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ISO: Op-Amp Boost-Only Design

Discussion in 'Effects [BG]' started by EricssonB, Dec 20, 2013.

  1. EricssonB

    EricssonB Supporting Member

    Apr 5, 2011
    CoSpgs, CO.
    I'm searching for a schematic/layout for a *transparent boost-only circuit based around an op-amp. I tried a of couple transistors-based circuits, but they weren't performing as I was expecting. The last build had its guts ripped out and is now a passive attenuator with a 500k ohm pot, dimming LEDs and 3PDT wiring -- love it for guitar.

    I've got packs of TL0XX op-amps sitting around, so if I can chuck one on a board, that'd be swell.

    Know of any? I've searched around, but didn't find what I was looking for.

    *as transparent as possible.
  2. dune2k


    Sep 26, 2009
    MXR Microamp.
    Put in electrolytic caps that are rated for 18V+ and run it at 18V. Doesn't get more transparent than this.
  3. MagicMan_841


    May 29, 2005
    Ithaca, NY
  4. Is your google broken? :) I found this pretty quickly, it's a minimal parts count op-amp buffer.


    I'm sure it will work fine as drawn for bass, but if you're concerned about bass rolloff you could substitute a 220nF cap on the input for the 100nF that's specified. If you're OCD about "tone" you might want to put in non-polarized 10µF electrolytic caps in place of the standard polarized electrolytics. I would also add power supply filtering and a polarity protection diode if this is going to be built into a stompbox.
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  6. EricssonB

    EricssonB Supporting Member

    Apr 5, 2011
    CoSpgs, CO.
    My Google is only partial; I'm at work and the best websites are blacklisted.

    Thanks for the links, guys. I'll go through this list when I get home -- none of these damned links work here. :rollno:

    I am concerned about frequency loss, so I'll be considering those mods.

    This one seems to work! Yeah, same website, but .com instead of .ca works.
  7. mrbell321


    Mar 26, 2012
    N. Colorado
    I recommend looking at the datasheet for whatever op amp you plan on using. There is usually a reference schematic in there that will be minimal parts and very transparent. You might need to change some of the caps for the right frequency range, but it'd be a good place to start.
  8. dune2k


    Sep 26, 2009
    If you don't have a way to run pedals at 18V, try getting your hands on an ICL7660S or a MAX1044 and slap them in there used as voltage doublers (schematic can be found on the net, e.g. in their datasheets).

    You don't need non-polarized caps in there btw, good polarized ones will do the trick as well, although using a non-electolytic 1uF cap on the input would work just as well. I doubt one can hear the difference between those (1uF, 10uF, polarized/non-polarized/non-electrolytic) though.

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