Grado Labs SR325 Black (Vintage) - Reviews
Pros: Airy highs, impactful bass, smooth midrange.
Cons: Heavy
This is the best grado I have owned and I put these about any RS1i/RS1e and RS1 I have heard (I didn't hear the pink driver RS1 yet). 
The SR325 was purchased in 1995, SR125 roughly 1997
First thing I will talk about is the bass not because I'm a bass head but because there is a very big difference between the two that even words can't quite seem to describe correctly and precisely.
When I first put on the SR325 for the first time, it didn't seem that much more bassy but at the time it was only for a minute at most which is not enough to make a valid impression at all. I listened to them for awhile then I stepped down to the SR125 , all of the a sudden the SR125 sound too light and weightless. The difference in bass in easily heard when comparing the two. I always thought the SR125 lacks in the low end and the SR325 is exactly the answer to it. The SR325 has a nice bass presence when a song calls for it, it slams hard and I can hear some of the low rumbling in some songs. There really is no comparison between the two, the SR325 do anything bass related better than the SR125. There is more bass texture and quantity; I never felt a lack of bass with the SR325 in any song. The bass gives the music a nice weight and body not present on the SR125. I have never heard the bass guitar so easily as I have on the SR325 of all the grados I have owned. The bass follows the rhythm of the song effortlessly; the SR125 on certain songs sounds like it has holes as it follows a rhythm because it  can suddenly dive off when low bass can't be reproduced loud enough to be heard. The SR325 with authority makes the SR125 lack bass; never again did I yearn for more bass after putting on the SR325 right after using the SR125. PRaT in this category is unmatched by the SR125. The SR325 bass is not bloated in any way; it is full,solid and possess a lot of weight. It keeps up with fast and tight bass rhythms with no effort. Bass slams and decays; something not easily heard on the SR125.
SR125 has a more modern grado sound, yet they don't sound harsh at reasonable listening volumes. I can hear that the upper mids are noticeably boosted; on the SR325 it's not like that. The SR325 only has a slight upper mid boost. The SR325 has a certain smoothness in the midrange that makes it sound transparent. It is not very colored at all compared to the SR125. The SR125 sounds very hyped compared to the SR325 which is more mellow. The midrange on the SR325 is full and lush, the lower midrange is more plenty than the SR125. Voices on the SR125 can sound thin but on the SR325, it is the best I have heard out of all the headphones I've owned. I never really thought a grado can present vocals in such a way the SR325 does; the RS1i does not compete against the SR325 in this area. The vocals on the SR325 is simply pleasing to listen to, something I couldn't always say even on a classic RS1 which is one of my top favorites of all time. The weight of the vocals is spot on. I have never cared much for vocals over guitars but this grado really changed my perspective; I now appreciate the beauty of vocals almost just as much as electric guitar performance. The midrange on the SR325 has a slight warmth, not overly warm like the RS1i. The SR325 is only sibilant if the recording has it; it will not create sibilance like the SR125 can. The SR325 sounds more mellow whereas the SR125 has some more excitement because of the upper mids. The SR325 does not present anything in a manner of extremely colorization, only just enough to give singers for example some emotion. The metal cups do not give the SR325 a cold steely sound characteristic at all. Electric guitars sound like they really grind and crunch on the SR125 and is definitely on the thinner and bright side; SR325 on the other hands sounds more full and rich again while being non offensive but not being polite and shy either. The midrange is where the SR325 and SR125 share most of the similarities despite SR325's better low midrange presence and SR125 upper mid peak differences; they both really do sound great for different things. The midrange on these vintage grados are very close to perfection for me; they really both do sound beautiful in this region. Sibilance is really a rarity on both cans 95% of the time. On the RS1, the guitars would sound great but sibilance in vocals (harsh shh) was the cost; I'm still wondering how these SR125/SR325 can sound great at electric guitars but with no sibilance in vocals or why the RS1 has sibilance in vocals if it's not caused by he upper mid spikes. SR125 sounds like the RS1 in upper mid peak in terms frequency response but the SR125 doesn't seem to compromise anything. The SR325 is probably the grado that also made me realize just how good everything sounds when weight of instruments in the recording to me sounds like it has its proper weight.
SR125 midrange may sound too thin on bowls. Comfie pads are more suited for the SR125 since it brings up the bass and midrange so it does not have a thin sound.
