why do some amps make thump when pwr up

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leftwinger57
leftwinger57 Posts: 2,917
edited December 2012 in Electronics
I ask this because thankfully my Adcom has no such problem but I do remember that a few expensive brand amps did.
Now mind you this was back in the 70's so I really do not know if it still holds true. One friend had the industrial
looking Mcintosh 2100 to power his bass guitar rig ala Jerry Garcia.He always told me before powering on the amp
make sure the volume pods were at low or off or a pop would occur and could blow his Gauss and JBLs. An other
friend had a Mac 2105 w/ a c-28 pre w/ ESS Heil AMT 1s and I was told the same thing.Is this an inherent thing w/
Macs or one of those amplifier anomalys that you just have to deal with?
2chl- Adcom GFA- 555-Onkyo P-3150v pre/amp- JVC-QL-A200 tt- Denon 1940 ci cdp- Adcom GFS-6 -Modded '87 SDA 2Bs - Dynamat Ext.- BH-5- X-Overs VR-3, RDO-194 tweeters, Larry's Rings, Speakon/Neutrik I/C- Cherry stain tops Advent Maestros,Ohm model E

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  • Drenis
    Drenis Posts: 2,871
    edited December 2012
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    My Adcom 5400 thumps to.
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  • EndersShadow
    EndersShadow Posts: 17,749
    edited December 2012
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    Lots of Carvers do this. My M1.0t does and so do many Carvers and other amps.
    "....not everything that can be counted counts, and not everything that counts can be counted." William Bruce Cameron, Informal Sociology: A Casual Introduction to Sociological Thinking (1963)
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  • Drenis
    Drenis Posts: 2,871
    edited December 2012
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    EndersShadow wrote: »
    Lots of Carvers do this. My M1.0t does and so do many Carvers and other amps.

    Yup. My TFM-42 did this when I owned one.
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  • Speedskater
    Speedskater Posts: 495
    edited December 2012
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    The Carver "TFM" series amplifiers had a delayed turn-on, never heard a power supply pop from them. Yes they may have had a turn-on noise when the relay pulled-in but not a pop.
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  • zingo
    zingo Posts: 11,258
    edited December 2012
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    It's caused by an inrush of current as the power supply filter caps charge; as already stated. There are very few modern amps that do this as most have soft-start circuits (inrush current limiting to slowly charge the caps) and thump protection to slowing drain the caps when the amp is turned off. This is a circuit that can be added to most older amps, but more the most part it is harmless.
    Jake
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  • helipilotdoug
    helipilotdoug Posts: 1,230
    edited December 2012
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    My TFM-45 thumped every time on shutdown since the day I got it, but did not on start up. Then recently, it started thumping a lot louder, and sometimes would squeal a bit on start up. I got afraid I'd damage my speakers, and took it out of service. It needs to be gone through and "refreshed".
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  • marvda1
    marvda1 Posts: 4,971
    edited December 2012
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    some highend companies believe this protection circuitry degrades the sound of the amp( the less the better).
    Amplifiers: Norma IPA 140, MasterSound Compact 845, Ayre v6xe, Consonance Cyber 800
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  • gdb
    gdb Posts: 6,012
    edited December 2012
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    That thump just indicates that the amp is gettin' ready to whup a$$ and take names ! :cheesygrin:
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  • Speedskater
    Speedskater Posts: 495
    edited December 2012
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    marvda1 wrote: »
    some highend companies believe this protection circuitry degrades the sound of the amp( the less the better).

    Some high-end companies believe (or at least write about) all sorts of strange nonsense!

    But a soft-start circuit is a lot trickier to design than it would first appear.
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