Input impedence mismatch?

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Kayne k
2011-04-04
2013-05-28
  • Kayne k
    Kayne k
    2011-04-04

    Hi,

    Just wondering if I should use straight cables in to rakarrack for best results or buy something like the maudio junk where you plug your 1/4" jack into a usb cable.  

    Issue i keep having..  lower 3 strings causes rakarrack to auttomatically attenuate volume a few dbs and its very noticable when your playing with heavy distortion (usually around tweaking the heck out of the Shall2) effects.

    Maybe somoene seen this before and can point me in the right direction.  I have almost tweaked the tones where I like them but this is driving me nuts.

    fury

     
  • Transmogrifox
    Transmogrifox
    2011-04-06

    You can plug direct into a sound card mic or line input.  You will have the best results for noise and sound quality if you use a preamp to drive the input impedance.  I built a little preamp into an altoids can…but  then, I am a DIY electronics geek.  I would think you can get a suitable preamp for less than most audio cards.  Even if you have a stompbox with active bypass (like most Boss pedals), then you can use that as your preamp in bypass mode.  Those pedals have proper impedance matching: high input Z for guitar, and low output Z with some drive for the line input on a sound card.

    About attenuating volume with lower 3 strings:  You are likely activating the output limiter.  In 0.5.8, this limits at 0dB, which is ideal for recording as it avoids ugly distortion.  In 0.6.2 the limiter was improved. 

    Watch the lmt and clip LED indicators at the top of the main Rakarrack GUI as you play.  If these ever turn on, then you need to reduce the output volume in Rakarrack, and boost it somewhere else (like your alsamixer).  If the output level is set so that the lmt or clip led's just barely flash on occasion, then you will be using full scale audio signal that won't cause your sound card or recording program to clip.

    In recent development version of Rakarrack (git repository - build from source) there is an option to increase this automatic limit level to +6dB so you can provide a little more boost. I have noticed my sound card usually clips when I allow the output to go to 6dB, so I personally like it to limit at 0dB and back off the level of my FX so it fits within that range.

    Big full distortion sounds will cause the most audible ducking because these signals have a lot of power - and this is translated to heavier limiting, which causes a longer recovery time.

    Take care,
    Transmogrifox

     
  • Kayne k
    Kayne k
    2011-04-06

    Ok.  Im sure I can google tjhose schematics… if its like most preamps its probably a transister or two and a hand ful of small parts not incredibly envolved.

    I've changed the order around its only on some presets.   So i wonder.. I dont really have a real amp to drive.. Just been using the PC.  I have crappy little solid state  I could drive but have yet to get the tube amp.  

    So with that being said,  I wonder if its a combination of what you are saying and the little 20W altec lansing setup.  But IT still sounds fuller than running it through my crappy line six clean.   I hate that amp, the one everyone hates.

    Or do you drive some kind of studio audio system?

     
  • Kayne k
    Kayne k
    2011-04-06

    That limiter setting helped alot..  

     
  • Transmogrifox
    Transmogrifox
    2011-04-07

    I'm glad the limiter setting helped.

    As you have guessed, the preamp is really simple.  Mine is pretty much an op amp, a few resistors & capacitors and an altoids tin :)  If you know basic electronics, then just make a simple voltage follower with the op amp, and that will do it - Input impedance > 47k (I recommend 470k) and maybe put a 600 ohm resistor in series with the output - that helps prevent the outgoing line from acting like an antenna for radio interference.

    DIYstompboxes.com forum can help if you aren't very experienced with electronics.

     
  • Kayne k
    Kayne k
    2011-04-07

    RFI is bad :D