Explain to me the benefit of a treble booster

Discussion in 'The Stomp Box' started by ftgjr, Sep 6, 2013.

  1. MilwMark

    MilwMark Doctor of Teleocity Ad Free Member

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    The reason I could buy, and play out, a BFVR is that it is not a museum piece cosmetically and needed some TLC. When I first played it, it sounded like bad solid state clipping actually. I wonder if among they many faults was that it was biased way cold. I also played a DRRI testing a Tele that had that same thing - clipping came way too early on the volume dial, way to suddenly, and in a solid-state kind of way.
     
  2. 11 Gauge

    11 Gauge Doctor of Teleocity

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    Even when trying to set fixed bias "properly," it is still a mercurial sort of thing. Some techs will literally put the amp into a dummy load and then into a scope, because crossover distortion is easily "seen" that way. It's the parts of the sine wave that "kink" as it crosses from the positive to negative swing and then back again - it happens around the region of "zero +/-," hence the term crossover.

    It gets hard to explain because you have to think in terms of time (or period) as well as amplitude. I'll just over-simplify it to say that crossover distortion occurs at "sensitive time portions," which almost is a fallacy, but I hope it suffices WRT what we are discussing.

    Or in another over-simplification - at the power section, you don't want things to go into cutoff, where the tubes will not function properly at all, or where there is excessive clipping at the peaks of the waveform. But the crossover point is also an area where this causes what is considered "just plain unpleasant sounding" distortion.

    The problem with techs trying to "bias out all crossover distortion" is that it essentially can't be done. Or if they think they've biased it out, it will come back later on. Tubes are not consistent thru their lifespans for the most part. But the more important thing is to not have tubes biased so "cold" that the crossover distortion is overly present - there's a better operating point that will not diminish tube life drastically.

    ...Many newer budget amps will come from the factory with a cold bias because cheap tubes can be plugged in and they will "work," and last longer than if set "properly."

    The more important thing for any tech to realize is that simply using the "70% dissipation setting" or biasing with a 'scope, or "biasing by ear" are all "wrong methods" if applied without any thought to other factors (especially biasing by ear! :eek:). I think the 70% thing is a decent starting point, and then there can be some mild adjustment up and down. Heck, 60% may sound equally as good. Why run them any hotter than you have to?

    But yeah, poor bias, maybe a trashed speaker (or stiff new one) - all other pieces can be dialed in ant that will just throw the sonics in the toilet!
     
  3. jefrs

    jefrs Doctor of Teleocity

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    The TB is a pretty simple circuit, its only tone shaping is to tilt the slope treble up, it doesn't select any 'certain parts of the signal' as such.

    Being a "small signal audio" the OC71 is very sensitive, which is good for picking dynamics, so is the front end of a valve and a lot of pedals in the way are often tone-suckers. Ditch the other pedals? A long stage lead does deaden the sound, Rory would be all over the stage and in the audience on occasion, and probably used something like 50-ft long. The TB was intended to recover those loses.

    I think you need to A/B the TB against an GEQ to set it up, the first time is tricky. The TB doesn't do anything much over 2kHz so set anything above that flat. I used an Arion MEQ-1 like this "/-" , straight slope up from about -10dB cut at 100Hz to +15dB lift at 1.8kHz and then flat, with about +5dB on the master. Not a perfect match but close enough.

    Going by how quiet the operation of the one I have built into the guitar is, I think I need to build one in a box I can clip to the strap or my belt, rather than placing it in front of the amp.
     
  4. artdecade

    artdecade Poster Extraordinaire

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    ^ Man, I dunno. I still don't see how you are going to get an EQ to do it. Make a demo and post it on Youtube. Ha.
     
  5. jefrs

    jefrs Doctor of Teleocity

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    I might be able to do a Sound Cloud but not today, I've just had a molar extracted and am not a happy bunny.

