spritzer

Happy Birthday!!!

Two of them actually, or the voltage divider doesn't work.

This is more what I was thinking about, except the audiophile version. Edit: They couldn't even spring for 1% resistors...

I guess it makes me the official SR-Omega repair center...

Yup, I heart TKD's. What I meant were those plugs you can add inline with the cables.

Nah, it's just great 10th century marketing...

Ok, some more progress. I took some time and fixed the gain issue of the 727, just swap out the 560ohm R5 and R6 resistors out for some 200ohm units. Again I was using RN60 pulls so they are way too big for the job... Now the amp has the same gain as the other Stax amps, sitting at 5 on the dial with my computer source. It does sound rather good with the SR-Omega even if it does bring out their bright nature a little bit once you push the volume. There is no excessive bloom here and it has a lot of control for a commercial amp. Why Stax couldn't just have made it like this in the first place is beyond me... As for the SRM-300, the LF353 had to go so I installed sockets and OPA2604AP's Edit: Damnit!!! I forgot to sand the chips...

It's just two resistors per socket so go for it. You could also buy some of those audiophile attenuator for a fortune...

Or move here.

Since Kevin asked me to check out some parts inside the SRM-300 I thought it was only fair to do some modding. The stock output caps are 103/630V units so I just put in some 105 (1uf) caps instead. Before: After: I also wanted to show how to set the voltage of this amp. Stax placed 6 holes at the bottom of the PCB but didn't use them on this unit except for one connection. They clearly intended for the secondary wires to be soldered here and then jumpered on the other side of the board. Since there are 99% odds of me selling this amp one day it made sense to do it like this. It's been a productive day too since I've also managed to bring a SR-Omega back from the dead. Yup. You can see the PCB used for voltage selection mounted to the side of the transformer. The setup is the same as above, you use jumpers to configure the secondaries and you have to move the wire from the power switch as well.

There is in fact no pressure on the socket if you use very little solder and solder to the very top of the gold pin. If the Yen wasn't so fucked up then I'd buy a few, mod them and sell to good people. Not terribly difficult really. These PCB's will not handle a lot of abuse so removing the old resistors is the biggest challenge, soldering in the new ones is easy. Just bend the leads to the correct form (I bent them so that they sit above the PCB but it isn't really needed) and solder them in. Also, as Marc said, you know people and the amp is dead easy to open up (the allen key is even included) so you could just send the small plugin cards to have the mod done.

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.