DIY Amp Construction Tips
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kerelybonto

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After building my first CMoy as a soldering project, I'm ready to build one that sounds good. I tore apart that CMoy and am ready to go as soon as the fried parts' replacements get here. Since I do want this amp to be more than an experiement in soldering, I have some questions:

1. Which type of solder should I use? I used 63/37 .050 diameter wire on my test amp, which worked fine except that the wire was a little too thick sometimes. I also have .032 diameter 60/40 and .022 diameter 62/36/2 wire lying around. I don't suppose any of them will have noticable sonic effects in a $30 amp, so should I just go with the easiest to use?

2. What type of wire should I use for the input/output/power lines? I tried using both solid and braided copper wire on my test amp and neither soldered well at all. I had all kinds of problems with it. Should I try some aluminum wire?

3. Do the power toggle switch or the input/output jacks need to be grounded?

4. How do I install the potentiometer? I have a 10kohm 12mm Panasonic, but I don't know which pins are which ... or basically anything.

5. How do I install a DC-in jack into the power supply apparatus? Is there anyway to wire it to automatically run on DC instead of battery when it's plugged in, or will I need a three-position toggle switch? Any suggestions for this switch? Also, any suggestions for and AC/DC converter that will give me the proper voltage/current? Any simple way to have the DC power charge a rechargable NiMH 9V?

6. Any suggestions on case design? Anyone have a schematic showing how they hooked up the main circuit to the case components?

7. Should I use pliers or something to heat-sink components as I solder them in? It's kind of hard to do with parts as small as what goes into these tiny amps, but I don't want to fry anything.

8. When testing the circuitry (using an analog Sperry SP-10A multimeter), am I just looking for current? Is it safe to assume that if there's current, everything's in working order? Any other testing tips?

9. I need a small volume knob. I've noticed that a lot of mint tin amps (at least those I've seen pictured) have volume knobs that are disporportionately large. I have a Kilo JD-50-1-5 (DigiKey 226-2033) and I'd like something a bit smaller, at least depth-wise -- the diameter's about right.

10. The op-amp. I used a pretty generic dual (DigiKey OPA2132PA) in my test amp. I think I may have fried it removing it -- how can I test it? Also, any suggestions on better dual opamps that will work in a CMoy?

11. I assume it's pretty difficult to design a circuit usable by both high- and low-impedance cans. Right now I only use Sony MDR-V6 and Grado SR80 anyway, so I can just design for low impedance, but it'd be interesting to be able to use high-impedance cans too. Too difficult?

12. Anyone know what the two IC socket .300 Gold 8 DIP (DigiKey AE7313) are in tangent's optional parts list or what they do or where they go?

13. Suggestions for a good mini-mini and RCA-mini interconnect? What about putting RCA inputs on the amp? Possible while still having the mini input?

Any other tips or suggestions are welcome. Also, I'd very much like to see some extreme close-ups of anyone's CMoy (or other simple amps), especially the case components and wiring that's not shown in tangent's pictures.

Thanks.

kerelybonto
 
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tangent

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1. The easiest to use would be a thinner kind with eutectic formulation (63/37). Since you don't have both of those qualities in one solder, I would either get some, or pick the quality you like best. Probably go with the 60/40, and then pay special attention to the precautions on avoiding cold joints that you can find in any tutorial on soldering.

2. You shouldn't have any problem soldering copper wire at all. Were you applying heat to the wire and then applying the solder to the hot wire, or were you soldering the iron tip and then trying to spread the solder onto the cold copper? Did you apply solder while it was still smoking, or had all the flux burned off by the time you got solder to stick to the joint?

3. Yes, and no, respectively. Beware that if you use a DC power jack, that it will also be case-grounded -- you can't have both your inputs (or outputs for that matter) case-grounded at the same time. Pick one or the other, and insulate the one you don't want grounded. This is not trivial, and it's easy to get it wrong. It's a lot simpler if you stick to plastic cases -- then you don't have to worry about this.

4. First, look at the datasheet. This tells you that -- looking at the back of the pot with the pins down and numbering from left to right -- the grounds are pins 4 and 5. The pot "outputs" are the two pins surrounding the grounds. The inputs are the leftmost two pins. Pin 1 goes out to pin 6, and 2 goes out to pin 3.

5. It's covered in my tutorial.

6. This hobby is half handicraft -- so go craft something!


7. I think you should instead improve your technique so that you get in and get out quickly, so you don't heat components up to the danger point to begin with.

