Entropy.

It will depend on your budget of course.

Personally In terms of stuff under $1000, my recommendations would be:

MH755 if you can find a genuine set ($25 ish)

Tanchjim Tanya (~$40)

Moondrop Aria ($80)

Moondrop KATO ($190) - These things are really worth stretching to if you can. They punch so hard above their pricepoint it's kinda ridiculous and they make most stuff even several times their price seem somewhat pointless. Either cause these are better, or cause the other stuff is so tiny of an upgrade it'd be pointless to pay the extra

used UM MEST MK2 (new $1500 ish but can be found used for ~$900)

If you have unlimited money, best I've heard are probably either the Anole VX or MAD24 depending on what sort of sound you prefer.

Kind of mixed.
 
I've got their flagship "HiFi" speakers, and then of course the MB2S' which are kinda mini main monitors, along with some lower tier bookshelves and towers.
 
For sure, they have a "house sound", they all make everything sound a little bit smoother than it actually is, especially in the upper mid range and treble.
 
I think some of this smoothing comes from the tweeters being crossed over fairly low. Usually around 1.5 to 1.8kHz for the two way designs.
 
Their older models have bass issues, which comes from the transmission line they use in all their models not being refined enough. They've worked it out now, and it's a very good addition to my ears. They have alot of presence for their size.
 
All of their models are very sensitive to amplifier matching. I've got the Fact Fenestria's hooked up to a pair of McIntosh MC2301 tube power amps and they work well together. Previously I had them bi-amped with an Mc1.25kW power amp handling the woofers and then the MC2301's handling the mid driver and tweeter.
 
I think they're effective for mastering. They're certainly not the most accurate things in the world, but they work incredibly well for mastering anything that isn't meant to be super harsh. They just cannot produce sound in a harsh manner.
 
They're certainly very high quality. I've never had an issue with them, even when feeding them quite a bit more power than they're rated for. The crossovers are bulletproof and made with very high quality components, the veneer is amazing and just in general they're well made I think.

LOTS of variables.  Any audiophile will tell you that cans that sound good for electronic/dubstep/bass heavy will not necessarily sound good for opera/classical or stadium rock/heavy metal.
 
Lots of good brands out there.  Some with good products across their lineup.  Some with only 1 or 2 good products among a lot of garbage.  Some brands masquerading as good based on mass marketing/appeal and lots of product visibility (e.g. bose/beats/apple).  Some you should probably just steer clear of altogether (e.g. skull candy).  Some that masquerade as quality by trading substance for panache (e.g. many gaming headsets); and in this vein, they are a lot like how gaming chairs try to appeal to the market.
 
Since you appear new to the audiophile scene, my suggestion is this.  Get a pair of midrange Sennheisers, 569's or something.  One thing that seems to be a common thread for many people (myself included) is that Sennheiser was the gateway drug that opened their "ears" to the world of high-end audio.  From there, you can decide if you care to continue down the path; if you really want more/better/more expensive.
 
I recommend starting with cans, not towers, ATMOS or anything else.  This is because cans (without amp) are about as pure of an experience as a newcomer can have.  You won't miss out by forgetting an LPF setting, or from speaker delay that you didn't mitigate, etc.  If you want apples-to-apples difference that you can HEAR...cans are, imho, definitely the place to start. 

This thread is far to long to read at the moment, maybe I'll peruse later.  But for now I'll just give my $.02
 
I have spent the past 5 or so years in the headfi space, much longer if you count my Sennheiser HD 465 from 15+ years ago that set me on the path of hifi to begin with.  Those headphones opened my eyes and I have made quality listening one of my few major hobbies ever since.
 
