ONKYO ES-FC300 headphones – review and mod: replacing the disastrous MMCX connectors with 2.5 jacks

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Onkyo ES-FC300 are the first headphones from Onkyo. Lots of effort went to their development, and the end result is a respectable product, unfortunately with one terrible flaw.


These headphones are very aesthetically designed. The external parts of cups are made of aluminium, shaped to resemble a large volume knob of an amp or receiver. They are also single coloured – all white, all black or all violet. Even the white version looks classy. Black version comes with red cable. There are three more models in the family, two of them are pretty much the same headphone with different cable: ES-HF300 is ES-FC300 with a supposedly (but not according to reviews) better quality cable that is silver; ES-CTI300 has a cable with in-line iOS remote and mic and comes in either black or silver and brown. The latter colour combination is rather strange, silver and black would work much better, but even this version looks really good. So good in fact that I bought these headphones despite being very disappointed with their sound after first listen. There is one more version developed in collaboration (reportedly an actual one, not the slap-my-name-on-your-product-and-pay-me sort) with Iron Maiden’s Steve Harris, called ED-PH0N3S after Iron Maiden’s mascot. This version is quite different in (different driver coils and grilles) and out (very in-your-face IM related graphics on cups and headband).


Like I mentioned, I was very disappointed when I first tried them in a store. They were on display with some 30 other headphones, and were the worst of them. But then I re-read user reviews that were unanimously good (which almost never happens) and Tyll Hertsens’ glowing review at Innerfidelity and concluded there was probably something wrong with that particular pair. So when I spotted white ES-FC300 second hand, new and sealed for less than half the retail price, I bought them and it turned out that pair I had tried earlier was indeed faulty. The headphones I bought sounded really good straight from the box.
Onkyo ES-FC300 have a very good clarity throughout the spectrum, more than decent sound stage for sealed, on-ear headphones and a bit (but not excessively) fun signature, that is, emphasised bass. It works very well because the bass boost is not your average hump around 100 or 150 Hz, but rather a consistent, few dB lift that extends from 150 Hz down to 20 Hz and below; up from 150 Hz the curve and is mostly flat until the upper midrange and gets a bit jumpy from there, but that is quite normal. High frequencies are clear and well balanced. Overall, this gives ES-FC300 (and other family members) a very good sound: slightly warm, clear, detailed, fast, and with a nice bass slam. ES-FC300, ES-HF300 and ES-CTI300 sound the same because they are the same except for the cable. The family members with different sound are ED-PH0N3S; they have more emphasis on midrange, which could make them sound better with rock and metal. I don’t know, but Steve Harris says so, and the few reviewers that have actually heard that version confirm.
With 32 Ohms nominal impedance and 97 dB/mW sensitivity these headphones are quite easy to drive. Even an average player (like Sansa Clip+ or a mobile phone) will be enough for them. They can handle 1W input power, which means that they can go insanely loud with a more powerful source (although probably not as loud as the 16 Ohms, 105 dB, 3.5 W Philips A5Pro that will take your head clean off). The Onkyos also isolate very well (provided you position them properly and get a good seal).


These are on-ear headphones with leatherette ear pads, they’re not small and some parts are metal. Obviously they are not comfort champions, but after some headband bending to reduce the clamp they are quite comfortable to wear. People with very small ears might have a bit of a problem, because the ear pads are 80 mm instead of more common 70 mm, so these are almost circumaural – but with average and large ears they rest on ears as they should and provide a good seal. It does require positioning them properly on ears though. They are not very light, but not heavy either. To me, while a bit heavier, they are more comfortable than AKG Y50 or Yamaha HPH-PRO300, but less than Philips SHP 5401 or Sennheiser HD 465. Headband is padded and the cushion is soft enough for good comfort. When hanging on the neck ES-FC300 are not very comfortable, but then again very few headphones are. The headband does not fold, but the cups do fold flat, making transport a bit easier. Cable is flat, tangle-free, appears sturdy and is detachable. That is usually good, but not in the case of these headphones. Read on.


This is where things get a bit tricky.

