unbalanced to balanced connection

[JulesFW]

I have a consumer grade receiver/amplifier (Marantz 6012) with 2 unbalanced line outs feeding a professional grade stereo amplifier (Crown DSI 4000) that drives 4 18" drivers in an infinite baffle system. It was "professionally" installed (I think wrongly) by cutting off the ends of two RCA cables, stripping them, and attaching them to the + and - posts of the Crown's Phoenix connectors while leaving the ground post empty. Sound does come from the subs, but it hardly does justice to its potential.
My research suggests that, while I can simply wire this differently, I will obtain much better results if I introduce a dual channel DI-box splitter into the mix, and I was thinking of a Behringer DI 20 which I can find on Amazon. This of course is not the intended use of this passive DI and I haven't found anyone else having posted this as a solution and so before hitting the buy button I thought it best to check my conclusions with people with far more knowledge than I possess. I thus have the following questions: 1) without the DI box, what is the correct way to make the connections, 2) Is the DI box the best way to go, 3) if using the DI box I assume the connection from the Marantz to the DI box should be as short as possible...is that correct and what would be the recommended cable or cable specifications and 4) what would be the recommended cables from the DI box to the Phoenix connectors on the Crown?
Many thanks in advance for your sage advice.

 

[TLS Guy]

I have a consumer grade receiver/amplifier (Marantz 6012) with 2 unbalanced line outs feeding a professional grade stereo amplifier (Crown DSI 4000) that drives 4 18" drivers in an infinite baffle system. It was "professionally" installed (I think wrongly) by cutting off the ends of two RCA cables, stripping them, and attaching them to the + and - posts of the Crown's Phoenix connectors while leaving the ground post empty. Sound does come from the subs, but it hardly does justice to its potential.
My research suggests that, while I can simply wire this differently, I will obtain much better results if I introduce a dual channel DI-box splitter into the mix, and I was thinking of a Behringer DI 20 which I can find on Amazon. This of course is not the intended use of this passive DI and I haven't found anyone else having posted this as a solution and so before hitting the buy button I thought it best to check my conclusions with people with far more knowledge than I possess. I thus have the following questions: 1) without the DI box, what is the correct way to make the connections, 2) Is the DI box the best way to go, 3) if using the DI box I assume the connection from the Marantz to the DI box should be as short as possible...is that correct and what would be the recommended cable or cable specifications and 4) what would be the recommended cables from the DI box to the Phoenix connectors on the Crown?
Many thanks in advance for your sage advice.

First of all that is not really a wrong connection. Ideally you should connect the -ve and ground connection of the Phoenix connectors, but you might get a ground loop.

I suspect your real problem is that domestic unbalanced and pro balanced connections have different sensitivities. So the signal requires amplification between the receiver and Crown amp.

That DI splitter is not what you need. First of all it is battery powered or 48 volt phantom powered from a phantom powered mixer input. Your Crown amp can not phantom power a unit like that.
In addition that unit provides no gain, only 20 or 40 db of attenuation. So that device is useless for your purposes.

What you need is an active RCA to balanced line out with gain. This unit will provide 4 db of gain which should be enough to boost consumer unbalanced out to pro balanced input.

 

[Speedskater]

I would think that the Crown amp can deal with the small difference in level without an active booster.

Just use drawing #17 or 18.

Sound System Interconnection
Rane Technical Staff
RaneNote 110 written 1985; last revised 11/15

Cause and prevention of ground loops
Interfacing balanced and unbalanced
Proper pin connections and wiring
Chassis ground vs. signal ground
Ground lift switches


http://www.rane.com/note110.html

 

[TLS Guy]

I would think that the Crown amp can deal with the small difference in level without an active booster.

Just use drawing #17 or 18.

Sound System Interconnection
Rane Technical Staff
RaneNote 110 written 1985; last revised 11/15

Cause and prevention of ground loops
Interfacing balanced and unbalanced
Proper pin connections and wiring
Chassis ground vs. signal ground
Ground lift switches


http://www.rane.com/note110.html

His current connection is acceptable and certainly not causing signal loss. The difference between domestic line and pro balanced is actually 4 db which is why the type of units I recommended pretty much all offer 4 db gain making the connection he wants to. Certainly there is a gain mismatch at present by his report, which is not unusual in these cases.

I would bet if he does what I advised it will solve his problem.

Added to which a lot of receiver pre outs are only 0.75 volts full modulation and should be 1 to 1.2 volts. Pro line balanced is 2.4 volts for full modulation generally.

Clearly by his report his gain structure from pre out to Crown is not correct.

 

[lovinthehd]

Where are the gains set on the Crown amps?

 

[TLS Guy]

Where are the gains set on the Crown amps?

I would assume they are turned up on full, otherwise he would not be posting here. In any event the knobs are not gain settings on pro power amps, only attenuators.

