#1
Hey guys! im looking to build a "little gem" amp from runoffgroove.com (http://www.runoffgroove.com/littlegem.html)

this is the bill of materials (http://www.generalguitargadgets.com/pdf/ggg_little_gem_bom.pdf?phpMyAdmin=4a28f86a515b7883e7bc35a68d4e7b6d)

let me just say i have never built anything before. this is my first amp build.

so according to the BOM, R3 needs to be a 25 ohm rheostat pot. now i have bought everything else i need, excluding speakers, ill talk about that in a sec. my problem is that i cant find a rheostat pot. the shops tell me they dont make them anymore or something. so is there an alternative i can use in the place of the rheostat?

2nd problem.

refer to first image in (http://www.runoffgroove.com/littlegem.html)

i dont know how i can connect to speakers. if i just use speaker wires, what ohm speakers should i use? i also want flexibility to use with a cab. but i dont know how to make a 1/4 inch jack thing. T_T

i have more questions to come.

thanks in advance everyone!!!
Last edited by Luxifer at Jun 25, 2009,
#2
you can find the rheostat at radioshack, and use this for figuring out how to connect the speaker but I'd use the runoffgroove one to base your layout off of still.

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#3
just look for a 25 ohm potentiometer. Should be easy enough to find. If you're local places really turn out to be that anal about it, just look online. Mouser.com and digikey.com are both good websites to find everything you need on, but there shipping is a touch expensive to justify ordering just one or two things. They also have every variation of everything on them, which means it's easy for someone who doesn't know exactly what they want to get lost.

I built a ruby amp awhile ago (just a touch more complicated, but based off the same circuit) and although I don't remember the exact range you can use for the speakers, I believe it was something like 4 ohm at the low to 12 ohm at the high. So I would go with an 8 ohm speaker.

I'm afraid I don't quite understand the last part of your question. Are you saying that you want to have both speakers attached to the preamp, and an extra 1/4 inch "out" so that you can hook it up to a cab? Or are you just wanting to hook it up to a cab?

If you're adding the speaker in yourself, I'm pretty sure you just ground the negative and attach the "out" on the layout you have to the positive on the speaker. It should be the same if you only want it to connect to an output jack for a cab. Just connect the "out" lead on the preamp to the tip(hot) and the grounds to the sleeve.

EDIT: Or you can just ignore this post and follow the easy layout kindly provided by the above poster.
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Last edited by C/ruel at Jun 25, 2009,
#4
someone was just talking about how they want to build an amp to go with a leftover 8 Ohm .5 watt speaker in this thread. isn't it great how forums bring people together.
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#5
so whats the difference between a 25 ohm rheostat and a 25 ohm pot? i dont buy online usually and i wouldnt buy online just for this pot.

my last question was if i dont use a cab, how would i connect the speaker and what ohmage should the speaker be? i also asked how i would connect the amp to a cab because i dont know how to add an output jack thing.
#6
the output jack is supper easy. its the same two wires you have running to the speaker. make the amp output to a speaker jack only. then chop one end off a speaker cable and plug it into the jack. hardwire the other end to the speaker in the combo. so when you want to use an external speaker you just unplug the internal speaker and plug in the external speaker. no switches necessary.
EAT YOUR GUITAR GEAR BLOG
Quote by BigDC
how difficult is it to build your own guitar?
Quote by Gibshall
It's hard, annoying, and makes you want to punch a baby.
#7
ermm im sorry but im a bit confused with what you said there... not your fault or anything but im like SUPER noob at this stuff.

whats hardwire? so i connect the two wires to the jack... then what. im not making a combo. its really like a head and then a speaker, which i might make a cab for. or im gonna connect it to a real cab. maybe an egnater 1x12, cuz i might be getting a rebel 20 yum.
#8
A rheostat is just like a pot but instead of using a strip of resistive material like a pot, it uses a coil of wire. Rheostats are like high-current pots.

For more info on pots, google "the secret life of pots". Also check this out:
http://www.sound.westhost.com/pots.htm

And to learn about various components, Check out the List sticky and click the UG Electronics link.