I started the whole thing with a pair of Blue Microphones Lola and while everything was top notch... it didn't tickle my pickle and to this day I still have VERY little use on them.  They have great sound quality and excellent bass along with stellar build quality while being redonculous at noise isolation.  Soon after that i got myself some hifiman he400i (2017) 5ish years ago with a cheap chinese tube amp and was unsatisfied   I actually got the Topping DX7 pretty quick and dailyed that pair for a few years with my Sennheiser Gaming One as my communication device though I did eventually put a modmic uni with it that I still use today.  Since then, the headfi bug hit me hard and with the onset of covid and 2020 I decided to start watching Zreviews only to put my entire wallet and focus behind headphones and amps. The whole thing has been a journey of simply wanting to have firsthand knowledge of the terms that reviewers used.  I found along the way that Zeos, while being highly subjective and all over the place, hasn't spoken a single word that I didn't agree with other than the Fostex T50RP shure pads which I hated at first but grew to love if it's the right genre of music.
 
I don't have golden ears by any stretch of the imagination and I'm not good at expressing the nuances of different headphones but when I hear someone explain what I'm experiencing I can either agree or disagree with it.  One of the greatest thing's I've come to learn in recent month's is that no matter the chain you have, whether that's a YouTube video with onboard audio and a $40 pair of headphones (maybe another $10 for an aux extension) or tidal premium with $1k including cables behind it, you are going to enjoy the content that you enjoy, after long enough it comes down to the experience not the hardware.  There is always something to be gained even into the tens of thousands of dollars.  However, for me it's about a solid daily setup with comms and then every now and then I like to sit back and listen to my setup.  Kick back in a recliner and zone TF out without blinking lights or perriph's or anything else that soaks up your attention.  Because when you're playing a video game or focused on forum content, are you really listening to the music?  At that point I can soak in what differences there is between various pieces of equipment.
 
Past that I can safely say that for daily use I can easily recommend the shp9500 with a vmoda boom pro mic running with onboard audio.  I don't have this setup myseslf as it would be a downgrade, though I have thought about purchasing it just because I want my recommendation to be honest.  I have the Fidelio X3 which in a round about way is a comparable sound signature to the 9500 and the boom pro is a microphone that can be added to any headphone with the proper plug..... what's not to love about that setup?  I have done a few tests with onboard audio and if we're talking about daily use, it is completely acceptable.  But, given that I had to sell my entire collection and I only had a certain budget that is the setup I would go with.

Also, what would be very interesting (given what his main speakers are) would be for @Derkoli to give impressions on the Linkwitz LX521, since a lot of people consider it to be among the best they've heard. 

To start off, most of my experience with audio kit is with MBL, McIntosh, Martin Audio, PMC and Crown.
 
Below I'll write a list of audio gear I have experience with, and that I recommend. I'll also note any quirks I've noticed, whether they may be good or bad.
 
I'll also put a * infront of products I currently own.
 
Amplifiers;
 
*McIntosh MC1.25kW solid state power amp - Seems to have more power than McIntosh claims. I've never been able to get it to enter protection mode, even when feeding passive subwoofers and driving the input as hard as I can
 
*McIntosh MC2301 tube power amp - The best sounding amplifier that I own
 
*Yamaha MX-A5200 power amp - Doesn't sound amazing, but it's been faultless
 
*Emotiva A-800 power amp - Currently only used for multi room background music duties
 
*Hegel H190 integrated amp - Brilliant little integrated amp. Absolutely love it
 
*Crown I-Tech 9000HD power amp - Need power? here you go. Only really ever used properly with a pair of JBL M2's
 
*Cambridge Audio Topaz AM5 integrated amp - Sits next to me on my desk at all times. Drives a pair of cheap Sony SS-NX1 speakers. Actually a combination I love.
 
*Martin Audio iK42 power amp - Need tonnes of power? Here you go. Stable at 2 x 10kW at 2 ohms. The only amplifier I own that scares me a bit.
 
McIntosh MA9000 integrated amp - Sounds amazing, weighs a tonne, impossible to clean properly, highly recommended.
 
Speakers;
 
*MBL Radialstrahler 101 x-treme - annoying name, annoying to position, annoying to buy, annoying to clean, can't take much power, make you crap yourself slightly when turning on your system and bloody nightmares in general. Bloody amazing. Second to none.
 
