Balanced to single-ended converter (XLR to RCA / BAL to SE)

Thanks. I'll try calling.

 

rythmdevils is correct I you have to call them when I did they shipped them out promptly

 

Ok, wiring assistance please. Maybe @atomicbob can help.



It seems to me, the Gray would go to Pin 1 - since that is Earth ground (ignore the switch because on, that resistor and cap are bypassed).

It also seems to me that the White is the only one that goes to chassis ground.

And so the Black and Orange are the signal ground to the RCA connector.

It also seems there should be a 10K resistor (R2) across the RCA connector. Am I missing something? These need a 10K resistor?

 

I am not entirely sure but I know the jensen jt-11p-1 transformer datasheet shows for basically the same circuit (minus a grey/2 wire) that the load must be 10K or > and if it isn't exactly 10k they expect you to use an RC damping network across 8/5. They both specify a 13k input impedance with a 10k load.

 

Ok. Thank you. I take it then that is the load.

 

And with all of this, shouldn't we all be using the CineMag CMLI-10/600B?

"The CMLI-10/600B transformer takes a professional level signal (“600 Ohms”) and convert it to a signal that
is compatible with consumer electronics devices, or from consumer level to 600 Ohm level."



It does show a 2.43K resistor before the RCA jack I take it to ensure there is a load on the other end if disconnected and to even out the 13K impedance.

 

The 15/15B has two faraday sheilds, and the mu-metal can that acts as a shield. The idea is that these each go to different ground systems-- one shield for input ground, one shield for output ground, and the can goes to the chassis. The Cinemag App Note for the DI box makes this a bit clearer, but you got it right in your post.

https://cinemag.biz/application_notes/PDF/CM-DBX Applications AN-108.pdf

In terms of the resistor-- the datasheet specs a 10k or 15k load resistor. The 15/15b datasheet actually shows FR and distortion (!) for both. To my eye, 15k looks a bit better; I'd pick a load so that the total does not drop below 10k with your amp's input loading it further. A 20k load resistor with a 47k amp input impedance presents a total load of about 14k.

It's also worth knowing that the reason why it's spec'd for a 13k input impedance with a 10k load is because it has an absolutely gargantuan ~2k winding DC resistance. This means there's a little bit of insertion loss. Sizing the load resistor will impact the sound of the chain, and it's certainly worth trying with no resistor at all.

The 10/600B has similar level handling, but a 1:4 ratio-- which means it will either provide or eat a lot of gain. I'd be weary saturation if using it for step up. Some sources might get cranky driving the 600 ohm side, too. I'd try something with a larger core, such as the CMOL-2x600, if low winding impedances aren't a problem. Or perhaps a Lundahl.

 

Take into account that the primary load is actually the reflection of the secondary load times the square of the turns ratio. So, for example, 10k on the secondary of a 1:4 turns ratio would give a reflected load of 600 ohms on the primary.

 

I am actually doing a rewire on this box, so it is not mine. It has two 15/15B's and there is no load resistor. So I was curious when I looked at the datasheet if needed one or not. If no load, 10k, 15k....one idea is to use a three way switch I guess.

It is on my bench because of some hum. And I can clearly see why when I look at the datsheet and look at the box. They wired the white (chassis), gray (earth), both to chassis ground. Easy fix.

I am also putting together another one, but this one has CMLI-600/600C. Only single Faraday shield. But it too looks like the wiring diagram calls for a 15k resistor across the output.

From what I understand, the owner is using these boxes to go from balanced output to unbalanced amp inputs. I doubt anyone here are going unbalanced out to a balanced input. Now that would be silly. Even the Schiit Mjolnir that only has balanced headphone output has an un-gimped unbalanced input.

 

I guess I'm silly but I have lots of diy stuff that doesn't do any conversion at all

 

You want to be careful with balanced pin 1.

Gray should go to chassis ground, which should be different than earth ground from the AC mains power inlet ground.

R1 + C1 create an RF ground while avoiding creating Pin 1 AC mains ground loop back to the component providing balanced input.

