Balanced Instrument Cable?

[nschroe1]

I understand that instrument cables are unbalanced and generally have a conductor and a shield, whereas a microphone cable (generally) has two conductors and a shield(balanced). Balanced cables can travel much further and have much less interference because the noise is cancelled out in the end. This much I understand. I am simply wondering what the benefit is to creating guitars and guitar amps with unbalanced connections? Everything seems to point towards balanced connections being a better choice. Why don't people make guitars that can use balanced connections? Is there a benefit to sending signals unbalanced?

[Mr.Grumpy]

There have been a few instruments made with balanced outputs, the Les Paul recording model being one that I know of. I guess it's intended to go straight to a recording console for that surgically-clean jazz tone. I've seen some high-end bass guitars with balanced outs too.

 

I think the big reason electric guitars and basses are unbalanced is because of lower cost and tradition. The first electric guitars used unbalanced high-impedance cables, and the standard never really changed from the late 40's to today. Noise wasn't a big concern back then because guitar amps were little more than beefed-up radios.

[nschroe1]

Ok, but you agree that creating guitars and guitar amps with balanced outputs and inputs would indeed reduce noise and ultimately be better, even though it would involve everything to transfer over to have compatibility I suppose.

 

And one other thing, do you know if you can balance an audio signal using only passive elements?

[WRGKMC]

Yes, you can use small high to low transformers and convert the high impediance signal of the guitar to low impediance, send it over a mic cable, then convert it back to high impediance before the amp. There will be gain losses though.

 

All amps amplify with high impediance. The inputs on most mixers convert the signal from low to high before the signal is amplified. Inside a dynamic mic there is also a transformer. The signal a mic diaphram creates is high impediance, it gets converted to low bu the transformer in the mic, gets sent balanced over a low z cable then converted back to high Z for amplification either through a transformer or electronically. I've even seen mixers that simply ground one side of the signal and turn the low Z cord into a hi Z cable.

 

In a studio you often use DI boxes to do this conversion. You can also use this for your guitar. http://www.parts-express.com/pe/showdetl.cfm?Partnumber=240-398 and this for your amp http://www.parts-express.com/pe/showdetl.cfm?Partnumber=240-396 You may have to switch a jack on one end of the mic cable. Unless you're running over 50' it really makes no sence to do the low Z thing. The thing you loose with distance is high frequency.

 

An amp has a trebble knob that can make up for any attenuation a cable might produce due to capacitence. Noise is not tha main problem running high impediance, Capacitence and high frequency loss is. If you have a noisey high Z cable under 25' its because its a crappy cord, not because its the technology running high Z

 

Even then you can used a buffered preamp to make up for losses. I have a few guitars I installed preamps in. They have very low battery drainage and a battery will last for a year. The boost will overcome any losses a high impediance cable might introduce. With a highly shielded cable of 95% and good quality copper, Any noise induced into the signal will likely get introduced before or after the cord. Converting to low impediance wont help that.

 

Again, In my opinion, converting to low impediance is a waste of time. I've used it recording when sitting playing in a control room in another part of a building, and I've used it on stage playing through the a PA system that was a few hundred feet away in the balcony as well. You could even go wireless and still have great tone. Noise just isnt an issue here unless you're using crappy High Z cords, that noise has other sources.

[nschroe1]

Ok I understand that it doesn't make much sense to do the conversions and all, but is there a reason (other than its just because its what people have always done) that guitars and amplifiers are built to handle hi-z inputs and outputs. Is it tougher to build guitars and amps that can do that really?

[onelife]

 

Ok I understand that it doesn't make much sense to do the conversions and all, but is there a reason (other than its just because its what people have always done) that guitars and amplifiers are built to handle hi-z inputs and outputs. Is it tougher to build guitars and amps that can do that really?

 

 

It really comes down to Ohm's Law and the relationship between electricity and magnetism.

 

If you move a coil of wire in a magnetic field, it will induce an electric current in the coil of wire. An electric guitar pickup uses this but the coil remains stationary. The field produced by the magnets in the pickup is altered by the vibration of the string causing the field to move in relation to the coil. When the current generated passed through a resistance, a voltage is generated across that resistance. Ohm's Law describes the relationship between voltage, current and resistance. The higher the resistance for a given amount of current, the higher the voltage produced across the resistance will be.

 

Impedance is a slightly more complicated version of resistance. To simplify, resistance applies to direct current and impedance applies to alternating current. The main difference being that impedance is frequency dependent.

 

As we all know, the early guitar amplifiers were vacuum tube driven. Tubes are voltage controlled devices. To get a workable voltage out of something as small as a guitar pickup (you don't wand big heavy magnets and coils of wire in your guitar) a high impedance is required because of the low current output by the pickup.

 

If you've ever tried to plug your guitar into your stereo amplifier's aux inputs, you've heard what happens when the input impedance of the amplifier is too low for the pickup - the sound is mushy and distorted.

[nschroe1]

well being an electrical engineering student I am very familiar with everything that you speak of, so I suppose I can see how that makes sense. Thank you very much. I guess it would only make sense with an active pickup. Thanks

[onelife]

That is why low impedance pickups are usually active. The active circuit acts as a buffer and a bit of a boost. As WRGKMC mentioned, you could match impedance with transformers but that would result in noticeable loss of signal strength and perhaps even color the sound.

 

I would also like to add that the tube itself, because there is no actual current flow into the control grid, has a virtual infinite input impedance. There are resistors used on the input of a tube amp and that is what actually determines the impedance of the amplifier.

 

A normal transistor is a current driven device and has a much lower input impedance. FETs (Field Effect Transistors), like tubes, are voltage controlled and are usually used as the front end of a solid state guitar amp. They have other tube characteristics as well and were used in the early distortion circuits of SS amps.

[WRGKMC]

Onelife pretty much stated it. Amps are high impediance, and unless you need to transmit the signal long distance, its best to leave the signal high unless the the diatance running high begins to degrade the frequency responce. Then the conversion to Low and back would begin to have benifits.

 

I have seen acoustic guitars with low Z setups. The conversion is done via the preamp board and allows you to plug into a PA direct. In that case a Piezo or actual low impediance mic mounted inside the guitar would benifit from the low impediance. Acoustics have a much wider frequency responce than an electric getting up into the 10~12K frequency range.

 

An electric guitar pickup tops out iin the 5~8K range for its highest freqiencies. An electric can take quite a bit of capacitence from a longer cable before the high frequency loss works itself down from 20K to start affecting an electric.