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An Amp's voice: circuit vs tubes?

Discussion in 'Amps and Cabs' started by bohemianbrian, Jan 23, 2012.

  1. dangeroso

    dangeroso Member

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    Here’s another example then:

    Engl Savage vs. Fender Twin. Now we are talking a high gain metal amp vs one of the highest headroom amps ever made. Speakers, tube or circuit?

    I don’t disagree that the tubes and speakers make a difference, but the vast majority of the sound is in the circuit. If this wasn’t the case, why not just buy the cheapest Bugera amp, and swap out with the best speakers and tubes?
     
  2. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    :agree - wholeheartedly! However, you can achieve slightly improved crap.

    - T
     
  3. Rambergwest

    Rambergwest Member

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    Wow 11 pages of discussion and maybe half a dozen good comments, is this a record? Its the circuit that defines the range of potential and that is so obvious as to not deserve an explanation.
     
  4. Nolatone Ampworks

    Nolatone Ampworks Member

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    Wow, there is sooooooo much to talk about here, and it's near and dear to my heart as I've stirred the pot considerably in recent designs I've completed.

    There is no set percentage any one part plays, it's all dependent on numerous factors.

    For example, the AC30: Many tend to equate el84 based amps to that. To me the classic AC30 sound is a combination of:

    1) light power supply filtering, which delivers the unique combination of bloom and dynamics the AC30 is known for.
    2) low power alnico speakers
    3) el84s.

    Contrast that with our Wicked Garden design. The clean channel has essentially the same preamp as the AC30 top boost, and yes, ac-30-esque tones are available, but because power supply is different from an AC30 and I'm not presenting it with Alnico speakers as the standard choice, it's quite different than a pure true to form AC30 because of the differences in power supply and speakers.

    Another example, take the Marshall Plexi. I learned from an intensive trial and error what makes that amp sound the way it does (and of course driving a 4x12 will deliver a different sound than an open backed 2x12 or 1x12). I'd done a lower power design that offers great versatility and the ability to dial up fendery, voxy, and marshally sounds all in one single channel preamp. It's very popular as a 15 watt grab and go and sounds great, offering a great representation of many types of amps.

    I wanted to scale that up to high power and it just didn't sound quite right to me. I wanted to make a more flexible JTM-45 type thing. It never actually had the punch I really needed from a pair of KT66s. I tried everything I could to get it to stand up and bark more like the 50-watt Plexi clone I have. I finally decided to wire up the cathode follower and Marshall style tone stack, and *smack* there it was. Everything in the circuit was the same, just stick in that cathode follower stage and tone stack and all the frequencies stacked up and produced the energy needed in the low/low-mid to give it that Marshall Plexi "bark". In that circuit I'd say the circuit is a larger percentage of the sound because I can get that sound with Fixed bias KT66's, EL-34's, 6V6's as well as cathode biased configurations as well. I've not done that one with EL84s yet, but I expect it will deliver the same type of bark, but with more subtle nuances between the different styles of tubes. It's there with whatever speakers I use as well, again, with the voicing differences of the different speakers slightly coloring the tone as expected. Speakers are a huge part of any sound, BTW.

    So, I can say from direct experience, *it depends*.
     
    Last edited: Jan 8, 2013
  5. DT7

    DT7 Member

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    With the Engl, it's mostly the circuit...the more the circuitry, the more it takes over the tone. Then take a TR, play it with Sylvania big-bottle 6L6s and D120Fs...then swap to EL34s and play it through a 4x12 with Blackback G12H-30s. Blind-tested, I doubt you could even tell it was the same amp anymore.
     
  6. pima1234

    pima1234 Supporting Member

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    Agree with Nolatone; "it depends". That is the truth.

    Some amps are more circuit-dependent than others. Some amps are very picky about speakers. Others sound great no matter what speaker(s). Some amps that accept a variety of tubes are greatly altered by simple tube changes. There are others where it may not make as much of a difference. Frenzel comes to mind. They are design around a specific circuit. Different tubes change certain characteristics, but not the overall voice. It makes a more noticeable difference with Emery Sound amps. Maven Peal amps fall somewhere in between, in my experience.

