The DIY space often has quite a few interesting and awesome pieces of gear but I’ve noticed that this forum doesn’t have a thread dedicated to it so thought I’d start one! Maybe we’ll even witness the birth of a famous new brand here!
Feel free to post headphones, DACs, and amps in here. Headphones.com has a pretty robust IEMs section so we can leave any DIY ones in there 
To kick us off, here’s a review I just finished for a DIY headphone called the Philphone:
Philphone Review: A DYIer’s Personal Solution to Audio Nirvana
Review written by @Fc-Construct
Review unit on loan from Zerousen (Phil)
Introduction
Let’s start today’s review with a question. How many of you are reading this while in pursuit of some form of audio nirvana? For some, it might be the HiFiMan Susvara paired with the Bakoon AMP13-r and CHORD Qutest. For others, maybe it’s a simple Schitt stack with the Sennheiser HD6XX. Perhaps a more exotic solution represents the holy grail, like a special edition 30-year-old headphones with a $12,000 DAC/amp setup. If you’re a true audiophile, you’ll install your own power pole for the purest possible sound to your system. Or maybe you just don’t believe that perfection can be achieved and live at peace (?) with that fact.
For a select few, the path to enlightenment means taking things into their own hands. One such person is community member Zerousen AKA Phil. Some might recognize him as a mod on the Headphone Headquarters and In-Ear Fidelity Discord servers. Unsatisfied with the options available to him, he decided to create his own headphones. Enter Philphone.
Fundamentally, the Philphone is a simple headphone. Take Fostex’s TH-series biodynamic drivers and put them in a comfortable open back headphone shell. In this case, the AD series from Audio Technica. That’s it. The Fostex drivers are well-known for their excellent bass response and dynamism within a closed shell, so the idea here is to hopefully maintain that performance while conferring the openness of an open back. Hopefully, this will create a basshead’s dream headphone that’s comfortable for all day listening. For its creator, this dream was realized. But how does it sound to someone in the general public? Let’s find out.
Note: Technically yes, the Fostex TH909 exists as an open back version of the TH-series headphones. However those are $1,800 headphones compared to the $600 that the Philphone is going for.
Build
The Philphone I have on hand for this review utilizes the ATH AD900x shell, stock velour pads, and a special felt as a front damper. Though the drivers are transplanted into a non-native shell, Phil’s mod work is near impeccable. It’s as if these Fostex biodynamic drivers meant to be placed in these shells. The only minor imperfection I found was near the detachable cable mod where the cup’s plastic is ever so slightly bowed out to accommodate the 3.5 mm jack. As with the AD shells, the drivers are angled and leak a significant amount of sound with the open back.
The Philphone is lightweight and quite comfortable. However, it uses Audio Technica’s infamous wing suspension system for a headband. Some may find that the wing system isn’t robust enough and causes the headphones to slide down their head. I use the rubber band mod to keep them up like I do on my ATH A900x. This has the effect of also increasing the clamp force. Like many headphones, I do get a bit of headband soreness after a few hours of having it on without break. But otherwise, these are headphones I can see myself wearing for extended periods of time.
The final production version of the Philphone will use an AD700x shell with TH600/X00 drivers. Phil builds each by hand in small batches so if you are interested in getting one, definitely check in with him . He’s able to accommodate requests for a different chassis or custom grill paintings.
The rubber band mod applied on the ATH wings.
Sound
Before I had a chance to hear the Philphone, it had the reputation of being a hugely dynamic bass cannon with one of the hardest slamming bass of any headphone. It does however stumble in the treble with some rather piercing peaks. To my ears, about half of that is true.
At first listen, I’m pretty happy with the tuning. It has an aggressive, energetic V-shaped sound that’s strangely balanced. Bass is absolutely large and in charge, upper mids have a clear forwardness to them, and the treble has a sharp brilliance to it.
On a technical level, the Philphone has solid resolution for the price and an open soundstage. Genre wise, the Philphone is pretty good all around but shines with EDM/hip-hop/pop. It’s a highly engaging headphone to listen to and will make you want to turn up the volume to hear more.
Bass
With the Philphone initially touted as the ultimate basshead headphone, I was expecting brain crushing, mind numbing, teeth rattling amounts of bass. It doesn’t. What it does have is a downright reasonable bass curve. To my ear, it sounds like it’s hitting about 6 – 7 dB at 40 – 50 Hz while sloping down to level out in the low mids at about 400 Hz. This gives a decidedly bassy response that doesn’t sound overbearing. Like many headphones, it does start to roll off in the lowest octaves below the 40 Hz mark. Altogether, the bass of the Philphone is generally boomy. But this doesn’t disqualify it from having well defined bass lines.
Now let’s talk bass quality. But first, let me define two pieces of terminology. In my mind, I define bass slam on notes as having extremely clean, explosive attack and decay characteristics. The Focal Elex is a great example of slam to me. In contrast, I see impact as having a weighty, hard-hitting determination paired with a sense of totality when a note lands. Slam and impact go hand-in-hand and the way a headphone handles them is a critical contributor to its sense of dynamism.
