could this connection cause a short?

[cordura21]

Hello, guys. In page 34 of "Getting Started with Digi 001", it says that to connect the Digi to a home stereo you should use the monitor output.
This output is balanced, while most home stereos are unbalanced. It also says to use a 1/4" cable, and to use a special adaptor for to convert to the common RCA inputs on the stereo.

The instructions doesn't say if you should use a TRS connector or a TS connector, it just says a 1/4" cable. I am currently using an RCA cable with two 1/4" TS (mono) adapters on the output of the Digi. Is this dangerous, could it cause a short in the output? What's the proper way of connecting them? even using individual cables for left and right, there's still the doubt between TRS and TS.

Can you help me? Thanks in advance, Andrés

 

[Slackmaster2K]

Don't sweat it, it's fine.

1/4" TRS -> RCA wouldn't make sense anyway, since RCA only has one hit wire and a ground, and TRS of course has two hots and one ground.

TS and TRS are interchangable as a rule. Balanced equipment can be hooked to unbalanced equipment as a rule as well, you just won't get any balancing.

The only thing to be concerned with is whether the digi outputs at +4 or -10 or somewhere in between (a home stereo will be in-between probably)...just be careful initially, listen for any distortion. Since the manual says you can connect it to a home stereo receiver, I think you'll be just fine and dandy. (it might even have switchable output levels.

Slackmaster 2000

 

[cordura21]

hey Slack. The monitor output doesn't have a nominal level, yet it has a pot to regulate the volume.

I was asking this since using a TS adapter will mean that you are joining the machine's R and S outputs. You can then add totally out of phase signals (hot signal + cold signal) in which case you'll have just silence. On the other hand if you add one of the signals to the ground, then you will have a reference voltage that will be always fluctuating. Is my reasoning correct? Cheers, Andrés

 

[Slackmaster2K]

Ok, I see what you mean. The standard way to handle this is to design the circuit such that it'll run balanced or unbalanced...that's the only way I've seen it done, but I haven't seen much (not by a long shot).

My gut says you're fine. It would be really stupid if it was otherwise.

If you're really concerned, you can wire up a TRS plug leaving the ring unconnected (good)...or half insert the plugs (not too good). Even better, figure out what this "special adapter" is.

I don't think you'll short anything, because every time you plug a TRS plug into a TRS jack, you're shorting the R & S for a brief moment.

Slackmaster 2000

 

[cordura21]

I was thinking [really!] about it. If you short the Ring and the Sleeve, you're adding the Cold + Ground. Suppose a 0 volts ground, then basically you have the cold. So now you have a moving voltage reference, which is basically you're signal out of phase. This will change your readings, multiplying your voltage by a factor of 2. Am I right?
So is it correct to asume that a balanced signal carries at the Hot 1/2 the voltage of the original signal?

(I am attaching a little chart about it) Cheers, Andrés

 

[Slackmaster2K]

Yes, but that won't happen because nobody would design a circuit that way

I really think you'll be fine. If you want to play it safe you can do a number of things:

1) Use a TRS plug but don't wire up the ring (just use 2 conductor cable).

2) Use a TRS cable and an adapter that lifts the ring.

Probably not necessary though. My Delta and my POD and a my symetrix SX202 all have 1/4" balanced outputs that work just fine when you use a TS jack (you don't get balancing of course).

Slackmaster 2000

 

[TexRoadkill]

I was thinking [really!] about it.

Cordura, You are dangerous when you start thinking too much

Don't sweat it. Just hook them up and you should be okay. Nothing will burn up and nothing will explode. If you are concerned with the audio quality then get an amp with balanced imputs.

 

[Slackmaster2K]

God I'm really not the guy to be answering these questions, I wish somebody would jump in.

You are partially right, except that a balanced signal carries full strength signals on both conductors....one out of phase as you've drawn there. The two are *added* together at the destination, which leaves you with your noise which is then subtracted from the in phase signal.

In other words, no, a balanced connection does not carry 1/2 voltage on each line. Yes, you're theory is correct that if you added the cold + ground and the receiving circuit subtracted ground from hot, then you should end up with twice the voltage. I don't think that is something that will happen in this case, however.

Slackmaster 2000

 

[cordura21]

hey Tex. Sorry to make you nervous, I know what you mean. I get the effect myself too

Reading round I found something like this

"Remember that in a balanced circuit, both signal wires carry the same voltage level with reference to common, and they are 180 degrees out of phase. In this case only half the voltage will appear on the meter, so the engineer must mentally double the voltage level when making a reading."

(http://www.montagar.com/~patj/db_db.htm)

And something like this:

"The loss of this signal would normally mean only receiving half of the signal voltage. The cool thing, though, is that the transformer automatically compensates for the lack of the third wire and delivers the correct voltage to the unbalanced input anyway! "

(http://www.fmraudio.com/balanced.html)

The first one is quoted by Digidesign as a correct procedure, the second one is from the makers of the Real Nice Compressor and Pre.

So, what's the real deal about this? It can't be that hard to establish. Is it time to use the Harvey-signal?

Cheers, Andrés

 

[Slackmaster2K]

Sigh, this is over my head. I obviously misunderstood how balancing works.

I'm not sure if this is what you found, but it's good info. You're concerns are certainly valid:

http://www.fmraudio.com/balanced.html

You need to contact digidesign and find out. It's not a thing we can solve by thinking about it. If they didn't design the output to work unbalanced, then it's not going to work unbalanced (unless they have a way to correct it...inline transformer or something), simple as that.

Slackmaster 2000