*Genelec 8351APM Studio Monitor - Super neutral
 
*Genelec 7380SAM Subwoofer
 
*Adam Audio S5H Studio Monitor - Very loud, very large, very imposing. But the sound? Corr blimey. My favourite studio monitors
 
*PMC MB2S Studio Monitor
 
*PMC Fact Fenestria Loudspeaker - Big, very picky about amplifiers, need perfect positioning, but bloody amazing
 
*JBL M2 Studio Monitor - Need neutral but very loud? Here you go. My second favourite studio monitors
 
*Focal SM9 Studio Monitor - Nothing to note really.
 
*PMC Fact 10.C Loudspeaker
 
*PMC Twenty 5 22 Loudspeaker
 
*PMC Fact 8 Loudspeaker
 
*PMC Fact 12 Loudspeaker
 
*KEF LS50 Loudspeaker
 
*Q Acoustics Concept 500 Loudspeaker
 
*Sony SS-NX1 - I believe these came from an old "audiophile" all in one type system. They're made fairly well, aren't very large at all and have a weird sound signature which I love. You probably won't love these though.
 
*JBL LSR308 MkII Studio Monitor - not very big, live on my desk at all times. They have a nasty hiss though. Also managed to blow a tweeter on one not too long into owning it. Was doing measurements at roughly 90dB and it just made a small pop sound and died.
 
*Polk T50 Loudspeaker - not very big, and sound like pure trash unless they're extremely well isolated from the ground. If you isolate them well, they sound decent.
 
 
PA stuff (probably not necessary but eh);
 
 
This entire section is mostly a Martin Audio simping section. Feel free to ignore.
 
Most of my experience with PA speakers is with Martin Audio. They're not a huge brand and are based out of london. Literally everything they make sounds great.
 
You can tell the speakers where to avoid chucking sound, and they'll just not send sound there. It's amazing.
 
I own 8 MLA Mini's, which are essentially tiny versions of their full on MLA line arrays (same model used at glastonbury each year)
 
They weigh under 15kg each, can achieve 130dB per "cell" and sound amazing. Combine 4 and you can get 142dB.
 
You then combine them with an MSX subwoofer, which has the 9 channels of amplification built in. 1 channel for the subwoofer, then 2 for each MLA Mini cell. It's a lovely compact system that sounds amazing, has plenty of SPL and throw, and is very simple to rig and then fly out. Only need 2 cables, 1 for power and 1 for signal.
 
I can happily recommend any Martin Audio product.
 

@Derkoli, what are your feelings on the PMC speakers in general? Most of them don't seem to have a very flat anechoic response, but I haven't had any opportunities to do a controlled listening test (that is to say, in a familiar environment) with any, so I'm not real sure what to make of it. 
 
 
 
 

Haha, I wish they were 100k USD.
 
I'd honestly say some affordable speakers can reproduce the same amount of detail as my main loudspeakers. It really isn't hard to get good detail out of a cheap speaker now-a-days, but the holographic imaging and true omnidirectional nature of them is second to none.
 
I'll write a quick summary of the gear I have lots of experience with in another reply, which I suspect will be done in ~30 minutes.

What do you mean by this specifically? 

I mean, you are writing a guide to be posted on these forums?
 
 
 
If that is the case, I am not entirely sure this is the best way to approach creating such a guide.
Specifically you have asked people to give their opinion without asking what their frame of reference is for that opinion. I mean someone jumping from a crappy knockoff $5 set of headphones jumping to something in the +$100 range might have a very high opinion of that more expensive set of headphones as their only frame of reference was the low quality headphones they had before. While someone comparing that same set of expensive headphones compared to equally priced competition might find them lacking. Just asking people what they find good will yield you a list but it will not be a meaningful list, it will just be a popularity contest which doesn't say anything about quality. 
 
Not to mention that you have started with such a broad scope you made it really difficult to categorize things to begin with. Not to mention that unless you are willing to maintain this guide it will be slowly grow outdated over time as new products are never included. 
 
So if you want to compile meaningful data that can help people in making their choice (other than the excellent resources already stickied in this forum) I think it might be worthwhile to make your questions a bit more specific. Not just ask people to list their experience but make sure to ask what their frame of reference is (previously owned similar products), how they approached buying this product specifically, etc. 

