spritzer

Yup, your right, no need to compensate for anything there. The SRM-Xs has those as well (green board version).

Ok, now I'm back so I'll continue this monologue but I can report that the mod is a complete success. No problems fitting the boards back in place and the sound is as it should be now. The amp is still on the warm side of things (pretty much the same output stage as the 717 so this is to be expected) but the bass has far more control now and the top end isn't misbehaving any more. I still have to do some more surgery to raise the gain at least 6dB to match the other Stax amps but as it stands now the 727 has mafia approval.

Happy Birthday Dr. D!!!

Yup, that's what I tired to explain to them but I don't think they actually understood it. It's the same people who think opamp based designs are "simple". Sure my gainclone has very few components plus single chip per channel...

...and we have people complaining about it being too complex...

It shouldn't be more than 4kYen and Stax should sell you one directly. It will be a SR-404 part though...

Now for some progress and me officially admitting that I'm a bit impatient. First off, here is how I fixed the cut windings on the transformer: I just used some cut off resistor leads for this. Made a loop around the cut wire and clamped it in place with pliers then I flooded it with solder. As for the purpose of this thread, how we can convert a SRM-727 into something more then it is today, I hit a bit of a snag. The resistors on these boards at least are glued in place so there is virtually no way of removing them in one piece. The plan is to remove one 150K resistor from the 300K feedback line and relocate it. Since these resistors are a pin to work with on a good day then I just did this instead: I had to run out so I can't test it until later today.

Now I have the SRM-300 up and running. While it uses a Kitamura Kiden R-core transformer (not the standard Bando) Stax have maintained the same wiring setup so aside from the 117V wires cut way too short, rewiring is dead easy. Now just to be clear, the SRM-310 is the exact same amp with a different name for the export markets. Now this amp is fairly unique in terms of what Stax normally does. It doesn't use the tried and tested SRM-1 Mk2 design (which the SRM-252 uses) but rather it is a SRM-001 on steroids, fully AC coupled and with a regulated PSU. As for how it sounds, it's not bad at all. No real bass output with the SR-007 but that could be due to the tiny output caps and the very limited power output (it consumes just 10W) but it is just fine with the Lambdas. I really like the form factor though and I hope Stax will produce the SRM-353S which also functions as a stand for the headphones.

Thanks for the offer Doug but I have the KGSS here and that will suffice for comparison purposes. On the whole this design is an improvement over the 717 in the same way that the KGSSHV is an improvement over the older design. It is fully CCS loaded (including the third stage), the build quality is a step up from the 717 and it looks much better to boot. That tiny amber power on led is a very neat touch. Now the bad news, Stax got the bright idea to cut the feedback loop short so it stops at the third stage (i.e. on the plugin cards) and the output stage is outside of it. I for one can't see any reason to do this unless you want an nonlinear design so you end up with an rather odd sounding amp where everything is bloated and larger than life. It even makes the SR-007Mk1 appear bright on some recordings so good sounding it is not. Another nasty side effect is the lower gain (needed for the amp to remain stable), by far the lowest of any Stax amp I've ever tried so you are pushing the volume level quite a bit even with a normal 2V source. Now here is what you have to do to fix the amp. Stax were nice enough to leave all the feedback traces on the boards but it will be a tight fit get wires onto those gold tabs. Next up is the SRM-300 for some surgery but I might get to the 727 later today.

This reminds me to bring a small SS amp to the Senn distributor here so that the SR-007 can poop on the HD800 again. Last time they said it wasn't fair to pit a 1960's tube amp against the Auditor so a modded 727 should be a "fair" comparison...

I just my SRM-727 and SRM-300 from Kevin. Stax were being a pain as usual and had cut the 117V windings on the 727A but it took all of 3 minutes to solder in new wires. What a pointless thing to do... Anyway, with it running at 240V all I can say is just how fucked up is the sound. The bass is just horrible, loose and woolly with textures which shouldn't be there. The midrange is distant and the whole sound lacks energy. It's just all a bit bloated and lifeless IMO. The gain is also way lower then it should be, I'm listening at 7 on the dial when normally on this source I never go past 5 on any of my Stax amps. I'm going to try and hold on for a couple of days until I'll mod the amp and see how it compares. In simulation it is no competition but we'll see... Kevin was talking about a Mk2 but I've never seen it. Some users talked about some mysterious Mk2 version which was supposed to be superior but it was just sleazy salesman talk since the only thing Stax changed were the fets since they ran out of the duals. There is a switch but it is only to ground the - part of the input for SE use. It wouldn't be too hard to put in a 4PDT ON-ON switch for real input switching though... That one is indeed very similar to mine. Those compensation caps near the input wiring are missing on mine though...

