Op-amp, diode, Transistor, FET????

Discussion in 'Effects, Pedals, Strings & Things' started by centsmin, May 3, 2008.

  1. centsmin

    centsmin Member

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    This questions if for all of you builders and tweakers that really know about the design of overdrives......

    I've been wading my way through all the pedals we have to choose from. Definatley lots of kool choices out there. I'm glad for the variety that we have from all the great small builders out there. But I'll tell ya, at the end of the day, I'm just looking for something that works for my rig and I'd like to be able to focus my search.

    I don't know squat about electronics so I'm not goint to try to ask questions in terms of actual design. However, electronic terms do show up the marketing liturature of pedals quite frequently so I was wondering if I can use that to my advantage?

    I know that tube screamers are "op-amp" pedals and that the 4558 chip is an op-amp. Do all op-amp overdrives have little IC chips? If I see an IC chip can I assume its op-amp? Are all TS designs op-amps? I ask becuse after trying several overdrives/boosts/distortions/fuzz, I found that I tend to prefer the ones that don't have little chips. I've often heard the term "clipping diodes" used along side "op-amp" as well.

    I don't really dig TS or their clones as much as I like ones that are marketed as having "Transistors"(germanium, silicon, JFET). I tend like things that are reffered to as beeing germanium or silcon fuzz, germainum or silicon boosters, JFET boosters, cascading FET stages etc....... The marketing of these types of pedals never seem to mention op-amps or clipping diodes?

    I don't know what's going on electircally, and I know that fuzz and JFET boost doesn't sound alike, I just know that these types of pedals have something I like. If i'm having trouble geting to like the distortion characteristics of a pedal, 9 out 10 times I pop it open and find a little IC chip in there.

    I guess I'm asking you guys to validate these five assumptions? Then I could use these as criterian to narrow my search.

    1) TS clone = op-amp = IC chip

    2) Op-amp always means there's an IC chip in there

    3) clipping diode has something to do with op-amp pedals?

    4) If it doesn' have a chip inside, its some type of Silicon, Germanium, JFET, or MOSFET design.

    5) If its a Silicon, Germanium, JFET, or MOSFET design, it doesn't use op-amps or clipping diodes.

    Thanks for the help,

    Yours Truely,

    Confuzed
     
  2. sabby

    sabby Member

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    I was thinking of looking for this thread again, and you gave me the impetus to do so. Thanks. Check post #6.
     
  3. Jack DeVille

    Jack DeVille Member

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    Confuzed,

    this is a pretty broad subject to begin, and quite frankly, i think i'm a lot better at explaining stuff than my mind can punch into the keyboard, so i'll do what i can and give you a few resources to explore...

    1. ts clone = op amp = ic chip
    yes, no. here's a quick n dirty explanation courtesy of wikipedia:
    http://en.wikipedia.org/wiki/Operational_amplifier
    as previously stated, op amps do not necessarily come as ics.
    http://www.uoguelph.ca/~antoon/gadgets/741/741.html
    here are a few ideas for uses incorporating op amps:
    http://www.national.com/an/AN/AN-31.pdf
    the list continues...

    2. in short: usually. not all the time, everytime, but mostly, yes.

    3. again, in short, usually. diodes are pretty f-ing neat. this page has a pretty good tutorial detailing how diodes work:
    http://www-g.eng.cam.ac.uk/mmg/teaching/linearcircuits/diode.html
    clipping diodes are often used in guitar pedals to ..... clip the signal! once the amplitude of the sine wave reaches the forward bias voltage of the diode most of the signal above that threshold will be shunted to ground creating a "clipped" waveform.
    this page does a MUCH better job explaining this than i ever will:
    http://privatewww.essex.ac.uk/~mpthak/Distortion/

    4 & 5: not exactly be cause there are MOSFET, FET and JFET based op amp ics available....

    i hope these short answers help out a little... they're a little short, but so am i!
    :BEER
     
  4. fr8_trane

    fr8_trane Member

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    1) TS clone = op-amp = IC chip

    An operational amplifier IS a specific type of integrated circuit. The very popular TS and its clones are defined by the use of an opamp with clipping diodes in the feedback loop. There are also pedals that use an op amp with clipping diodes to ground. The rat and the distortion + being the standards.

    2) Op-amp always means there's an IC chip in there.

    In general yes but ALWAYS is a strong word. You could build an op amp from discrete components but I don't know why you would when an IC does it smaller, cheaper and faster.

    3) clipping diode has something to do with op-amp pedals?

    See very basic explanation above.

    4) If it doesn' have a chip inside, its some type of Silicon, Germanium, JFET, or MOSFET design.

    Yes and no. There are some pedals that actually derive their distortion soley from the IC chip. The EH hot tubes for example use a CMOS IC (mosfet based) to generated multiple stages of gain with no diodes or discrete transistors. Also some pedals may have an IC to perform some separate function but derive their OD strictly from discrete transistors. Another setup uses transistors in place of clipping diodes in the feedback loop of an op-amp. The FD II mosfet is a good example of this. Vintage Transistor based pedals would be from the treble booster, fuzz face, tone-bender, Big Muff continuum (although there was an IC version of the big muff to further complicate things). There is a new breed of transistor based pedals (the menatone pedals for instance) that uses transistors as direct substitutes for tubes in pedal based recreations of actual tube amp circuits. The Box of rock and BSIAB use cascaded transistor based clean boost circuits to generate their distortion.

    5) If its a Silicon, Germanium, JFET, or MOSFET design, it doesn't use op-amps or clipping diodes.

    See rambling explanation above.
     
  5. BillyK

    BillyK Supporting Member

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    Sabby:
    Thanks for that reference.
    Paul knows his s**t, for sure.
    -bk
     
  6. centsmin

    centsmin Member

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    Wow! Thanks sabby, Jack and fr8_train. This is alot of great and very usefull info. I'll digest slowly but its starting to make sense.
     

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