Completely agree,
If you're writing a guide, you should start by reading the other pre-existing guides and creating some contet for yourself. 
Once you've started off we will have a better frame of reference for what you're looking for. 
For instance, @Derkoli has hundred thousand dollar speakers, obviously they sound great and I'd imagine he'd recommend them, but that's not a fair fight against the budget options others have mentioned. Many of us who have spent time with audio gear ina  professional capacity will have drawers or cubboards of gear and unless we know what you want our opinions on we can't help too much.

 

One more for fun: AE Techron 7782. An absolute BEAST of an amplifier, will happily drive 70 amps into a 1 ohm reactive load. This is a single-channel amplifier with 240V 3-phase input power. Fans are somewhat noisy. BNC Twinax input connector is an expensive pain in the butt to connect to. 
 
All kidding aside, you could use one as an audio amplifier - it's full-power bandwidth is DC - 50 kHz.

I have a guide linked in my signature explaining inputs and my recommendations, take a look there for more in-depth takes on mics and other studio options
If you want some other recommendations from my personal experience here goes - 
Now to be clear, I am financially able to replace the below hardware with much more expensive options if I felt the need to, I just don't feel the need to, beyond this point seems like diminishing returns to me.

Over-ears on a budget:
ATH-M20x have been my daily drivers for years, it's widely known that the M40x have a flatter sound signiture and are better for production work than the M50x but it's not widely known that the cheapest set in the lineup aren't too bad themselves. I don't do any critical listening with them and mostly their job is delegated to providing me with audio when it's either too late to use my speakers or I'm in calls. Not overly bassy, no crazy harsh highs, overall, they're not HD800s but for the price they do a damn good job (and I got them for under $20)

In-ears on a budget:
It's no secret that I love products by KZ but semi-recently I decided to give the KBear KS2 a try and man do they sound good. Same form factor that I love from the KZ wired IEMs I've used previously and honestly the inline mic is excellent. I work in a field with lots of collaboration so in COVID times working from home I'm prettymuch in voice calls all day and these provide both the audio from my phone and input to my phone (yes I'm aware of the Microsoft My Phone feature and Dell Mobile COnnect but they have massive technical issues). Again, these serve a similar purpose to the M20x when I'm not working, just another option if my speakers would be too loud but DAMN the bass is clear. For inears at this price point (about $20) the clarity and depth is honestly amazing. 

Wireless In-ears on a budget.
KZ SK10, that's it, they're the best budget inears. I mean, of course they're no hyper-premium set so there's the standard white noise you expect from the price point but I use these when shopping, exercising, running, cooking, just basically everything. Great battery life and the bass is far clearer than my old inears be they wired or wireless (KZ ZS3, ATE, ATR, S1, etc etc). I'm not the sort of person to look at a spec sheet and decide whether I like something based on the specs but dang this newer generation of hybrid inears really do it for me.

Speakers on a budget:
Any decent used studio monitors. Personally I use the Tannoy Reveal 5A and I have done so for more than half a decade. Looik at your local classifieds, see if there are any studio monitors that are decent, check reviews, do your research, brands to watch out for are KRK, Yamaha, Tannoy, Adam Audio, Focal and Fostex to name a few but I stress this list is nowhere near exhaustive. Studio monitors are designed specifically to provide excellent audio quality and 99/100 will beat any consumer option at double the price. If you don't have any studio monitors near you the Tannoy Reveal lineup is excellent for the price.

Other speaker option is to just build your own, I had an old surround sound receiver / sub and I wanted some more fun speakers than my clinical R5As so I obtained / built some custom speakers and wired them up, now in my bedroom I have a full surround sound system fo when I'm watching shows in bed (though I usually only run the system as a 2.1 ch)
 
 

Yep, I can agree with rice guru wrote about the DT880 and 770. I had them both in 250 ohm and the DT880 is indeed the best of the 3 and it's a bit underrated too. The DT770 is fatiguing quickly, can't really recommend it too unless for reason mentioned by rice guru.
 
