STAX SRM-D50

[Rob80b]

Oh ok, I assumed they would've left the amp circuit entirely through-hole like all their other amps and just squished the layout, but it does look like that isn't the case. I thought it was just the DAC that is surface-mount.

Almost everything is SMT these days and with the D50 manufactured in China it makes sense. I was surprised that even Bryston here in Canada went with SMT on their BHA1 Headphone amp in 2012 and they're manufactured mostly by hand solely here in Canada,

But if done correctly its been shown to be more precise and reliable but tricky to repair if need be for us DIYers.
I find the charm of Stax is that old school on hands approach though.

 

[babyoh]

Is Stax D50 a good match for driving Baby O (with Stax adapter obviously)? I'm concerned 400V output will arc the Baby. Thanks.

 

[newbluesuit]

@babyoh Looking around this forum and elsewhere on the web, I see several people happily running the HE 60 off of other Stax energizers with similar maximum outputs (ranging from 300 to 450 V). As far as I can tell, the only Stax energizer that is currently in production and has a significantly lower maximum output is the portable SRM-D10 (200 V).

The volume knob on the D50 has a fair amount of resistance, so it's fairly easy to raise it slowly and set it precisely, and there is little risk of moving it accidentally.

If you want to be on the safer side, you can look at the iCan Phantom from iFi, which can be adjusted to match the requirements of most brands of electrostatic headphones, but it's three times the price of the D50 and has many features that you probably won't need (but no DAC).

Something to note about the D50 is that its DAC is disappointing and you will get much better performance out of it using an external DAC feeding its analog input. That's probably also true of the D10 but I don't have any experience with that model.

Another thing to note about the D50, if you haven't read the previous messages on this thread, is that Stax changed its color from silver to a dark metallic grey (which they call ‘dark silver’) around 2022–23, although most resellers haven't been briefed about this and are still advertising it with pictures of the older silver model. Unfortunately there does not seem to be a way to tell which color you are buying without opening the box and looking at the unit itself.

 

[purk]

Is Stax D50 a good match for driving Baby O (with Stax adapter obviously)? I'm concerned 400V output will arc the Baby. Thanks.

You may want to run the Baby O off from a warmer sounding amplifier. You need to use the correct adapter with the right resistor to bring down the bias voltage. I believe Mjolnir or even Moon-Audio can build you that adapter.

 

[newbluesuit]

@babyoh If the info on this page is correct (and I can't see why it wouldn't be), the HEV 70 (the energizer that was sold with the HE 60) also has a maximum output of 400 V: https://www.stereophile.com/content/sennheiser-he-60-headphones-specifications. So with the proper adapter it seems the D50 would in fact be a good fit for the HE 60, at least in terms of voltage.

@purk The HE 60 is known for its speed and detail. In order for a warmer-sounding energizer (typically a tube one) to deliver in this respect, you'd probably need to look at high-end models like the SRM-T8000 from Stax or similarly-priced offerings from other manufacturers, several times the price of the D50. Personally, if I were to go for a less expensive option, I would focus on preserving as much as possible of the accuracy required to get the full benefit of the HE 60's strengths rather than on warmth. The D50 is a good value in this respect in my opinion, as are the other solid-state energizers from Stax. I've also read that the HE 60 (unlike the HD 800) is rather EQ friendly, so that may be another option to ‘tame’ its trebly response if needed. My EQed SR-009s sound great out of the D50 (better than out of any of the tube energizers from Stax, except the T8000, in my opinion).

 

[babyoh]

You may want to run the Baby O off from a warmer sounding amplifier. You need to use the correct adapter with the right resistor to bring down the bias voltage. I believe Mjolnir or even Moon-Audio can build you that adapter.

I got the Mjolnir adapter. Are you saying the D50 is cold / neutral sounding?

 

[newbluesuit]

Are you saying the D50 is cold / neutral sounding?

I would say that the energizer part of the D50 is very neutral, definitely not cold. The DAC part as I said is not that good, and rather on the lean side, so it's better to bypass it and use an external DAC instead.

 

[newbluesuit]

So I finally found a second-hand silver 230V SRM-D50 from 2022. It came in its original box with all the original manuals and accessories. Before listing my 2024 ‘dark silver’ unit for sale, I thought I should do a thorough comparison of the two side by side.

Visually, all the parts that are silver on the early version are dark grey (‘dark silver’ according to Stax) on the current one, which means not only the ‘hood’ but also the input switch as well as the frames around the VU-meter and volume knob on the front. The vents on the bottom are a different shape, and as already noted the current version has vents on the back as well. Finally the optical input on the older version is ‘bare’, while on the current one it has a cover flip. Other than that, the only differences I can spot are with what is printed (or not) on the back and bottom of the units. (The LEDs that highlight the selected input and light up the VU-meter are the same orange color on both units.)