    Everything makes a difference, there is no doubt about that. What makes the biggest difference? It really does depend. To refine my previous post, speaker/circuit are nearly equal. When we talk about different circuits, we're essentially talking about different amps altogether. So it reasons that the circuit is the primary factor. That has to be true. As far as what simple changes will make the biggest difference, most of us are not capable of altering an amp's circuitry.
     
  7. vibrostrat43

    vibrostrat43 Member

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    One amp may have a wider variety of sounds it's capable of achieving with different tubes and speakers than another would be capable of, but that's because of the circuit inside that allows the amp to sound different with different speakers and tubes than another amp.

    Therefore circuit design itself makes the biggest difference in an amp's sound, and what sounds the amp is capable of, and then the other factors like speaker/tubes can help shape that sound.

    Not trying to be rude (and I know it's going to sound rude so I apologize ahead of time), but it's just common sense to me. I do think that yes speakers and tubes can make a huge difference in tone, but more drastic changes have always come from circuit modification/design/redesign FOR ME.

    Also I know that not everyone can go inside an amp and make those changes themselves to actually hear what differences just a few capacitor or resistor value changes can make, or how much more drastic a change you can make by altering where the tone stack is, or adding a cathode follower before it, or taking out or adding a gain stage, etc...so I can understand if those people are skeptical about how circuit design can actually make a difference. However, there are a TON of amps that are very closely based on the classic 5f6-a Fender Bassman design (Marshall JTM-45, Marshall Super Bass and Super Lead amps, Vox AC15/30 top boost, tons of boutiques), and lots of others based on the blackface era Fenders (Mesa Lone Star, Dumbles, still more boutiques), and yet most people accept that most Marshalls and Vox top boosts sound quite different from tweed Bassmans, and Dumbles and Lone Stars sound quite different from blackface Fenders.

    Anyway, just my opinion on the subject.
     
  8. ekp

    ekp Member

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    I build Pritchard Amps. And my amps, in the M voice do sound more Marshally than a Marshal, at least according to some players.

    I hope to be hearing from you, ERic
     
  9. ekp

    ekp Member

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    Thanks. Unfortunately, for both me and players, is that the solid state stigma is quite alive and well. And that keeps players from solid state reliability and low weight while enjoying a somewhat exaggerated tube character.

    Have a great day, Eric
     
  10. dangeroso

    dangeroso Member

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    Yeah, I could see that.
     
  11. mxvin

    mxvin Member

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    a TR is not meant to have EL 34s and you would have to mod the circuit for that. its no longer a TR. Bad analogy.
    The thread is meant, I believe, leaving all things as they are what will give the greats tone dif. Tubes, speakers, circuit.
     
  12. mxvin

    mxvin Member

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    how does an amp sound more "marshally" then a Marshall?? Then "what" Marshall????
    It may sound better but......
     
  13. pima1234

    pima1234 Supporting Member

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    No sweat at all. I'm still very much in the learning process, and that's why I joined TGP. Good post.

     
  14. ekp

    ekp Member

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    First, since I am not a player, this comment is second hand by some players.

    However, from a design standpoint this character comes about by exaggerating the characteristics of a tube amp. The sag that is associated with tube rectifiers can come about by other means. I use transformers that have poor regulation and my output stage has a no-signal current of about 70 milliamps and a max wattage distorted signal current of about 5.5 amps. By comparison a typical push pull pair of tubes will run 70 milliamps and a quarter amp respectively. Consequently, my amps have a substantial sag. A witness to that is in the power ratings. The pre-clipped power is 60 watts, but the peak distorted power is 180 watts, estimated. This characteristic emphasizes the attack.

    Next, a general characteristic for tubes is the more current that passes through them, the higher the gain (transconductance). In a push-pull output stage this translates to odd-harmonic generation in a good phase. While the ear is generally not phase sensitive, it is to odd harmonics because they can radically change the shape of the wave. For example, clipping thirds make the sound blanketed. But the thirds in the opposite phase make the sound more open and tends to compensate for the blanketing of clipping.

    My output stage is actually a audio power chip with a lot of extra circuitry to make it tubey and provide the power scaling with my Watts Knob. The preceding stage, nominally where the phase splitter would be, unlike tube amps does not drive the output stage as hard. It drives it as hard as necessary to distort, but no more. And it drives it single ended because the output stage is externally single ended, although push-pull internally. Consequently, the output is more akin to the fundamental.