My experiences I can share and the headphones I have are both popular and very unpopular.
 
HD560S. This one sucks in soundstage but the seperations in instruments is nice tho. But I don't like this one bit so I got rid of it.
 
Tygr 300R is an excellent headphone too and I love it. Powerfull bass that hits hard and the treble is silky smooth, the ssss in sibilance is just good to hear too :3 Comfort is excellent and great for movies aside gaming and music.
 
Fidelio X2HR is excellent too, the earpads are damn nice and fluffy too. Sound is great too, not as bassy but the treble smooth too, not ear-piercing and soundstage is wide. Doesn't need a powerfull amp at all.
 
Amiron Home. This one is heavily underrated! Pair it with a powerfull amp and you can crank up the volume without ear damage and the sound gets even better! This one is pure enjoyment! Warm sounding headphone with cinematic audio and one of the best for gaming and movies, not just for music. The design might be a bit boring but to me, it's a love/hate design. Simple and yet to so ugly and simple and yet to beautiful. I wish it would have been available too in black/copper.
 
Amiron Wireless Copper. Yep, I got the copper version because I love the black/copper colors. Despites it's 400gr, you won't even feel it it's on your head. Comfort is amazing too. Treble is silky smooth and bass is controlled. Its sound is a pleasure.
 
Beyerdynamic T5p 2nd gen. (Discontinued) It has a great clarity, comfort is excellent and very light-weight. Design is simple and elegant and soundstage is wide too for a closedback. It has been replaced by the T5 3rd gen but not planning to get it as I'm happy with my 2nd gen.
 
Klipsch Heritage HP-3 Walnut. (Discontinued and no longer to be found) Design is damn pretty, replaceable magnetic earpads and sound is great too and soundstage is holographic. It's a very rare item now.
 
My audio source that I currently use: Fiio K5 Pro with Lake People G103-S.
 
I'll be selling my Meze 99 Classics Walnut/Gold because this one sucks after using the other headphones often. The tiny details in audio is quiet too or missing on the Meze. Can't really recommend it. The design is really beautiful tho.
 
The next headphone I'm waiting is for when Beyerdynamic has sorted out their issue so I can get the DT880 600 Manufakturer. With the Manufakturer, you can customize the DT880 and 990 to your likings and even the lenght of the fixed cable. I'm not sure if they are available too for your country. The Tygr unfortunately has the same fate too as it's not available for everyone. The DT880 250 was my first real headphone and since then, I started to discover more about the world of audio.
 
And as for speaker, I have the Marshall Stockwell 1st gen with the OEM flipcover. Design is damn cool, sound can get really loud and knobs to regulate volume, treble and bass. Can be used as powerbank to charge you phone or tablet.
 
As you might get the impression, I'm one of those looking for something unique, different and underrated to add to my collection.

No point,  I've seen a bunch of self confessed audio nuts rave about the sound coming out of a shitty behringer power amp,  they thought it was a $20K boutique amp under a velvet cover.   The more you think you know about hardware the more you think you can hear the difference.   
 
My advice is to ignore everyone and go try whatever it is you want to buy and if you like it get it, if you don't then try something else.  I'm long past telling people which headphones I think are best because I've learnt not everyone hears the same thing let alone likes the same thing. 

Honestly when it comes down to audio experience *IS* the best experience, people can tell you that there certain DAC, amp/headphones combo is the best, or that they love using certain products over other stuff. What you need to know is that you should consider starting cheap, and working your way upwards.
 
Looking at suggested recommended beginners headphones/Dacs/Amps is a great start, because then you can get a feel and learn about each subject. That is al, carry on

this is exactly why I lay out my preferences basically immediately so there is context to any of my opinions in the thread. 

here is some quick words then 
The DT 770
I like My 770 a decent amount it’s a good workhorse nice bass that digs deep, mids suck and has very sparkly treble, the timbre can be a bit unnatural sounding due to the treble. Hard to recommend the lower impedance models. I use this guy to help out other people with some mixes as the unforgiving ass treble helps out finding anything wrong with the mix. But its not something I only rely on. This headphone sucks for listening to for enjoyment unless I put it on my hybrid amp to fix the timbre. Also easiest to drive out of the 3. Sounds best out of a warm source. While I still think for the price it is the best gaming closed back honestly as a all rounder headphones like the akg k361, and 371 are better or just go open with much better options.
 