I do agree these headphones are similar but you can drive the SR-007 off a 200$ amplifier with good results. The SRM-323 is a very nice unit so any claims of needing truly insane amps are just utter fucking BS. The LCD-2 is by no means something you should be driving off a cheap amp either, it will clearly show you what amps aren't up to snuff. I'm not a Stax fanboy since I fail the biggest requirement which is blind devotion. I applaud Stax when they do something correctly but I'm also their harshest critic when they fuck up. A fanboy sees nothing wrong with his most admired product and even goes on the attach should anything negative ever be posted, just like those LCD-2 idiots do all the time.

The 717 is a far better design than the 600 and the 727 could be even better with a simple fix. More power in every way, not just voltage swing. The SRM-600 is nothing but a T1 save for some slight refinements in the PSU and using better tubes. I even have a T1 here which I'm going to turn into a 600 just for kicks.

The O2 comparisons came from the fanboys. The idiots claim this is the best headphone ever made so naturally, to them, it is superior to the SR-007.

No phase splitter is needed with these amps since the gain is so high. The WES is basically a GES with the front end removed so to run it SE they had to add the front end to the circuit again. The ESX also has gain issues when running in SE mode which are due to the amp not using ECC81's like it should.

Isn't it about equal in Class A?

The different parts are mostly due to the amp being made from 1982 to 1992. The 2SJ109 didn't exist back in 1982 hence the J75 used instead. That layout is indeed the final one as the original Mk2 normal bias amp had only two main PSU caps instead of 3. The first A models used that PCB as well and an off board Pro bias supply.

Marc and Justin pretty much covered this but yeah, even with minimal matching and thermal drift you shouldn't be able to hear the difference between SE and XLR, assuming the outputs of the source are of equal quality which they almost never are. Also to add to what Justin said, there are quite a few sources out there which only have SE output stages but then generate a balanced output from that. There are also plenty of Euro and Japanese gear which simply isn't balanced even though they shipped with balanced outputs.

There is no way to nail down the SRM-1 Mk2 amps in terms of serial number or series. Way too much crossing over and since this is by far the most popular amp Stax ever made, there are a lot of revisions and different parts used. That amp doesn't have the 2SJ109 dual fet but otherwise it is the same circuit. Here is a pic of the PP I'm rebuilding, this is what a late C-type should look like on the inside (minus the balanced pot and my other mods): It would have been nice to have the heatsink as well but one can't be too picky...

I've had something like this happen before so now I triple check every solder joint.

Ok, that is funny...

The voltage swing would naturally only be half of the XLR inputs. In practice this shouldn't make any difference.

The pot is simply added between the input terminals on the chassis and the input terminals on the board, just like it is on the Crack you built. I would recommend a 4 gang pot and XLR inputs even if you are using SE only since these can be a pain to add later on. If you want to have both XLR/RCA inputs then you need to have a switch to ground the - part of the amp when running it SE (XLR/RCA adapters do this already so no need to worry about it). I for one use a 4PDT ON-ON switch on my amps so the two inputs are isolated from one another but you can just use a 2PDT switch if you do not want that. There is also the option of using bridging pins as you can see on many power amps.

Why the fuck are you bumping this old thread for a retarded comment like that?

They are two pieces of neoprene rubber with adhesive backing, one on top of the other use to damp any ringing from the two metal grills. The first units didn't have them so they were a later addition. That hasn't been my experience. I've gone up to 900V and they really couldn't have cared less. What the SR-007 really needs isn't more power, just a very stable amp that doesn't give a damn about the load it sees. It's a bit high since there is nothing special about this amp. The whole C-series stigma only applies to some units which had the same PCB as the rare PP units. They had better wiring (massive solid core PC-OCC wires) and better resistors. I would ask for an internal shot to verify that this isn't just a plain old SRM-1 Mk2.