The SR125 has a very evident boost. On a few occasions, highs can sound shrill. The highs on the SR125 tend to stick out more than the SR325. The SR325 treble does not sound boosted or emphasized in any way. The aluminum cup doesn't make the SR325 sound brighter than the SR125 at all. Does the SR325 sound bright? Maybe coming from a HD600 but not from a SR60i. The treble is very pleasant to listen to, it is not very aggressive and would never annoy or offend me in any way. SR325 is not harsh at all; no ears will cringe from the sound produced by these. The treble is very refined; it sounds true to the recording over the SR125; the SR125 can exaggerate the highs.  The decay in micro details can be heard easier on the SR325. The SR125 I feel is a headphone that most people can agree to it being bright when heard. It would definitely need more time to get used to than the SR325 but once I did get used to the SR125, I found it acceptable. Some of the plucky of an acoustic guitar is more edgy on the SR125; it sounds more hard where the SR325 is simply "natural" because there really is no exaggeration to be heard on the SR325. The SR325 really reminds me a lot of the vintage SR60 I had, the treble between those two sound very realistic compared to the SR125. HD600 sounds like its treble is just there, just enough to be heard; the SR325 isn't recessed. Its treble simply doesn't demand for attention by becoming all splashy and peaky but it is easily heard without trying to listen for it (not that you ever need to for a grado)
The balance between the midrange and the highs on the SR325 is perfect. The SR125 sounds tipped towards treble. The bass on the SR325 does not overwhelm or hide any of the midrange or treble detail. The SR325 makes the SR125 sound like it could use a little more meat on the bottom end.
Both are still in the realm of a grado but the SR325 is slightly wider and deeper because of the cup dimensions
SR325 is one of the best grados I have ever heard and the SR125 is surprisingly very enjoyable to listen to and is no slouch either but the SR325 simply does a lot more right than wrong compared to the SR125 over a broad number of music genres. The SR325 is what I could call versatile compared to the SR125. The SR325 needs to be heard to be believed; you will know why this vintage sound is so sought after by some. After hearing the SR325, I wonder why grado moved away from this sound. Sometimes a person's tastes changes as quick as the tides in an ocean; in this case it might be John 
. I feel that the modern sound has taken a step backwards from what it once was in the past from all the grados I have heard or owned so far in my life. I think anyone who is a fan of the grado brand should at least hear a vintage grado once in a life time, to know and appreciate the sound of the past. Does it sound better than its modern version? That's for you to decide upon listening but to me, it's a yes for both the SR125 and SR325. It would be a steal if vintage grados of their modern models were priced the same and sold today.
The comfort on the SR325 is somewhat less than satisfactory for me, the weight doesn't allow me to listen to them for a long time (which is a big bummer for me) but I enjoy every second and bit of sound I hear reproduced by it. I never thought I could say this about a grado without hearing a HP1000 but the SR325 presents sound with grace and power while being the most natural grado I have heard. ( I don't like using the word "natural" but that's all I could think of at the moment 
Vintage SR125 vs Vintage B RS1:
After listening to the RS1, the SR125 sounds thin and quite bright. SR125 sounds more airy though
Treble : SR125's boosted treble makes micro it sound more detailed but it can be fatiguing after some time. The highs on the RS1 is not hyped up but they both are still bright headphones. SR125 has a certain crispness to the sound the RS1 doesn't have, some may like this while some may not.
Midrange : The midrange on the RS1 is thick lush and colored compared to the SR125. I'm not 100% it is the wood but the tonality is not quite to my taste on the RS1. The SR125 midrange sounds thin in comparison. Vocals surprisingly sound better on the SR125, the RS1 is a little too thick for my liking. The vocals on the RS1 don't sound quite realistic to me at all, not as transparent as I would like it to me. What I hear on the RS1 is a bigger sound, definitely more full. The upper midrange is thicker on the RS1, but not as boosted as the SR125. Guitars sound good on both, depending on taste either can be preferred. I feel the upper midrange spike on the RS1 covers too much detail; when the guitar kicks in it sounds too dominant over anything else being played. I like electric guitars but this trait actually annoyed me the most when listening to the RS1. The midrange on both is more forward than the SR325 with bowls.
Bass : RS1 has more bass than the SR125 and has more body. The SR125 sounds quite tame here; it doesn't quite have the warmth and punch of the RS1. They both have less bass than the SR325.
Which one do I prefer? Hard to say, I like the bass and treble on the RS1 but I like the midrange presentation better on the SR125.
Vintage SR325 vs Vintage B RS1:
RS1 makes the SR325 sound like the SR325 is the most balanced and transparent sounding headphone of the two. I have stated above that the SR325 is one of the most "natural" sounding grados I have heard meaning it sounds the most uncolored and realistic.  The RS1 just reaffirms what I stated about the SR325. The SR325 sounds very airy compared to the RS1 without sounding weightless.
