Electronics noobie cmoy help.

[thegeek]

Hi, I'm planning to build a chu moy amp, I've been following these instructions and I've made lists of what I need from elfa .
I've included two shopping carts from elfa, and as far as I can see they contain all I need to get started. Some components are double(ex. 3.5 jack) because I'm not quite sure which one I need.
I'm almost a complete noobie when it comes to electronics, I'm not stupid, but I don't have much experience; I need some advice

I was going to use the amp with my iriver ihp-120(h120) og a sennheiser 595(not yet bought), if anyone has anything to comment, please reply

Basics:
Quote:

82-302-291Spare Sponge WHS-series 82-302-451Soldering Tip 1,2mm WHS40 82-302-521Soldering Tip 2,0mm WHS40 82-302-031WHS40 Soldering Station 82-930-03160-1-5 Solder Wick 0,8mm 82-930-11160-2-5 Solder Wick 1,5mm 82-917-873Pocket Pak 285 0,8 mm 3,8 m 76-043-331Multimeter UT33D

Chu moy amp:
Quote:

50-146-001Box XP-9VB Black 67-009-002Rad.el.cap.220uF/25V 3,5mm 65-226-842Cap. 0,1uF/63VDC MKT 60-734-233Resistor 10,0kohm 1% 0,6W 60-730-432Resistor 4,70kohm 1% 0,6W 60-745-612Resistor 100kohm 1% 0,6W 60-722-842Resistor 1,00kohm 1% 0,6W 73-120-361OPA2134PA op-amp 48-135-492IC-sockel 8-pol löd 75-053-241HLMP-1790 LED 3 mm green 42-708-492Jack socket 3,5mm 4-p.PCB 42-701-122Jack socket 3,5mm 3p.panel 48-396-761Protot.card 110001 100x160 35-305-321Toggle switch SP SP-3 64-125-141Carbon pot.2x10kohm log 38-129-061Alu. Knob A14 16 469 42-042-022Battery clips 6F22 69-518-912Holder PC-mont 6F22

 

[skyskraper]

swap one of the solder wicks for a solder sucker and you should be in business

 

[Dreamslacker]

You might want to pick up just one chisel tip and get the thinner conical tip for fine soldering work instead.

For the coupling caps, try and get better pieces. Elfa carries the SCR caps which are essentially similar to Solens.
I'd recommend the 0.47uF part since you're using a 100K input impedance resistor.
The part number for this: 65-475-82

See the following link for more details:

http://www.tangentsoft.net/audio/input-cap.html

 

[thegeek]

Thanks for the comments so far

can anyone recommend any good solder suckers?
(preferably from elfa, since that is where I'll be ordering from)

 

[skyskraper]

82-888-98 would be good to start with.

other handy tools are miniature screw drivers, pliers, helping hands (couldnt find any at elfa), solder flux, etc

 

[thegeek]

Ok, after reading some of your excellent advice, I've changed the lists a little.
As for tools, I already have some I think will do. The solder I'm buying has solder flux embedded, do I need more?
I'm having a little trouble finding any good wiring on elfa and as skyscaper said, some helping hands could be very handy, if anyone has bought any from elfa earlier, please reply

In addition, does anyone know of a good pot with a switch? Elfa does not have the rk097(tangent), are there any alternatives?

Quote:

82-302-291Spare Sponge WHS-series 82-302-451Soldering Tip 1,2mm WHS40 82-302-031WHS40 Soldering Station 82-930-03160-1-5 Solder Wick 0,8mm 82-917-873Pocket Pak 285 0,8 mm 3,8 m 76-043-331Multimeter UT33D 82-302-371Doldering Tip 0,8mm WHS40 82-888-981Soldersucker 1003 82-888-991Spare TipSoldersucker 1003

Quote:

50-146-001Box XP-9VB Black 67-009-002Rad.el.cap.220uF/25V 3,5mm 65-226-842Cap. 0,1uF/63VDC MKT 60-734-233Resistor 10,0kohm 1% 0,6W 60-730-432Resistor 4,70kohm 1% 0,6W 60-745-612Resistor 100kohm 1% 0,6W 60-722-842Resistor 1,00kohm 1% 0,6W 73-120-361OPA2134PA op-amp 48-135-492IC-sockel 8-pol löd 75-053-241HLMP-1790 LED 3 mm green 42-708-492Jack socket 3,5mm 4-p.PCB 42-701-122Jack socket 3,5mm 3p.panel 48-396-761Protot.card 110001 100x160 35-305-321Toggle switch SP SP-3 64-125-141Carbon pot.2x10kohm log 38-129-061Alu. Knob A14 16 469 42-042-022Battery clips 6F22 69-518-912Holder PC-mont 6F22 65-475-822Cap. 0,47uF 5% 400VDC MKP

 

[Megaptera]

I think you'll have more luck with the panel-mount jacks than the PCB-mounts. In the picture on the website it looked like the panel-mount ones will be easier to solder, anyway -- they have big solder tabs to hook the wire onto.

It looks like you're shooting for a gain of 11, right? A lot of people find that's much more gain than you really need. You could probably drop down to a gain of 5-6 and still get a lot more volume than you'll ever need.

Also, for a sponge, you can pick up a cheap sponge pretty much anywhere -- some plastic types would probably scorch, but otherwise if you can find a better deal off-line, you can be flexible on that.