Let’s get the good out of the way first: in addition to classy looks, the headband and cups are very well made, everything is well fitted and sturdy, moving parts are durable. Much better than, say, certain AKG or Sennheiser headbands that crack when you look at them. Contrary to what marketing blurbs and pretty much all reviews suggest, the cups are not all-aluminium, only their outer part is. The inner part is good old plastic. Which is actually good, because this allowed Onkyo to do some careful sound tuning with dual inner chambers. Easier and cheaper to do that with plastic than metal. Leatherette on ear pads and headband padding is of good quality, soft but fairly durable. Ear pads do not disintegrate as quickly as they do in many other headphones.

Now for the not so good: unfortunately the white leatherette becomes yellowish with wear, but at least the ear pads can be easily swapped for fresh new ones. I recommend 80 mm pads for Sony MDR-V55, MDR-V500 and Audio-Technica ATH-WS70. Unfortunately the headband cushion wears faster than the ear pads, and it can’t be replaced.

And finally the ugly: the cable (actually cables, as this problem affects all versions with the exception of ED-PH0N3S – thank you, Steve Harris). It is detachable and on the headphones side terminated with MMCX connectors. These connectors are a complete disaster. They become intermittent very fast (a matter of weeks or even days) even if you do not detach the cable once, and none of the workarounds help. There is no sensible reason for using such an unusual connector other than trying to monopolize replacement cables, and guess what? Onkyo charged $30-63 (depending on the version) for a replacement cable, which was obviously just as good as the original one, meaning only good for a few weeks or days. Onkyo did absolutely nothing to address this issue – no recall, no solution offered to many dissatisfied buyers. They’re certainly aware of the problem, but pretend it does not exist. At least their current headphone models use different cable connectors. ED-PH0N3S have non-detachable cable so they do not suffer from this problem. It is the ONLY difference between ED-PH0N3S and ES-FC/HF/CTI300 that is NOT mentioned in rather extensive ED-PH0N3S marketing materials. In fact it was really difficult to find this information, my guess is Onkyo omitted it in attempt to hide the problem with ES-FC/HF/CTI300 from potential buyers.

Now, I love the sound of these headphones and find them comfortable enough for my portable needs. I even got used to them being white, despite a few jokes my friends made. But the cable connectors are the worst thing I’ve seen in (otherwise decent) headphones. In my Onkyos they started acting up after no more than 2-3 weeks of not too intensive use, and became seriously intermittent after a few more weeks. The problem was caused by the MMCX cable connectors Onkyo decided to use. MMCX is a coaxial connector that looks like a miniaturised antenna cable connector, with a hair-thin centre pin (+) that loses connection very easily. These connectors eventually become intermittent in all phones that have them (Shure earphones for example), but they are particularly ill-suited for headphones, and in the case of the Onkyos their quality is simply ridiculous: they start losing contact almost from day one. I bought the headphones new (in a sealed box), but from a private owner, so I had no warranty. It wouldn’t help anyway – the connectors did not malfunction, they were simply badly designed, the same thing would happen to a replacement cable as well. I tried the two fixes I found/came up with: slightly bending the pin in the male connector (that helped for a day or two) and fixing the connectors with some white-tack (like blu-tack, only white) so that they would stop moving and losing connection every time I move my head. That helped, but didn’t remedy the situation completely.

Because of the cable problem I used the Onkyos less and less and eventually stopped using them altogether, but recently I put them on again for the first time after a few months. The sound was still great, but I got ultra annoyed with left connector losing contact all the time – despite the white-tack.

So I grabbed a screwdriver and attacked the bastards with great vengeance and furious fire. Here’s what I discovered:

1. You can safely (without doing any damage) disassemble these headphones to the point that the female connector (the one in the cup) is exposed.

2. You can pull the wretched thing out easily – it’s just pushed in its place, no glue or anything. It is reversible, you can easily put it back; there’s also good access to the points where the internal wiring is soldered to the connector.

3. There’s quite a lot of space available once the connector is removed (looks like about 6 x 6 x 15 mm) – and of course there’s a nice round 6 mm hole where the connector used to be.

I came up with the plan to remove the damn things and either run a new cable straight into the cups and solder it directly to the internal wiring, or better yet find 3.5 mm or 2.5 mm jack sockets that fit in the space where the MMCX sockets were, and replace the MMCX crap.

