A question about tone stack bypassing.

Discussion in 'Amp Central Station' started by etype, Jul 3, 2021.

  1. etype

    etype Tele-Afflicted

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    I have watched a few comparisons between the Fender 57' Tweed Champ and the new Vibro Champ Reverb. Honestly, without reverb or tremolo, I prefer the tweed clean tone. And that got me thinking. The tweed has no tone knob.

    I have owned both a Gries 5 and a Vox AC4HW. Both had the ability to bypass the tone stack. On the Gries, it was the middle control that once turned up all the way, somehow allowed the signal to bypass the tone stack. On the Vox, it was a "Hot/Cold" switch that did it. On both amps, I eventually played it that way 90% of the time because it sounded so good. On the Gries, all tone knobs maxed meant it was bypassed, so no way to compare. But on the Vox, the "hot" setting did not seem to me to be the same as turning both the bass and treble knobs all the way up.

    1. Am I the only one who can hear the difference? In discussions about the VoxAC4 vs the AC4HW (or the AC15C1 vs AC15HW) I never hear this feature mentioned.

    2. Why not more of these switches? Doesn't seem like an expensive addition. Allen amps offers this on most models. I'm wondering if the some of the Swart switches do the same.

    3. Can one be added relatively easily to a PCB board amp (by a tech, not me)?

    4. Do features like reverb or tremolo similarly reduce tone?

    5. The AC15 normal channel seems to have no tone stack, is that essentially a channel that effectively does what I think it does?

    I know it is all complicated, but if anyone is willing to drop some knowledge, I'd appreciate it!
     
  2. uriah1

    uriah1 Telefied Gold Supporter

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    Ya. Be nice to have a baxandall switch. I think I got name right.
     
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  3. Killing Floor

    Killing Floor Friend of Leo's

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    Most components in your guitar and in your amp on the PCB or turret board affect tone. Some a lot, some minuscule. So you could rightly argue that bypassing those sections sounds more like your guitar. Vintage amps for the most part didn’t use true bypass around trem or vibrato or other. If you’re after the sound of your guitar through a simple tube preamp circuit to a simple power circuit to a speaker you could certainly bypass the EQ and any effect section and come as close as possible to that point.
     
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  4. TwoBear

    TwoBear Tele-Afflicted

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    Shouldn’t be a hard thing to add at all. I put a tone stack lift on my super reverb first channel, all it required was adding on a resistor and a pot. I’m definitely a fan of that tone. I built a 5e3 deluxe, And a tweed champ, and I was more partial to the tone of the champ when played through the larger deluxe cabinets speaker. That little champ was actually the amplifier that got me to like that feature. I went on to build something called a tweed bluesmiester that was designed with a tone stack lift/mid boost, and to add the same lift to my super reverb, and also my Carvin V16. I’m planning to add one to my Fender Bantam Bass when I open it up to do a cap job. I have heard that when you add a switchable tremolo defeat to super R’s, and the other similar Fender circuits, there is a noticeable volume boost with possibly a mid bump. If memory serves me correctly, to do the trem lift all that is required is to change one of the pots-I can’t remember if it’s speed or intensity-with a pot that has a switch on the back, interrupting the signal from one wire, giving a quite noticeable volume boost.
     
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  5. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    It is a thing. One of the *Hasse* or *Hasserl* Richard Hassebrock mods for Carvin amps is what is know as *Raw Control* It is a pot that is used to bypass the tone stack.

    Tone stack types vary from amp to amp. Some remove over 90% of the signal. Ime, one should have a clue before installing a one size fits all circuit change. OMMV.

    The single ended 5F1-ish amp circuit operates with no tone stack. 5F1 variants with tone stacks can have the tone stacks bypassed without a problem.
     
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  6. edvard

    edvard Friend of Leo's

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    Most tone stacks in the Fender/Marshall/Vox family sport a pretty deep (-10dB to -35dB, depending on the component values and settings) and narrow mid-scoop, the reasoning of which is that Leo felt that a guitar pickup was a very mid-rangey device, so the tone stack was designed accordingly. If you look at many FMV tonestack response graphs, you'll notice that with the Mid control up full and Bass and Treble backed off, you can get an almost-flat response.
    http://www.guitarscience.net/tsc/info.htm

    1. You're hearing exactly what you should be hearing; a boost in volume (tone stacks are lossy), and fuller mid-range content, as the tone stack mid-dip is gone.

    2. History. Most folks probably don't see the need for a no-tone-stack option, because they'd rather have the control than not.

    3. As long as the tone stack has one way in and one way out, you can bypass it just like a true-bypass effects pedal. 1 DPDT switch and a cut trace (or wire) would do it.

    4. I'm sure reverb adds its own harmonic content, but then again, you kind of expect that. The way most reverbs are constructed, it doesn't really touch the dry tone, just feeds off it. Tremolo, maybe. But if you like and use Tremolo, you kind of expect the results, whether it subtracts from the tone or not.

    5. I can't find any AC15 schematics that confirm your observation, but it could be.
     
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  7. Paul G.

    Paul G. Friend of Leo's

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    To bypass the tone stack, you need to lift the ground connection coming from the bass pot. You can do with with a switch, or a pot so you can dial it in (raw control). Replacing the bass pot with one with a pull switch can maintain the look of the amp, and would be reversible because you don't need to drill. Amps with a midrange control are even easier, as you can replace the typical 25K mid pot with a 100K and then from 0 to 3 your mid pot will give full range, then will progressively bypass the tone stack from 3 to 10.

    A tech shouldn't have an issue. Personally I would leave the amp as it is and spend time understanding its properties and not try to make it into something else.
     
  8. JustABluesGuy

    JustABluesGuy Friend of Leo's

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    I have a Fender Bassbreaker and as I understand it’s tone stack, maxing the mids and cutting the bass and treble give me the flattest response. I don’t know that it actually bypasses the tone stack, but it sounds great, and I tend to leave it that way.
     
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  9. etype

    etype Tele-Afflicted

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    So here is a follow-up question. If you have an EQ pedal, can that be used to effectively modify the tone coming out of an amp that lacks any tone control (e.g a tweed Champ or Supro Super)?

    Yes, I have fallen for the idea of a one-knob amp, so am trying to figure out all that is involved with that.
     
  10. NoTeleBob

    NoTeleBob Tele-Afflicted

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    Yes, although some would argue it's a different sound at the end. But, as long as the amp has NO tone stack, that works.

    Keep in mind that most amps with no tone control actually have a tone stack, it's just not adjustable. See the posts above.
     
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  11. Willie Johnson

    Willie Johnson Tele-Afflicted

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    I'm contemplating a 6g2 tone stack and variable NFB bypass for my SF Princeton. SPST click-on trem would be nice too. It's hardly pristine, so any mods would be on an amp I plan to keep forever. But I also like the amp as-is.
     
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  12. etype

    etype Tele-Afflicted

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    Yeah, I just sort of answered my own question. I dimed the mids on an amp with T/M/B. The T and B knobs became ineffective. But my GE-7 did a fine job affecting the tone.
     
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  13. fretWalkr

    fretWalkr Tele-Holic

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    I've done the tone stack drop mod on a SFSR reverb channel. The mids and lows got a huge boost as did the volume. I found it to be an intersting experiment but not that useful to me at the time. I was playing humbuckers mostly and the sound was too muddy. I reversed the mod pretty quickly.
     
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