I’d say the Philphone is more impactful than slammy. Bass notes are heavy and full-bodied and land with a purposeful intention that makes it impossible to not head bang along. While the bass of the Philphone may be deeply indulgent, it is fairly clean given its bass curve. Though the attack of each note does have a slight softness to it, the Philphone does sound quite natural. Note decay lingers just long enough to give notes a fullness without overstaying its welcome.
Mids
The tonality of the mids in the Philphone is surprisingly respectable. I thought it was going to be a headphone that sacrificed the mids in uncompromising pursuit of bass. Instead, it has a solid upper/lower mids balance without a big hole in the center-mids like you’d expect from V-shaped headphones. Vocals are fairly forward and can be on the aggressive side at times. While it does have enough lower mids elevation to prevent it from sounding thin, there’s a hint of hollowness to the vocals. Instruments have a minor colouring to their timbre that’s pleasant to listen to, a sort of texturing if you will. The lower mids do an excellent job here to give instruments the body it needs to reproduce satisfyingly rich tones. I’ll note here that due to the elevated lower mids and softer attack, rock/metal tracks with busy instrumentation in the that region may come off as a little congested compared to cleaner, more neutral headphones. To an extent, that’s the price you pay for bass I suppose.
Treble
The Archille’s heel of the Philphone is in its treble. Specifically, a cluster of peaks in the upper mids around the 12 – 13 kHz mark for my ear. These peaks are a very real double-edged sword for the Philphone. On one hand, they give the Philphone a great brilliance in its sound that’s bright and energetic. It lends a breath of airiness to the vocals and elevates not only their clarity but that of the other instruments e.g. the plucked strings of an acoustic guitar. It works wonders for note definition through emphasized upper harmonics. So-called “fake detail” if you want to call it that. The treble also does extend well into the upper treble, highlighting treble-specific notes that can often get lost.
On the other hand, these peaks make the treble of the Philphone piercing on some tracks and vocals undeniably sibilant on others. The particular killer in these cases being sharp S’s or particularly crystalline recordings of hats/cymbals or chime-like sounds. Personally, I would consider myself to be quite treble tolerant and the occasionally piercing treble of the Philphone isn’t a dealbreaker for me. It happens more than I’d like but only on a small handful of tracks does it actually become a real issue.
Thankfully, there is an easy solution to the treble problem: a single band EQ . Cutting 4.5 dB at 13 kHz with a Q value of 0.7 greatly alleviates brightness issues even on my most problematic test tracks. You do sacrifice some of that treble brilliance noted above, however. Feel free to adjust for your own sensitivity and preferences. Set and forget.
Presentation
The staging ability of the Philphone is a pleasant surprise. Unlike other popular open back headphones like Focal’s lineup or the HD6x0 series, the Philphone isn’t nearly as closed in or intimate. It sounds open with a large soundstage and clear imaging. Of particular note is the stage depth that allows for a nicely layered sense of instrument separation. This is a headphone that uses its open back nature to its full extent. Instruments have an abundance of space to play in, vocals are cleanly separated and centered, and the imaging positions notes in a way that it shapes a coherent landscape of music. The staging of the Philphone may not be its main selling point but it is not an insignificant cornerstone of its sound. Something about the angled drivers of the ATH AD series shells does a ton of work.
Similarly, the resolution of the Philphone is really quite good. Even disregarding the treble peak and “fake detail”, the Philphone is able to bring nuance between notes, accentuating the little characteristics that give life to each note or making me notice tiny details I don’t always pick up on.
The dynamics of the Philphone is its raison d’etre. I think the best way to describe it is that the Philphone “pushes air” extremely well. This is in contrast to Focal’s headphones that focus on muscularity and physicality of its drivers. The Philphone sounds big . Bass drops are deeply satisfying, and notes are given an unrestricted volume range to express themselves. At the risk of using audiophile terminology, the Philphone is a great example of macrodynamics. It focuses on the dips and swells in music and delivers on them beautifully.
Comparison to the Sennheiser HD600:
I consider the Sennheiser HD600 (or HD650) to be the starting point for headphone audio and a good benchmark for comparisons due to its performance and ubiquity. Known for its tonal accuracy in the mids, the HD600 has a smoother, more complete, mellow tone to it. While it’s not a night and day difference, it definitely sounds more correct to the ear. Here, the HD600 is still the unquestionably the king of timbre.
But other than tuning, the Philphone takes it handily. The staging of the Philphone is a step above the closed-in affair of the HD600. It boasts noticeably better resolution and instrument separation. And when it comes to bass dynamics, well HD600 sounds almost flat in comparison. Then again, the HD600 are about 2 – 3x cheaper than Philphones are if you can find a good used deal.
Comparison to the Focal Elex:
If a used HD600 at $200 is the best value for headphones, the next step up would be the Focal Elex at $600 depending on (Mass)Drop sales. This makes it a perfect comparator to the Philphone. I reviewed the Focal Elex in the past and considered it to be a super HD600. It trades blows closely with the Philphone. From a tuning standpoint, the Elex takes it in the mids and treble. Bass is a matter of preference; do you want the lean, reference-style bass of the Elex or the bombastic, boosted bass of the Philphone?