The DT 990
The most popular headphone of the 3. Dare I say a bit overrated. The lower impedance models suck the most. And I don’t think they become that great until the pads get basically flat which kills the treble. The midbass is elevated making them sound loose especially when the amps cant drive them. I do like my 990 though but that’s because I'm both used to the sound and really enjoy it when playing games. Due to ear shape flat pads don’t bother me. To me this headphone sounds best out f a warm source.
 
The DT 880
The best one of the 3 in my opinion. The 600 ohm sounds much tighter, much less prone to distortion as the other 3. Less sparkle in the treble than the 990. Bass extension not as good as the 770 but I get better mids and better timbre than the other 2. And basically, the same soundstage and imaging performance as the 990. The lower impedance models are not that bad with this guy either while it hurts me to recommend them they are the most recommendable low impedance models of the 3 sets if the tygr is not available to people.
 
He 4xx
Good starter planar. People like to Mod them to get the most out of the headphone. My biggest problem with them is the metallic ass timbre that I’m not a fan of but My band aide to the solution of bad timbre these days is plugging them into my liquid platinum which basically just fixes the timbre. It’s a hybrid amp so it has low enough output impedance and is clean enough for sensitive low impedance headphones. Or planars which often doesn’t work well with OTL tubes.
 
HD 58x
Still one of my go to budget headphones . not a lot of people seem to like this headphone too much these days since the 560s’s release but IMO still a good headphone especially if found on sale, still great for gaming. And if you want it mainly for gaming still a better pick than the HD 650 IMO mainly due to it having better staging and easier to drive.
 
HD 650
Recent buy for me bought it mainly to restore. Bought it for cheap lots of things need to be replaced but it’s a classic for a good reason. Hard to drive to its full potential but sounds good out of weak ish sources regardless. Very warm headphone, the mids sound awesome bad bass extension but super smooth treble. Love this guy out of most of my source gear. And soesn’t sound bad at all out of a neutral or bright source like a jds labs atom or thx 789.
 
Fostex Purple hearts
These are my bass Cannons as Cans rocking biodynamic drivers. Its like a nice in between of planars which digs deep in the bass, with speed while having that impact from a dynamic driver. Speed wise not as fast as a planar but faster than a typical dynamic driver. This is tuned to have a ton of bass so even while having some speed to the driver it can muddy up the mids but not as much as you would think considering the quantity presented the treble can be a bit sparkly for some people and the mids are clearly not the highlight for this headphone. This is just a super fun headphone so I keep it in the collection. Love it for occasional EDM or rowdy ass hip hop.
 
Audioquest nighthawk carbons
These things measure like ass and to most audiophiles who like flat sound hate it too. This is one that I needed brain burn in to enjoy. It’s a semi open back headphone with speaker like imaging due to having thick pads and angled drivers. The imaging isn’t super accurate but fun to have in single player games. And once you get used to the very dark signature its great with most music. I still don’t recommend this for most people. i only recommend it  only to those who are looking form something unique and different to add to the collection and want to  burn cash on something they potentially  hate or love.
 
 

so like, the internet

You won't get much useful information out of this. There are simply too many different pieces of audio equipment. Could be fun though.
 
I'll throw in a few bits on some amplifiers:
 
MC2 MC series amplifiers - these all will sound more or less the same, just with different power levels. They all use the same topology, and all of the 2U ones share the same PCB layouts. THD+N for an MC650 measured to be 0.0042% at 1 kHz at 80% output power. Subjectively one of my favorite solid-state amplifiers. Quite reliable, but a huge pain to service. The cooling system in these amps creates a lot of turbulence and is quite noisy even with quiet fans. They're also a big class AB amplifier, and that means they kick out a lot of heat.
 
