do power amps wear out?

Discussion in 'Archived Threads 2001-2004' started by Ben Hanrahan, Jan 20, 2003.

  1. Ben Hanrahan

    Ben Hanrahan Stunt Coordinator

    Joined:
    Jan 7, 1999
    Messages:
    87
    Likes Received:
    0
    A very general question here...do power amps lose any of their juice over time or can they be expected to maintain their performance for many years? Also, will playing the amplifier more cause it to wear out earlier or is this a non factor?
     
  2. Ted Kim

    Ted Kim Stunt Coordinator

    Joined:
    Apr 11, 2002
    Messages:
    214
    Likes Received:
    0
    See the following link http://www.passlabs.com/pdf/aleph/a3man.pdf.

    Look at the bottom of page 3. Generally, it all depends on the quality of the parts in the amp and the design of the circuit as to how long they will last. Nothing lasts forever, but when you consider the number of amps from the 60's and 70's that are still working -- with maintenance of course, you can get a lot of mileage out of an amp.

    BTW, Mr. Andre of YBA says the biggest enemy of longevity is heat, so cooler running components will have an easier time lasting longer.
     
  3. Jack Briggs

    Jack Briggs Executive Producer

    Joined:
    Jun 3, 1999
    Messages:
    16,738
    Likes Received:
    129
    Yes to the above.

    A well-cared for transistor amp of good design and built with good parts should last and last and last. Of all electronic components, an amplifier is the only one I'd consider buying used.

    When McIntosh was conducting its famous amplifier clinics, it was not unusual to see twenty- and thirty-year-old units being brought back into spec'. (Now there's an electronics manufacturer whose products retain their value!)
     
  4. AaronBatiuk

    AaronBatiuk Second Unit

    Joined:
    Aug 23, 2002
    Messages:
    333
    Likes Received:
    0
    An amp is the sum of its parts. Its part will wear out, so the amp will wear out. Using the amp more, and playing it louder, will contribute to wear on its components. Excessive heat should also be avoided.

    Amoung the first things to go will be the capacitors, especially those in the power supply. Power supply caps are generally large electrolytic types, and the electrolyte is usually a liquid based one. (some proprietary technologies such as a carbon powder or polymer based electrolytic exist, but are uncommon). This electrolyte can (will) dry out over time, especially if the cap is subjected to high temperatures or to undue stress (greater than normal ripple currents). Usually electrolytic caps are rated at a couple thousand hours of use. For a power amp, the strain put on the caps is usually low, but occasionally very high, so the rated on-hours are probably lower than the actual useful on-hours. Re-capping is relatively inexpensive and easy to do.

    The output transistors can wear out if they are operated beyond or even near their maximum ratings. Low impedance loads (4 ohm speakers or any "difficult" speakers) will have a significant impact on transistor life, as halving the impedance of the load will double the power dissipation in the transistors, which can cause them to exceed their ratings. Most often, receivers will have only one pair of transistors on the outputs of their amps. These can wear out more easily than the typical multiple pairs of transistors in the output stages of separate power amps.

    If I was to rejuvenate an old amp, I would replace, in this order: the power supply caps, the power supply rectifiers (old rectifiers can 'leak' and can have higher forward R), any capacitors in the signal path (usually at least one per channel, at the input), maybe the output transistors if I could find suitable replacements, and maybe even the transistors in the driver stage of the amp (the driver stage provides most of the gain and provides the higher currents necessary to drive the output transistors). This will take care of the power supply and the most stressed components in the signal path.
     
  5. Ben Hanrahan

    Ben Hanrahan Stunt Coordinator

    Joined:
    Jan 7, 1999
    Messages:
    87
    Likes Received:
    0
    Aaron,

    nice to see that you live in Ottawa...so do I!! It's a small world. Now, let's say I'm considering an older Rotel amplifier (rb985 mkII), if these parts were to be replaced, would they have to be replaced with rotel specific parts or could these parts be located elsewhere? Also, do you consider rotel to be a quality amplifier maker?

    Thanks,

    Ben
     
  6. AaronBatiuk

    AaronBatiuk Second Unit

    Joined:
    Aug 23, 2002
    Messages:
    333
    Likes Received:
    0
     
  7. kevitra

    kevitra Second Unit

    Joined:
    Apr 24, 2002
    Messages:
    364
    Likes Received:
    0
    Rotel makes very fine amps. I have owned the 980 (120x2), 985 MKI (110x5 THX) and now the 991 (200x2). All were purchased used and have had no problems. They also hold their value very well on the used market. I sold my 985 for $50 more than I bought it for 18 months earlier.
     
  8. Yogi

    Yogi Screenwriter

    Joined:
    Jul 25, 2002
    Messages:
    1,741
    Likes Received:
    0
    The only thing that wears out are the electrolytic caps in the power supply. They dry out over time. Their lifetime shortens exponentially with temperature so the higher temp you operate your amp at the sooner they will die. I forget the right equation to calculate cap lifetime but if I remember right a capacitor thats running at room temperature will last well over 25 years. So run your amps cooler and they will probably outlast you[​IMG] that is if you dont upgrade in the mean time. All the other parts in an amp like the output devices, rectifiers, transformers, wiring etc will last forever, for all practical purposes.
     
  9. BenK

    BenK Stunt Coordinator

    Joined:
    Aug 27, 2002
    Messages:
    205
    Likes Received:
    0
    Would cycling an amp off and on everyday compared to leaving it on all the time factor into this?
     
  10. Yogi

    Yogi Screenwriter

    Joined:
    Jul 25, 2002
    Messages:
    1,741
    Likes Received:
    0
    If the switching on/off is done once a day it should be OK, but even then like I said the amp will most probably outlast you even if its kept on (well ventilated). If you have to turn it on and off every time you sit down to listen to music and if you do that 5-6 times every day then you might be inducing thermal stresses that happen due to cycling the power on and off so many times wherein the components inside the amp heat up and cool down 5-6 times a day. In that case turn on your amp every morning and turn it off when you retire to bed. I have found leaving my amp on all the time works best for me. I have long forgotten that the amp is in my system. I just turn on the preamp and off I go...[​IMG]
     
  11. TimForman

    TimForman Supporting Actor

    Joined:
    Dec 4, 2002
    Messages:
    847
    Likes Received:
    0
    I agree with Yogi about thermal stress on an amp. Turning an amp on is potentially the moment of highest stress on an amp. A well designed amp will incorporate soft-start and power protection circuitry so even this becomes a non-issue.
     

Share This Page