I bought small 2.5 and 3.5mm sockets online – the smallest I could find. They were 30 cents a piece. Ultimately I decided to use the 2.5 jack sockets and managed to replace the ridiculous MMCX connectors with them. Nothing got damaged in the process (not even the old MMCX connectors), no drilling, gluing was necessary, I just removed the old connectors, soldered the new ones, fixed them in place and that’s it. The mod is fully reversible. The whole process took me a little over one hour. A fixed cable would be much easier to do, but I like the idea of detachable cable, just not one that makes headphones useless šŸ™‚ Plus, I already had cables terminated with 2.5 mono jacks for other headphones.

Now I can use the Onkyos without the cable losing contact all the time, hell, I can headbang with them on! And if the cable goes bad, I can make a good one for about $10, or buy a cheap one (like the one in the photos below) for even less.


Step by step modification guide with photos is here.


Later I also made a nice white and silver cables šŸ™‚

Here’s an alternative mod: cut off the MMCX plugs from the original cable, remove the MMCX sockets from the cups and solder the cable directly to the wires that run from the drivers to the connector chambers. This mod will be much easier and cheaper, so I recommend it if you’re less experienced. The drawback is the cable will no longer be detachable and not as easy to replace if it breaks.

Onkyo ES-FC300 (and other ES-XX300 family members) are very good sounding headphones with decent comfort and extremely good looks. They have mostly above-average build quality and one nearly fatal flaw: MMCX cable connectors. If you’re planning to buy them, be prepared for some DIY action. If you already have them and they sit in your drawer because of intermittent cable – do the above mod, or a fixed cable mod and enjoy their awesome sound. Onkyo ES-FC300 can now sometimes be found for $100 or less, and they are certainly worth that price. At MRSP of $150 (which is still their price in most places) – a lot depends on the intended use. If you’re looking for all-rounders for use at home and outdoors, with good isolation, closed and easy to drive by an average player – definitely consider them. If you need something for home use only, in this price range there are several good over-ear (read: more comfortable) headphones, both closed and open.

Technical information

Weight: 240 g

Driver Type Dynamic Titanium
Driver Size 40 mm (1 9/16)
Frequency Response 10 Hz – 27 kHz
Maximum Input Power 1000 mW
Output Sound Pressure Level 97 dB/mW
Nominal Impedance 32 Ohms

Type Low Noise Tangle-Free Flat Elastomer
Length 1.2 m
MMCX Connector Gold-Plated Detachable
Stereo Plug Gold-Plated 3.5 mm (1/8) L-Type

ONKYO ES-FC300 – gallery


ONKYO ES-FC300 – mod




  1. Hakki Post author

    Hey! Thank you so much for this article. It’s very well written, clear and concise. Very helpful. I had the same problem and just like you IĀ  just put the headphones away for a long time and always felt terrible about it. However, with this article, I have some hope again. My only question is where did you find the 2.5 mm mono jack sockets? I have been looking for them and can’t find ones that would fit. I would really appreciate if you can shed some light on where I can purchase them. Thank you!

    1. rafal lisinski Post author

      I did not use a mono socket, it’s a stereo socket (actually a 4-pole socket). I simply used the 2 pins corresponding to the right poles of the mono plug. I bought these sockets locally, but they are quite easy to find, search for 2.5 mm SMD Headphone Jack Socket. They are very cheap, so my advice is to get 3-4 different sockets and use the one that fits best.

    1. rafal lisinski Post author

      The information you’re asking about is in the article.

      The space to fit the new socket is 6 x 6 x 15 mm. Any socket that size or smaller should fit. A socket that has larger dimensions will not fit.

      You can use a 3.5 mm jack socket if it is 6 x 6 x 15 mm or smaller and fits the space. I used 2.5 mm because I already had a few cables with 2.5 mm plugs.

      You can also solder the cable directly to the internal wires in the headphones, or even directly to the drivers, if the cable you use is thin enough to run it through the existing hole or you drill a bigger hole. This is the best solution if you don’t need a detachable cable.

      The sound with most decent quality wires will be pretty much the same as with the original wires. If you use a very high quality wire, it might improve slightly. If you use a poor quality wire, the sound will get worse.

      The thing that will improve is the connection – no more intermittent sound.

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