Pretty basic question about unbalancing an audio signal.

[TheGuitarist]

So this might be tech 101, but i never learnt it so here's my question.

Whats the best way (no colouration to the sound at all) to passively unbalance an audio signal. Would it simply be just connect the 3rd pin of an xlr to the ground?

My situation is i have balanced outputs out of my speaker controller, but unbalanced RCA ins on my amp (why is all hifi unbalanced.... seriously.) And i'd like to get the best signal quality i can to it.

Any help would be great.

 

[mikefatom]

It all depends on what kind of output stage you're coming out of. If it's floating/TX balanced, just attach the XLR-pin2 to RCA-center-pin and XLR-pin3 to RCA-sleeve.
If we're talking about an electronically balanced output, the best solution is to use a transformer to take care of the unbalancing as well as the signal attenuation.

check out this link: This guy knows what he's talking about.

cheers,

mike

 

[TheGuitarist]

Well it will be three sources, two of them being interfaces (digi 003 and motu 828, one is a di (ipod to balanced DI) and one is a mixer) So i guess they are all sorts of outputs.

Looks like its best to use a couple of DI's, whirlwind things should do the job, maybe proco Iface. They seem pretty clean to me.

 

[sodderboy]

Are the amp's inputs also at -10dB operating level?  I think that you can switch one or both of the interfaces, but if not you will be slamming the inputs.
If you are looking at transformer options, you cannot go wrong with this.
The other option is to use an active box to do the work.  You can use the other side to amp-up something.
Are you really running an iPod through a DI?  Either unit above is a better interface, and will give you better gain.
Mike

 

[TheGuitarist]

Yeah its a ProCo Iface (the ipod DI) which is designed for that kind of work, i use it at a live venue i work at for big corporate stuff and it seems to work well, its mostly just for client reference, doesn't have to be great, just looking at what i'll have to do if i get these monitors i'm after.

That box looks awesome though, the interfaces are my main units so they would be +4, didnt think about the +4 -10 thing,  though it could be advantageous if i need more level. hmm... i think that line level shifter is the way to go though.

 

[sodderboy]

I checked that iFace.  It is only a Di in that it matches a headphone output to mic inputs, not line inputs.  The Ebtech actually bumps them up by 12 db to hit +4 inputs right nicely.  And does the opposite equally as well.  The MCM goes both ways which is good in fixed situations, and it is readily DIY upgradable.
Be aware that the "gain" that you will get connecting a +4 signal into a -10 input only goes as far as the headroom of the input, which is not very far.  You are better-off making gain inside the power amp, which is a gain factory, rather than fight with distortion at the inputs.
Mike

 

[TheGuitarist]

Yeah i see your point, i can only assume its -10 as its a hifi amp, why those guys never converted to balanced +4 is beyond me. Sorry which MCM box is this? There wasn't a link in your post.

i'm guessing its this?

http://www.mcmelectronics.com/product/MCM-CUSTOM-AUDIO-555-8485-/555-8485

Just looking for the best solution, it'd be a pretty permanent setup, or everything would move together anyway. And obviously as long as the cicuit is sonically transparent i'm happy.

 

[Michael Tibes]

If you know the input circuit of the receiving unbalanced circuit and it is opamp based, I'd perhaps mod it as a simple unbalancing circuit. I just did this using the circuit in fig 2 here: http://sound.westhost.com/project51.htm and it works like a charm. It's a matter of changing a few resistors - if you're lucky to have a simple opamp input circuit. The noise suppression won't be stellar, but even 40 dB are 40 dB better than running unbalanced. 

Michael

 

[sodderboy]

Yeah i see your point, i can only assume its -10 as its a hifi amp, why those guys never converted to balanced +4 is beyond me. Sorry which MCM box is this? There wasn't a link in your post.

i'm guessing its this?

http://www.mcmelectronics.com/product/MCM-CUSTOM-AUDIO-555-8485-/555-8485

Just looking for the best solution, it'd be a pretty permanent setup, or everything would move together anyway. And obviously as long as the cicuit is sonically transparent i'm happy.

It is the same thing.  I linked to it with the word "this" in my first post.  It is a good box using 5532's, which are transparent enough.
You can't go wrong with either external solution.
Mike

 

[conleycd]

In terms of why does hifi gear run unbalanced - unbalanced gear (for the most part) is a 'more pure' signal path.  Bob Katz for example prefers unbalanced gear except in a couple of situations. 

