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Old 15th September 2012 , 07:34 PM
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Default Mixer 1/4" inputs



On page 89 of Home Recording for Musicians it talks about the 3 basic types of mixer inputs: balanced XLR for mics, 1/4" jack (TS or TSR) for line or instrument, and 1/4" Hi-Z (TS) for the home recordist to plug his electric guitar, bass, fiddle or anything with a pickup.

I am curious as to the difference between a 1/4" instrument input and a 1/4" input for guitars, basses and fiddles - which I have always considered to be instruments.

Is the author confused or has he only confused me? DO you know what he is trying to say? And if so, could you tell me? Thanks.
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Old 16th September 2012 , 02:30 PM
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Default TS, TRS and XLR nightmares

Hi. the majority of mixing desks have all three types of input by way of XLR (balanced input/output) and 1/4" Jack (usually TRS. Tip - Ring - Sleeve).

Pin2 and 3 of the XLR are signal and the preamplifier senses the difference between pins 2 +ve signal and 3 -ve signal, amplifying the difference ensures low noise on long cable runs. The same is for TRS jacks. Tip is +ve signal Ring is -ve signal and Sleeve is ground/earth/chassis etc.

If you have a long cable run, hum and unwanted noise can be picked up. By using a balanced cable with either TRS or XLR connections, the noise or hum is equal on +ve and -ve leads. The preamplifier rejects the noise as it only amplifies the balanced signal's differences.

If pin 2 has a positive peak and pin 3 has a negative peak, the preamplifier will produce a large peak output. If pin 2 has a +ve peak and pin 3 also has a +ve peak, there will be no output from the preamplifier.

If you use a 1/4" jack with just Tip (unbalanced signal) and Sleeve (unbalanced ground/earth/chassis etc). This is ideal for high impedance instruments and microphones with a short cable run.

TRS jacks are also used as Inserts for mixing desk effect units and graphic equalizers etc. Tip is usually send and Ring is usually return.

I hope this information is useful.
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Old 16th September 2012 , 07:02 PM
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Not being new to these things and thanks especially to PA experience where cable runs are long I already know what you said, although it was a useful reminder, so thanks.

I am only confused about the difference between line/instrument and Hi-Z inputs because I thought they were the same thing. Is this is the difference between +10/-4 (db or v, I've forgotten)?
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Old 17th September 2012 , 11:56 AM
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As far as I am aware, Line input is around 600Ohms impedance and a level of about 700mV for full power. Instrument outputs vary from a few millivolts at 47K impedance (magnetic guitar pickup) to a few volts at 2Meg Ohm or more impedance (Peizo Cell in a kick box etc).
Line and Instrument inputs are effectively the same thing, just less or more gain from an unbalanced jack socket, except as you quite rightly state the gain requirements for instruments needs to be higher than line level.
Most mixing desks allow for 0dB up to 60bB gain and some PAD switches reduce the gain between -10dB and -30dB. Other PAD switches reduce the sensitivity between +4dB and -10dB, that serves as a Mic/Line selector without the need to adjust the gain pot so far.
Hope that explains it a bit better.
Regards.
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Old 17th September 2012 , 03:59 PM
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Quote:
Originally Posted by Harleyjon View Post
Hope that explains it a bit better.
It does. Thanks. It might have helped if I was clearer with my initial query.
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Old 18th September 2012 , 10:28 AM
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Probably my fault as being dyslexic, I don't make myself clear or read the correct meaning of a sentence. Pleased to help where I can.
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Old 23rd December 2014 , 02:58 AM
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Default Mixer 1/4" i

Just to clarify, the 18i20 has 3 input modes. The XLR input is Mic level only, but the when connecting via 1/4" you are accessing a line level input. These do share some circuitry, but the 1/4 input is a true line input stage and is very transparent. Inputs 1 and 2 also have an instrument mode on the 1/4" portion of the input.
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