Sonic Frontiers SFD-1mk2 Vintage DAC for $750 That Stomps Most Modern DACs

Hope you all had a happy thanksgiving. With your assistance (thanks again all for the photos!), I completed the power supply section and am moving on to the output section. Decided to update the ERO film caps to WIMA MKP4 as well. Now, just need to receive a few parts to complete.

In the interim, here is the BOM based on the PCX invoices posted and that I finally decided upon. Not sure yet about updating the switches though:

 

She's Alive! The PCX SE+ update went slowly but well. I let the DAC burn in for a day and have started listening. I've been listening to the updates for a few days now. I'm impressed by the mods. Main differences:

- Tighter and more tuneful bass (but not more bass). I can now differentiate much better between very LF notes in very very soft passages from the SW.

- Cleaner sound throughout, especially noticeable in the mids and highs - especially on crashing cymbals and such. Vibrato and resonances seem to be heard more distinctly. Even my wife said it sounded cleaner with less fuzz or some sort. LOL. I have to agree.

- A bit more depth in the soundstage but location and width seem about the same.

Very nice and worthy improvement with the same setup and tubes prior to the update. Enjoying this very old, but updated, DAC.

 

So here is a before pic after I pulled the PCB. It is fairly easy if you go carefully. Desolder the outputs from the main PCB, desolder the inputs from the mini-PCB out back, unscrew the ground lug and power socket, and unscrew the bolts holding down the main PCB. The mini-PCB is held on by its wire connections to the main PCB. The 3 front LEDS are press fit. The toggle switches have a threaded bushing with a circular nut but it has 2 sides that are flat for a small wrench. Be careful pulling out the main PCB as there is not much clearance for the toggles to come out. No mess no fuss...

 

As I indicated in a prior post, I kinda went a bit overboard and replaced most of the blue ERO and 2 large red WIMA film caps for new WIMA film caps. LOL. I pretty much followed the BOM I posted earlier. Of course tightly matched Mundorfs and tightly matched resistors went into the output section. Here is the after pic...

 

And a few close ups of the output, DAC, and power sections. The mods were mainly in the output and power sections, although per @lehmanhill , I decided to replace the 2 small caps in the DAC section that control the gradual turn on...

 

Added the damping as well per the PCX SE+ mod, in a similar way to the damping I've seen on a SFD2, MkII ...





And a quick test to make sure all is working...

 

As an added bonus, for those of you looking for HDCD's to take advantage of HDCD chip in the SFD, see:

http://www.goodwinshighend.com/music/hdcd/hdcd_recordings.htm

https://wiki.hydrogenaud.io/index.php?title=List_of_HDCD-encoded_Compact_Discs

Enjoy listening!

 

Congrats on your upgrade. It looks like you did a really good job. My turn, I guess. I have most of the bits, just lacking time.

I'm happy to hear that you found a clear improvement in sound. This wasn't just updating because parts were old, it was following what the manufacturer did as an upgrade.

The real question. When asked, is your now an SE+? Maybe upgraded to SE+ specs? I think it deserves the SE+ moniker.

 

Yes, a definite improvement in sound and well worth the cost and effort via DIY. It was not that difficult as long as you go slow. Everything is laid out on the PCB well. Funny thing is that large output caps (that were replaced by the Mundorf's) still measured dead on at 3.3-3.2uF and still had low ESR. But the Mundorf's do seem to make a difference. Only thing I may add to them is some hot-melt glue or neutral cure silicone rubber to "lock" them in place for purposes of vibration. Also looking for some high temp tape for the gold labels on the chips.

As for the moniker, it won't matter so much as I am enjoying this "new" DAC. But I agree, it is essentially upgraded to SE+ specs - and then some!

Looking forward to seeing your upgrade and impressions.

 

Stupid question, but I'd rather be safe than sorry.

Can I attach both XLR and SE amps at the same time? I know this isn't a problem for new dacs, but since this is my first vintage (and first tube) dac, I just want to make sure.

2nd question that is delving into nervosa... after reading thru the threads here, I've noticed a couple mentions of AES in being superior to coax SPDIF. My SFD doesn't have an AES in... just curious how much I'm leaving on the table and how hard it would be to take out the optical and put in AES...

Thanks

 

Most of the time, this is not a problem. I have my Theta hooked up to XLR and RCA all the time.

AES is 110 ohms, balanced and can output 2-7V peak to peak. SPDIF is 75 ohms and more like 0.5V peak to peak.

I know I have seen SPDIF connected to just the two pins on AES and it works, not ideal, but it works. I would never do this the other way around because of the higher voltages. I would think though that most AES boxes have a similar circuitry to that Hosa converter box.

Here is an interesting article on the subject:
https://www.ranecommercial.com/legacy/note149.html

Although I don't think many use AES3id or AES over CAT5. I suspect in that Hosa box is a step down transformer just like it shows in the circuit. I suspect you could do the same thing inside a converter as well.

 

I don't know the answer to both XLR and SE outputs, but I do note that there are relays right next to the output, so you could figure out what happens

Regarding your second question, it is a pretty easy mod, but you should check that your Toslink circuit works first, since the XLR mod uses the same connections. My Toslink doesn't seem to work, so there would be some fixing before changing to XLR.

 

Are there any new opinions on SE vs BAL performance of the SFD-1 ? I've never ran it balanced to this day. I've sold off all my balanced headphone amplifiers.

 

Well, maybe someone can, but that's far beyond my level. I can solder and follow directions, but I'm not an circuit/EE guy.

Those photos definitely help, now I guess I just need to figure out what the black resistors are...

I don't have an amp that has both, but I will say that I don't feel that the SE out is holding back my SW51+... and that the XLR to my 3F is pretty dang special.

 

Yes, I've done it in the past and the manual says it is ok.

Difficult to say and it will depend on a lot of factors. Note that the manuals for the SFD1 and SFD2 state with respect to the ST (Glass Fibre) Optical Input "This connection type is considered best for optimum performance and sound quality; if your source unit has this type of digital output, we recommend its use."

YMMV.

 

47.5 Ohm, 0.5%

 

Also note the resistor underneath the input PCB:

 

Hi Ed,

Is the resistor under the circuit board also a 47.5 Ohm?

I didn't even realize that there were relays under that board until today. I got my Toslink to work (worn switch) and was surprised to hear a click.

By the way, thank you again for all the great pictures you have shared during your upgrade. They are my workshop manual for this thing.

Jac

 

From the looks of it, it seems to be 3.7G Ohms, 2%, 100ppm

See pics below.






The relay diagram is shown on the top of the PCB.

 

I've also used two red dots to indicate where this resistor is soldered when looking at the input board from the top.




As an aside, attached is a pic of the bottom of the main PCB. Note the adjusters.