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Posts posted by ben23

  1. would the KEMO #M40 pre-amplifier module be ok to amplify a guitar output to line level so i can play my guitar thru a normal amplifier when I dont have access to a proper guitar amp.

    here is the link for it:


    and this is how i figured i should wire it, the guitar input being a 1/4" jack and the outputs being dual RCA's


  2. yeah theres nuthing on the 5V rails, ill have to try that, i have a little 12v pilot light, ill measure the resistance and see if it will be ok, that way i can see if the PSU is on as well.

    there is an orange "power good" wire, should i ground that or power that or anything, maybe so the PSU thinks the "power's good"
    or is that so the MB knows that the power's stable
    if i used the 12+ and 12- rails instead of 12+ and ground would it get more power?

  3. ok first your going to need it to work like this

    phone rings - relay closes - computer starts up
    you hang up - relay opens - computer keeps on running

    to turn off
    phone rings - relay closes - computer begins to shut down (as long as you have configured the Power settings in Control Panel to do so)
    you hang up - relay opens - computer proceeds to shut down

    you observe to see whether you can access the computer anymore, if you cant, your successful, if you can, you need to ring, and let it ring until you lose connection, which will do the same thing as holding the button on the front of the computer until it turns off.

    you will need a TTL type relay (which work on tiny voltages) to switch the green wire from the computer power supply (turn-on) and one of the black wires from the computer power supply (ground) just splice into these two wires, just splice and solder and tape/heatshrink.

    I will have a look for a suitable relay and get back to you with the details.
    This is actually quite a good idea.

  4. i have a old 220w computer psu, so old that its an AT, and was built in '94, im using it to power my 12w x 2 amp that usually is in my school bag with the speakers, but im sick of charging the battery all the time at home, so i rigged it up to this PSU, but i measured the voltage between 12v+ and ground, and i only had about 10.5, dropping to 10.4 when pushing it. with no load its at 10.6
    should i just get a new PSU? or is there something I can do

    btw i hooked up the fan to the 12v supply but it couldnt be drawing that much, its only an 80mm fan.
    its a regulated switching supply (well i assume its regulated), so shouldnt it be at 12v exactly?

    btw I have 2 of the 12v+ twisted together and soldered to a wire going to the positive of my amp and 2 of the grounds twisted together soldered to a wire going to the negative, should i maybe just use one of each?
    or diodes?

    any help appreciated

  5. yeah i think ive just had bad luck with the PSU's, that 5+5+3.3 sounds pretty good actually, nice work Ante, cos that gives 13.3 like u said, but its not voltage that worries me, admittedly, it wasnt a 300w now i think of it, it was actually a small mini-ATX 80w power supply, with 2.7A on the 12v rail, and it was a cheap CD/tuner

    how many amps can u pull with the 5+5+3.3 setup safely?
    would a 300w psu be enough to power a small BOSS CD/Radio head unit, that is probably about 4 x 35w - obviously theoretically it could run 2, but im making room for heat dissipation and that so yeah, was thinkin of settin that up in my shed.
    set that up with 2 x 6 inch's inside and 2 outside the shed
    that would be all i would be running

    btw if u start to overload the PSU 12v rail, do they tend to start poppin capactors, or do they just fail?

    sorry to hijack the thread but its the same thing

    and to Frank, the only concern is the small gauge of wire that will be connecting the amp (18 gauge) to the psu, unless, you modified the PCB and allowed it to fit 8 gauge straight from the PCB.
    i only recommend the battery as u will be able to run any amp you want and not have to worry bout blowing a PSU up
    and u will avoid having to control the volume around the PSU's amperage.

  6. ok first of all, how much does the amplifier draw in amps (the fuse rating is a good indicator of what it is) or check how many watts the amp it is. then divide the wattage by 12, you will get the amperage draw (this would obviously be at maximum volume)

    second of all, once you have found that, u will need to see how many amps you can draw from the 12 volt rails of your power supply. the equation 600/12 = 50A would not be right, as that 600w counts for the 5 and 3.3 volt rails, which will not be used here. on most PSU's there is a label which will tell you the amperage of the 12v rails, and as far as i know its per wire, so if it says something like "+12v = 8.2A" thats the maximum you can draw from each wire, hence the diodes, so they dont cancel each other out, once u have found the amperage, multiply that by the number of wires, noting that there must be the same amount of ground wires (must also have diodes) as there are power wires.

    third of all, a computer power supply isnt a very rugged source of power, an amplifier really needs a beefy source of around 13.8volts
    it will work, but it will not be very efficient, and will most likely be short-lived. when the power supply makes a sound reminiscent of a cap gun going off, you have blown the output capacitors and the power supply is pretty much finished. i have tried to use a 300w psu to power a small car radio (no cd or tape, just radio), it had a capacity of 8.2amps at 12v, but i still blew it! because they aren't solid enough.

    best bet is to get a small car battery (or even a 12v motorcycle battery), and a charger. or order a 20amp 13.8v power supply for AU$99.95 (works perfectly) from www.jaycar.com.au and that should have enough grunt to power any amplifier up to 300w. if you arent in australia it is ok, as you have 220V as we do (actually 240v but there is really no difference), just buy it, change the plug or use an adaptor, so there will be no problem with mains voltage.

