Metrum Octave Mod and cable suggestion

Further down the Head Case Forum was this little ditty.

Craig Sawyers
High Roller

High Rollers
1,072 posts
Posted 04 February 2012 - 11:49 AM
I bought one of these around 10 days ago, based on Martin Colloms' recommendation in HiFi Critic, in which he billed it as a real giant-killer. Initial thoughts were exceptionally good, and as it warmed up progressively better. But I can't resist getting things right that are wrong. The first problem is common to most DAC's and CD transports - RCA connectors. I did a whole host of measurements using Time Domain Reflectometry, and basically putting a fast pulse into a 75 ohm coax terminated with an RCA, into an RCA socket, with a surface mount 75 ohm resistor tacked onto it - and it is a disaster. Massive reflections - and reflections add jitter.

The only way to do things *properly* is to maintain a clinical 75 ohm environment for the whole digital signal chain, and that means 75 ohm BNC connectors throughout. And most digital cables, if not terminated in RCA's are terminated in 50-ohm BNC's! In fact the only audio high-end 75 ohm BNC's are Oyaid. I just use regular clamp-on greenpar and RG302 teflon cored coax.

After doing that (and measuring the TDR response into the Octave) the DAC really started to sing.

Then I spotted the hokey little pulse transformer (visible in the picture above). This is a $2 part, a standard Murata ferrite cored pulse transformer. I replaced it with a far better (electrically) Lundahl LL1572, which uses an amorphous ribbon core. In the UK this is £35 - so not cheap.

After swapping transformers (invalidating the warranty of course) I can honestly say I have never heard a DAC sound that good regardless of cost. I've just ordered an Audio Note toroidal pulse transformer wound on a mumetal ribbon core, so it will be interesting if that improves it further, or otherwise.

I can't stop listening to it!


PS The DAC's are intersting. They are 16-pin devices (with the type number taken off, of course), so they are definitely not Burr Brown or any of the other audio DAC's, which have far more pins. So I think they must be DAC's intended for instrumentation or data acqisition applications. And they are supposedly R2R ladder DAC's too. I've done an initial trawl of manufacturer's data, but have not been able to find anything that looks like those.
When all is said and done, lots more gets said than done.

If a job is not worth doing, it is not worth doing well.

It's a Norwegian Blue.
Mine works fine with RCA. Of course the digital cable I use most costs more than the Metrum. The digital cables I use were measured by an engineer friend who it really into measurements and they all measured 75 ohms.
Vicdamone: So what are you saying?
Devilboy, this is a post by a DIY'er describing his experience with the DAC.
Just got myself a proper 75 Ohm BNC connector. My plan is to do some initial listening with the standard RCA connector, and then change to BNC and see is there is any change. Both USB/SPDIF converters I currently use (Halide and JKSPDIF3) have BNC outs anyway, so a BNC connector on Metrum will make my life easier.
Elberoth, have you added the BNC and did you hear any appreciable difference?
Yes, I did. I think it made a small but noticable difference in my system. At $10, it is a no brainer.
PS The DAC's are intersting. They are 16-pin devices (with the type number taken off, of course), so they are definitely not Burr Brown or any of the other audio DAC's, which have far more pins. So I think they must be DAC's intended for instrumentation or data acqisition applications. And they are supposedly R2R ladder DAC's too. I've done an initial trawl of manufacturer's data, but have not been able to find anything that looks like those.

Burr Brown DAC8580. Datasheet

Best wishes,
Alex Peychev
Alex, that was easy for you!
I have had my Metrum Octave for some weeks now and am truly shocked how good it is!
I have compared it to a number of much more expensive upsampling DAC's costing 3 to 4 times the price and also an Audio Note NOS costing 3.5 times as much. The Octave was faster, much more saturated and preferred due to its excellent balance of detail and timber of the instruments. Equally at home with Biffy Clyro or Bruckner. I have found though its is very sensitive to the SPDIF cable used which needs to be as near to true 75 ohms as possible. I have tried VDH First Ultimate, Black Cat Veloce and Mark Levinson Fat Boy, all of which sound slightly different.
Has anyone else used the Lundahl transformer in their Metrum? It seems like an affordable modification which yielded a very nice upgrade for Craig and I want to do this modification to mine...
Welp, I took the plunge and purchased a Lundhl and sent mine out for modification. The surgery was a success and it's due back on Tuesday... I'm pretty excited to hear the improvements though my transport's PSU is in the shp for some tweaking...
Gopher, looking forward to your feedback about the Lundhal tweak. Have you tweaked your Octave in any other way?
Not really. I am using herbies baby booties under the dac and psu which actually made a nice little improvement. I'm pretty much down for now except for an AMR fuse which i'm planning on ordering.
Thanks Gopher. Does your DAC section kind of rings internally? When I knock gently on the top of my unit I hear things vibrating inside, and I'm wondering if there is room for improvement by treating those somehow.

