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Bought an amplifier, trying to disprove the company

Discussion in 'General Electronics Discussion' started by sndscientist, Feb 10, 2014.

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  1. sndscientist

    sndscientist

    47
    1
    Jul 10, 2013
    usually i am on top of things, but this has me baffled. i bought a certain amplifier for a permanent instal job i have from a notoriously cheap manufacturer. the price was right so i figured I'd buy a test unit to see if it would do what i needed done. it seemed to work very well. but it was ridiculously light so being the nebby person i am i cracked the case. now i am used to seeing switching power supplies in these things and smt transistors on huge heatsinks. but this one seemed different. it had 2 output devices per channel one pnp and one npn. i started thinking that there is no way on earth this can output nearly the claimed 500 watts per channel. so i started metering it. the power supply to output board had a rail to rail voltage of 100 Volts. (+/-50 to the Ground) so i began being a bit more skeptical. the output devices are a single A1941 and a single C5198. which according to the datasheet are rated 10Amps continuous at 140VDC. resistor to the output is .25 ohms.

    According to my math this setup is capable
    (6.06A) 303 watts at 8.25 ohms figuring 50 volts and
    (10A) 500 watts at 5 ohms again with the 50 volt supply.

    understandably the power supply will limit the output by not being able to produce a solid 25 amps. however the rectifier is a nice 12 amp unit.

    so like i said mathematically it checks out. on the meter it checks out but i have taken apart and tested amplifiers rated the same power with 12 devices per channel and power supplies that weigh more than 3 of these units

    :confused:
     
  2. davenn

    davenn Moderator

    13,673
    1,892
    Sep 5, 2009
    the 50V calcs you have done are not relevant are they ?
    as you have already told us its working off a 100V split supply

    but apart from that you should never believe all the sales hype like these ridiculous peak music power ratings etc
    most of that is garbage

    Dave
     
  3. sndscientist

    sndscientist

    47
    1
    Jul 10, 2013
    i don't believe the sales hype but the price was right for me to check it out. that's why i only bought one. the way i am i test stuff before i install it. and when things seem to good to be true i open the cover and start taking measurements. these amplifiers cost less than blank rack plates. yes i know the dc voltage specs don't entirely apply to an ac load, and the measurements i took represent peak power it's just odd that they would actually measure up close to what the manu actually said. i know for a fact that no matter what the internal measurements said it cannot be close to the rated specs as it has a 6 amp fuse on the 120v mains meaning it will blow if the amplifier draws more than 720 watts from the line and granted that this is a class A/B amplifier with 2 fans i assume it will give off roughly 30 watts in heat/light and noise. so i know it cannot be nearly what it claims but my confusion point is that it seems as though the amplifier modules can actually produce the rated power safely. i am half tempted to take one and place it on a 260 volt center tapped supply just to see what will happen giving each transistor 10 volts less than it's rated.
     
  4. shumifan50

    shumifan50

    548
    56
    Jan 16, 2014
    I am no fundi, however would it not make more sense to measure the output of the amplifier and see at what point, turning up the volume, does it start clipping. In my past experience this has always been the biggest limitation on how hard you can drive an amplifier. Some of the amps I had also started behaving very badly when driving them hard for a longer period of time(components overheating), so this might be something else to look at. In the end it is not how the circuit is made but whether it produces the expected/required output(quality and power).
     
  5. sndscientist

    sndscientist

    47
    1
    Jul 10, 2013
    i can say it does fairly well compared some of the other garbage I've bought. i know it's just a waste of time at this point but now its got me wondering what level of normal usage would it take to kill it. reason behind this is it is being installed in a church, nothing ridiculously hard, no super duper bass response needed, just a nice light duty job for it. the only reason i'm going through this is i want to make sure that if an unexpected cable pull, or mic pop gets to it that it will not internally explode as i have seen some of the big ones do. the building is wired in series parallel giving me 8ohm drops and services are generally 2 hours a day so this bugger will be on maybe 12 hours a month totally. i know i'm over analyzing this like i usually do but like i said it peaked my curiosity as to what they are actually capable of
     
  6. shumifan50

    shumifan50

    548
    56
    Jan 16, 2014
    As longivety goes I would check the temperature it runs at under the expected volume and I would also check the brand of capacitors used - some of the Chinese brands have a very limited life, worsened if they run in a hotter environment.
     
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