    Have you yourself tried it?
    Do you have a 'Dallas Rangemaster' type treble booster?
    Do you have a Graphic EQ pedal?

    I'm not sure what you think a treble booster is. You previously said, "All an EQ will ever do is add/subtract frequencies and gain", well that's actually all a treble booster does.

    My Arion MEQ-1 only runs to +/-15dB but some GEQ run to over +/-20dB. That amount of tone cut/boost, plus the master gain on top, is pretty excessive for a tone control. It can add plenty of 'grind'.
     
  6. artdecade

    artdecade Poster Extraordinaire

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    I have a Treble Booster, but no EQ at the moment. Otherwise, I would give it a whirl. I don't deny that you can emphasize the right frequencies, but a Treble boost also added dirt at some frequencies and not others. That's where I am feeling that it will differ.

    More importantly - feel better!
     
  7. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

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    Some select quotes from Geofex article on the Rangemaster:

    "What does this secret weapon do?
    First and foremost, it’s a treble booster. It provides gain of up to 24db at
    frequencies above about one to two kHz. It has about unity gain at the lowest
    normal guitar notes, and the gain about doubles with each octave. Since a
    doubling of level is a just-perceptible change in loudness, not a perceived
    doubling of loudness, this amounts to a fairly mild increase in level for higher
    notes, enough to make the guitar more “present”. It shares this characteristic
    with other treble booster effects. If that was all that happened, there wouldn’t
    be much excitement.
    However, the Dallas Rangemaster has some other tricks. As a result of the use
    of germanium devices and careful biasing, there is a subtle distortion added, as
    well as a changeover to harder distortion on loud notes, and the built-in ability
    to overdrive a tube amp input for some more serious distortion. These effects
    get more prominent as frequency goes up, so there is a very characteristic note
    added by the Dallas Rangemaster."


    "Normally transistors are biased as close to the middle of their linear
    swing area as possible to get the biggest possible non-distorted signal out. If
    you bias a bipolar transistor near cutoff, the gain of the transistor is heavily
    dependent on the instantaneous signal in a way that compresses the signal more
    the closer to cutoff it gets. Even for signals that do not fully cut the transistor
    off, the signal is softly compressed more on one side than the other, which
    amounts to asymmetric distortion of the waveform since the compression is
    instantaneous.
    This asymmetric distortion adds a sweet, liquid quality that gets more
    noticeable as notes are hit harder. Hit a note hard enough (or just use a high
    output pickup) and you can actually drive the transistor fully into cutoff, and
    get a changeover into harder distortion."



    "From what I’ve been able to see, the ideal biasing point for the Dallas
    Rangemaster’s sound effects seems to be to have the collector at between -6.8
    and -7.1V with a –9.0V battery supply. This puts the static bias at a place that
    lets the soft cutoff distortion show through and allows a smooth transition to
    heavier clipping in cutoff with much louder notes."


    "The Dallas Rangemaster has an output impedance no higher than the output
    pot resistance of 10K, and lower than that over most of the pot travel. This is
    substantially lower than the equivalent forward biased grid resistance of a
    12AX7, so it can drive an input grid somewhat positive. The resulting
    distortion is smoother than a high impedance source would be. Note that amps
    that have series 68K resistors for “mixing” two inputs may not show the full
    benefit of this effect."

    http://www.geofex.com/article_folders/rangemaster/atboost.pdf
     
  8. luckett

    luckett Banned

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    I've compared the two and the descriptions above pretty accurately reflect my experience. You can get the EQ close to the rangemaster frequency curve, but you don't get the clipping or compression that the rangemaster has. The rangemaster gives you a more saturated overdrive tone than an EQ will. Also, with the EQ, you don't get the change in frequency response by rolling off the guitar volume that the rangemaster gives you.
     
  9. 11 Gauge

    11 Gauge Doctor of Teleocity

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    If I didn't mention it, I wanted to say that this is a critical piece to the puzzle as well - clipping characteristics that affect harmonics, as well as the swing back and forth from a nice attack on the notes to the compression that follows.

