Identical amps but one of them quieter

Discussion in 'Amps and Cabs [BG]' started by generalduncan, Apr 26, 2019.

  1. I am playing these two identical Marshall B25 MK.II amps side by side. One of them is considerably quieter than the other at the same settings. When I crank up both volumes, they sound similar. But in mid levels there is a difference. I open up their inside. Nothing seems different at first sight. Anyone has an idea why?

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  2. Kro


    May 7, 2003
    New Jersey
    Could even be just as simple as natural variance between pots. In other words, "the same settings" visually might not really be the same as far as the amp is concerned.

    Or heck, one of the knobs might even be pushed on just slightly differently.

    Either way, if the amp functions similarly when turned up, I'd say there's likely nothing wrong with either. Some natural variance is to be expected when it comes to potentiometers.
  3. And I

    And I

    Feb 19, 2009
    Witchtown, MA
    both amps have the original factory speakers?
  4. BassmanPaul

    BassmanPaul Inactive

    How are you connecting the amps together?
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  5. lz4005


    Oct 22, 2013
    They're tiny, shifordable 25w amps. Don't expect quality or consistency.
  6. beans-on-toast


    Aug 7, 2008
    This is normal. One amp should be able to be dialed in to sound like the other.

    There’s not just differences in the pots, all the components have tolerances. Resistors could be +/-10%, pots could be +/-20%, for example.

    The bias of the two output stages could be set differently enough to affect the performance.
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  7. Al Kraft

    Al Kraft Supporting Member

    May 2, 2016
    Northern Virginia
    Normal variability in will often see this even in high end gear. In fact, Tech 21 has actually discussed this relative to identical knob positions on different boxes not reproducing exact sound/tone/voicing.

    Unless you have specially designed and calibrated (against a known standard) gear such as high end test or laboratory equipment, there is going to be perceivable variability.
  8. Yes. Same speakers. No tweaking as it seems.
  9. I am not. I am connecting to each amp one by one for testing purpose. They just sit side by side:)
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  10. And I

    And I

    Feb 19, 2009
    Witchtown, MA
    ok before you just chalk it up to variances in the components used in the amp... turn all the knobs all the way down. do they all point perfectly to zero? if one of the knobs was removed and put back slightly rotated, it might look like you have the knobs all in the same place but the pots and knobs may not all be aligned the same way?
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  11. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Different control tolerances can result in this, also it's not uncommon for amps to go through a number of small revisions throughout its life and it's quite possible that you have 2 different revisions. Either way, it's generally not a big deal, especially on a budget amp.
    hasbeen, And I, Al Kraft and 2 others like this.
  12. AudioTaper


    Sep 23, 2018
    Good comments here.
    Are the volume pots the same taper? One could be linear and one could be logarithmic. One could have been changed in a revision to the design or even product substitution at the factory.
    Worker: we are out of the volume pots
    Boss: just use whatever, I'm going on break....
    generalduncan likes this.
  13. AudioTaper


    Sep 23, 2018
    20190426_201245.jpg The value is usually printed on the part. Here is a 10K linear for example. See the little mark next to the value?
    "A" for logarithmic taper or a "B" for linear taper; "C" for the rarely seen reverse logarithmic taper
    generalduncan likes this.
  14. You might want to dress the wiring the same on both to make certain you aren't inducing any kind of noise or hum. Power supplies can also vary and have an effect.
    generalduncan likes this.
  15. Common enough on higher end gear that you can pay a premium for matched tubes, matched microphone pairs, etc. Certainly nothing to be concerned about on a pair of budget solid state amp.
  16. Wisebass


    Jan 12, 2017
    Lost in Space
    hi Kro :)


    "Natural" like "they grew on different trees"? :laugh:;)


    agedhorse likes this.
  17. First I removed all knob caps (to clean). Then I dialed down all pots to zero. Then recapped all the knobs in a position that they pointed towards their initial markers (min level) and all were in parallel. So I'm sure all knobs are at the same level relative to their pots.
  18. interp


    Apr 14, 2005
    Garmisch, Germany
    There is no such thing as two manufactured items being completely identical.
  19. Kro


    May 7, 2003
    New Jersey
    No... from my understanding it's technically more like they grow on a flowering plant of some sort. I didn't know that pots were illegal to grow and distribute except for under very controlled circumstances, but it seems like all everybody can talk about these days is legalization, so...

    The more you know, right?
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  20. Al Kraft

    Al Kraft Supporting Member

    May 2, 2016
    Northern Virginia
    It's not the knob markings/positions where you have the variability you're hearing (although that is also a variable), it's in the electrical properties/characteristics of the potentiometers themselves, along with the variability in the electrical components in the circuitry in the amps. The best you can hope to do with realigning knob markings (and this assumes consistent and/or linear variability in the circuits) is to turn the pots and find an obvious point where you have identical sound and then place the caps back on with the markings showing the same setting.

    What you are experiencing is normal IMO unless one amp's control goes 3/4 the way up with the volume at a whisper and then suddenly goes to full power - in that case it's broken. Decades ago before we had 6 Sigma manufacturing process control programs and most things from cars to televisions were assembled from parts with simply "acceptable manufacturing tolerances" we would see a wide variation in performance, reliability, longevity, etc. When higher precision (i.e. tighter tolerances with minimal or no variation) was required, prices went up rather dramatically. Often times today that broad variability is present in lower cost mass produced items where high precision isn't a concern and the variability can be easily tolerated given the lower cost.
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