A Simple Question??

Discussion in 'The Workbench' started by MarshallDog, Mar 14, 2019 at 10:41 PM.

  1. MarshallDog

    MarshallDog Well-Known Member

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    Are older vintage amps typically more noisy than newer amps? That’s the general question?

    I ask this because I have a few newer amps and they are very low noise but then I have a few older “vintage” amps and they are more noisy meaning white noise hiss.

    For all you MFers with “vintage” amp experience, what are your experiences?
     
  2. Thiez

    Thiez Well-Known Member

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    Most older amps use carbon comp resistors, which can be a bit more noisy.
     
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  3. ampmadscientist

    ampmadscientist Well-Known Member

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    Older amp designs ignored the noise but as time went on the amps had more and more gain.
    The noise was hiss, filament buzzing, and hum in the power supplies. (3 separate problems to solve)
    Then on top of that was microphonics and oscillations ( a 4th problem)
    The more gain, the more noise.

    In more modern amps, the design paid more and more attention to noise.

    Like for example:
    The first Boogie amps were extremely noisy and had really bad oscillations and microphonics. (I bitched about it)
    Then as time went on, they started adding stuff like DC filaments to get rid of some of the noise.

    Eventually high gain guitar amps will become like Hi Fi amps. (not quite there yet)
    The more we talk about it - and the more we develop solutions, manufacturers will be making quieter amplifiers to meet the popular demand.

    The amp makers hate this...of course.
    It's not the brand of tube specifically. It's the design of the amp itself and the parts that are used to build it (like the resistors).
     
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  4. ampmadscientist

    ampmadscientist Well-Known Member

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    Yes carbon resistors are extremely noisy largely because they are glued together.
    The leads are glued to the carbon....cracks form due to thermal cycling etc.
     
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  5. MarshallDog

    MarshallDog Well-Known Member

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    Good stuff, thanks guys!
     
  6. anitoli

    anitoli Well-Known Member

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    Carbon comp resistors used on the plates of preamp tubes can introduce tons of noise. Replace with metal oxide and feel the silence.
     
  7. MarshallDog

    MarshallDog Well-Known Member

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    Interesting...might be worth doing!!!
     
  8. anitoli

    anitoli Well-Known Member

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    My Fender Dual Showman red knob had comps on the plates and god did this thing have noise. Swapped those out and it was like having a new amp.
     
  9. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Tone is in the carbon glue!

    There goes all that sweet mojo.



    :D
     
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  10. myersbw

    myersbw Well-Known Member

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    As anatoli mentioned, there are ways to improve the "old school design method" and keep op amps out of the mix. The JCM900 on my bench was my first introduction to IC's placed in the signal path (well, regarding "old school amps that are more a hybrid").

    I don't like IC's in my amp's signal path, but solidstate and microprocessor design was my education path in the mid-80's when layoffs forced me into college to change career paths from toolmaking to electronics.

    That said, there are two basic general methods for reducing noise...eliminate the source and/or split the signal - invert it - and combine it to cancel. OpAmps are the mainstay of the current analog world. Read up on OpAmp and CMRR or 'Common Mode Rejection Ratio' and you'll get an idea of the concepts behind bandwidth, noise floor and noise rejection in regard to op amp use in a circuit.

    Many OpAmps are FET or Field-Effect Transistor based in their composition (a lot of variety these days). And, many discrete FET's are/were used in some amps for channel switching. But, note that many of those FET's are some of the first device to fail in an amp when things go south (surge spikes, brownouts, etc.)

    Yet, if not designed properly...even devices solely designed around opamp circuits alone will generate their share of noise. Yes, I'm deviating a little, but consider a TS9 pedal. That one is my fave to mod. Back when those original TS' were designed, no real care was made to design it to be quiet...like amps, we were slamming the signal, clipping it every way imaginable...of course you'd have hiss! :p

    However, as some have found, pull out and replace a half dozen components in those pedals in the key spots and use low noise equivalents...voila! You can get a pedal that's MUCH reduced in unwanted hiss, note-articulate and is world's above the production model sonically.

    My point is, back to AMS' plug..."we don't much like silicon in our old school amps" (Yes, even the diode bridges of old are being upgraded with faster transitioning diodes to reduce noise sources.)

    There are many here with more experience than I on the amp-building/repair side, but I've had enough come across my bench to know that it just takes a lot of care in every area and anyone can achieve an acceptable (if even discernible) level of hiss in an amp by abiding certain rules of circuit building that serve to reduce or eliminate it.

    I have played some current amps that sound great. And, then I open some up and the smile turns upside down. Thin & fragile PCB's, ribbon wire that's subpar, transformers utilized to their edge of design spec, cheap and fragile pots, tube sockets soldered to PCB's that flex just inserting a tube. It's sad.

    Brad
     
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