Crest CA9: Good sounding amplifier, THD+N is around 0.02% at 1 kHz at 80% output power. Very difficult to service. They've got +/- 120 V rails, and they've got that across MPSA42 and MPSA92 transistors, so slipping with a probe can total the amp. IMPOSSIBLE to troubleshoot without extender cables. From an audio standpoint, they sound excellent and have as much power as you could ever want. Fans are relatively unobtrusive. 
 
Crest Pro 3301: Basically the same design as the CA9, except the output stage is class AB rather than class H. Good sounding amplifier. Difficult to get the output modules out of the chassis for servicing, but it's a relatively good design otherwise. 
 
BSS EPC780: Engineering masterpiece, and probably the best-sounding amplifier I've ever heard. Amazing for low-frequency use, but also sound fantastic on highs. Unfortunately, they're the most complicated audio power amplifiers ever designed, and also the most difficult to service. Aligning the switching power supply is very difficult and requires a service manual that isn't available online. The N-channel output MOSFETs (IRF640s) are still available. The P-channel MOSFETs (don't remember the part number) they used are not. The output devices on these amps also need to be matched. Uses a pair of COMAIR ROTRON fans that are very, very loud and also difficult to replace. Cool amplifier, but unless you're best friends with someone who was a BSS tech in the mid 1990s (and has a lot of parts left over), best left for some other nerd. 
 
Crown Macro-Tech 3600VZ - loudest amplifier I've ever encountered and louder than most rackmount servers. In fact, it's louder than the BSS EPC780. Fan motor is also the transformer for the +/- 15 V rails, which makes it difficult to replace. Measured THD at high power is low, but subjective listening impressions were not so positive - sounded very harsh. Crossover distortion maybe? Mine is on long-term loan to someone for lab use, so I never had a chance to dig deeper into it. Not a good amplifier for home use.
 
Crown CTs 1200 (applies to the whole CTs series)- Very unreliable amplifiers. Switching power supplies in them tend to blow up. The amplifier itself is an ancient quasi-complementary design. I have absolutely no idea why they chose to use a 1970s amp design in this. 
 
QSC PowerLight 2 series - Great amplifiers. Measured THD+N was about 0.0065% at 80% output power at 1 kHz. Good sounding amplifiers, extremely reliable, with unobtrusive fans. Not the easiest things to troubleshoot, but rarely necessary.
 
Rotel RA-840 - decent little amplifier. Not super powerful, but acceptable for most use. Uses fuses instead of a proper protection circuit, but for an amplifier of this size that can be tolerated.
 
Hafler P125 / DH120 - A nice little lateral MOSFET amplifier. Measured THD+N at 1 kHz and 80% output power was about 0.007%. A lot of these were kit builds, so construction quality is a bit of an unknown. Very susceptible to ground loops, but otherwise is a pretty good-sounding amplifier.
 
Omniphonics/Quested S200 series - These are 1U convection-cooled MOSFET amplifiers. Some versions used HEXFETs, others used Hitachi Lateral MOSFETs (2SK1058 / 2SJ162). Uses the LM391 driver chip, and they run this chip about 20 volts over its maximum rating. This combined with lackluster input protection means that these things have a tendency to blow up if someone connects / disconnects the inputs while it is running. Other than being unstable, they sound excellent. PM me if you need schematics, I likely have them.
 
QSC RMX amplifiers - more or less bulletproof linear amplifiers that are among the most reliable ever built. THD+N is generally around 0.01 - 0.05% at 1 kHz. I don't think I've ever seen one blow up. When there isn't a semiconductor shortage, you can get spare output modules from Full Compass. They take abuse well, are flat past 40 kHz and aren't overly loud.
 
Kenwood KA701 - Run for your life if you don't want a big project. Black flag caps, oscillation, unobtainium output devices, overheated and leaking electrolytic, corrosive glue, you name it. Just about everything that goes wrong with old high-end Japanese amplifiers goes wrong with these. I did one and evaluated (and rejected) another. 
 
