Balanced to unbalanced connections

[2moggy]

___Hi___, not new here, but my first post. First a small sketch; I'm electronics engineer and like to combine old systems ( Dynaco 70 tube amp, Sansui AU 919 & AU 9900 amp + B&W DM6 + Sony 557ESD + vinyl player) together with newer technology ( PC HDD drive with FLAC format music, Halide USB to RCA DAC hd and some Behringer toys ).

So lately i bought myself these secondhand toys Behringer (SRC2496,MDX2600,DSP2024,PEQ2200...) on the cheap.... And suddenly I'm stuck with electrical connectivity incompatibility ..... The old unbalanced vs balanced hot topic..... I understand all their advantages and disadvantages, I think i know something about their electrical levels and shielding and what not, BUT.... I cannot seem to find a solution for a connection from unbalanced to balanced. Vice versa there seems to be a lot of options; staying on my playground; there is the Behringer DI20, DI4000 and DI800 for instance... but they only seem to transform from unbalanced to balanced, not the other way around...

-> Sooo; Searching for an easy and / or cheap way to connect my new toys (the "Behringer-Bunch") to my old school cd player, amplifiers,... via active or passive DI , but i need both directions; unbalanced to balanced and balanced to unbalanced! Searched plenty around here & internet but found no satisfying answer. ---_____Thanks in advance!_____

 

[iQ Speakers]

Hi Maplin do both, Macspur i belive bought some yesterday. Have a look at these.

http://www.maplin.co.uk/p/neutrik-na2fpmf-phono-socket-to-3-pole-xlr-female-n27gb

http://www.maplin.co.uk/p/neutrik-na2mpmf-xlr-plug-to-phono-socket-adapter-n64fl

 

[andyjm]

The best way to balance and unbalance is to use a transformer balun. These are available from pro audio suppliers. You can achieve a similar outcome by wiring the connectors as follows. This isn't perfect as depending on the design of the circuitry the levels can be a bit odd, and it does remove any benefit of the link that is balanced. It is however widely used.

Balanced has three connections, screen, +, -

Unbalanced has two connections, screen, signal.

To connect an unbalanced source to a balanced input:

Unbalanced Balanced

Screen -> Screen

Screen -> -

Signal -> +

The other way is a bit more complex as it depends on the output circuit topology. If an active differential output (most are these days), to connect a balanced source to an unbalanced input:

Balanced Unbalanced

Screen -> Screen

+ -> Signal

- Not connected

If the output uses a transformer, then you need to use

Balanced Unbalanced

Screen -> Screen

+ -> Signal

- -> Screen

 

[davedotco]

There is also the issue of the '4th connector', the 'shell' of the XLR connector.

This is often connected to the earth pin 1 of the connector but this ties signal ground to chassis ground. I some equipment they are not at all the same thing and getting it wrong can cause an earthing problem, usually manifested as a mains buzz.

It does mean that there is not really a 'standard' for unbalanced > balanced connections, sure the solutions noted above work most of the time, but not necessarily all of the time.

 

[2moggy]

HI, everyone, thanks very much for such informative answers!

It is indeed not an easy matter, also considering also the 4th wire (screen).

Thanks so far for your help!

 

[2moggy]

Hi, what still baffles me, is how a balanced signal (differential voltage not in phase) can be connected to an unbalanced input, with totally different voltage levels and different DC offset as wel...

 

[andyjm]

I guess electronic engineering isn't what it used to be.

There is no DC offset, where would a DC offset come from?

Depending on the topology of the driving circuit, the levels may well be wrong - but not so wrong that it won't work. Probably have to turn the volume down, but unless the input stage on the amp gets swamped, you will probably get away with it.

 

[davedotco]

Hi Andyjm.

While you are about, can I trouble you for your thoughts on 'the 4th connection' in balanced cables.

I often use unbalanced out (rca) to balanced in (XLR) and occasionally get a low level buzz, sounds a bit like a 'sawtooth' waveform. I can usually get rid of it by playing with the earth connections, disconnecting the XLR shell from pin 1 usually solves the problem, but seemingly not always.

I am guessing it is all about keeping signal and chassis earth separate but wonder if it might be something to do with the differential inputs......*unknw*

Any thoughts on this?

 

[2moggy]

you're right; i got mixed up with power amp output (to speakers) where DC offset is on the signal when the amp is not properly regulated. (and it was getting late at night)

regarding your statemant "levels may be not so wrong that it won't work" ; when i look up line levels; I find following definitions; a consumer level (RCA) is 0dBu or Vpk 0.447 volts , a professional (XLR) level is +4 dBu or Vpk 1.736 volts. that is a BIG difference to connect, no?

 

[davedotco]

you're right; i got mixed up with power amp output (to speakers) where DC offset is on the signal when the amp is not properly regulated. (and it was getting late at night)

regarding your statemant "levels may be not so wrong that it won't work" ; when i look up line levels; I find following definitions; a consumer level (RCA) is 0dBu or Vpk 0.447 volts , a professional (XLR) level is +4 dBu or Vpk 1.736 volts. that is a BIG difference to connect, no?

Your definition is correct, but few manufacturers stick to those standards, hi-fi and 'pro-sumer' brands like Behringer particularly.

A lot of pro gear will have some form of input gain or 'Trim' controls to make the matching easier, but in any case, the arrival of CD with its standard 2 volt output has pushed hi-fi levels to much higher voltages.

 

[2moggy]

Your definition is correct, but few manufacturers stick to those standards, hi-fi and 'pro-sumer' brands like Behringer particularly. A lot of pro gear will have some form of input gain or 'Trim' controls to make the matching easier, but in any case, the arrival of CD with its standard 2 volt output has pushed hi-fi levels to much higher voltages.

and many other standard line out RCA is 2V too, you're right, i did not consider that. I'm probably trying to be holier than the pope... Well, lesson learned; "standards" is good for theorethical stuff.

Thanks very much for your contribution, you've helped me a lot. I do a lot of engineering, but totally not in this audio field, it's all very new to me. thanks!