ADI-2 PRO balanced adapter and HD650 balanced cable mod

[DonDish]

I bought the ADI-2 PRO fs r be a couple of months ago, going from an ADI-2 DAC fs. The heftier PRO model gives alot of new functionality over its little brother. One option is to drive your headphones in a balanced fashion via two quarter inch TRS connectors. Im not going to dig into RME technology, its best explained in the manual here: adi2profsr (balanced mode p.44 and p.77) I do want to highlight though; PRO feeds + and - with an AC music signal inverted to each other, no ground. Output level is doubled from +22dbu to +28dbu. Output power is quadrupled. Minus signal inversion is done in digital domain. 19.5 volt maximum. 3db rise in SNR. There is no promise to "better" sound per se, but those having challenging and unsensitive phones will indeed get better sound. This brings me to the next topic. The Sennheiser HD650 cable mod.

Sennheiser HD650, the much popular, not very hard to drive allrounder. Searching around, and reading up on a balanced combo of ADI-2 PRO and HD650 you might find, like I did that its essentially pointless. HD650 is just fine with standard operation from PRO. Playing around at higher levels you are more likely to hurt your ears and phones. Anyway the reason for the cable mod is to test balanced mode, the adapter itself and why not! Also HD650 is what I have to work with now, the adapter is for future headphone purchases.
The main obstacle to the mod was dealing with those pesky enameled wires, you know what I mean. Ive lost 10+ headphones to this over the years. You get a solder that will stick 2 - 5 days tops. Self esteem destroyed, I have set out to challenge this and just "get back in the ring" about it. So I have shapened up and found a way to do this that works for me.

The adapter is quite simple. XLR4 - two 6.35 TRS. In this small blog I will post some pictures and go through some challenges and design choises.

Thanx to people at this thread : DIY cable and adapter making. Looking for others. and this guy AJ ONeal A nice 43 minute video on the topic of enameled wire.

 

[DonDish]

First of to my main nemesis, the laquered wiring of the HD650 cable. I found out that this is actually easy Set the iron in a small sturdy vice. Set iron to 400c and apply a nice drop of solder to it. Drive the wire end trough the drop a bit. The laquer evaporates and voila! Ends tinned. PS. Dont drive more than one wire trough a tin drop. The tin builds up slag quickly so clean and repeat for each wire, for best result.

Iron in a vice.

Time for a thootbrush comb. To get the nylon core out.

Nylon between thumb and index finger ready for cut. Dont mind dirty nail, im a user of swedish wet tobacco.

Ready for a twist and some solder.

End result. Nicely tinned wires.

Note: I havent got around to order flux, rosin wax or any of that. This is all soldered with rosin cored tin. Some extra would probably be smart at these high 350c+ temperatures. Work fast whitout! Cleaning is isopropyl alcohol. Solder station is Weller WE1010 my son bought for a Gameboy mod. Nice entry level station.

 

[DonDish]

As for the Neutrik XLR4 NC4MXX. This is just a dream to solder. The solder cups make it easy. Pins are numbered front and back for female and back for male
.

Im very sorry to say that at this point photographing takes a backseat. Top point of making a blog is to actually document the process. I will try and talk it trough anyway. Here you see the contact with left channel attached, isolated with clear heatshrink tubing. A really smart thing for extra protection. Problem is if tube gets anywhere near the heat from the iron, you wont get it to fit over the solder pot. Specification for the contact is 18mm loose wire with 4mm stripped. So with 14mm left, it gets quite cramped. I think I could easily fit another cm and this could solve the heat problem. Or one could shield with aluminum foil or something. Suggestions welcome!
About soldering. I cut a 3 - 4mm bit of tin and stick it in the pot. Heat up with 350c iron and insert the tinned wire. Cant get much easier

This picture of the female counterpart XLR4 shows the obstacle with the clear heatshrink tube. Too close to the heat.

Finished soldering.

Sennheiser HD650 cable mod!

Heatshrink over joint. There is another layer of heatshrink under here coming out from the contact. This is to make the strain relief get a better grip over the flat "side by side" HD650 cable. You can see the bulge coming out of the contact under top layer heatshrink tube. Today I noticed the outermost heatshrink is loose, I can pull it back, exposing the joint. Maybe I should get a tighter dimension or some other "shrink ratio". Something to learn.