    ...All done with a very simple circuit design. The limits of the germanium device was kind of like 'accidental built-in R&D," since they would be hard pressed to get a silicon device to do the same thing back then.

    You could basically get something very similar with a silicon bipolar fed into a jFET. You'd want a silicon w/the same hFE (gain) as a germanium, and you'd want to "sack the bandwidth" with a small cap between base and collector (to roll off trebles above 2KHz). You'd then want the jFET to do little more than add the subtle harmonics/distortion/transitional dynamics - it would barely need to operate much above unity gain.

    ...And - the bipolar silicon transistor for Q1 would give all the cleanup w/the vol knob stuff, too.

    Even by adding a 2nd transistor, the parts count would still be stupid low - possibly as low as a Fuzz Face. The jFET would need a trimmer just like a fine-tuned FF does anyway.
     
  10. jefrs

    jefrs Doctor of Teleocity

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    Waparker4, very interesting, thank you.

    I only have my own experiences, and those from here to go on.
    I have used a Hawk 'Rory', it is a completely different animal.

    The top note of a guitar is under 1200Hz. By comparison to my MEQ-1 the TB I built did little above 1.2kHz, I put the 3.2kHz and 6.48kHz slider flat at 0dB.
    I ended up with the MEQ-1 sliders in a straight line from 100hz at -10dB to 1.6kHz at +15dB, and with the master at +5dB. This is roughly the +24dB response spoken of in the Geofex article. I did not use the frequency analyser (I do have one), nor blag the use of an oscilloscope, just 'calibrating' the MEQ-1 by ear ;)

    MEQ-1 sliders were approx
    100 -10
    200 -7
    400 +3
    800 +10
    1.6k +15
    3.2k 0
    6.4k 0
    Level +5

    Interesting point on the bias. The OC71 is a rather variable little bugger, the ones I have are all different. To my ear it is fairly clean, not perfectly so, more of a searing sound than over-drive. Of course it can overdrive the first valve in an amp. I say valve because over-driving solid-state doesn't always sound very nice.
     
    Last edited: Sep 18, 2013
  11. jefrs

    jefrs Doctor of Teleocity

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    I have used similar silicon pre-amps made by electronics engineers for me. They all sounded disgustingly hifi. I refer in particular to a 5-channel solid-state >100W head I had. The problem with pro-EEs is it really pains them to build anything so badly designed. I virtually had to kneecap my mate to get him to make it as crude and musical as the Rangemaster. I finally managed to communicate the concept that I wanted the input stage to clip softly like a valve, super-sensitive, too much gain, brilliant!
     
  12. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

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    I am interested in this circuit

    http://www.runoffgroove.com/omega.html

    It does have a 2nd transistor but it is a jFET loading the guitar pickup and a MOSFET for Q2

    It sounds pretty good and fun
     
  13. jefrs

    jefrs Doctor of Teleocity

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    Bias variation with temperature?

    Ok but do we need to be so super-fussy?
    Solid state silicon stuff is most sensitive to fluctuations in temperature at and around room temperature. It is most stable if we cryogenic cool it in LN2 at -192°C (77.2K), which is rather impractical for an FX pedal. But if you are playing in a room then it is likely that the temperature is going to be stable, stability being more important than the actual temperature when it comes to precision amplifiers, and an FX pedal is not a precision amp.

    That circuit does look fun for the hobbyist :)
     
  14. artdecade

    artdecade Poster Extraordinaire

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    That goes against what most people would agree on... germanium is unstable due to sensitivity to temperature. That is why builders went over to silicon. There is even a rumour that SRV actually kept a Fuzz Face in a fridge on tour. So that when one went wonky from the heat of the stage, he would go to the cold one.

    Am I missing something?
     
    Last edited: Sep 18, 2013
  15. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

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    Actually geraniums are pretty stable w/ heat, but may have trouble due to root rot or bacterial blight.

