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Guitar rig: Using a receiver instead of an amp head?

Discussion in 'Sound Science' started by jmrogers, Aug 29, 2011.
  1. jmrogers
    Alright, what does a receiver do?
    Put simply, a receiver has two main functions: firstly, it amplifies the sound so it can be fed to your speakers, and secondly, it allows you to select the audio and video you wish to watch.  
    Alright, and what does an amplifier do?  
    Generally, an amplifier or simply amp, is a device for increasing the power of a signal.
    Alright, and what does a guitar amplifier do?
    A guitar amplifier (or guitar amp) is an electronic amplifier designed to make the signal of an electric or acoustic guitar louder so that it will produce sound through a loudspeaker. Most guitar amplifiers can also modify the instrument's tone by emphasizing or de-emphasizing certain frequencies and adding electronic effects.
    Okay, so I understand that a receiver has many of the same functions as an amplifier.  Albeit on a receiver, tonal controls are limited, and certain inputs are limited, is there really that much difference between using a receiver and an amplifier for playing guitar?
    The past few weeks my setup has been:  Epiphone Les Paul > Digitech Multi-effects Pedal > Ipod Cord > Receiver > Speakers.
    Things have been sounding great so far.  I have no distortion/buzz and enough power for my liking.  Tonal controls (equalization) are limited on my receiver, but an equalization pedal or equalizer are an option to better shape my tone.
    I play lots of ambient music, so power isn't too big of an issue for me.  What I need to know is, what would I benefit from a combo amplifer, or an amp head?
  2. geetar7
    Hi jmrogers,
    assuming you are working with a passive guitar (i.e., there are no batteries in your guitar)....
    I am not directly answering your question, but I think one important thing to keep in mind when talking about the need to amplify a guitar is the need for a high impedance input.  A good guitar amp, or preamp, will have a very high input impedance of about 1M Ohm (1,000,000 Ohms).  There are 2 reasons for this:
    1) A passive guitar has a high output impedance, approximately 100k Ohm, or greater.  Varies with guitar model/pickups.
    2) A passive guitar is a highly inductive source.
    If an amp does not have a very high input impedance, the guitar's upper frequencies will be increasingly attenuated with an increasingly longer guitar cable.  This the due to the combination of the capacitance in the cable, and the inductance of the guitar pickups.  In other words, it is like EQ'ing the high frequencies DOWN.  Some guitarists would say this kind of amp "sucks tone".
    So, with a "receiver" type amp, you will need to keep your guitar cable short, approximately on the order of 6 feet or less.  Again, it depends.
    For more in depth reading ..  http://whirlwindusa.com/support/tech-articles/high-and-low-impedance-signals/.
    Addressing your actual question... you could possibly get a guitar preamp, one that has no power amp, and use the line-level output to feed your receiver.
  3. jmrogers
    I appreciate the response.  
    My guitar is passive.  It has two humbucker pickups. 
    My speakers have an impedance of 8 ohms.
    Now in comparison to other mini practice amps I've used (100-200$ range), my receiver setup far out ways what I could accomplish with those amps.  Albeit they were combo amps; so the speakers were pretty garbage in them.  
    I get what you're saying about higher frequencies.  I've noticed that my treble sounds pretty thin and less powerful than other amps.  
    But if matching impedance towards the speakers is the thing that is important, does it matter where in the line the impedance is from?  Like you were saying I have a passive guitar so the output is low impedance, but what if I got an active pickup.  Does this lower or increase the impedance?  
    If you want to hear my music, you can check it out here.  I recorded songs 3 and 4 with this setup.  Song 3 I used a condenser microphone and song 4 I used a mac microphone.  
  4. jmrogers
    So yeah, if there is anything you think I could use in terms of tone or power or just my sound in general, any advice would be appreciated : )  
  5. geetar7

    1) a passive guitar has a HIGH output impedance.  Therefore, to prevent some signal loss, you need to plug the guitar in to an input (i.e., preamp, guitar amp, etc.) with a much higher impedance than the guitar.  Your receiver is designed for line-level signals, and therefore has an input impedance of approximately 10k Ohm (10,000 Ohms).  10k is 100 times less than 1M Ohm, and that makes all the difference to a passive guitar.
    An active pick-up will look more (if not exactly) like a line-level output device, and therefore have a significantly lower output impedance.  This would be more compatible with your receiver.  I am not familiar with all of the variations of active pick-ups, so please double check specs.
    2) Matching the guitar to the speaker impedance is incorrect.  (sorry if that sounds blunt.  It is not meant to be. :)
    Signal chain is this:
    passive guitar --> preamp --> effects (e.g., distortion, chorus, etc.) --> speaker amp  --> speakers
    A regular guitar amp (e.g., Fender, Line 6, etc) can contain the entire signal chain above, sans guitar.  However, based on my understanding of your setup, you already have "speaker amp --> speakers"; that means you just need a preamp.  Also, keep in mind many FX boxes/pedals are designed to plug the guitar directly in to them, albeit, not necessarily as versatile as a dedicated preamp.
    A guitar is kinda like a microphone in the sense that you need a device that is specifically designed to achieve optimal signal (i.e., preamp).  Otherwise, you face limitations, like high frequency roll-off.
  6. jmrogers
    So if I get an EMG pickup for example, it will serve as a preamp?  I'm guessing if it does then that will solve my high frequency roll-off problem and cause less strain on my receiver.

  7. geetar7
    Hi jmrogers,
    Let's backup for a moment.  Do you like your guitar's sound?  I'm not referring to your system, rather just your guitar.  Or do you not fully know it because your setup has imposed some limitations (e.g, hi freq roll-off), making it difficult to fully ascertain the depth of your guitar's tone?
  8. barleyguy
    The simplest solution, if you want to use a stereo to amplify a guitar, is to buy a direct box.  It converts from High Impedence to mic and/or line level, and many direct boxes also have amp modeling.  Just go to a pro audio site (my favorite is AmericanMusical.com) and search for "Direct Box".  Prices range from $25 up to $1000.
    Also, there are many guitar pedals and "stomp boxes" that have line outputs built in.  You get the added benefit of whatever wacky thing the pedal does.  (EDIT: The Digitech you're already using has a line output, which is one of reasons it's sounding good.)
  9. jmrogers
    Yeah my setup does sound pretty good right now.  When I play the "e" string though the high frequencies usually have a weak signal.  I have an Epiphone Les Paul, so maybe it has to do with the build of the guitar.
    That makes sense, because when I go straight from my guitar to the receiver it sounds really thin and quiet but when I add my Digitech into the line I get a lot better sound.  Would it be better to get a Direct Box than use the line output from the Digitech pedal?  
  10. barleyguy

    It depends on the direct box.  Your Digitech is probably better than a cheap direct box, but if you got into something higher end (the pro quality direct boxes generally start in the $125 range) the direct box would sound better than the Digitech. 
    Also, if you look for a direct box, make sure you get one with a line level output.  Some only have a mic level output, and are designed to go into the mic preamps of a mixer board.

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