    All of this gives the amp a "clean distortion" character, which translates to being able to better hear individual notes in a power chord. This helps players who can play to sound better and suggests to others that they need to practice more. As Jeff Healey commented to his bass player, Joe, he had to pick all the notes right because he could hear them.

    The extra circuitry around the output chip produces harmonics and compression. The Watts Knob related circuitry also produces sag when the amp is turned down. This combination gives feel and character to the amp even when it is turned down to a few watts.

    Although the preamp gain is derived from FET input op amps, the tube character is produced by a special circuit that emulates a generic triode plate characteristic. This gives the design a split design personality. The output of the FET op amp is akin to solid state in design philosophy. But the special plate circuit transforms this to tube design philosophy as it requires a "plate" resistor, a coupling capacitor, and a "grid" resistor for the following stage, which then also has a "grid" current circuit as well. This feature helps with the effects loop as the split in the amp created by the effects loop occurs in the solid state philosophy and then the tube philosophy is picked back up after the loop.

    Winn Krozack (now the PRS artist relations guy) inspired a first stage feature because he cherry picked 12AX7's for the first stage. So I put in a first stage gain control to marry you and your guitar to the amp. The idea is to set this IN control so that playing hard makes the first stage just about clip. In this way, the first stage adds to the harmonic expression as well as dealing with humbuckers and single-coils equally well.

    So all this suggests that to sound more tubey than tube amps, more Marshally than a Marshal, is created by exaggerating the characteristics. This came about in the evolution of my amps. I designed prototypes with an effect exaggerated so that it could be heard well. Then the exaggeration was reduced to sound good.

    I hope this answers your question. Have a great day, Eric
     
  15. DT7

    DT7 Member

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    Mod the circuit? I don't consider soldering a piece of wire across two side-by-side terminals on four tube sockets a modification...especially since you could go back to 6L6s without removing them. You'd have to rebias the amp, too...but that goes without saying.

    My analogy shows that tubes and speakers have a serious effect on the tone...that's all; nothing more.
     
  16. guitarcapo

    guitarcapo Senior Member

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    Circuit 85%
    Speaker 10%
    Tube 5%
     
  17. tapehead

    tapehead Member

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    I agree. This post takes into account just how many variables there are to consider, with each one mattering. There are a few other absolutely crucial variables, and if I had to assign importance from most to least:

    User. Some are simply capable of spinning straw into gold...so to speak. Also, some users pay more attention to detail, like-
    Power. No power, no electric circuit. Using an isolated voltage regulator/line conditioner/circuit breaker plays a very underrated role. Garbage in garbage out. See also: User.
    Circuit. By circuit I mean the path from input to output and the component selection/topography. A circuit is greater than the sum of its parts, tubes included...however, as pertaining to their importance, it's equally which tubes are being used, where they are being used and how they are being used. Transformers, rectifier, caps, wire, connectors are similar; what/where/how. Pickups, strings, tone woods are also part of the circuit. What/where/how. Changing tubes alters the circuit, but it can range from negligible to critical. The parts and their relation to each another is what makes the most impact. Once the basic circuit path is assembled you're 75% there. Changing component values from that point is what makes up the final 25%.

    Driver/speaker sensitivity and frequency response/eq curve are the final piece of the circuit. They transfer the electrical energy to mechanical, physical waveforms. They are part of the circuit, like the electric instrument itself. They merely occupy space outside of the amplifier.

    Signal chain is an appropriate term; you're only as good as the weakest link, which is most commonly user. There are exceptions to the rule...but in general if I were to assign numerical values:

    User: 55%
    Circuit: 40%
    Chance/margin of error: 5%
     
  18. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Thanks. I appreciate your more global perspective.

    - T
     
  19. enroper

    enroper Member

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    Nobody ever gives any credence to the positive effect transformers can have on an amps sound as well...
     
  20. DT7

    DT7 Member

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    I sure do. The right amount of saturation can turn a mediocre amp into something glorious...with the right tubes and speakers, of course. :D
     

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