XLR input VS. 1/4 inch input...any difference?
 

Hi all!

I own a Fishman Loudbox Performer amp and on channel two there is a choice of the regular 1/4 inch input and an XLR input. Can anyone tell me if there is any signal difference between them?

Thanks!

Tayloralf, there is a difference in signal to noise ratio and gain. The XLR will have higher signal to noise ratio and higher gain than a plain 1/4". This means the XLR will sound louder and cleaner than the 1/4" even if the source guitar output is unchanged.

Ken

At the risk of over simplifying, the xlr is for a microphone.
Other than that, I don't know.

Tayloralf, Orphan may be correct in that the XLR connection you see may only be for a mic. I am not familiar with that amp so i can only speak about the relative merits between a XLR and 1/4". Since some guitars output balanced signals (ie., Taylor A/E guitars output balanced signal) these guitars can be directly connected to a PA system (XLR connection). Note though the key here is that the line is balanced or unbalanced and not really the connector type (XLR vs 1/4). I dont know if your amp's 1/4" is a balanced or unbalanced line but i suspect it is unbalanced. XLR is by its design a balanced line. But there are 1/4" balanced lines too (ie., TRS 1/4" is balanced and TS 1/4" is unbalanced). If you do some search on this forum for TRS or XLR you should see more discussion on this. 2 cents.

Ken

OK, I'll add my $.02. It's all about matching the impedance of the input to the impedance of the source. (Impedance is kind of like electrical resistance.)

XLR is a low-impedance balanced connector. Professional-type microphones are low impedance. The advangages are that you can use a really, really long cable to hook things up without picking up a lot of noise or losing any of the signal.

On an acoustic amp, the 1/4" input is typically very high impedance. This allows you to hook up a high impedance source, like a piezo-based pickup without a preamp, e.g. K&K Pure Western, etc. The high impedance input puts almost no load on the signal source, so the piezo doesn't sound as brittle and quacky. Even a passive magnetic pickup sounds better hooked to a high impedance input. The downside is that long cables can get noisy or start to sound bad. As opposed to an acoustic amp, the 1/4" inputs on a typical mixer aren't all that high impedance. If you need to hook up a high impedance source to an XLR input, or to a mixer, it's best to use preamp or an active DI box (one that needs power) in between the source and the input.

If your guitar pickup has a battery, you could probably hook up to either input without a problem . . . but if you're going to need something like a 50 foot cable, the XLR may give you better results.

The XLR jack on the Loudbox Performer is intended for a microphone signal. It is not for a signal coming from a preamplified guitar pickup. If your guitar uses a battery, then its signal is preamplified. See page six of the amplifier's manual.

I have hooked up my pre-amped Ibeam equipped guitars directly into an XLR microphone input on at least one occasion, with nothing more than a TRS to XLR adapter plug . . . and no impedance matching transformer. The results were quite good. LR baggs pretty much says that their active pickups can plug right into almost any input with any reasonable length of cable . . . and I think that the Taylor ES is pretty much the same. I'm not so sure about other brands. Plugging a passive pickup into an XLR input would almost certainly sound terrible.

It is possible, but unlikely, that the Loudbox mic input is somehow different than other mic inputs. I will defer to those who have more specific knowledge than I do.

As a teenager, I plugged my Silvertone solid body into the tone arm of a record player by rapping small gauge wire around the 1/4 inch jack of my guitar cable and running the wires to the pins of the phono cartridge. It worked even though the the record player's circuitry was never designed for the output of an electric guitar and the manufacturer would have advised against it.

Plugging in a preamplfied signal into a high gain circuit increases the liklihood of clipping, introduces more noise and may adversely affect tone. Still, some pickup systems may happen to sound good through a particular mic input anyway.

I don't know about the Loudbox, but most XLR inputs have a gain control that can be adjusted to compensate for a variety of input signals, and of course the guitar output level can usually be controlled by its own volume contol. Impedance matching is the imore difficult thing, and most guitar preamps have a pretty low output impedance. As long as the impedance of the input is at least ten times that of the source, it usually works OK. I have a compact passive DI with an impedance matching transformer that I usually use anyway, because it also acts as a jack adapter, but sometimes there are more guitars than DI's. Active DI boxes, those meant for plugging into an XLR input, have a signal that's at least as hot as any of my built in guitar preamps . . . at least the ones I've used.

Impedance:
High into low, it won't go.
Low into high, it will fly.

Each channel has a gain control plus a 10 dB attenuation switch so one should engage the switch if one were going to plug a guitar into the XLR input and turn the gain down very low.

Nominal Input Level

1/4 inch input:.. -20dBV (-10dBV with 10dB attenuation switch)
XLR input:........ -40dBV (-30dBV with 10dB pad attenuation switch)

Maximum Recommended Input Level:

1/4 inch input:.....6dBV
XLR input:........ -14dBV

Input impedance

1/4 inch input:..10,000 Ohms
XLR input:.........2,400 Ohms

Thanks, Herb!

Wow, the loudbox input impedance for the 1/4" input is really low. A typical 1/4" input on a mixer is around 30,000 Ohms, and my Behringer Ultracoustic amp has a 10 million Ohm input impedance on the guitar channel.

The K&K Pure Western pickup requires a 500,000 Ohm input, minimum, so I guess you couldn't even use it with the Loudbox without a separate preamp.

Impedance compatibility is important, but that's not all.

Look at the nominal input and maximum input ratings in Herb's post above. Inputs operate best at a certain voltage (nominal) and can only work within certain voltages (range). If the pickup's output range matches that preamp input range, all is good (as far as this particular parameter is concerned), otherwise things are not so good.