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fundamental amp question

Discussion in 'Amps and Cabs [BG]' started by Phaidrus, Apr 11, 2021.

  1. Wasnex


    Dec 25, 2011
    Tube output sections have different tubey qualities than tube preamp sections. A lot of the serious all-tube connoisseurs tend to prefer the type of compression and drive you get from a pushed output section, rather than the result of a pushed small signal tube (preamp).

    Some reasons for these differences:

    Tube preamp circuits are generally single ended and produce more even order harmonics. In bass amps, tube output sections are generally push pull. The even order harmonics tend to cancel out in the output transformer. These comments should be taken as generalities.

    Preamp circuits have a relatively low current draw even when they are pushed to the limit. So they don't tax the amps power supply. The output tubes draw high current when they are pushed to the limit, and this introduces sag in the power supply. Sag means the high current pulls the power supply voltage down. This sag will have an impact on how compressed the amp feels and also how it transition from clean, to OD, to full-on distortion. The general assumption is you have a wider window where the transition is taking place, but this is not always the case because global feedback has a significant impact on how the amp transitions.

    Most instrument amps use a global negative feedback loop between the output transformer and the phase inverter. The phase inverter is the part of the circuit that splits the single ended signal into it's push-pull components. It's a small signal tubes, but it's part of the output section. AFAIK, higher amounts of global feedback extend frequency response and tightens up the feel of the amp, but when the amp transitions into distortion, the feedback loop becomes unstable and can collapse suddenly. This causes the amp to transition quickly from clean to distortion and the sound may be rather nasty. Lower levels of feedback reduce the amount of clean power, but the amp transitions more gracefully from clean to OD, to distortion. So choosing the amount of feedback is a compromise.
    Phaidrus and Pulverizor like this.
  2. Sid Fang

    Sid Fang Reformed Fusion Player Supporting Member

    Jun 12, 2008
    I was sure someone must have tried that. I was thinking of the possibly apocryphal story of the architect of one of the large Gothic cathedrals in the Rennaissance. He'd worked out how to keep a huge vaulted space supported by the external flying buttresses, but the local Church hierarchy thought it was too radical and too dangerous. There had always been supporting columns down the nave of a cathedral, and this was to be no exception. The architect protested, but to no avail, and he had the columns cut, built and installed. Several generations later, the project of cleaning the surfaces of the cathedral was undertaken, and when the workers got up to the top of the columns, they discovered that the architect had made the columns all a centimeter or two shorter than was required to make contact with the roof - they were, in fact, supporting nothing.
  3. Killing Floor

    Killing Floor Supporting Member

    Feb 7, 2020
    Austin, TX
    Tube tone is in the fingers.
    mikewalker and 2tonic like this.
  4. JeezyMcNuggles


    Feb 23, 2018
    Santa Maria, CA
    I suck, but nobody really notices
    The micro vr is really close. Tone wise and dynamically. The only noticeable difference between the micro vr and my v4b was flat eq, and various levels of drive and saturation. But, the vr does drive, and has a certain saturation that is hard to find in solid state amps. Hard to find, not non existent. It's not stale like a lot of ss amps. By any means. But, it doesn't sound half as good as an all tube beast. But, like with everything, that's a matter of preference and interpretation by the beholder.
    Wasnex, Socobass and Phaidrus like this.
  5. Ampslut


    May 15, 2017
    I don't think there is much difference in the sound from the listeners perspective. It's the feel while playing through them that is different. I've grown to prefer SS amps. I've used tube pre with SS power and while there is somewhat of a tonal difference, the feel is still SS. 808 hit the nail on the head when they wrote that it is the output transformer of the tube amp that gives it the different FEEL from that of a SS amp.
  6. 808State


    Dec 30, 2020
    " Warmth" is a very generic common description and not sure what it means.
    Since to each individual it has a different meaning.

    It could mean the player likes the compression of the pre or output stage.
    Or it could mean they like the tone controls.
    One person could say its not bright enough, one person could say its dark sounding and that is what they like.

    But most of that can be done with tone controls or filters. Has nothing to do with the tubes.

    Usually " warm " is just a term people use when they enjoy the overall sound of the amp

    Far as " Break up" that is clipping distortion.
    Far as getting symmetrical or asymmetrical distortion. For either stronger even order or odd order harmonics.

    It can be done with Bjt or Fet Transistors, Operational amplifiers or tubes.

    They main key to making good distortion is multiple gain stages and filters.
    I have heard really good tube distortion and have heard garbage tube distortion.
    Its more related to circuit design. High gain distortion is difficult to do with SS or Tube
    The tube output section and the transformer make it relatively easier to get good distortion.
    But can be done either way

    As a musician, yes having a transformer coupled tube amp has a different feel.
    As far as the actual waveforms it can be done with transistors or tubes.
    And can be simulated electronically with software models

    The sound in a recording or playback will be the same.
    The feel of a real tube amp in the room with you little different.
  7. 2tonic


    Dec 22, 2015
    Smartass!! ;):thumbsup:
    Killing Floor likes this.
  8. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Someone ought to design a solid state amp that glows like a tube amp. Sand based devices and colorful LED’s can be mounted in evacuated glass envelopes.