When you have a balanced transmiter and receiver you are adding more components to your signal chain.  So unless you have big problems with noise or like colouration (such as an input and/or output transformer) unbalanced is pretty good (but for some reason implies a bit of a bad name).

CC

 

[fdew]

Hi.  I just discovered this forum yesterday.  wow.  Great resource.

You have received good info so far. I just want to add a question and a comment.  First,  why are you running the Ipod through a DI?  Why not direct to the amp, or if you are changing it to mono then through a passive resistive Wye?

I agree completely that the best way from balanced to unbalanced is to just build an adapter cable and try it.  If the balanced output is true balanced it will work fine. if it doesn't then a transformer.  As far as transparent sound through a passive DI, The transformer is everything and a Jensen transformer is the top of the line. Many vendors including Radial and Whirlwind and LBP INC (me) sell them.

Frank
http://lbpinc.com/DI.html

 

[TheGuitarist]

The ipod is going through a speaker/input selector, i'm not going to modify it just so it can run an ipod. Its only for client references anyway. No big deal.

 

[sodderboy]

Check the specific box fdew.  It is designed to Directly Inject a headphone signal from an iPod into mic inputs.
And I would agree with a straight cable in the case of something that is +4 unbalanced, but not -10.  You will distort the input very easily.
I had a job to "fix" a broken Yamaha mixer being used as a cue mixer.  It sounded horrible not because it was broken but the user had 828 outputs plugged directly into the mixer's -10 line inputs.  Once he lowered things in the DAW, by 20db actually, the mixer sounded great and was "fixed".
Gain structure 101.
Mike

 

[fdew]

Check the specific box fdew.  It is designed to Directly Inject a headphone signal from an iPod into mic inputs.

Thanks for the info.  It is good that we have lots of tools to chose from. (Grin) My live sound needs are usually Mono so I have become accustomed to using a passive Summing Wye, built into a oversize shell 1/4 in plug and, either line in, or through a conventional DI box.  Just the tools I have handy.

Frank
http://lbpinc.com/DI.html

 

[TheGuitarist]

fwiw that iface has a mono summing option.

 

[wtmnmf]

Studying these pages will tell you everything you need to know 

http://www.dself.dsl.pipex.com/ampins/balanced/balanced.htm

http://www.dself.dsl.pipex.com/ampins/groundloops/grndloop.htm

 

[sodderboy]

Thanks for the links!  Great info for all.
Mike

 

[JohnRoberts]

In terms of why does hifi gear run unbalanced - unbalanced gear (for the most part) is a 'more pure' signal path.  Bob Katz for example prefers unbalanced gear except in a couple of situations. 

When you have a balanced transmiter and receiver you are adding more components to your signal chain.  So unless you have big problems with noise or like colouration (such as an input and/or output transformer) unbalanced is pretty good (but for some reason implies a bit of a bad name).

CC

Nonsense.. consumer gear is unbalanced because it's cheaper.  2 wire connectors and cable is cheaper than 3 circuit paths.

If noise from two channels of active send concerns you, just use a resistor impedance balanced output for the minus send. 

Two circuit wiring between products it fundamentally flawed because the shield is also a signal conductor, so any shield noise pickup will corrupt the audio signal integrity. Further any ground potential differences between the chassis can also conduct through the shield if grounded at both ends.

Professional 3 circuit wiring with proper shielding and ground isolation of both audio conductors, is the only high purity audio interface.

I guess opinions vary .

JR

 

[Kingston]

Professional 3 circuit wiring with proper shielding and ground isolation of both audio conductors, is the only high purity audio interface.

I'm pretty sure the reason some mastering engineers prefer unbalanced signal path is due to the amount of extra signal path stages needed for any balancing. I've had this discussion with a few of them, and the consensus is that since every single balancing transformer or chip can be heard, some more than others, it's best to leave them out to begin with, and live with a well designed unbalanced system. Technical grounds etc. careful planning needed of course. Naturally this is for the most serious golden ears only, but I understand why they do it.

 

[Gold]

I can see this logic holding up for a discrete circuit where balancing the input means a more complicated input stage. For opamp based gear the concept doesn't doesn't hold water. How is a a four resistor balanced single opamp input stage worse than the same opamp as a unity gain buffer?

I doubt anyone bothered to actually look at the specific circuit and decide. It probably comes from the LA camp who built their own stuff and hate opamps. Everyone else is just parroting this without thinking.