Treble : Where to begin, the treble on the SR325 sounds very refined compared to the RS1. It is like listening to a 128kbps mp3 file then going to lossless. The resolution of the treble on the SR325 is on another level. The SR325 has a crisp and clear treble that does not sound harsh; not a hint of grain. The RS1 treble sounds a little muted and due to the upper mid/lower treble spike it makes it very difficult for me to pick out details.  The details on the SR325 I can hear very effortlessly; I don't need to strain to hear them. The way the treble is presented with the midrange on the SR325 also gives the perception of a larger and wider soundstage. The RS1 sounds more closed in and intimate. The SR325's treble is capable of being sparkly not overly exaggerated but helped by the aluminum cups. Something as simple as a triangle sounds realistic and metallic like it should on the SR325.
Midrange: SR325 wins in transparency, this is the area that really beats out the RS1 the most. Any voice produced on the RS1, undoubtedly sounds better on the SR325; simply lifelike on the SR325. The SR325 never seems to sound sibilant with vocals at all. If the singer's voice is dry then it will sound dry on the SR325; it will not pave a smoothness over it.There's a certain colorization that makes vocals sound a little nasally on the RS1; the switch to the SR325 makes it more obvious.There is no weird colorization on the SR325; the RS1 sounds like it tries to make everything sound sweet and warm. It is similar to wanting to just drink water, but someone always adds some flavor to the water when I don't want flavored water. The RS1 has a certain warmth in the midrange not present on the SR325; this might be from the wood housing.The midrange on the RS1 is more aggressive than the SR325 and is more forward. RS1 sounds like I am in the singers' face, the SR325 sounds like I am in the first row. The layering on the RS1 is not quite the level of the SR325. The forwardness of the midrange combined with the upper mid spike makes the sound somewhat more two dimensional; sometimes it's hard to hear behind the vocals,guitars,drums. When everything gets too busy, the RS1 sounds like it blends everything together instead of separating it out like the SR325. I can always listen "deeper" into the music with the SR325 changing my focus into the background sounds or foreground vocals because of the layering on the SR325.  I actually hear the distortion on the guitars much easier on the SR325 than the RS1 even though the RS1 makes guitars sound louder. The RS1 makes nearly anything that sits between the upper mid and low treble sound loud enough to the point where it can sound grainy and lose its texture; I'm not hearing quality but rather quantity. The plucking and individual strokes on the SR325 are distinct. Everytime I switch from the RS1 back to the SR325, it sounds like the balance and clarity has been restored. I never thought I could say this about a RS1 but the SR325 makes it sound muddy and sloppy at times. The RS1 can sound grainy on recordings the SR325 plays back with no grain because of certain peaks and emphasized loudness of frequencies to a flaw.
Bass : The bass on the SR325 is more and it goes lower as well.  The bass on the SR325 is very solid and punchy on the SR325, the RS1 is slightly more loose and wolly sounding. Both have noticeable more bass than the SR125
Soundstage : RS1 sounds more closed in from the forwardness of the midrange and a lack of transparency in the midrange. SR325 sounds noticeably more open with more depth and width; spacious is the word. Audible differences but SR325 is not like a K701 in soundstage width just for perspective sake.
Weight : RS1 weighs almost identical to the plastic SR125. An aluminum cup is about 2oz heavier which does not seem like much but it is definitely noticeable when worn. I would preferably like to have the SR325 weigh lighter but the sound makes up for it.
I have yet to find another Grado that will make me give this up.
How does the 325 compares with GS1000 and PS1000e?
You may want to get an opportunity to listen to the PS500e or even an set of the earlier PS500.  I have had both and currently have the e version and as good as the PS500 was the e does outdo it in refinement and quality and detail of the bass.  It truly stands out as a Grado with it's own approach and it thoroughly enjoyable and can be listened to for long sessions without any fatigue and just pushes you to listen to more of your favorites.  It is not amlifier fussy but does scale up very nicely.  Right now I find it does very well but with the Ray Samuels Emmerline HR-2 but it is just magical with the TEAC UD-501 Dual Mono Class A design.  It peforms well above it's range competing with the more expensive competition including higher priced Grados.  Well worth a listen if you can get to hear a pair that has a proper amount of break in on them.  In the Grado corner I have a vintage RS-1 and have spent time with both the PS1000 and PS1000e.  In the meantime enjoy your SR-325's and most importantly the music.
Pros: Not as harsh as the newer 325i models. Amazing bass without overwhelming the mids and/or highs. King's X sound amazing with them...
Cons: Very slight mid-bass hump that adds a miniscule amount of mud when using the flats.
These are great headphones. They are fun sounding and prog metal particularly sounds good. Actually all rock as well. The bass is definitely there and you can feel it. The soundstage is wide for a Grado! Highs aren't as harsh as the newer 325 models. Just an all round great headphone. 
Only complaint is that with flats on they can be just a smidgeon muddy sometimes, with bowls it's not a problem but you lose some bass. 
They're also easy to drive.