Replacing the RCA for a BNC connector is one tweak I have noted a couple folks claim worked well for them.

Using an after market power cable of course is another one. I'm still using stock. What are you using?
Do you have the details of the lundhl and where to buy it? How does it sound? I noticed an improvement with the chassis NBC connector to my metrum, be nice to improve it more if possible.

Which BNC connector did you install?
RS Components 75ohm, they sent me a few for some reason. I can post 1 to you if you PM me your address.
Does anyone know if there's a way to remove the toslink input and add a second spdif input?
I have 2 digital sources both with coax.
So far resolution was significantly improved as has stage width and seemingly bass impact/tightness. That said it does feel like it needs to do a little more relaxing and I'm hoping over the next hundred hours or so this transformer will mellow.

I think it was purchased through K&K, my buddy ordered a couple and got me one.
i just received my Octave DAC back from being modded... replaced the stock pulse transformer with the Lundahl LL1572, replaced the stock coax input with a 75 ohm BNC, replaced the stock fuse with an AMR gold fuse.

i felt this DAC was a tremendous performer in it's stock form - it is the best of the several i've owned - and now it's gotten considerably better. i really wasn't expecting much from such simple and inexpensive mods, but am extremely impressed. the basic character of the dac remains, the extraordinary clarity and musicality haven't been altered, but now the stage has opened up considerably and the mids/upper bass are fuller. apparant detail, particualrily low level detail, are improved, too.

i'm looking forward to clocking a few more hours and seeing how things develop. right now, i'm very impressed.
Srosenberg, who did the mods? What was the cost?
@ Vicdamone: Noble Electronics performed the mods. i purchased all the necessary parts and sent them along with the dac. K&K Audio stocks the pulse transformer, avatar sells the fuses and the bnc is widely available. noble's work was flawless and timely - highly recommended.

i've now put some time on the dac and it has smoothed out nicely - it really has the most analog sound i've ever heard from a dac. difficult to describe the presentation - finely detailed, yet with an extraordinary musicality. this one one incredible sounding piece now.
had the house to myself this morning so was able to goose the gain quite a bit. i agree with gopher - there is a solid improvement in the low end. robert plant / allison krauss please read the letter from raising sand is playing now - the opening has never sounded this powerful and controlled.
Can you put the photos with Metrum Mod (Lundahl LL1572 pulse transformer)?
Whatt's the AMR gold fuse that you use in this mod?
Thanks a lot.
I'm out of town for the holidays, but wanted to quickly chime in that things were coming around in my system before I left.

As with many changes to your rig some coaxing may be necessary to reaxhieve your desired balance. In my case I moved my amp out of an oyide r1 outlet and into a Maestro outlet and my Metrum out of a Maestro and into a Furutech FPX gold.

Sounds tweaky/fringy I realize but they made a notable improvement. Im planning on buying a nice fuse, probably AMR shortly.

While i was still undecided about the mod, i purchased another stock Metrum so ill have that to compare snd ecperiment with in a week or so.
Gopher, Excelent news.
Gopher, when you compare the two DAC, we have the dimension of improvement with these changes (Mod).
Gopher, Can you put the photos with Metrum Mod (Lundahl LL1572 pulse transformer)?
Thanks a lot.
If Scott can't handle that I will see what I can do. I think Craig Sawyers took pictures of the mod on the original head case thread.

In any event I got back from vacation in Chicago this evening and the dac is sounding nice. Quite ballsy now, I think the right fuse may flavor things just right...
Hi there,

I'm about to modify my Metrum Octave. It is the version without the fancy power supply, but comes with an on-wall black power supply.

Question about your transformer swap:
The standard pulse Trasformer has 6 connections and the new Lundahl LL1572 has 4. How did you connect this?

I'm thinking about replacing the standard cheap wall connected power supply with a sollid toroidal transformer. The DAC housing has 3 lines comming in while on the outside of the dac housing it says 9V AC. Do you (any) know what the three incomming lines represent?

Thank you so much!
Hi Andre
i believe the three lines are 9v @ 9v @ earth,i am also looking to build a bigger tranny feed to the metrum to power some new paul hynes shunt regs,how are you getting along ?
i have done the bnc connecter and din output mods with solid silver,havent got around to the pulse trnsformer yet as it looks a bit fiddly.
just found this from a Russian site