PlusSound Copper+ Apollonian Series for the HD650

Match made in Heaven.

PROS:  Excellent synergy with the HD650, great build quality, very good ergonomics, infinite customization options, I expect the Copper+ to be very versatile in pairings.

CONS:  Price.


I would like to thank Christian of PlusSound Audio for providing me with the Copper+ Apollonian Series cable for the Sennheiser HD650 in exchange for my honest opinion. No incentive was given for a favorable review.

Copper+ Apollonian Series

  • 2-in-1 coax type Litz
  • UP-OCC Copper
  • New proprietary dual shield + semi-conductive layer
  • New matte black finish
  • Price: from US$1,025



This has become one of most challenging reviews to do. People who know me, know I take my reviews seriously and spend a lot of time building up my impressions of anything I review. I will put in a lot of hours and will go out of my way to explore synergy between different components of a setup. For instance, when I review a cable, I will try pairings with various IEMs and switch sources to get a good feel for how the cable works within various setups. This time though, everything was different and that made it much more challenging to make a sensible and informative review.

What’s the problem? Well, because this is my first venture into headphones, I am not setup like I am with IEMs and herein lies the problem. How then to say something sensible about using this cable with headphones? At the risk of sounding philosophical, in the problem was found the answer. See, there was only ever going to be one option for my first headphones: the venerable Sennheiser HD650. I have been pestered, bullied and manipulated for years by people who insisted I buy them and, in the end, the crushing peer pressure from my colleagues at Tw6 pushed me over the edge and I bought a brand new 2019 model HD650. I was of course not interested in the HD650 in any way. Just as Bill Clinton definitely did not have… Okay, I won’t finish that joke. I admit, I absolutely had to have the HD650 and I finally found the right excuse.

At long last I had the HD650 in hand and then I lost access to the most useful source on my desk, the Violectric V380 demo unit I had on loan. I was going to buy it, but then my dog needed a bigger car and so that didn’t happen. Least credible excuse ever, you say? Trust me, you haven’t seen the size of my bear dog. So, this review ended up becoming an experiment in itself: Would it be possible to use the HD650 in a portable setup? I thought that would be a fun little experiment, completely fail and ultimately present me with a good excuse to buy a new amp anyway. How good is that for experimental design? Knowing up front you get to buy new gear… Well, no. No, I did not get to buy that new amp after all.

The cable.

At the center of my little experiment is the cable, because even if you do not consider cables to have any influence on sound, the stock cable of the HD650 is never going to work in a portable setup. It is too long, not very ergonomic and Single Ended. I needed something short, comfortable and balanced. Enter the PlusSound Copper+ Apollonian Series.

PlusSound released their new Copper+ a few months ago and it is a step beyond conventional cable designs. No fancy exotic materials this time though, instead PlusSound focused on a completely new design of the cable as a whole in order to improve internal conductivity and isolation from electrical interference. Christian explained that it is basically two cables in one, where the cable is shielded with a new coax type of design with a secondary wire at the core. For this they came up with a new proprietary dual shield and semi-conductive layer, they replaced large size bundles from their Type 6 Litz design with smaller ones with more strands, gave the secondary wire its own insulation and finished the outer bundles with an enamel coating. All this resulted in a slightly thicker cable, but only by 15% so that it would not be a problem for use with IEMs.

Of course, PlusSound would not be PlusSound if they did not add something for the looks as well, this time a matte black finish to their excellent PS insulation. I absolutely love that. The PS insulation helps to create some of the most ergonomic cables out there and to have it in stealthy black is a great option. Additionally, PlusSound now offers the lower braid of their 4-wire cables in Twist option, which improves the suppleness even further.


It has been a while since I last reviewed a cable from PlusSound and since then they have updated their packaging with a sturdier box that has classy gold detailing. Opening up the box reveals a clear plastic cover that I expect offers a bit of extra protection, while also creating a nice presentation.

Inside is of course the cable itself with a warranty card and a few accessories such as a microfibre cloth, leather strap to help organize the cable and a soft leather pouch. The pouch is perhaps a bit less useful for a headphone cable compared to an IEM cable, as of course the headphone can’t fit in alongside, whereas IEMs would. It is still a nice addition for storing the cable when not in use. Although having said that, I would probably not use such a soft pouch for travelling with IEMs anyway, much better to use something like PlusSound’s recently released leather storage case instead. (Those look really good, btw.)

Build quality.

The build quality of PlusSound’s cables is always excellent and this cable is no exception. Personally, I would have preferred sleeving on the full cable like PlusSound offers with their Poetic Series, instead of the half-sleeve of the Apollonian Series. Of course, in this case the half-sleeve is functional, as it shows off the new matte black PS insulation that would have otherwise been covered by the sleeve. This is something I love when it comes to PlusSound: the endless options to customize each cable to your heart’s content.

