Need a little help with a L 20 amp

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ibuildstuff4u

Member
2012-11-25 5:22 am
  • #1
    My 15 year old nephew built his own speakers so I figured it would be cool if we built an amp to power them with. I bought a L 20 amp kit from china and taught him how to solder it up. I picked up a broken amplifier off E-bay for the case and transformer and put the new L 20 amp boards inside. The broken amp was a Samson Servo 240 and was air cooled so there is a nice heat sink on the back to mount the new L 20 boards to. The transformer puts out 55 volts DC after the bridge rectifier which should match up nicely to the L 20 boards. I was also able to reuse two 10,000 uf 71 volt capacitors from the old amp.

    The question is do we need a pre amp for this project? My nephew plans to run his I pod or a CD player threw this so they are at line level, but when I tested out the amp with my I pod I ran out of gain really fast and wasn't able to get the full volume out of the amp.

    The amp sounds great with no hiss or hum, but I can't get enough volume out of it. I have it hooked up to a smaller PA monitor speaker which is good for 50 watts and can barely make it distort before running out of gain on the I pod volume. I hooked up a 100 watt sub woofer and easily maxed out the volume with out any distortion. The amp is no ware near clipping.

    Please let me know if I need a pre amp for this amplifier and if ether one of these boards would be a good choice.

    Thanks, Dale P.

    [wiki=http://www.ebay.com/itm/320915557448?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649]%[/wiki]

    [wiki=http://www.ebay.com/itm/220866124397?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649]%[/wiki]
     
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    rfj5106

    Member
    2006-03-05 3:27 am
    Richmond, B.C CANADA
  • #3
    I have built several L20 amplifiers and run them without preamps using a CD player as a source and get huge amounts of volume. I use 50K potiemeters to attenuate the input which act as a volume control. I would try a regular CD player rather than an Ipod. I suspect there is some serious impedance imbalance for the Ipod. To use the Ipod you probably need to add some op amps to act as a buffer between Ipod and amp.
     
    I

    ibuildstuff4u

    Member
    2012-11-25 5:22 am
  • #4
    I tried running a CD player through it and still don't get enough gain. The CD player was run straight to the amp with out a pot switch for volume control, just wide open.

    I'm putting 55 volts DC to each side of the amp for a total of 110volts DC to the board. The transformer and capacitors are from the Samson Servo 240 amp which put out 120 watts per channel at 8 ohms. Right now I'm just powering up one of the L 20 boards so the transformer should have plenty of power to put out more Watts. I don't have any type of pre amp here or I would give that a try. Perhaps I will run down to radio shack and pick up a cheap audio mixer to hook in line with the CD player and amp as they have a pre amp inside that should boost the line level.

    Adding a pre amp isn't too big of a deal if I do need one, except for the fact that I'm running out of room inside the case. The original transformer only has high power taps so I would have to add a second transformer to power up the pre amp and then also find room for the pre amp it's self.

    Dale P.
     
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