The shrinking is done with a hair dryer. A slab of wood, and a piece of sheet metal to reflect back the heat.

I did measure for resistance with my new multimeter. It came back between 0,1 - 0,3 milliohm I think. Everything not connected and between pins was OL. Multimeter was a bit wiggly, got those 3mm ballpoint type probes. I wish I had gotten those crocogaps instead.

Notes on the process: I found with my low level of experience. Best is to plan ahead and mostly stick to that. When problems arise take a step back to consider. When straying from this path, thats when problems arise. Im not just good enough to do much quick improvising here. Panic is always the worst. That said, im not born with ten thumbs. Fretting out the wiring reminds me of flytying I learned as a kid. There is always a knob to hang knowledge to, and thats building experience I think.

 

[DonDish]

About the adapter.. Well im embarrased to say photographing completely went out the window.

This is two leads of Sommer Cicada SO-D14 Going straight from XLR4 to twin TRS.

A closeup of leads coming out of XLR4 before making the "Y". The cable hose is just scavenged from an old PSU. Ended with two layers of heatshrink.

TRS end. Cable diameter is a dilemma between TRS and XLR4. I didnt have any of that nice heatshrink for this cable diameter. I fixed internal strain relief with some electrical tape. Cable only connects to TIP and RING. SCALE/Ground is completely omitted! Cable shield and drain wire is simply cut off.

With the right wind direction you could probably kill a man with this, and I dont mean strangling My only objection to XLR´s, too heavy! Bare contacts is 70g. Cable weighs down in picture.

Thoughts: This has been a very interesting project and a breakthrough for me. I have had these parts for a while and I have just been fermenting them in my mind, fighting windmills of laquered cable and whatnot. Finally coming to action, with the help of peers and betters here at ASR.

Design considerations: Aesthetically I think it turned out nice. The nickel contacts, zinc housing and black cabling gives it a professional, and working tool look. Something thats meant for some serious use. Shrink hose and (last minute idea)braided cable hose gives a "manufactured" and clean feel. It also adds to flexibility instead of just using shrinktube. Looks aside, why didnt I make this a meter long so I wouldnt have to have this lump of metal hanging over or laying at the top of my hifi shelf? These are just how adapters are made, small. Next time I will do my own thinking.
I have some other Neutrik contacts laying around. The gold plated stuff, but since I only had zinc barrel XLR4, I just went for a uniform look.
There is a small, round and debossed Neutrik logo in the cast TRS barrel. Im thinking of pigmenting some epoxy glue, and putting a droplet in each to mark blue/red for left/right. The green/yellow electrical tape in the picture below doesnt look so good

Perspective here makes it appear larger. Anyway two xlr´s is a lump of metal!

Parts list:
Neutrik NC4 FXX and NC4 MXX. €5 each
Neutrik NP3 X times two. €4 each
Sommer cable Cicada SO-D14. With length used here. I wont bother to calculate. This is inexpensive thin microphone wire. 80 eurocent/m
Sommer cable shrinktube 2.4 mm clear, €15
Sommer cable shrinktube 4.8 mm black, €19.5
Sommer cable shrinktube 9.5 mm black. €17
Scavenged braided black cable hose. Free
Sennheiser HD650 spare cable(Sennheiser original) €12

Notes to parts: Im pretty sure all the shrinktubes has a 2:1 shrink ratio. Shrinktube are rolls with meters of tubing so ill probably have enough in this and the next life. These are sold pr/m too. I bought some extra meters for cabling. The Cicada has perfect diameter for headphone cabling. Parts list is all good quality, but really non expensive stuff.

Currency conversion is loosely based on NOK100.- to €10. Whitout VAT, tolls and shipping. This will change from country to country ,and day to day so.
An Euro is also somewhat equivalent to Dollar, so no calculator needed. Everything bought from German shop Thomann webstore.

These specialized adapters usually come out atleast at €100++. RME´s cablemaker ALVA´s variety is €116. So if I spent €35 its a steal. The non monetary value has been the most important for me. Learning how to solder. Moving forward in DIY. Technological insight. Inspiring and helping others. Coming back here to talk about it, and so on.

Looking over my inventory yesterday I realize, I spend money on good ideas like a maniac, and these projects tend to pile up. Finally I have made something out of it and im pleased with results. I would do this allover again. Easy.!