Unbalanced output ground should be completely floating from the chassis.

There is no need for an input load resistor unless the transformer mfg specifies otherwise. There is already a 10K load on the transformer output which is referred back to the input of the transformer.

For more details on pro audio grounding check this link: https://www.ranecommercial.com/legacy/note151.html

 

Thanks for the info. This is an isolated box with XLR female connections and RCA's for the output. I have no idea about AC mains ground because that happens before it gets to this box. I do believe most keep pin 1 away from earth mains AC ground.

So if gray goes to chassis ground, where should the white wire go?

Right now both white and gray are connected to the same XLR chassis (not pin 1) grounding point.

 

I would be inclined to use a switch or pc jumper from white to chassis ground. Then measure the system and see which provides lowest residual noise, connected or floating.

 

I guess the whole idea of “chassis” ground is confusing in an isolated box.

The diagram shows white to chassis ground and pin 1 with the switch to earth ground.

Now two transformers in an isolated box, the only choices I have: that chassis, floating, and pin 1.

Now with the isolated box, it makes more sense to me to make pin 1 chassis, because otherwise pin 1 from the output is going nowhere. The whole shield of the output cable now has ground lifted on one the input to the box. Shouldn’t that continue on to the chassis of said box? And the Farady shields?

Most are adding these transformers within other equipment and not an isolated box.

Now as it is (white and gray tied together to chassis, pin 1 lifted), I got no hum on my system. However, @rhythmdevils says he is getting some ground hum from Yggdrasil. And I am not and I even checked with IEM’s.

 

You might want to look up the concept of telescoping shields for balanced audio connections. Other research topic is "pin 1 problem".

 

Gotcha. I don’t want to inject signal INTO the ground plane. I guess the reason why switches might be needed. Connection may help or hinder or vice versa in another system.

 

I'm just copying this here from the discord because I kinda like how the explanation came out, even if it's not quite true but what analogy ever is.

 

So I was thinking... Sorry for the ms paint monstrosity ;/



But basically with 2 transformers and a "few" switches I think I can make a PI-2XX 2XR 2RX / CI-2RR and/or passive attenuator box ;/ I'm sure the wiring will be fun, will try to keep output wiring (&attached cables) short.

Other than it takes multiple switches to flip between passive pre or ... transformer isolator/balun thing (with or w/o the attenuator) or to switch inputs... I think it should work? Probably.

A little fiddly...

 

Going back to the resistors from this post...

I wired up a 10k resistor across the unblanced output. It did cut back the level just a bit, but not by much. However..

I have a Theta DS Pro Basic II DAC that has unbalanced outputs as well as balanced. The way these outputs are wired is such that the unbalanced are basically the same as the balanced outputs. The PCM-67 chip has two outputs, and this DAC has two PCM-67's. They are wired that the unbalanced only uses one output per chip and the balanced uses both outputs per chip in balanced configuration. Quite genius...no loss for either connection...it is kind of like cheating. But basically, it is the best source to check between balanced and unbalanced.

When I first hooked up the 15/15B converter, the output was was slightly hotter compared to the unbalanced direct from the DAC, and also a bit peaky. I then put in the 10k resistor, and they are very close to the same. The output from the balanced conversion to unbalanced is ever so slightly brighter, but very close to the same in level and almost no difference at all.

The 600/600C has a noticeable difference in level as it feels like it is not attenuating at all. Either way a 15k resistor across the unbalanced output seems to also make it "less peaky" and fuller sounding, although harder to compare to the unbalanced output of the Theta since the levels are so different. Kind of the same thing with the 10/600 transformer - it also does not seem to attenuate at all and hard to compare. That one one calls for a 2.43k resistor across the unbalanced connection.

 

The value of the resistor you use will vary depending on the input impedance of the load. If you really wanted to be anal, you could use a variable resistor and dial in for individual load (when switching between amps for example). You could go even further and use jumpers to set individual fancy metal film resistors based on the load you're using.