setain
Meter Reader 1st Class
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Post by setain on Jul 12, 2008 16:02:33 GMT -5
I know balanced output is used on microphones to reduce noise/hum, but would this serve any practical use for a guitar? The biggest hurdle I see is finding a transformer to change the phase of the signal. Also, how would the volume control be wired?
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Post by ashcatlt on Jul 12, 2008 21:42:50 GMT -5
Well, it won't reduce any noise that's already in the signal before it gets balanced. The bulk of the noise in the guitar signal comes from the pickups themselves, then the unshielded wiring in the cavities. Compared to that, a well constructed guitar cable adds a minimal amount of noise.
Of course, every little bit helps.
There are other (and some might say better) ways of balancing a signal. The transformer would accomplish the job in a passive manner, sure. Wouldn't be too hard to find, either. Just pull one out of your nearest direct box. Hopefully it'll fit within the cavity.
Now, if you're willing to put a battery inside your guitar*, you could go active. A dual opamp could be used to both buffer and balance the signal. This would have the added benefit of allowing you to choose the optimal impedance to present to your pickups, improving the hi-frequency response of the circuit by essentially taking the cable capacitance out of the equation.
But then there's the question: What are you going to do with it once it leaves the guitar? Wanna use your favorite stompbox? Plug into that vintage tube amp? You may have noticed that these generally don't come in balanced varieties, a fact which has been lamented around these parts once or twice.
* Almost forgot the darn asterisk! There are ways to power the circuit from outside the guitar. Somewhere around here is a buffer circuit built into the barrel of a guitar cable. It gets power from a pedal, I think, and could likely be adapted for this purpose.
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Post by D2o on Jul 13, 2008 9:26:47 GMT -5
I know balanced output is used on microphones to reduce noise/hum, but would this serve any practical use for a guitar? The biggest hurdle I see is finding a transformer to change the phase of the signal. Also, how would the volume control be wired? Good thought, setain. I am not sure that what you're going for here can't be better achieved through good shielding, though. Just to throw a little curve at you, I have come to discover - coincidentally through a similar inquiry - that this 60 Hz interference we're trying to block is not always exactly 60 Hz. It varies depending on the typical demand placed on the system at any given point in time, and - to really confuse the issue - 60 Hz is not universal. JohnH, a very great asset and friend to this forum has to find ways of impeding 50 Hz interference in his neck of the woods.
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Post by sumgai on Jul 13, 2008 12:50:42 GMT -5
As it happens, running an unbalanced signal into a transformer that both splits the phase and lowers the output impedance will reduce some portion of any noise on the input. The theory behind this is a bit hairy, but it works - just ask any in-house soundman worth his/her salt. To test this yourself, you need only insert a impedance-reducing but non-splitting transformer into your signal line. Check the noise at the amplifier's output. Now insert a transformer that also splits the phase, and check the amp's output again. Which lash-up sounded quieter to you? (Be aware, this test assumes the same amp, but that means that it must be able to properly handle both low- and high-impedance input signals.) Actually, while you could, in theory, get a quieter signal with a balanced high-impedance line, you'd still have the tone-loss issues that you get with an unbalanced line (high capacitance, etc.) - balancing the line won't overcome that particular bug-a-boo. Hence, we have both low impedance and split-phase balanced lines feeding signals over a long distance, with very little extraneous noise. (I won't comment on the kind of noise that the microphone picked up intentionally! ) HTH sumgai
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Post by JohnH on Jul 13, 2008 14:28:41 GMT -5
I’ ve been getting my head further around some of these issues over the last three months, due to a practical issue of needing to plug directly into the mixer desk at the rehearsal studio without an amp. This is because I have to travel on public transport to get there, and can’t face up to paying hire fees on the rubbishy amps that they rent.
I use my pedals to get the sound I want ending up with a home-brewed box which adds some cab-sim filtering, and a low impedance output buffer which boosts the signal to line level. Sometimes this goes into the desk line-in directly but in one studio, it sounds better into the balanced mic input via a step-down DI box (ie a passive transformer).
My impressions relative to this thread are:
The DI box transformers are better with an active buffered signal – i think they would load a normal pickup too much if used directly.
Low impedance is great for allowing long cable runs and reducing interference. This can be done with any decent active stage (eg, a tuner pedal, or similar non-true bypass pedal at the front of the chain), or as I do, with a buffer cable or in-built buffer. Les Paul had his LP Recording model, with special pickups wound for low impedance.
For guitar signals, I don’t see much real benefit in going for a balanced signal from the guitar itself. Although this would in theory cut out a little more interference, it would make the output incompatible with just about every device designed to receive a guitar signal. I think there is more residual noise and interference from the pickups anyway, even in a shielded guitar with humbuckers, and this would not be reduced by a balanced cable.
Just random thoughts.....
John
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Post by ashcatlt on Jul 13, 2008 18:37:50 GMT -5
The DI box transformers are better with an active buffered signal – i think they would load a normal pickup too much if used directly. This speaks (somewhat tangentially) to this question. The transformer reflects a multiple of the mic pre's own Z. That Z could be anywhere in a relatively large range, but will still generally multiply up to too little for most pickups. And this: Is a paraphrase of what I said above. Somebody who knows more about this than I agrees.
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Post by gumbo on Jul 14, 2008 8:42:21 GMT -5
JH.. Down here in Shmadelaide (same electricity as yours, only more expensive!), we use the Good Ol' Behringer DI-100's (the band has a case of them) to wack all sorts of things direct into the PA at practice (including my Roland-Ready Strat at times)..works fine! ;D The amount of gear we tote to rehearsals is important..we're all too old to tire ourselves out before the gigs! We suffer from a six-piece affair where everyone is a multi-instumentalist...on stage we are using all of our 24 channels and DI everything..apart from the obvious FOH mix, it's the only way we can get all the stuff in the foldback so that us geriatrics can hear each other Behringer also make (as I'm sure you know) a version of their DI-100 that is more electric-guitar-friendly, but we never got around to buying any, and are happy with what we are able to achieve currently... While the 100's all have a 9-volt in them for emergencies and individual other use as and where necessary, on stage and at practice we run all of the units off the phantom power from the mixing desk and have found this a reliable system for the past couple of years we have been set up this way. PM me if you want/need more info.. Cheers Gumbo
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