Listening with balanced Sennheiser HD650:

As expected sound quality isnt any different from standard unbalanced output. The first thing to notice is level is up compared to unbalanced. -43 in the picture used to be comfort zone, now its, well louder. At -34 right before ADI-2 Pro switches into Hi-power mode and SNR takes a dip before starting to climb again thanks to hybrid digital/analog volume control autoref level. Iistening is loud, but whitin limits for me. Good news since this Is where ADI-2 Pro will give its best in terms of SNR. In high-power mode SNR max out at +28 dbu, but show me the phones that can handle that! Whitout knowing I think ADI-2 PRO balanced mode can handle the toughest to drive headphones with a respectable level of control and authority.

So while HD650 thrives better at lower power and this setup mostly scews my volume settings, Im looking forward to throw some harder to beat headphones at this.

Next time I do something blog-like I´ll be sure to remember to take the damn photos. This tinkering is just so absorbing. Photography here is all done with my Sony Xperia. I have an Olympus and a macro lens too for insane level of detail. So that will come handy for similar projects.

The future: An adapter that will take this back to single 6.35 TRS to not wear out the proprietary Sennheiser contacts. Prospect for a nice DIY friendly 4.4mm to make a XLR4 to pentaconn adapter.

Best wishes! ..and happy DIY!
Mikael

 

[HarmonicTHD]

About the adapter.. Well im embarrased about my blogging skills here.! Next project will be planned in a correct way.
View attachment 230118
This is two leads of Sommer Cicada SO-D14 Going straight from XLR4 to twin TRS.
View attachment 230119
A closeup of leads coming out of XLR4 before making the "Y". The cable hose is just scavenged from an old PSU. Ended with two layers of heatshrink.
View attachment 230126
TRS end. Cable diameter is a dilemma between TRS and XLR4. I didnt have any of that nice heatshrink for this cable diameter. I fixed internal starin relief with some electrical tape.
View attachment 230129
With the right wind direction you could probably kill a man with this, and I dont mean strangling My only objection to XLR´s, too heavy! Bare contacts is 70g. Cable weighs down in picture.

Thoughts: This has been a very interesting project and a breakthrough for me. I have had these parts for a while and I have just been fermenting them in my mind, fighting windmills of laquered cable and whatnot. Finally coming to action, with the help of peers and better here at ASR.

Design considerations: Aesthetically I think it turned out nice. The nickel contacts, zinc housing and black cabling gives it a professional, and working tool look. Something thats meant for some serious use. Shrink hose and (last minute idea)braided cable hose gives a "manufactured" feel. Looks aside. Why didnt I make this a meter long so I wouldnt have to have this lump of metal hanging over or laying at the top of my hifi shelf? These are just how adapters are made, small. Next time I will do my own thinking. Edit: There is a small, round neutrik logo at TRS housing. Im thinking of pigmenting some epoxy, and putting a droplet in each to mark blue/red for left/right. The green/yellow electrical tape doesnt look so good
View attachment 230130
Perspective here makes it appear larger. Anyway two xlr´s is a lump of metal!

Listening with balanced Sennheiser HD650:
View attachment 230132
As expected sound quality isnt any different from standard unbalanced output. The first thing to notice is level is up compared to unbalanced. -43 in the picture used to be comfort zone, now its, well louder. At -34 right before ADI-2 Pro switches into Hi-power mode and SNR takes a dip before starting to climb again thanks to hybrid digital/analog volume control autoref level. Iistening is loud, but whitin limits for me. Good news since this Is where ADI-2 Pro will give its best in terms of SNR. Its max SNR at +28, but show me the phones that can handle that! Whitout knowing I think balanced mode can handle the toughest with a respectable level of control and authority.

I have written this in a stretch now, minus two cig/coffee breaks. My mind is empty. I will get back to fill in with parts list and other.

Best wishes!
Mikael

Now wrap it with some fancy looking cover and expose it for 2 days to the Norwegian mid sun and pop, you can sell it for 2k. That’s how snake oil is born.

Joking aside. Nicely done.

 

[DonDish]

Thnx man!