    [​IMG]

    IDK How SRV dealt with this problem :p
     
  16. artdecade

    artdecade Poster Extraordinaire

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    Whoops!
     
  17. 11 Gauge

    11 Gauge Doctor of Teleocity

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    Not a rumor. Diaz talked SRV into using the FF, saying that Voodoo Child just wasn't right w/o it. So there's no point in Diaz lying when it became a PITA to keep those things going. So yeah - one kept on ice while one was heating up on stage. When it started to fart out, they'd swap them between songs.

    Diaz expanded on the immense PITA that germanium transistors were - the rigors of touring would typically have a FF ending up dead. Replacing germanium transistors in a hotel room is not the best of makeshift shops, and you have to sort thru them for leakage. Even when you find one w/leakage and gain that seem like they might work, there's no guarantee that the pedal will sound the same. You can't simulate the heat of a stage in a hotel room, either.

    So they had the little mini fridge or whatever, and Diaz tried to make that work as long as possible. The Squareface was not solely created as a "better Fuzz Face" - it merely used the "more stable and reliable" transistors of Diaz's choosing. So for Diaz, it was infinitely better. That said, it was still 1:1 with the FF spec's. And germanium is germanium. The only exception there is some stuff of Russian or Chinese manufacture for military purposes, but that's not what guitarists are paying 3 months' rent for. It actually amazes me that the Bonamassa FF has been as well accepted as it has been, since it uses Chinese/Russian military surplus transistors.

    And this doesn't even cover the issue of hiss. It's so easy to not realize that germanium was "state of the art" up to the 60's because they didn't have much silicon stuff to choose from. We just get the nostalgic warm fuzzies with it today. There haven't been as big of attempts to press silicon into functioning with the same effectiveness simply because the germanium devices get the builder off the hook with that, IMO. It's like pre-mixed paint for the exact color you need. Who cares if it hasn't been manufactured in 40+ years? I do, but I'm in the minority.

    If you say silicon can't sound like germanium, you've just set the parameters for what it's capable of. It's no different than saying that it's impossible for valves to survive for 100K+ miles on unleaded gas. Horse puckey.

    ...We now have pedals of all types that use jFET and mosFET transistors, and they are silicon-only units that have capabilities that no bipolar - either germanium or silicon - is capable of.

    But IMO, something becomes an unreliable noisemaker if the devices don't have at least a reasonably low noise floor, if they are very inconsistent and utterly obsolete, and if the need to replace one constitutes a bit of anxiety or aggravation for the average pedal owner (I'm not talking about tinkerers like myself when it comes to this).
     
  18. jefrs

    jefrs Doctor of Teleocity

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    Just a little bit. Silicon is not all that much more stable.
    We get fussy about thermal stability in a calibration laboratory where the electronics are kept at equilibrium, and powered up 24/7.

    My collection of OC71 are no two alike. I think it true to say that more modern components are better made and more consistent.

    Silicon will run hotter than germanium, you can burn a finger on silicon power transistors, but both will trot along at 35-40°C under the lights without problems.

    I recently repaired an old pedal and found the snap, crackle and pop wasn't wonky germanium but riddled with dry joints. Simple board so I re-flowed everything with some nice tin/lead. Sorted, quiet as a mouse.
     
  19. Jagg76

    Jagg76 Tele-Holic

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    If you need a treble booster get a deluxe reverb! :D
     
  20. CyanideJunkie

    CyanideJunkie Tele-Holic

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    Running my Keeley Java Boost into my Vox AC15 Heritage was a moment of pure revelation for me. Honestly, I fail to hear any difference between Ge and Si-based TBs(set properly of course). The only caveat being that Ge trannies can be unpredictable.

    I've been dying to try Andy Fuch's Jersey Lightning though. A JFET-based TB sounds awesome.
     
    Last edited: Oct 13, 2013
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