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Thread: Symmetry vs. Asymmetry

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    Bent Member Chuck H's Avatar
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    Symmetry vs. Asymmetry

    I'm at a crossroads in a design. It's actually a standing design, but that doesn't mean it can't be changed (improved?).

    Any high gainers here, please plug in your scopes and chime in. This circuit of mine exploits a pair or a quad of el84's being overdriven. Phase inverter and preamp clipping also contribute the "clipping a clipped wave form" at higher gain settings. The last stage of the preamp is biased a little cold and drives an effects loop. So I have the option of using either the plate or the cathode for the FX drive. If I send from the plate the PI goes asymmetric when clipping. If I send from the cathode the PI is more symmetrical. The specific drive differences change the duty cycle. The asymmetric wave form is more mid focused, looser and hairy sounding (I like it). The more symmetrical wave form is rounder and fuller with more authority (and I like it too). Both designs have appeal. So what I'd like to know from any high gainers here is...

    Do YOU prefer a symmetrical or asymmetrical clipped wave form. Maybe you could plug in your scope and see what your favorite amp does when it's clipping the way you like. Since this is a design I have sold to customers and may sell more of I'm interested in public opinion because I'm really on the fence about which I like better.

    Symmetrical clipping vs. asymmetrical clipping?

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    "I'm just going to perform a bit more scientific investigation, turn it up to 11 and rip of the knob." überfuzz

    "...less ear-friendly but handy for jazz." Leo_Gnardo

    "A pedal, any kind, will not make a Guitar player more dangerous than he already is." J M Fahey

    "If you build it, it will hum..." Justin Thomas

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    Senior Member Malcolm Irving's Avatar
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    Sounds like two good options. How about a change-over switch between the two? You can have fun labelling it as 'rock/blues', 'liquid/viscous', 'chime/clang' or whatever.

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    Bent Member Chuck H's Avatar
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    Thanks Malcolm

    That did occur to me. And I have set it on a switch for testing purposes. But my aesthetic for this design is to keep it simple and still have a do all circuit. The clean tone is admittedly workman like. Good, but not special. The tweener tones, just barely clipping to "classic rock" tones are great and cranked into really hard clipping is has that elusive crunchy but saturated thing. And with a cap circuit on the guitar volume it's very good controlled from the guitar. So it really is a do all. I guess I just want a set it and forget it type of rig. No reaching for novelty switches.

    I probably lean toward asymmetrical a little. I may try heating the bias on the cold stage to reduce asymmetry a little and see how that sounds. But really, the question still stands. Who likes it one way and who likes it the other? Since I'm only one owner of this model (and I can make it however I like ) I'm wondering if there's any general consensus on the matter. This isn't the kind of question I can ask the average guitarist. Just nerd guitarists

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    "I'm just going to perform a bit more scientific investigation, turn it up to 11 and rip of the knob." überfuzz

    "...less ear-friendly but handy for jazz." Leo_Gnardo

    "A pedal, any kind, will not make a Guitar player more dangerous than he already is." J M Fahey

    "If you build it, it will hum..." Justin Thomas

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    Senior Member Malcolm Irving's Avatar
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    Quote Originally Posted by Chuck H View Post
    .... This isn't the kind of question I can ask the average guitarist. Just nerd guitarists
    I think you've come to the right place!

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    Neither really. Or both.

    Seriously the trend appears to have been steady-state-symmetical, transient-asymmerical to (over)simplify the case...

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    IMO,for highest gain playing you want symmetrical because this gives the highest average power. I think that is where the authority comes from.

    This might not be of interest in your current design, but one interesting approach is to design for asymmetry at lower gains, changing to symmetry as the gain increases. Most amplifying devices turn off slowly, but saturate on quickly, and so a single ended preamp stage is inherently asymmetrical. It may not be easy to take advantage of this if you want mostly power stage distortion.

    The waveform from the pickup has dynamic range and is asymmetrical. At lower gains, the level of distortion varies in different parts of the waveform, and as the waveform decays. So I think that an asymmetrical distortion enhances its natural properties. But as you increase the gain, you have a more constant power versus time and authority becomes more important.

    Quote Originally Posted by Chuck H View Post
    I'm at a crossroads in a design. It's actually a standing design, but that doesn't mean it can't be changed (improved?).

    Any high gainers here, please plug in your scopes and chime in. This circuit of mine exploits a pair or a quad of el84's being overdriven. Phase inverter and preamp clipping also contribute the "clipping a clipped wave form" at higher gain settings. The last stage of the preamp is biased a little cold and drives an effects loop. So I have the option of using either the plate or the cathode for the FX drive. If I send from the plate the PI goes asymmetric when clipping. If I send from the cathode the PI is more symmetrical. The specific drive differences change the duty cycle. The asymmetric wave form is more mid focused, looser and hairy sounding (I like it). The more symmetrical wave form is rounder and fuller with more authority (and I like it too). Both designs have appeal. So what I'd like to know from any high gainers here is...

    Do YOU prefer a symmetrical or asymmetrical clipped wave form. Maybe you could plug in your scope and see what your favorite amp does when it's clipping the way you like. Since this is a design I have sold to customers and may sell more of I'm interested in public opinion because I'm really on the fence about which I like better.

    Symmetrical clipping vs. asymmetrical clipping?

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  7. #7
    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Mike Sulzer View Post
    IMO,for highest gain playing you want symmetrical because this gives the highest average power. I think that is where the authority comes from.

    This might not be of interest in your current design
    Thanks Mike. All the excellent info/perspective that I didn't grab for the quote not withstanding... It may not be right for this design for one reason. This design works from the guitars volume control. By sacrificing maximum power for a different tonal character the amp doesn't "sound" disproportionately loud distorted compared to cleaner tones. That's more useful for stage or live mix recording if there are no peripheral volume control systems in use, making it a more plug and play amp, which was my original intent. So there's that. OTOH there is a litany of high end dirt pedals that players love to collect and use. An amp that comes across with more authority and stays more symmetrical into clipping is appropriate for these players. Historically, solid sounding amps with a good basic tone have been popular because they are sometimes more applicable tools for professional players. An amp with a "characteristic" tone is more of a novelty. I'm starting to reexamine putting the option on a switch. But, the subject of my personal project aside...

    Whose got a favorite overdrive tone and a scope (I bet SOMEONE here does)? Anyone willing to look and see if their clipping is symmetrical or asymmetrical? The more the merrier since I'm shooting for a consensus of sorts.

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    "I'm just going to perform a bit more scientific investigation, turn it up to 11 and rip of the knob." überfuzz

    "...less ear-friendly but handy for jazz." Leo_Gnardo

    "A pedal, any kind, will not make a Guitar player more dangerous than he already is." J M Fahey

    "If you build it, it will hum..." Justin Thomas

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    On the topic of output symmetry, a guy I know in a popular tech/prog metal band round these parts brought in an Engl Fireball 60 for me to retube. The envelope on one 6L6 had entirely broken away from the base and when I tried to remove the tube the glass came clean off, leaving the rest still in the socket. I asked him if he'd noticed that the glass had broken or that the getter at the top had gone milky white from oxygen exposure. He said that it had been white for a good 6 months but it still sounded fine. In that time it had been used in countless rehearsals and a whole bunch of shows, including festivals. He'd only brought it in because he wanted to put some new tubes in because of the recent heavy use and looming european tour!

    So, maybe try disconnecting one of the PI outputs? It seems with sufficient clipping and shaping that half of the waveform can be thrown straight in the bin

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