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question about davemade amps

Discussion in 'Amplifiers' started by loosecannon, Sep 11, 2008.

  1. loosecannon

    loosecannon break on through

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    im thinking of trading some equip to a buddy for a davemade 4x2879 amp.
    no variable power, and no driver transistor, just a straight 4 pill, but he says it is called an M400.

    he also says that there is no RF keying circuit in the amp, and that i will have to add one to either the radio or the amp to key it with a cb radio.



    i have never heard of this in a cb type amp, as i thought this was something that was done with ham amps because of the way the ham transceivers transmitters work.

    so, does this mean that this amp is meant to be keyed by another amp?

    there is a 1/4" jack on the amp, and im guessing this goes to another amp???

    will i be able to use this amp using just a cb radio to key it?

    will i have to add my own RF sensing circuit?

    anyone with experience with amps of this kind, i would really appreciate a lesson in how this all works.
    not too experienced in the "comp amp" world.

    thanks,
    LC
    #1

  2. 9C1Driver

    9C1Driver Well-Known Member

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    Someone modded it to work that way. If the keying relay is still inside then a tech could re-do it to stock and you would be fine. Thats odd for a Davemade since it's not really a SSB amplifier.
    #2
  3. mackmobile43

    mackmobile43 Jock Supporter

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    If there was never a keying circuit in that amp it most likely was for keydown use and was keyed manually as to eliminate the possibility of the keydown opponent from keying before that amp did and blowing out the transistors in the radio.

    Therefore the radio attached to that amp never had recieve, only transmit when the output circuit was applied.

    Installing a key circuit is a piece of piss as bob85 would say to install.

    Pictures are greatly appreciated if possible.
    #3
  4. loosecannon

    loosecannon break on through

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    thanks for the replys!

    so, i just need to add a keying circuit.
    shouldnt be too hard to breadboard one up.

    i dont have the amp yet, but if i can get it to key with a regular radio without spending too much money, i am going to get it.
    will post pics when i do.

    in the meantime, i am still interested in learning anything else i can about these amps.

    is one car battery enough for something like this, or should i use two?

    thanks for any advice,
    LC
    #4
  5. formulamojo

    formulamojo Active Member

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    The 1/4 inch jack is probably for a remote to turn the power to the amp off and on.

    The easiest way to do this is go to rat shack and buy a microphone cable and a 30 amp toggle switch, lop the end of of the cable and solder in the switch, plug the other end into the amp and mount the switch to the dash.

    You now have what we like to refer to as a f@#k switch.



    Your stock charging system should run a 4 pill just fine.

    I run a 2 pushing a 6 on my stock 150 amp alternator, i just added a battery.
    #5
  6. loosecannon

    loosecannon break on through

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    FM,

    usually, that is what the "remote" jack would be for, but not on this amp.

    that jack is actually the input.
    driven by another amp is my guess.

    why use a 20 amp switch and then use such small conductor cable?
    seems like you would need either a 20 amp switch and heavy conductor, or dont need big switch and use mic cable.

    im not sure, but i thought that the power switches on these things were small because they switched the relay which switches the high current.

    still learning about all this stuff.
    LC
    #6
  7. formulamojo

    formulamojo Active Member

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    LC,

    you have a touched amp!!! lol.

    mine aren't labeled remote.

    I like to use the larger switches, you can use a smaller ine if you like. Matter of preference on this one.
    #7
  8. loosecannon

    loosecannon break on through

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    i gotcha, big switch looks much better on the dash than the wimpy little toggle switch. LOL

    i do not have this amp yet, but i will post pics when i do get it.
    FM, just so you know, i am getting this from FD.

    later,
    LC
    #8
  9. formulamojo

    formulamojo Active Member

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    Is that the one he was fuming about last week?

    If you need it worked on I can put you in contact with a couple guys. One of which worked for the original Dave, not this new guy.
    #9
  10. loosecannon

    loosecannon break on through

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    thanks for the offer FM.

    if you happen to talk to either of those gentlemen, you might ask them if there is a certain way that "they" would convert it back. (like, the davemade way or something LOL)

    i already have an idea for the keying circuit if they dont come up with anything, so, no biggie either way.

    thanks for the help,
    LC

    PS-yes, its the same amp.
    #10
  11. mackmobile43

    mackmobile43 Jock Supporter

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    the key circuit is only a 5 amp dpdt relay/2n2222a transistor/a small value gemanium diode and a 7 to 10 pf silver dipped mica cap for sensing rf voltage. total less than $10 at ratshack.
    #11
  12. loosecannon

    loosecannon break on through

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    thanks MM!

    hopefully will be getting the amp by next week some time.

    anyone have any suggestions, tips, ideas, stories etc, about using two car batteries in the trunk to power the amp?

    since ive had problems in the past with this vehicle and using an amp in it, i want to use separate batteries just for the amp instead of powering it with the vehicles electrical system.

    but ive never done an amp install like this and am very open to hearing about how it has been done in the past.

    4x2879 davemade amp
    uniden PC78xl will be the driver. (am going to use stock final, and just do the RC/NPC mod to it.((dont need opinions on this mod thanks LOL)))
    two car batteries, both the same kind, bought at the same time.
    wilson 1000 antenna on the roof of the car.


    thanks!
    LC
    #12
  13. formulamojo

    formulamojo Active Member

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    LC,

    Remember the big long post I made on the other site? Start there and feel free to ask lots of questions.

    Braided ground strap, 6 gauge cable, copper ring terminals, solder all connections.
    #13
  14. loosecannon

    loosecannon break on through

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    FM,

    way ahead of ya! LOL
    thanks,
    LC
    #14
  15. loosecannon

    loosecannon break on through

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    FM,

    ive been reading and researching about ground loops and such for a few days now, and i have to say i have found some very interesting stuff!

    while reading on a ham forum, i ran across a guy who has been dealing with RF grounds and mobile installations his whole working life.

    he said the same thing you did about running the negative wire of the radio right to the battery terminal, but not running the amp's negative to the terminal.

    not sure if you know the "why", but he said its because the radio's negative lead is isolated from the chassis, so its ok to go to the terminal.

    however, with the amp, (or most ham transceivers), the negative lead is tied to the chassis, and therefore needs to be at the same potential as the shield of the antenna coax.
    therefore, connecting the negative lead of the amp to the vehicle body puts it at the same potential as the antenna coax shield.
    makes sense to me!

    i am learning alot, and just wanted to let you know i found someone "in the know" about this stuff who agreed with you.

    cant wait to get the amp and try some of this stuff!

    later,
    LC
    #15


: ground loops

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