 

[lovinthehd]

I would assume they are turned up on full, otherwise he would not be posting here. In any event the knobs are not gain settings on pro power amps, only attenuators.

He didn't specify so thought I'd check. Okay, level controls as Crown calls 'em in this manual....

 

[JulesFW]

Decision made...I will absolutely purchase the recommended Rolls MB15b. A primary reason for my post was uncertainty of buying a passive unit after reading posts too technical for me at this stage which spoke of the differences in impedance between balanced and unbalanced lines. I hope I got that right but the main point is that I was not surprised to have an active unit suggested and am most grateful to have received the link to an appropriate solution.
I also want to ensure I am buying the right cables and will want to purchase everything at the same time from the same place, sooo... For the input (Marantz to Rolls) I am guessing these, and for the output I am guessing two of these. I changed suppliers because Parts Express doesn't seem to carry an TSR to Phoenix cable and I didn't want to cut off the end of a cable and strip the wires. I am mildly concerned by the fact that neither of my choices boasts an AWG. Parts Express has these and these which are AWG 22 but I would have to do the modification to the microphone cables which doesn't strike me as ideal.

The knobs on the Crown were set at 50% when I balanced the speakers to the room which is what was recommended, but I did try turning the bass up during a movie and the thunder/explosions/jet aircraft etc. didn't exactly have me ducking. I have spent a lot of money (though perhaps not by some standards) on my home theater and don't want to cheese out on relatively minor expenses. I want to do things right and value the advice I am being so generously offered.

 

[lovinthehd]

You raised sub trim levels in the avr or on the amps? Are you still running levels at only 50%? By balancing speakers you mean you ran Audyssey?

 

[JulesFW]

I turned up the bass volume on the amp...not yet sure how to do it from the Marantz. By balancing the speakers I mean using the built in procedure of the Marantz where I plug their microphone into the front and move it to 8 different listening positions while the Marantz sends out test sounds and adjusts for room dynamics. The Crown has its own software and multiple settings which I have not yet played with. I have a ton of new equipment, a ton of manuals to read and absorb, and a major problem getting my CRT projector to do 3D which is a whole other time consuming matter. But my research on connecting an unbalanced signal to a balanced amp definitely suggested that while it is possible it is far from ideal, so I would rather just get the suggested Rolls to start with rather than playing around with trying to get a result that may not be possible, and worry about fine tuning the system once the speakers have been broken in and I have properly absorbed all the relative manuals. This way I at least know I have started with appropriate hardware, i.e., no weak hardware links, leaving any other problems I encounter thus related to user ignorance.

 

[TLS Guy]

You don't need to spend a fortune on cables. You can tell the Audioquest cables are Loony, because they have arrows on them which the electrons can't see!

 

[Johnny2Bad]

" ...
Sensitivity at 8 ohm rated output: 1.4V, at 4 ohm rated output: 1.3V, At 2 ohm rated output: 1.0V
Input Stage : Input is electronically balanced and employs precision 1% resistors*
Input Impedance (nominal): 20 k ohms, balanced; 10 k ohms, unbalanced
..."

It does not seem there is an issue with gain structure or input sensitivity.

According to the brief and informative owner's manual, on page 10 the correct connection to the Phoenix Connectors is for unbalanced cable to tie the shield and (-) cable terminal together, and connect the hot (+) cable terminal to the positive input terminal.

So, you should be using shielded RCA to bare wire interconnect(s)
connect the hot (+) wire to the positive input of the Phoenix connector;
connect the negative (-) wire to the negative input of the Phoenix connector;
connect the cable shield to the ground input of the Phoenix connector;
... and connect a short jumper wire from the shield to the (-) input of the Phoenix connector.

Repeat for the other channel.

* RE:
" ...
Added to which a lot of receiver pre outs are only 0.75 volts full modulation and should be 1 to 1.2 volts. Pro line balanced is 2.4 volts for full modulation generally.
..."
I am assuming by "electronically balanced" Crown means a differential input, not a fully balanced construction. That explains the low input sensitivity (balanced construction is essentially two amplifiers per channel; differential input would convert the "balanced" input [the term used improperly; should be "differential input"] to single-ended internally).

 

[Speedskater]

....................................................................
I am assuming by "electronically balanced" Crown means a differential input, not a fully balanced construction. That explains the low input sensitivity (balanced construction is essentially two amplifiers per channel; differential input would convert the "balanced" input [the term used improperly; should be "differential input"] to single-ended internally).

This thread is about 'balanced interconnect systems' which is completely correct!
Internal circuit design is another subject entirely. It should be discussed in another thread.

 

[Johnny2Bad]

This thread is about 'balanced interconnect systems' which is completely correct!
Internal circuit design is another subject entirely. It should be discussed in another thread.