Hardwire just means wiring it to something.
#11
Either Luxifer has two accounts or therealschnebly is trying to jack TS thread
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#12
i know where to buy speakers.... well ****ty ones and some guitar ones.

if your in canada, you can buy them from long & mcquade. they stock some celestions IIRC.
#13
bump

alright, so i went to the states and finally found my 25 ohm rheostat from radioshack . im gonna start building soon!

ok so the BOM and the diagrams for the little gem is quite bare. i wanna add an LED and an on/off toggle switch. do i just attach these wherever or do i have to calculate something?
#14
Quote by Luxifer
bump

alright, so i went to the states and finally found my 25 ohm rheostat from radioshack . im gonna start building soon!

ok so the BOM and the diagrams for the little gem is quite bare. i wanna add an LED and an on/off toggle switch. do i just attach these wherever or do i have to calculate something?
yes. An LED requires about 2V run it on 9V and you will destroy it. Calculate the current you want the LED to run at and divide 7V by that. This will give you the value of the resistor you'll put in series with the LED.
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#15
Quote by SomeoneYouKnew
yes. An LED requires about 2V run it on 9V and you will destroy it. Calculate the current you want the LED to run at and divide 7V by that. This will give you the value of the resistor you'll put in series with the LED.


will the LED tell me what current its supposed to run on? if the LED is 2V, is it supposed to run on 2V or what... im really confused by this.

but the on/off switch i can put anywhere right?
#16
Put the on/off switch anywhere really. I built a Ruby (and I love it) and I put the on off switch as an spst switch in between the wire from the 9v battery/dc socket and the board, so it just stops any power from going to the board when I switch it. For the LED I just put an LED AFTER the switch on the 9v supply (with a 2k2 - 5K resistor, anywhere between that is fine). Then the negative side of the LED just went straight to ground. It's not this simple with a pedal, but with an amp you do not need sound to go through it when it's turned off, so you can just do it this way.
#17
Quote by Luxifer
will the LED tell me what current its supposed to run on? if the LED is 2V, is it supposed to run on 2V or what... im really confused by this.

but the on/off switch i can put anywhere right?


The easiest way of doing the switch is to use a stereo jack.
The grounds go to the sleeve and ring of the jack so that a complete circuit is only made when a plug is in the jack. This saves you installing a switch.

Different LEDs require different amounts of current. Even then it will be a range, generally in mAs. Say you wanted 10mA in your 2V LED usinig a 9V battery. You'd select a 700 ohm series resistor as 7 / .01 = 700 (V=IR).
#18
Quote by lbj273



i built the little gem based on this diagram on a breadboard. i didnt get any sound at all. however, my battery got hot so i think i shorted it, but i couldnt find the short im gonna post some pics soon to help you guys help me troubleshoot the problem...

i had a few problems building the amp.

1st up is understanding ground. for example, if i were told to ground something, do i just connect it to the negative bar on my breadboard which connects to the negative terminal of the battery?

2ndly, i found out that caps have negative and positive terminals... how do i tell which is which?

im using a mono 1/4" jack for input. im also using a 4 ohm 10w speaker from a bass unit i had from a speaker set. is the input jack fine if i use mono or does it have to be stereo?
#19
Quote by Luxifer
i built the little gem based on this diagram on a breadboard. i didnt get any sound at all. however, my battery got hot so i think i shorted it, but i couldnt find the short im gonna post some pics soon to help you guys help me troubleshoot the problem...
yeah, you probably have a dead short from battery (+) to ground. the internal resistance of a battery causes it to heat up when you try to draw a lot of current from it.


Quote by Luxifer
i had a few problems building the amp.

1st up is understanding ground. for example, if i were told to ground something, do i just connect it to the negative bar on my breadboard which connects to the negative terminal of the battery?
yyyup.


Quote by Luxifer
2ndly, i found out that caps have negative and positive terminals... how do i tell which is which?
Not ALL caps do, only electrolytics. They'll have either a + or - on one side, and an arrow pointing to one of the terminals


Quote by Luxifer
im using a mono 1/4" jack for input. im also using a 4 ohm 10w speaker from a bass unit i had from a speaker set. is the input jack fine if i use mono or does it have to be stereo?
Yeah, you could use a stereo jack and connect the (-) of the battery to the ring terminal. That will disconnect the power, unless a mono cable is plugged in. But you don't have to do it that way. You could use a mono jack and unplug the battery.
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Last edited by SomeoneYouKnew at Jul 4, 2009,