Heathkit AA-121 - Fantastic EL34 tube amplifier from "back in the day". Obviously an amplifier of this age should be recapped. Heathkit's instructions for biasing are insane - they run the tubes right on the bleeding edge of stability, with something like 24 watts of static plate dissipation on each EL34. Given that these were kits, watch out for construction quality issues. Output transformers are COMPLETELY unobtainium - so 1/2 W screen resistors are a good idea. 
 
Dynaco ST35 - Great little EL84 tube amplifier if you have higher impedance speakers. The Z565 output transformers used in the ST35 are among the best ever wound. Modern reproductions are tapped for 4 ohm or 8 ohm speakers (rather than 8 or 16 ohms) and are still excellent transformers. These things sound great, but are quite limited in power. 
 
 
Not amplifiers:
 
Crest X20R rackmount console - very good little mixing console for what it is. Will need to have all of the switches cleaned. Mine needed the SMPS rebuilt, but it's worth the effort. Good microphone preamplifiers and decent EQ circuits. This is a real console that's been scaled down, while most small consoles are a scaled up toy. Noise and distortion is low, and it uses acceptable pots and switches. 
 
 
 
 

The thing about expressing an opinion is just that, an opinion. RG may have a sound preference that differs from you, me? I like it a tad to the sparkly side, while some may tilt toward warmth, others might go for bass. It all depends on one's sound preference, all is good, none is wrong. It'd be pointless to wax lyrical about a certain headphone that is more balanced, very resolving, wide soundstage and good imaging, but these may not be what you're looking for as it may not be suited to your sound preference. You can glean whatever opinions that are expressed here as a point of reference, and refine your search or expectations.
 
As for my setup, mine's more simple audio chain compared to RG's, though I do have a good number of cans:
Computer USB -> iFi Micro iDSD Black Label/Oppo HA1 (2nd rig)/Fostex HPA4 (HTPC) -> Sennheiser HD800/HD600/HD6XX/ENIGMAcoustics Dharma D1000/Grado GS1000i/Denon AH-D7000 + Lawton Angle Pads (modded with SMC plugs for cable rolling)/HFM HE1000 v1/HFM HE4/HFM HE560/HE4XX/AKG K812/AT ATH-A900X Ltd/modded Fostex T50RP + Alpha Pads/Beyerdynamic DT 990 Premium (600 Ohm)
Main rig - GPU (RX 6900 XT) HDMI -> LG Soundbar SL8YG (for gaming, music appreciation when not using headphones)
2nd rig - SPDIF -> Philips Fidelio HTL9100
HTPC - GTX 1080 HDMI -> Philips Fidelio B97/98

Here is my current chain taken off my profile. I also run a audiotechnica ath 2005 for my mic.
topping d10---> Liquid spark dac-->Liquid spark or bifrost 2 ---> liquid platinum/asgard 3---> dt 990,hd 58x, he 4xx, audio quest nighthawk carbon, fostex purple hearts, dt 770 600 ohm, dr 880 600 ohm, hd650
topping pa3-----> micca RB 42
 
Im a gamer and music lover and use my gear mainly for those. if you have any questions regarding my gear ask away. I tend to lean subjectivist with a preference leaning towards warm. I don't consider myself an audiophile because I am into audio for my personal pleasure and don't much care for what the Artist intended. your welcome to ask away on any gear listed or are curious on opinions on other gear I may have tried. My experience with this hobby revolves around trying gear personally and discussing gear on various forums and even other discords. and By no means claim to be no professional. 
 

Microphones:
If it is for a voice SM58
If it's for an instrument: SM57

What exactly are you looking for? You're going to get a lot of random information that's going to be really hard to sort into any real usable data.
 
Personally, I have Mackie CR5BTs for my desk and I love them.

As my first more expensive Headphones I really like my Beyerdynamic DT-990s. They're comfortable, sturdy, easy to repair and sound better than most headphones out there (considering all the crap headphones in this world). Having bought them new for around 130€, they were also quite affordable.