    Warning: if you are intending on using a large 4 channel amplifier it really isnt worth the trouble, as any power supply capable of powering a large amp like that will be expensive, large, and heavy.

    you never know u may be able to power it, i just need to know the amplifiers power, the amperage of your PSU's 12v rail

  7. first of all, make sure of these few things
    - you have a quality power supply
    - your power cables are in good condition and are plugged in tight
    - you have a RCD = residual current device (safety switch) or a GFCI for americans whether it be at the switchboard of your house or as a plug adaptor DO NOT LOOK PAST THESE DEVICES THEY SAVE LIVES.
    - you have a reputable surge protector, as excessive surge current passing through a computer will do more than fry it, it will create excessive heat that can start a fire
    - you keep the computer clean of dust and all fans are working
    - you have good ventilation space around the computer
    - you turn the monitor OFF, not let it go into standby when not using the computer and that the monitor is free of dust

    personally i dont leave my computer on at night as there is no need, the only thing i leave on is my DSL modem (which i had to permanently fix on cos the switch broke and most modems dont have a switch anyway)

    but if you are going away for a length of time and the house is going to be empty, do what i do - UNPLUG THE LOT


  8. now i know i have the system thats in my school bag (the 12w x2), but i need one thats smaller, i have a small amp pcb from a pair of multimedia speakers.

    it has the usual tone and vol control pots on it, but, its made to run on 12v AC from the mains transformer, but right after where the power leads solder to the pcb, there are 4 diodes and a capacitor, me thinks that is a rectifier circuit.

    i tried running 12v DC (using the SLA battery from my bag system) into the amp and it sounded ok, but a bit distorted, if i tapped into the pcb AFTER the rectifier, and determined the polarity, it should be ok right?

    im on holidays at the moment, when i get back i will get pics of my bag system for my other post, and pics of this amp


  9. yeah i know what you mean, im not too fussed on SQ, it just has to relatively clear, not distorted and loud.
    Car speakers dont have a specific enclosure requirement, as they are usually mounted in car doors.
    i would use the box i have but the way i have built the bottom has been built around the existing speakers, plus im going to make the next one from scratch
    i use it at school to play music at lunchtime and that (got told by one teacher never to bring it again haha, but the rest love it, so f*** her!!!


  10. in reply to audioguru, you say that my amps deliver less than specified, it does have a bit of high volume distortion, but it is quite a bit louder than 2.2 watts could make.
    my estimate about 4 watts per channel, without being optimistic
    in regards to the amplifier u had, what kind of inputs and speaker outs did you use, i was going to use banana plugs but thought it would be stupid, plus this had to be a budget amp, so i just used speaker spring terminals and they work fine!

    im going to make a smaller box and use 5" 2 way 4ohm car speakers, so that way i save space by not having a seperate tweeter, and get more power out of the amp by having a 4ohm impedance. and i can make a storage space for the amp and battery so it is all in one box.

  11. heres the full specs

    Modules: KEMO #M32 12W ampl modules x 2
    Pot: 10k linear double gang
    Input: stereo RCA
    Output: Speaker wire spring terminals
    Battery Voltage: 12 - 13.5v DC
    Batt max amps: 2.2Ah

    Speakers: 4 3/4" Sharp woofers and 2" Sharp tweeters
    Impedance: Woofers 8 ohm, Tweeters 6 ohm.
    Box: Particle board, used to be an old speaker box, used to house one of the woofers and one of the tweeters. Other box was destroyed!

    Soon to come

    5" 4 ohm 2 way car speakers

    I will get a pic of the enclosure soon
    they are in the same box but there is a divider between the 2 sets, so that way they aren't cancelling each other out (which was happening)
    im going to put a 1 inch port into the back of each section, to put relief on the speaker cones and to aid the bass reflex.

    i will add more pics soon

  12. how do I use a standard 240v single phase ac motor driven by a petrol engine to create 240vac between the active (hot) and neutral wires of the motor?
    if i got a 2400w motor and drove it at the appropriate speed would it push out the full 10 amps that it would normally draw. (maximum capacity of australian powerpoints in the house, except for 15a air con / specialty sockets)

    is there any components i need to make it work and is there anything i need to watch out for?


  13. Hey ppl I'm ben and finally built my first proper amplifier, which is just built into a plastic jiffy box, with a 10k double gang pot for vol and runs off of a 2.2Ah 12V SLA battery, the amplifier modules im using are made by KEMO in germany, i picked them up for AU$23.95 each here, all up the whole thing costed AU$107.38 to build including SLA battery (AU$24.95) and charger ($19.95)
    i have it in my school bag along with a wooden box containing 2 x 4 3/4 inch woofers and 2 x 2inch tweeters, i just hook my mp3 player up to the amp.
    it has RCA inputs, speaker spring terminal outputs.

    it sounds great btw, the modules need a bit more burning in but once thats one it will be mad.

    here are some pics

    top of amp

    front of amp

    rear of amp

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