    DrMole, 2tonic and agedhorse like this.
  9. spatters


    Mar 25, 2002
    There's no magic. It's physics, and easily quantifiable.

    As usual, the guitar tech is way ahead here. Several famous guitarists, who own their grail amps and can afford anything they want, have switched to using Kemper modeling heads. Either they say frankly that they can't tell the difference, or the difference is small enough that they don't think it matters.

    Herein lies the difference. Just because you can quantify it doesn't mean you can reproduce it with common solid state electronic components! This is why we haven't seen really spot-on tube emulation until the advent of real-time digital processing. We might understand what the output stage of a vintage Marshall or Fender or Ampeg is doing, but we can't necessarily build a simple solid-state circuit that does the same thing.

    (We're doing a lot better now than we did 40 years ago, though, as anyone who played a 70s transistor head can attest.)
    Phaidrus and drumvsbass like this.
  10. 808State


    Dec 30, 2020
    Who doesn't love tubes.

    There will always be romance , mystery and magic with tubes.

    I think it is how a tube amp should look.
    The McIntosh and many other HiFi amps are a good example.

    Visible tubes and transformers for all to see.

    First I wasn't sure about the metal grills on the Sunn Model T's
    But eventually on dark stages realized how cool it was to see the tubes
  11. drumvsbass


    Aug 20, 2011
    A solid state amp with a good compressor, will get you 95% or better. The romance of tube amps is the way they compress. Which always made me laugh when older guys would poo poo on using a compressor, but swear by using tube amps. These days, modeling has got it beat (if not absolutely 100% tonally, certainly with the added convenience). To mic up an SVT in a room, and get all the mics and lines in phase, studio time with an engineer... yadda yadda, or I could plug into the instrument jack on my Apollo and use the UA SVT plugin which is close enough for the Ampeg snob in me. The realest Ampeg in a box award these days goes to the Helix IMO. Considering it's the same parent company, I don't expect that to change.
    2tonic, agedhorse and Phaidrus like this.
  12. el murdoque

    el murdoque

    Mar 10, 2013
    I did not do it on bass, but I was present when a blindtest happened, a Kemper profiler with poweramp against three tube amps. Those were a Mesa Transatlantic (low power lunchbox amp), a Mesa dual (or triple) rectifier amp and a Marshall JCM (no idea which one, but it had 4 channels).
    The Kemper did not nail those amps 100,00%.
    There were subtle differences between the Kemper and the original amp - but it felt more like tuberolling than tube vs. digital. It was impossible to tell which amp is the tube amp and which is the digital copy - they sounded like two slightly different variations of the same amp.
  13. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Don’t forget that modeling is based on a single amp with a single set of tubes. IF specific “holy grail” tubes make such a difference in tone, the amp model with one set of tubes would presumably be different the a model with different tubes.
    2tonic, spatters, el murdoque and 2 others like this.
  14. OP, as noted above "the romance is in the bottles themselves." That SO hits the mark.

    Put your rig on stage with typical Lo-Fi bass cabinet speakers.
    Play it in a live mix with the band.
    Stand out front: any subtleties in tone difference will be not audible.
    Phaidrus and agedhorse like this.
  15. Freight Train

    Freight Train Earth-based Alternative Scientist, Sex Researcher

    Feb 25, 2012
    Dallas, Texas
    My opinion, based on experience. Nothing sounds like a tube amp but a tube amp. The sound I wanted, and what I think most who seek the 'tube sound' are after, comes from all-tube, preamp and power amp. You can get some cool 'modeled' simulations from solid state that you can be happy with, but if you compared it heads up to a tube rig, it is indeed just a simulation. Very much like a hologram - impressive, but it lacks the substance. I lug around two different tube rigs and it is more than worth it. Sound is more important to me than convenience, but that's just me.
    Phaidrus likes this.
  16. drumvsbass


    Aug 20, 2011
    I wish every bassist could do this. Everyone would understand the love affair with HPFs. That tone you think is fat onstage, it's a gorilla in the room, and not in a good way. My own bass tones quality increased immeasurably from doing FOH sound. It's quite eye opening.
  17. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    I had a 40 year professional career at FOH (both mixing and designing equipment for the pro audio industry), it's one of the experiences that guides all of my designs. What players think they know about what their instruments sound like in the audience space and what is really happening are usually two different things.
    DrMole, S-Bigbottom, 2tonic and 7 others like this.
  18. Negative feedback reduces high frequency extension, and makes the output behave in a more linear manner, at the expense of gain.
    Wasnex likes this.
  19. Read up about Bob Carver; he postulated that he could mimic in his own amplifiers the sound of any output topology of another amp, just by inserting passive components to vary feedback and output damping.
    S-Bigbottom, 2tonic, Sid Fang and 2 others like this.
  20. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    I do remember this, it was from an interview probably 30 or more years ago. Bob has designed many well known amps (both tube and solid state) over his career.
    DrMole and 2tonic like this.
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

    May 8, 2021

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