Help Design an unbalanced consumer Line level to Balanced interface

[Whoops]

Please build it the way I intended - put it in the barrel of a 2-C phone plug with a shielded-twisted-pair cable of any length exiting it. You can easily fit 3 resistors in the barrel. And extend the reach of it's output cable by adding as much XLR extension as you need. Build it any other way and you'll likely have noise issues in certain system setups - I'll feel no obligation to help.

Is this only related to Version 2 you posted or you also to version 1?

Is that in version 1 the components will not fit inside a JACK TS housing, so I don't really know what was your initial idea or where would the components be mounted.

Well if both circuits can have problems if built inside a box and have 1 or 2 meters of unbalanced cable (and signal) between the instrument output and the circuit, then although they're great anyway, they are not really useful at all to me.
As my goal is to use them in Live Sound, I need to carry with me 5 or 6 small boxes with a simple circuit inside, I don't want to carry around meters of cables. The cables with connector will take a lot of space inside my luggage, while 5 really small boxes are easy to organize inside the trolley.
Also I don't carry cables, the musicians already carry the unbalanced cables and the PA companies have the XLR cables, so I need something that uses the cables that will already be there, a small box (with a much simple circuit) to replace a DI box is what I need.

So thank you so much Bill for all your effort and help, but if version 1 shouldn't also be built in a small extruded box then I have to look for other circuits. It's unfortunate in that case as your circuits have low a low components count and looked perfect for what I needed.


Thank you Bill

 

[MisterCMRR]

The original idea, as well as the morphs, are intended to be built in a PLUG! It's not a DI box design for reasons I've tried to explain. If you insist on using the capacitors, their voltage rating can be 7 V or higher - that's the highest voltage they will ever see (unless the resistor values get fiddled with as well)!

 

[Whoops]

The original idea, as well as the morphs, are intended to be built in a PLUG! It's not a DI box design for reasons I've tried to explain.

Thank you so much Bill, your circuit is really nice and will be useful for many people I think.

But in my case, and the reason I started this thread, is to build a circuit inside a small box that can be used to replace a DI box, as I explained in the last post I'm not interested in cables with circuitry in the plugs.
Thank you

 

[MisterCMRR]

I guess I don't understand the issue about cables. Make the circuit in a 2C/TS plug, use a 6-foot STP cable to connect it to a XLR-M connector at its other end. Color or label it bizarre so it doesn't look like an ordinary adaptor cable. When the musician shows up, tell him to put that 6-foot TS to TS cable in his pocket. Then plug this "DI cable" into the instrument and connect the XLR-F stage cable (that would otherwise plug into the output of a "DI box") to the XLR-M cable from the instrument. The only thing that looks different is the mated pair of XLRs where the "DI box" normally is. I don't see the problem ...

 

[MisterCMRR]

Or build it in something like this?

Yes, that would definitely work! If there was a right angle version, it would help overcome mechanical advantage that could damage the instrument's jack.

 

[Whoops]

Dear Bill, I already explained that in post 121.
Everyone has their needs and their reasons.

I'm only interested in circuits that work well when built inside a small box, and that's it.
There's some other interesting circuits in this thread so I will focus on those.

Your 2 circuits are really clever and will be really useful for many people for sure, they just don't fit my needs and what I'm trying to achieve.

Thanks

 

[MisterCMRR]

Is this only related to Version 2 you posted or you also to version 1?

Is that in version 1 the components will not fit inside a JACK TS housing, so I don't really know what was your initial idea or where would the components be mounted.

Well if both circuits can have problems if built inside a box and have 1 or 2 meters of unbalanced cable (and signal) between the instrument output and the circuit, then although they're great anyway, they are not really useful at all to me.
As my goal is to use them in Live Sound, I need to carry with me 5 or 6 small boxes with a simple circuit inside, I don't want to carry around meters of cables. The cables with connector will take a lot of space inside my luggage, while 5 really small boxes are easy to organize inside the trolley.
Also I don't carry cables, the musicians already carry the unbalanced cables and the PA companies have the XLR cables, so I need something that uses the cables that will already be there, a small box (with a much simple circuit) to replace a DI box is what I need.

So thank you so much Bill for all your effort and help, but if version 1 shouldn't also be built in a small extruded box then I have to look for other circuits. It's unfortunate in that case as your circuits have low a low components count and looked perfect for what I needed.


Thank you Bill

The box isn't the problem, it's the length of unbalanced cable at the input side. It's resistance, although only a fraction of an ohm, will couple hum and buzz into the unbalanced signal.

 

[MisterCMRR]

The box isn't the problem, it's the length of unbalanced cable at the input side. It's resistance, although only a fraction of an ohm, will couple hum and buzz into the unbalanced signal.

For what it's worth, any circuit you put in the box, unless it has a transformer or an active balanced line receiver, will suffer the same noise issue caused by the unbalanced input cable.

 

[Whoops]

For what it's worth, any circuit you put in the box, unless it has a transformer or an active balanced line receiver, will suffer the same noise issue caused by the unbalanced input cable.

Actually my initial goal was for it to be an active circuit powered by phantom power,
in post 2 I showed some of the ideas:

https://groupdiy.com/threads/help-d...evel-to-balanced-interface.82656/post-1068703


I got interested then in your passive circuit because of the simplicity and the low component count but I wrongly assumed it would work well inside a box having a 2 meter unbalanced cable in front of it, but no worries, there's some interesting active circuits here is this thread already, I will check them again

Thanks

 

[MidnightArrakis]

There's this.....



And.....while I couldn't find anything like what is shown above in a "Male" version, the closest alternative I could find would be using something like this:



>> Of course, you could always shorten the length of the cable. The one shown in the above photo is 12" (304.8mm).

/

 

[abbey road d enfer]

Actually my initial goal was for it to be an active circuit powered by phantom power,
in post 2 I showed some of the ideas:

https://groupdiy.com/threads/help-d...evel-to-balanced-interface.82656/post-1068703


I got interested then in your passive circuit because of the simplicity and the low component count but I wrongly assumed it would work well inside a box having a 2 meter unbalanced cable in front of it, but no worries, there's some interesting active circuits here is this thread already, I will check them again

Thanks

I would suggest you build the circuit in a box, with a TS socket on one side and an XLR on the other, then test it in a live situation.
Indeed, the length of unbalanced connection should be minimized, but you will find that the performance is often adequate. It won't be bullet-proof, though.
Note what I said earlier (post # 113) about Zout impairing CMRR. You could add a 100r potentiometer in series with the 909 (or910). To be adjusted on site.

 

[Whoops]

I can do that for sure and try it out,
Actually I already have a prototype with the small extruded box shown here and veroboard almost completed.
It’s just a matter of finishing it and taking it to gigs