it leaves a gap, so I inserted a brass ‘Cup Washer’. Perfect fit! I also use a compact (but very clear) plug-in speaker from Amazon. Highly recommended!

Although I've got a SotaBeams EFHW and LINKED DIPOLE, I sent off for a QRP GUYS 'No Tune' End-Fed-Half-Wave antenna which covers 80-10M. This will be the perfect companion for the (tr)uSDX. It comes in Kit-Form and only take a few minutes to put together. All you then need to do is connect the appropriate length of wire to suit the band you wish to operate on. No counterpoise is required. Conveniently, all the wire-lengths are printed on the antenna former.

It was a simple task to cut the wires and trim them to attain the best SWR using my NanoVNA. I'm guessing that most of the time this antenna will be used in a Sloper configuration by throwing one end up into a tree, thereby allowing me to leave my telescopic mast at home.

Just bear in mind that although this antenna looks incredibly compact, you do have to carry around all the various lengths of wire for each band - and they range from 13ft to 125ft 😮

Super simple to build!


As I write this mini-review of the (tr)uSDX, I am reminded of the infinitely more expensive PreppComm MMX which I purchased a few months ago. The MMX is a small CW-ONLY 3-Band, Decoder/Encoder which has not only cost me a small fortune, but has caused me months of disappointment and anxiety. And even now when all the troubles are supposedly behind me, I am left wary and cautious about using it.

The (tr)uSDX kit on the other hand, has proved to be a product that just worked from the get-go. Not only does it do what it's supposed to do, it does it with ease and reliability. It has some amazing built-in tools to diagnose problems, has a built-in SWR Bridge and even a PA efficiency indicator to help you tweak the toroids, if you're so inclined.

The levels of support for such a cheap product are amazing and I'm very pleased to have it in my arsenal. I reckon I'm going to get more fun and enjoyment from this budget rig than some of my other much more expensive radios! We'll see 😊

* Super Cheap!
* Easy Kit build or Pre-Built.
* Super Light & Compact!
* Informative OLED Screen.
* Intuitive Operation.
* Robust Design.
* Built-In Diagnostic Tools.
* Built-In CW Decoder!
* Five Bands!
* Great Performer!

* Tacky 3D Printed Enclosure.
* Fairly High Noise Floor.
* Small Screen.
* Horrible Speaker.
* No Bandscope, Waterfall, ATU, GPS 😂😂😂

During my 2 weeks holiday at our static caravan in Scorton, I went up to Bodie Hill which overlooks Morecambe Bay and set up station using the (tr)uSDX and my 20/40 linked dipole. I had a great take-off point and will definitely go again.

It was pretty early in the morning (because I had other things to do in the afternoon) and there wasn’t a great deal of action but I still managed to have some great chinwags with operators across the globe with my 4W. I was very happy!

The radio performed incredibly well and I was impressed with how sensitive it was. You see  questions on the internet like “How good is the (tr)uSDX” and “Can the (tr)uSDX REALLY perform as well as people say”? Well the answer is yes!! For the money, it cannot be beaten as long as you give it a helping hand by choosing a decent operating location. Having said that, I've been having SSB chinwags with Americans from my home qth with a compromised antenna.
Here’s some pix from my BIWOTA ACTIVATION TODAY…

I love this radio❤️ so I ordered another kit in green.

When the green one arrived, I did the same as I'd done with the orange one - just plugged it straight into an EFHW and tuned around 40M. I heard a signal coming in from what I thought was Russia, but it turned out to be a Ukranian operator chastising Russia and Putin for their "Special Operation". Then I had a QSO with GM0WRR in Scotland and MI3JXG in Ireland and DL5PIA in Germany.

If video doesn't show, click here

Fitted a power lead directly to the PCB. Still kept the regular jack though, in case I need to power an accessory.

Quick PSKR Test - 3500 miles

Quick RBN Test - 3400 miles

Before I forget, DL2MAN has a great video on preparing the (tr)uSDX for Data HERE.


Although the built-in microphone really does work, it is not very convenient having to lean over and shout into the radio. There is a kit available in America for a small electret mic but apart from the fact that it looks pretty crumby, I don't want to pay the ridiculous international shipping fees. So looking on Amazon I found a Speaker Mic which was only £15 so I took a chance and bought it. 

Being a lowly M7 licensee, I have no knowledge of electronics but I figured out from the (tr)uSDX details on the net that I could possibly get this TYT Mic working, so I tried to get it right in my head before giving it a go. I sketched this little schematic...

Well that was the theory, but it didn't quite work out 😢 The microphone part worked fine! And on receive, the audio from the radio did come through the speaker-mic (great!) but when I pressed the PTT I got a high pitched tone (it wasn't acoustic feedback).

I wondered if it was because I hadn't included a ground wire to the audio jack-plug but I didn't think I'd need to because the ground was already supplied in the other jack. Perhaps that's my ignorance showing - I'll have to try again by adding a ground wire. No harm done (so far). I'll keep experimenting and update later.

DL2MAN's Schematic

Modified with new front-panels