The lower part of this cable is sleeved and has the new Twist option, which does make a big difference in ergonomics and works particularly well. It makes the entire cable incredibly ergonomic and that is especially important when using it in a portable setup.

The parts of the cable are again of a very high quality and I believe this one is fitted with PlusSound’s new rhodium plated 4.4mm balanced plug. The plug is a dream to use. I have become a big fan of the solid feel of a 4.4mm plug compared to the skinny 2.5mm that feels like it has less body than a high-fashion supermodel. The PlusSound 4.4mm feels very durable, it is solidly built and fits perfect in my 4.4mm sources (I have had some issues with other plugs being either too tight or too loose lately). The y-split is the familiar PlusSound design that is very light and nice and shiny, with a matching slider. The connectors are of course the HD650-specific connectors, but PlusSound gave those a little extra bling-factor. Quite discrete and a nice touch.


The big question is of course… Does this setup work? Can the HD650 be used in a portable setup? The answer is unequivocally “yes”. Yes, you can use the HD650 in a portable setup like this and expect the headphone to be driven properly.

Now, let me be clear here. I am not talking about volume, like I have seen in so many comments about whether or not a source is adequate to drive the HD650. Volume I can get with most portable sources, but the volume itself says nothing about whether or not the HD650 performs well. For instance, I can use the Lotoo PAW Gold Touch with the HD650 without having to push the volume very high, but the result is not very good. Lack of control in the bass and brittle treble tell me the LPGT simply does not have the raw power the HD650 needs. However, from balanced, the Shanling M8 on its ‘turbo gain’ setting drives the HD650 properly. Varying the gain setting on the M8 illustrates nicely how especially the bass and treble degrade when there is not enough power, even if the volume does not have to be pushed anywhere near its maximum level.

So how does it sound?


Here I of course need to reiterate that I have not been able to do the sort of extensive comparisons I usually do. I am primarily going by my notes of how the HD650 sounded with the stock cable and driven by the Violectric V380 and how it sounds with the PlusSound Copper+ driven by the Shanling M8. Comparing notes, I feel most noticeably that the Copper+ opens up the HD650 compared to stock. Not that you can expect an expansive soundstage or anything like that, the HD650 remains an intimate headphone, but there is more air, while the presentation feels cleaner and with a bit more transparency. The bass is tighter and feels more impactful, while the treble gets a hint more sparkle. The treble sparkle is still quite sweet and inoffensive though, so don’t expect any miracles there. The mids feel cleaner and as I mentioned already, transparency is improved by lifting the veil that some might associate with the HD650.

I don’t feel like the Copper+ fundamentally changes the HD650, I doubt any cable will ever have such an effect, but it does clean the HD650 up very nicely and creates a wonderfully musical presentation that is a joy to listen to. The HD650 remains an intimate headphone, yet the presentation becomes more strongly holographic with a feeling of notes dancing around your head. I was quite surprised by how strong this feeling was, even though I had previously used a high-end desktop DAC/amp such as the V380. While I couldn’t A/B properly, it did indicate just how viable this portable setup is, even when listening critically.

It is a shame that I could not compare the Copper+ to a cable based on the regular PlusSound Copper. That would have been more informative about whether or not the difference in price produces notable gains. I expect it does and then it simply becomes a question about whether or not a Copper+ cable is worth the extra investment for a $300 headphone. Mind you, people buy $5k tube amp for the HD650 because of how well they scale, so in this case that question is perhaps not as silly as it would for most other headphones.


What I can say for certain is that this has become one of my very favorite setups to use. The HD650 with the Copper+ cable sounds wonderfully addictive and I find myself using it over considerably more expensive IEM/cable pairings. It is just that good.


I must admit that I was surprised by the result at the end of this little experiment, that it is actually possible to use the HD650 in a portable setup that does not feel like a compromise. In terms of sound, I find that the Copper+ opens up the HD650, gives a bit more punch to the bass while keeping it tight, clears up the mids and adds a little sparkle in the treble. The Copper+ and HD650 pairing is also very holographic while maintaining the characteristic intimacy of the HD650. The Copper+ Apollonian Series cable also works great in a portable setup thanks to its excellent ergonomics and build quality. Overall, I am really impressed by the Copper+ and HD650 pairing, and together with the Shanling M8 it has become one of my favorite setups to use. If I can speculate based on my impressions here, I expect the Copper+ to work well with some of my favorite IEMs and perhaps replace PlusSound’s Gold-Plated Copper (GPC) as my favorite cable material.

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