Both versions come in the exact same packaging and with the same accessories. The microfiber cloth and RCA cables are identical, while the power and USB cables look slightly different but are of similar quality and finish.

After about an hour of listening, going back and forth between the two units, both units were running hot. The temperature of the ‘hood’ was about the same on both units. The bottom of the chassis was hotter on the older unit, while the back of it was hotter on the newer one (in fact on the older unit it did not heat up much at all). Overall the heat of the chassis was slightly better distributed on the newer unit than on the older one, but it was still hotter on the bottom than on the back and overall the newer unit did not feel significantly less hot. The front of the units did not heat up much.

Sonically the two units are very close, as one might expect since Stax chose not to advertise the second iteration of the SRM-D50 as a revision. One thing that surprised me is that the volume knob is calibrated slightly differently. When I was at 1 o'clock on the older unit, I had to be close to 2 o'clock on the newer one to achieve a similar gain using the exact same source (cable included) and headphones. Once I was able to match the gain on the two units, my impression was that the newer one had a tad less treble than the older one. That difference was exactly the same whether I was using the embedded DAC or an external DAC through the line input, which suggests that the embedded DAC sounds the same on both units and that the difference is down to the energizer part only.

With the embedded DAC, which is rather dull sounding compared to any external DAC I have tried, the older unit sounded a bit better to me. When using external DACs my preference between the two units would change depending on the DAC and the music I was listening to. It was a very small difference anyway.

One thing that is identical on both units and which seems odd to me is that while the volume is roughly the same with various external DACs (as it should be), when switching to the embedded DAC there is a drop of several dBs. It seems that the ‘output’ of the embedded DAC is not calibrated to standard line level (to be clear, there is no analog output on the D50, and I am merely talking here about the signal that is passed from the embedded DAC directly to the energizer internally). Because of this the VU-meter works much better when using the embedded DAC. With external DACs, even with music that is fairly dynamic, the needle tends to be in the red most of the time.

That being said, the D50 really benefits from being paired with a good external DAC. The DacMagic Plus from Cambridge Audio was a significant improvement over the embedded DAC, and the Gustard R26 went several steps further. So in spite of its price the D50 is really able to ‘scale’ quite a bit as the quality of the source improves.

In the pictures the ‘dark silver’ unit is always on the left. I have included a silver MacBook Air in one picture and my SR-009s in another for reference. I don't have a ‘space grey’ MacBook but would expect the ‘dark silver’ D50 to be pretty close to that in color.

 

[purk]

Is the grey D50 darker sounding with slightly blacker background than the silver D50? Joking aside…

 

[Rob80b]

So I finally found a second-hand silver 230V SRM-D50 from 2022. It came in its original box with all the original manuals and accessories. Before listing my 2024 ‘dark silver’ unit for sale, I thought I should do a thorough comparison of the two side by side.

Thanks for the update, so just to be clear when you mention older, newer and current, older is the older version vs the newer version and not your older or first one which is the current version.
So far I've been happy with my decision on getting the SRM400S, brought the L300 upper a few notches, soon to be replaced with a new pair of L700MKIIs but I'm sure the D50 would do like wise. Was tempted on a local pair of SR009 that came up had to pull the reins back a bit.

 

[newbluesuit]

Thanks for the update, so just to be clear when you mention older, newer and current, older is the older version vs the newer version and not your older or first one which is the current version.

Indeed:
- older = pre-2023 = silver = no vents on the back (bought second-hand this month)
- current/newer = post-2022 = ‘dark silver’ = vents on the back (bought new in January)

And @purk, yes, the ‘dark silver’ one does sound a bit darker than the silver one…

 

[purk]

Just saw that the vented holes are different on the bottom side. I wish that Stax used a better DAC on the updated version of the D50. It can’t cost them that much more to replace the 9018 with 9038 or 9039.

 

[SolarCetacean]

I've read that the new SRM-D10mk2 uses an AKM 4493 DAC vs the ESS 9018 on the mk1, so maybe an updated D50 would go with an AKM too.

 

[purk]

I've read that the new SRM-D10mk2 uses an AKM 4493 DAC vs the ESS 9018 on the mk1, so maybe an updated D50 would go with an AKM too.

That would be very nice if that’s the case. No D50MKII designation however.

 

[newbluesuit]

@purk @SolarCetacean The ‘dark silver’ D50 is indeed not intended as a revision. Stax did not even bother to inform their distributors and resellers that they had changed the color (and made small design adjustments).

Maybe there will be an ‘SRM-D50 II’ down the line, but for now the specs and reference are unchanged, so I'm assuming the DAC chip is the same as well.

That being said, in spite of its age the 9018 is well regarded and should not sound ‘dull’ like it does in the D50. My guess is that the issue is at least in part with Stax's implementation of it. The fact that the level drops several dBs compared to any external DAC I've tried suggests that there is indeed some kind of oddity there.

I have never tried the D10 nor the D10 II so can't comment on any difference with the D50, unfortunately.