So, let me get this straight ... a thread about an unbalanced (in any definition of the word) single-ended connection to a differential input connection is about "balanced interconnect systems" when in fact nothing ... not the source, nor the amplifier ... is actually "balanced", and the thread topic includes the word "unbalanced".

Gotcha.

Not only that, but you can have a balanced connection with just two conductors (both conductors have the same impedance to ground) but you cannot have a balanced differential connection unless you use three. Which is what we have.

Anyhooo ... for those that want to learn, PreSonus explains it pretty well.

https://www.presonus.com/learn/technical-articles/balanced-unbalanced

 

[WaynePflughaupt]

My research suggests that, while I can simply wire this differently, I will obtain much better results...

The Crown only requires 1.4 volts to drive it to maximum output. I’m sure the Marantz pre-outs do much more than that. Bottom line, there’s not much chance that you actually need the Rolls.

There is no issue blending balanced and unbalanced equipment, despite what you’ve been told. I have balanced equalizers and amps in my systems and it all works fine with no issues.

BTW, you can find an article about gain structure when using pro gear in a HT system in my signature.

Regards,
Wayne A. Pflughaupt

 

[lovinthehd]

Agree this is more the OP's gain structure issue than a thread dedicated to unbalance/balanced connections. He hasn't been very clear on what he's done other than reading about what are usually not the best solutions....

 

[WaynePflughaupt]

[

Agree this is more the OP's gain structure issue...

What issue? He never actually specified that he was having an issue (at least none that could be attributed to using an unbalanced signal into a balanced inputs). He’s running his amp gains at 50%, which means he doesn’t have a signal-level problem. The only issue I can see is that someone told him that feeding an unbalanced signal to a piece of gear with balanced inputs is a bad thing, which or course is nonsense.

Jules, the only time balanced signals are “ideal” is if you have a long cable run, say more than 50 ft. That’s a common issue in pro audio applications, but seldom in residential installations.

And consider this: Our signal sources are unbalanced. Converting them to balanced is just more electronics in the signal chain that’s totally unnecessary.

Regards,
Wayne A. Pflughaupt

 

[Speedskater]

So, let me get this straight ... a thread about an unbalanced (in any definition of the word) single-ended connection to a differential input connection is about "balanced interconnect systems" when in fact nothing ... not the source, nor the amplifier ... is actually "balanced", and the thread topic includes the word "unbalanced".

While the source may not be balanced, The interconnect cable and the input stage are a balanced system.

Not only that, but you can have a balanced connection with just two conductors (both conductors have the same impedance to ground) but you cannot have a balanced differential connection unless you use three. Which is what we have.

A balanced input stage is a sub-set of a differential input stage.

So how is the input stage different, depending on whether:
a] The cable shield is or is not connected at the receive end?
b] It's transformer coupled?
c] The interconnect cable is unshielded Cat5?

 

[lovinthehd]

[

What issue? He never actually specified that he was having an issue (at least none that could be attributed to using an unbalanced signal into a balanced inputs). He’s running his amp gains at 50%, which means he doesn’t have a signal-level problem. The only issue I can see is that someone told him that feeding an unbalanced signal to a piece of gear with balanced inputs is a bad thing, which or course is nonsense.

Jules, the only time balanced signals are “ideal” is if you have a long cable run, say more than 50 ft. That’s a common issue in pro audio applications, but seldom in residential installations.

And consider this: Our signal sources are unbalanced. Converting them to balanced is just more electronics in the signal chain that’s totally unnecessary.

Regards,
Wayne A. Pflughaupt

Only in that he is complaining about output and if anything he needs to turn his amp gain/level to 100% and learn how to use the sub trim level in the avr (Jules, many raise sub level 2-6 dB in the avr post-Audyssey). While I am somewhat enjoying the thread discussion about the balanced/unbalanced thing, don't think that's the actual subject in terms of what the OP is trying to accomplish, i.e. bring up sub levels to his expectations (and suspect that is all it is, an expectation).

 

[BMXTRIX]

The wiring seems like it is wrong from the start.

There is no negative connection in an unbalanced signal. There is signal (+) and ground. If an amplifier is wired with left on positive and right on negative, then the audio will cancel itself out as the amp flips the signal and sums the two. This often can eliminate vocals and mess significantly with the audio output levels.

I wouldn't expect anything more serious in terms of signal degradation.

If the incoming audio is mono, then the signal should be signal (center conductor) to + and ground (outer wire) to the ground connection. I would expect if this is for LFE, then it is a mono output from the source.

I assume that the two RCA jacks are connected to the LFE outputs of the Marantz, and that the amplifier then has the signal (center) on the two + connections on the amp. One RCA on one input, then the second RCA on the other input. Either move the ground to the ground connection, or jumper the ground connection to the two negative connections to get a solid signal.

I wouldn't expect a huge jump by putting a unbalanced to balanced converter in line with the amplifier as we aren't dealing with a mic level signal here.