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About to build my first amp, need some help.

post #1 of 9
Thread Starter 
My DIY side finally broke down and I decided to try to build this thing. Anyways, the extent of my electronics knowledge was one lecture on digital logic design (i.e. what a transistor is, how to build gates, how to use those gates to do addition), so I went over to sci.electronics.basics and read up on all the newbie guides. Just have a few quick questions before I start building these things. I'm trying to build the infamous Moy amp btw.

#1: Input and Output. These are obviously the headphone jacks, but what exactly should I be looking for to buy these? I don't see a part # on Moy's article, and was wondering if anyone know offhand exactly what I should be looking for. The wall of plugs at radio shack was fairly intimidating. Also, on the headphone itself, what part of the plug are the left channel, right channel, and ground?

#2: The "R1 1/2SW1" portion of Chu's diagram is a little confusing to me. This is how I'm reading it, tell me if I'm wrong. From the input, you have wires going to both your switch and the 100K resistor. The wires from the resistor and the pot both lead to the interconnect. The net effect being you get a high voltage when the switch is on because the resistors are in parallel.

#3: A connection to three parallel lines that get smaller (in the diagram, what R2 is connected to) means connect to a ground, right? Also, what exactly is your ground? Something tells me hooking these up the headphone ground is not a good idea, but that seems like the natural solution.

#4: For the power supply diagram, there is a "low current" LED in the diagram. Since my local rat shack doesn't have that part number (RS 276-310), can someone give me a definition of what exactly "low current" means?

In any case, thanks in advance for all your help.

-Chu, who is guaranteed to electrocute himself at least once putting this together.
post #2 of 9
You won't be able to get all the needed parts from radioshack (and anything you get from there is generally overpriced/inferior), so i'd recommend getting them online from digikey or equivalent. (right now, they even have the 134's in stock!)

1) i like to use RCAs for the inputs because you can hook them up to any interconnect instead of having to buy a special one.

For output, if space isn't a concern, then i like to use 1/4" jacks because you can easily plug in either 1/4" plugs or 1/8" plugs with an adaptor. The adaptor fits inside the jack, and doesn't take up any more space. With minijacks, its a real B*** to use anything other than miniplugs.


2) for your first amp, forget about the switch. Just wire up a pot for the input, and put the output of the pot into the filter cap.

3) The 3 parallel lines indiates GROUND, though a more logical way of calling it is COMMON. Simply connect all the points marked with that symbol together (ie, input ground, high-pass filter ground (the resistor at the input of the opamp), ouptut (headphone) ground, and the ground set by the resistor divider in the power supply section) Just connect all these points together, and to the chassis/housings of all switches/pots which are made of metal.


4) you don't need a low current LED, you can use any LED, just find a resistor that will set an apropriate brightness...


good luck!
post #3 of 9

Chu, welcome to hell! err, welcome to DIY! :)

1) Use either a 1/4" or a 1/8" three-conductor jack for the output. Also called a "TRS" or just "TR" (this is Tip, Ring, Sleeve) For the pinout of 3-conductor jacks/plugs, the tip is left, the ring is right, and the sleeve is ground... And then, use RCAs or 1/8" three-conductor for the input.

2) As Thomas says. The resistor(s) and the switch are for changing the input level... this is intended for when you want to use your source's built-in volume control, instead of a potentiometer in your amp circuit.

If for nothing else, the best reason to use a pot instead of a level switch is... rotating a pot will eventually wear it out; at least when it's your pot in your DIY amp, it's much easier for you to replace yourself - than say the pot in your portable CDP.

3) Yep, that's the ground symbol. Connect all of them together somewhere. You can implement a bus and tie everything to it, or just "star ground" - run all your connections with that symbol to one location, like spokes to a hub. (and yep, headphones get grounded too)

4) low current LEDs are usually 2mA. Sometimes you'll find 5mA. But a normal LED is 20mA. Other colors besides red and green, normal is 30-40mA. For a battery amp, this is insane... the one LED will draw more than your amp. The catch is - while you can limit a normal LED to use only 1mA or less, it'll be so dim it'll look "burnt out".

You're going to be going to other places than Radio Shack. I'd suggest downloading the Digi-Key PDF catalog... you can get alot of stuff there, including the opamps. (warning, ~25M, dialup takes 2+ hours!) http://info.digikey.com/T012/V4Complete.html
post #4 of 9
Here are some of the parts I use from Radioshack, all of which can be found in the stores:

Micro-mini DPDT switch (275-626)
SPST micro-mini switch (275-624)
Low Current LED (276-044)
Chrome LED holder pkg (2) (276-080)
Snap in LED holder pkg (5) (276-079)
Gold Plated RCA jack pkg (2) (274-852)
Mini-headphone jacks (274-249) [I don't like these]

For plugging your amp into the wall. Too big for a portable amp though:

3V-12V 800mA Regulated/Filtered AC-DC adapter (273-1667)
Adaptaplug M 5.5mm/2.1mm (273-1716)
DC Power Jack Panel Mount 5.5mm/2.1mm (274-1563)

Here are some components. Probably best to use Digikey though:

.22uF 50V 10% PC-mount capacitors 2pk (272-1070)
1.0uF 200V 10% Metal-film capacitor (272-1055)

--
Scott
post #5 of 9
Thread Starter 
Thanks for all the help! the IC's are in the mail, hopefully I can get this all together before I have to leave for college.

-Chu
post #6 of 9
Thread Starter 
One last (hopefully) newbie quest. Just got the IC's in the mail, and i'm wondering, how do you tell which pin is pin #1? And #5 for that matter, i'd assume it was the one directly across but assumptions have gotten me into trouble before.

-Chu
post #7 of 9
Hold the chip so the little notch on one end is at the top (looking from above). Going counter-clockwise from that notch, start counting from 1 all the way around
post #8 of 9
---- U------
1-0 0-8
2-0 0-7
3-0 0-6
4-0 0-5
------------

OP-AMP TOP

edit----not how it looked when I preveiwed it at all !
post #9 of 9
nice 'picture', rick
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