Balanced instrument cables?

As lifted from the Rane Glossary:
The IEEE dictionary defines a balanced circuit as "a circuit in which two branches are electrically alike and symmetrical with respect to a common reference point, usually ground." This is the essence of a balanced interconnect. Namely, that two lines are driven equally and oppositely with respect to ground. Normally this also implies that the receiving circuits have matching impedances.

Instruments do not use differential signaling, plus they are high impedance devices.

Link to Rane Glossary

 

No, it would not necessarily be true if the noise were generated in the instrument itself.

I have done balanced pickups and onboard wiring with low impedance passive pickups, then going to a studio mic preamp. This was with close to 600 Ohm Litz wire wound pickups. It worked fine, probably better than fine; it sounded great in fact. The only problem is that it is so non-standard that there's little commercial reality to it.
One of the guys who used to work at Bass Player had a set of J-bass pickups I did this way, and he said the only thing bad about them was that he could hear how bad the strings were on his bass. The clarity is amazing.

 

Thanks, Rick. To expand on Rick's comments, balanced cables help prevent noise from being picked up along the cable's path, but don't eliminate noise from the source circuitry.

The main reasons we don't use balanced cables for instruments are:

A) To balance a signal requires either an active circuit or a large transformer. Not everyone wants an active circuit, and a transformer adds weight, would be hard to fit inside an instrument control cavity, and adds greatly to the cost.

B) Gibson and Fender didn't design their instruments and amps to use balanced lines, and people liked the way those first instruments sounded. Subsequent guitar makers followed their lead, and amp makers designed amps to work with existing instruments.

Les Paul promoted low impedence pickups that did take balanced cables in the early 70s, and even had Gibson make an amp that has low impedence XLR inputs. No one much really bought them, though Les Paul still uses his on stage today.

Even if Rick won't toot his own horn, I will for those who don't know who he is - he is one of the founding guys of Alembic, and Alembic very much used and still uses XLR outputs and low impedence pickups. He's no longer with Alembic, and makes his own beautiful instruments today, but he had a large part in Alembic's progress. Though IIRC he was more on the luthier end and Ron Wickersham (sp?) was doing the low impedence circuitry work.

Please correct me if I'm wrong, Rick. I wish I had the talent to justify using some of your lovely instruments, and sorry if I've gotten drool on some of them at NAMM shows.

 

One thing you can do that has many of the benefits of a balanced connection is to used balanced cable (2 conductor with shield, ala mic cable) like so:

One conductor for positive.

One conductor for ground.

Only connect the shield at one end, tied to the ground connection.

Mark the end of the cable that doesn't have the shield connected. Typically this end will go into the input of the next device, and the connected end goes to the output.

This is called a telescoped shield, and it can work very well at reducing and often eliminating environmental noise in an unbalanced connection. It's a bit pricier than standard single conductor with shield instrument cable, but if noise is an issue it's worth it.

 

Ok, this might sound stupid to the electronician.

What about using each coil of a humbucker separately to feed the branches of an XLR balanced cable ?
Being out of phase, they're technically symetrical signals around a common ground.
Of course there's the impedance issue but a preamp should be able to take care of that.

Don't ask for practical uses, I have no idea.

 

It's not at all a stupid question. If you have a bass with only one humbucker, you could connect it directly to an XLR jack and plug it into a mic pre (if you can find one with a 1M input - some old Neves do) and use a balanced rack EQ for all tonal changes.

The issue is that if you had more than one pickup and wanted onboard controls, it would quickly get very expensive.

And it wouldn't be worth it, since you can have standard humbuckers and shielded standard electronics and a standard cable and a standard high quality amp and get the same sound quality as the balanced but limited theoretical instrument.

 

The transformer in my Passive DI is quite small (IMP2)

If the lines less than 20ft, theirs no reson to go balenced, esp. if the rest of your gear dosnt run balenced.


Ps: Proper shielding and RF chokes will do you better.

 

Yeah, that sounds pretty stupid. To the best of my knowledge, you have just invented a new word!

- Tim

 

I'm not a fan of the Whirlwind transformers. But good sounding transformers tend to be larger and heavy. Always a tradeoff.