About snake oil, there is a good saying; "everybody loves a sucker", but I wouldnt tap into that. Thats not me. Im like "Priceworthy, no nonsense" kinda guy and if I where ever to be priviliged to sell anything I made. Thats how I would sell it. Lol

I could throw some numbers at it, but it would just be factual stuff from the web. I did measure for resistance with my new multimeter though.
It came back between 0,1 - 0,3 milliohm I think. Everything not connected and between pins was OL. Multimeter was a bit wiggly, got those 3mm ballpoint type probes. I wish I had gotten those crocogaps instead. Well see. Ill be back soon.

 

[DonDish]

A couple of days now with ADI-2 PRO balanced mode and the HD650 cable mod I just missed the single ended mode. HD650 doesnt need, and neither was it built to handle these levels of power. It puts it out of the better SNR range, skews my volume settings and might possibly harm both ears and equipment from some level setting mishap. I might add I found a new "loud" setting at -34 so ill have that with a couple of cans some day. I dont mean those cans you put over your ears Ill retract my previous statement of this being pointless. Pointless is me writing that its pointless. Anyone could decide this for themselves. Im just new to this tut/blog/review thing so ill hope to be excused

Anyway! Instead of connecting the old cable back to the HD650´s I did the obvious. A balanced to single ended adapter.

The challenge here is to connect the negative ends back to a single ground/return to prepare for a single TRS output.

This was simply solved with a simple bridge wire at the XLR4 end. This goes between negative pins 2 and 4 to connect to ground. Connected here to the screen/ground(insulated with clear 2.4mm, 2:1 shrinktube). I might add I screwed this up a bit and did a channel swap. Quick fix in ADI or TMfx for me so that´ll do for now. I will open the contact up soon. Next time Ill do a proper schematics drawing first.

Last contact to go. The tool behind the TRS plug is a caliper. If you dont have one just get it quick and learn how to use it. It measures inside, outside diameter and depth down to 0.1 mm precisely. What was that cable diameter again, and will it fit? NP! Cheap, but invaluable.

The shop.

So here it is: HD650 cable mod. Symmetric adapter, and symmetric to single end. This time I made it long enough not to weigh down my equipment
Just over a meter long.

Parts:
Cordial CPK220 BK This is balanced patch/microphone cabel. Not first choice, but choosen most for diameter.
Sommer Schrumpfschlauch 4.8mm 2:1 Thats shrinktube. I just love german
Neutrik NC4FXX
Neutrik NP3X-BAG

Best wishes
Mikael

 

[Veri]

So here it is: HD650 cable mod. Symmetric adapter, and symmetric to single end. This time I made it long enough not to weigh down my equipment Just over a meter long.

I'm confused though. Is there any purpose to going through the symmetric TRS'es adapter just to 'bridge' it back to single ended the way you did?

 

[staticV3]

I'm confused though. Is there any purpose to going through the symmetric TRS'es adapter just to 'bridge' it back to single ended the way you did?

OP can now leave that 4pin XLR cable on his HD650 permanently and plug in one or the other adapter at the end depending on whether SE or Bal is required

It's like one of these IEM cables where you can switch the termination at the end:

 

[DonDish]

I'm confused though. Is there any purpose to going through the symmetric TRS'es adapter just to 'bridge' it back to single ended the way you did?

Absolutely! I can do a quick change whitout fiddling with the Sennheiser contacts. So thats the purpose

 

[staticV3]

In high-power mode SNR max out at +28 dbu, but show me the phones that can handle that!

Bal Hi-Power has 3W at 64Ω
With the HE6se that's 114dB SPL peak
Add a -6dB preamp for Harman EQ and some high DR orchestral music and you're looking at unsatisfying levels of volume real quick.

That's not to criticize the ADI-2 though, far from it.
It's just that the personal audio segment is ridiculously diverse and making an Amp that can do it all is nigh impossible

 

[DonDish]

It's just that the personal audio segment is ridiculously diverse and making an Amp that can do it all is nigh impossible

You mean to say there is some sort of trade of? You have to chose one or the other in design?

 

[DonDish]

OP can now leave that 4pin XLR cable on his HD650 permanently and plug in one or the other adapter at the end depending on whether SE or Bal is required

It's like one of these IEM cables where you can switch the termination at the end:
View attachment 230605

Nice contacts! Wouldnt wanna put my soldering iron to them though