8. Aside from the tests mentioned in my tutorial, one of the other tests I do before I plug an op-amp in is to turn the circuit on with no chip, and measure all 8 pins on the socket. You should get +V on pin 8, -V on pin 4, and 0V on all other pins. If you get significant voltage on the other pins or your supply voltages are off, find out why before you plug that expensive chip in, or you risk frying it.

9. If you're judging by my pictures, beware that there's an optical illusion involved since I'm using a cheap digital camera whose macro mode requires that I put the lens of the camera 4" from the subject. I won't go into the theory, but suffice it to say that when you put something that close to the camera, you get magnification distortion. To answer your question, though, I suggest you look through Mouser's stock -- they have a great selection of knobs, at good prices.

10. Answers to both are on my Audiologica pages. Not all the answers, just some of them.

11. Horse hockey. A more useful answer would take too much space. Do a search in the archives, or do some experimenting, or start another thread. (In that order of preference!)

12. There's only one socket mentioned, and it goes under the op-amp chip, of course! If you'd used a socket, you wouldn't have damaged the chip desoldering it. You'll notice in the pictures that I don't solder my op-amps down. There's a reason for that...

13. Check out Headroom's cable section.
 
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kerelybonto

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Thanks, tangent. You're a pal.

Couple things though -- neither my opamp nor my pot (or the jacks for that matter) came with pin diagrams. Anywhere I can get those?

... So that's what the socket's for! Ha, I actually have one that I could have used -- but remember that I know absolutely nothing about electronics outside of what I've managed to learn doing this. I'm over here going, "Ooh, a little wire thing! Ooh, a neat shiny thing! Let's solder them together!"


kerelybonto
 
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tangent

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Quote:

neither my opamp nor my pot (or the jacks for that matter) came with pin diagrams. Anywhere I can get those?


The DATASHEET?
 
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Maj0rMaj0r

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There is a diagram of some pots on cmoy's original article about the amp over on head wize.
 
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kerelybonto

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Ah, okay, thanks Maj0rMaj0r. That helps considerably ... although I'm still not sure if I'm reading it right.

tangent, is a datasheet supposed to come with the components? I don't know what you're talking about. ...

kerelybonto
 
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fyleow

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Do a search for the components you bought. if you got them from Digikey they should have a link to the manufacturer's website and there will be datasheets.
 
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ppl

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You might try some Practace upon an Old Circuit board that is from somthing that no longer works or you dont want. Practace unsoldering and then resoldering the Parts without Lifting the Foils or Burning the Board. Also smoewhere on this or the Headwize fourms was a soldering tutorial, do a search.

Hear it is http://home.att.net/~joemacjr/diyproject/soldering.html
 
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tangent

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kerelybonto, datasheets are PDF files you download and either save or print out. You'll need them again and again.

(Long long ago...before the Web...datasheets were actually professionally-printed pages you'd order from the manufacturer. Often they'd be bound into big "databooks" that you could get from distributors if you could convince them you were a big enough customer. The web made these practices obsolete, but they're still called datasheets.)

DigiKey usually links directly to the datasheet for each product it carries. On each product's page, there will be a link called "Technical/Catalog Information". Click it, and you'll be taken to a page that at least links to the DigiKey catalog page, which may have some useful info on it that the datasheet doesn't. Most of the time, you'll find a link to a datasheet here, and occasionally you'll even find pictures of the item, particularly for [electro]mechanical stuff.

DigiKey doesn't have links to datasheets for all the products it carries; in this case you have to go to the manufacturer's web site and get the datasheet from them. Other distributors do a worse job of linking to datasheets, so you might get really familiar with the various manufacturer's web sites...
 
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kerelybonto

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Ah, okay. I was thinking they were probably available online. I'll go find what I need. ...

kerelybonto
 
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kerelybonto

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I'm about to put another order through to Digi-Key ... someone help me with a couple parts:

1. Hook-up wire for case components: What sort of gauge works best? Copper or aluminum? Braided or solid? Different colors for keeping track of channel/charge/direction? Don't need much. ...

2. Looking for some high-gauge eutectic solder. Part KE1302-ND, shows up as the only good match when doing a search, but it ends up being a pound instead of an ounce when I add it to my order. I obviously don't need anywhere near that much. Is there really a one-ounce quantity, or are they lying to me?

3. Suggestions on some soldering braid?

4. Might be interested in getting a new soldering iron since the one I'm using is pretty bad. Would like the smallest, thinnest possible, with a cord that gets out of the way.

5. Would any shrink-wrap stuff be useful for covering joints, etc? If so, what kind shoud I use?

Anything else I should throw in before I submit my order? Oh, and where can I get a useful third-hand tool type thing? It gets kind of difficult holding the circuit board, the iron, the solder wire, and the component in place all at the same time, no?

kerelybonto
 
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