On a technical level, the staging of the Philphone is better than the Elex, though not as big of a difference between it and the HD600. Resolution is on par or slightly behind the Elex. Dynamics is another question of preference. Do you prefer the slammy, microdynamic laden Elex or the impactful, macrodynamically extravagant Philphone? Both headphones use their dynamism to great effect in their own way.
Personally, for a pure sound quality standpoint, I’d take the Elex between the two. That said, the Philphone realistically makes a little more sense to me. I’m apprehensive of the Elex’s longevity and quality control. In terms of comfort, the weight of the Elex can make it uncomfortable for extended sessions.
Should You Buy It?
Yes. The Philphone is exactly the type of headphone I like to see. It has a clear vision and executes towards it uncompromisingly. Is it perfect? No. The treble response can be a problem (though mitigatable with EQ) and its mids have a slight ring of hollowness. But it is comfortable, reasonably well-tuned, and wonderfully dynamic. And more than just being a good headphone, the Philphone fills a niche in the market. For the price, I can’t think of another open-back headphone that have this combination of openness and bass performance. That said, at $600 the Philphone is not a cheap headphone. But if you’re looking for a dynamic driver upgrade from the HD6X0 series, don’t want to get an Elex, and can’t afford the Clear, the Philphone is an excellent option.
If you are interested in possibly getting a Philphone, you can contact Phil on reddit here.
I happened to review an older version of Phil Phone, dubbed Phil Phone 3, last October, and here’s my impressions of it as well:
PhilPhone is a DIY project from a community friend, Zerousen, who many who lounge around on the various headphones and IEM discord servers may recognize. This 3rd iteration of the PhilPhone project is a Frankenstein-concoction of the Audio Technica ATH-AD500X, the Fostex TH900, and some extra goodies from Zerousen.
The TH900 driver is the centerpiece of this headphone and it’s been carefully placed inside the AD500X headphone housing, with its driver removed. The fit looks like it was made for this design as I do not see any gaps or flaws in the installation, and if you’ve seen this Audio Technica headphone before, you’ll know that you can see everything on the inside, as the grill is completely openback.
One of the very interesting things I’ve found personally with the Foster biodynamic drivers is that if you remove the outer wood cup, the sub-bass actually increases than with it on. This is a bit mind-blowing to me, but I guess you will get all the incoming air it needs to really slam, and I’ve tried this with my own set of Fostex TR-X00 headphones in the past.
And this is the basic premise behind the PhilPhone. Make an open-back headphone that can slam hard, and it does this well. There’s plenty of quality bass here, with a nice subbass rise, and bass shelf that kicks off at around 500Hz. Quite silly, but it works.
The TH900-series driver has some inherent and known trouble spots though. One, the upper mid-range can be a tad too forward, and the treble has a large peak at around 8 or 9 KHz. Both of these were present when I listened to the PhilPhone 3 with the stock ATH-AD500X pads that Zerousen included in this set.
The treble was the more annoying portion, as it does make certain music a bit too bright and piercing at times. But overall, the tonality, outside of that was quite nice, as is with most headphones using the Foster drivers.
The following measurements are using MiniDSP EARS with HPN Compensation:
PhilPhone Pad Swap normalized to 1KHz
PhilPhone Normalized to Bass
So… of course, I pad-rolled. I tried out every ZMF pad I owned on this headphone pairing and actually each one gave it a slightly different flavor, and each, in my opinion, improved upon the default AD500X pads.
The ZMF Universe Perforated Leather and the ZMF Verite Suede pads were my two favorites.
The Universe Perforated Leather pads took away the mid-range hump, and also slightly reduced the treble spikes and presented a more smoother sound overall, though it still suffers from the treble spike.
With the ZMF Verite Suede pads, which, for whatever reason is still not listed for sale on ZMF’s website, gave this a very warm and laidback sound. The mid-bass was a bit more and the treble was softened, giving this the most relaxing sound in general.
I don’t have a whole lot more to say, but I do think this is surprisingly a nicely-made set, which is super lightweight and comfortable to wear for hours. Dampening the treble spike somehow would fix a lot of my complaints, though I think adding additional clamping force would also alleviate some of the brightness issues as well.
Hooray for Philphone!
Update:
Here is the IEC-60318-4 compatible measurement of the stock philphone demo:
Link on Graph Tool https://headphones.audiodiscourse.com/?share=Antdroid_Target,3
The one you reviewed is the inferior version because it lacks the golden Hi-Res sticker.
Topping might need those back soon Ant.
Thanks for the review! 
Not sure where else to put these; but in my quest to become a passable solder-er, and to understand more about electronics:
The millet nuhybrid is a really really easy first project when you’re ready. I think it’s a very good amp too. If you or anyone else is looking for an easy one to start with, this is one I’d recommend.
It’s on my list!
I wanted to try for a little bit more structured learning about circuits. Assembling the kits is more of a Lego experience for me so far.