 

[thegeek]

Truth be told I had not really put much tought into how much gain this setup would give, I really just followed the instructions/parts list.
You have to understand that I have as good as _no_ theoretical knowledge of this stuff. I've done some basic soldering and electrical stuff before, but purely on a practical level. Thus I really don't have the knowledge needed to really understand how it all works. However, I'd really like to know, and hopefully this project will be a good step in the right direction. I find I usually learn much better when just beeing allowed to test things out(and having fun)

I will be using this amp for a couple of sennheiser 595 I've got my eyes on, and I've read that they are relatively easy to drive. So if you think I should lower the gain a bit, I'd seriously consider it. Especially considering that I have some shure E3's[26ohm] (ridiculouse easy to drive, since they are canalphones). I don't expect that they will be a good fit for this amp, but it would be nice to be able to use them sometimes. If a gain of 11 would make the amp way overkill for both the sennheisers and the e3's I agree that a little less gain would be good. How would I got about changing the circuit?

 

[Megaptera]

If you look at Tangent's parts list, he lists a few different R3s -- pick a gain you think is good, and then figure out what resistance corresponds to that.

So here's some of that theoretical knowledge:

In this context, when we talk about gain we mean voltage gain -- the increase in the voltage going out (V[size=xx-small]out[/size]), relative to the voltage coming in (V[size=xx-small]in[/size]). A gain of 11 means that V[size=xx-small]out[/size] is eleven times V[size=xx-small]in[/size]. Easy enough, right?

Opamps have two V[size=xx-small]in[/size]s, a positive and a negative. You connect the V[size=xx-small]out[/size] to one of them, usually the negative one, and the signal to the other one, and the opamp will try to equalize the two V[size=xx-small]in[/size]s by increasing its V[size=xx-small]out[/size]. If you look at the schematic, there's two resistors involved here: R3 and R4. As the signal from V[size=xx-small]out[/size] passes through here, it gets reduced (resisted) a bit, so the opamp's negative input sees a lower voltage than its positive input. It increases V[size=xx-small]out[/size] to where they're equal -- so exactly how much voltage you're gaining depends on those two resistors, in the ratio of R3/R4 + 1. Once you really understand this, you understand the CMoy amp.

Now, the reason you'd want a gain of 11 is that opamps tend to be more stable in higher gains. It's not hard to get a stable CMoy with a lower gain, but since it does depend a bit on your workmanship (and your ability to troubleshoot problems), Tangent recommends starting with the higher gain and then reducing it when you have it working. It's ultimately your call how you want to do it, and what gain you find works well.

All that make sense?

 

[thegeek]

Thanks, I got it

I actually was doing some reading up on gain ( which I realized I had just skipped

), and your explanation clearified it even more

I figured I'd just add a whole bunch of them, since they are so cheap anyway. There is one thing however that I'm not quite sure of, the resistors I've listed are rated at 0.6W, 1/4W is what I need, but elfa does not have them. Tangent also says that 1/8W is good, but the 0.6W's is what I got from another cmoy partslist from a forum here in norway. Which ones are best?
Should I just get both types?

Again, thanks a lot guys, you've given some invaluable advice. If I'd had to read up on all the theory behind this, I would have given up long ago

Updated parts list:
Quote:

50-146-001Box XP-9VB Black 67-009-002Rad.el.cap.220uF/25V 3,5mm 65-226-842Cap. 0,1uF/63VDC MKT 60-734-233Resistor 10,0kohm 1% 0,6W 60-730-432Resistor 4,70kohm 1% 0,6W 60-745-612Resistor 100kohm 1% 0,6W 60-722-842Resistor 1,00kohm 1% 0,6W 73-120-361OPA2134PA op-amp 48-135-492IC-sockel 8-pol löd 75-053-241HLMP-1790 LED 3 mm green 42-701-122Jack socket 3,5mm 3p.panel 48-396-761Protot.card 110001 100x160 35-305-321Toggle switch SP SP-3 64-125-141Carbon pot.2x10kohm log 38-129-061Alu. Knob A14 16 469 42-042-022Battery clips 6F22 69-518-912Holder PC-mont 6F22 65-475-822Cap. 0,47uF 5% 400VDC MKP 75-042-101WU-A-3 mount.bez 3 mm chr. 60-726-072Resistor 2,00kohm 1% 0,6W 60-726-492Resistor 2,20kohm 1% 0,6W 60-727-222Resistor 2,55kohm 1% 0,6W 60-727-712Resistor 2,80kohm 1% 0,6W 60-728-542Resistor 3,30kohm 1% 0,6W

 

[skyskraper]

1/4w and 1/2w will more then likely be more useful in to the future. don't just buy two of each resistor or whatever, buy like more then double what you'll need so you can 1) match them between channels. 2) have spares just in case something happens.

i tend to buy 4x as many as i need. i have a nice little collection now

 

[Megaptera]

I would be most concerned about their size -- the wattage mainly just indicates how much power it can take before it affects its performance (or sometimes burns up), and higher wattage ratings usually means a bigger size. If you've seen that other people have used them for a CMoy, it probably means they're not an unworkable size.

For your first CMoy, I wouldn't be particularly worried about how different resistors will affect the sound. Get it working first, then tweak it

 

[skyskraper]

i will say in general tho the 1/4w and 1/2w resistors usually come in the same package size, 1/8w being smaller by a touch. 1w are usually bigger and 2w onwards are really big