[chews89]

Oh Ok cool. Also, on the Amb instructions, when testing the opamps it says:

"Use your multimeter and check the resistance between each pin of the opamp and the pad to make sure you don't have a cold solder joint (i.e., your meter should read close to zero ohms). Also check continuity between adjacent pins for solder bridges (meter should read infinity). "

What does it mean by the "pad"? Also, I think I know which settings I need to set my multimeter to check resistance, but how about for continuity? Same settings? Still ohms? Is it possible to somehow damage the opamps while trying to test them? Sorry, I'm a huge noob.

Again, thanks for the much needed help, amb.

 

[amb]

Quote:

What does it mean by the "pad"?

The shiny portions on the board that the pins are supposed to be soldered to.

Quote:

how about for continuity? Same settings? Still ohms?

Yes, continuity = 0 ohms, no continuity = infinite ohms (or really high resistance)

 

[chews89]

Ohyeah, another quick question that I forgot before. Is flux absolutely essential when installing the opamps? Because I don't have any at the moment.

 

[v3nom]

Continuity doesn't have to be 0 ohms. If you have a completed circuit it will have continuity and most likely will have resistance. Now a SHORT on the other hand will be 0 ohms because it bypasses any circuit components.

 

[amb]

Quote:

Originally Posted by chews89 /img/forum/go_quote.gif Ohyeah, another quick question that I forgot before. Is flux absolutely essential when installing the opamps? Because I don't have any at the moment.

Yes, IMO flux is absolute essential for SMD soldering. It's mighty difficult to do a good job without it.

Quote:

Originally Posted by v3nom Continuity doesn't have to be 0 ohms. If you have a completed circuit it will have continuity and most likely will have resistance. Now a SHORT on the other hand will be 0 ohms because it bypasses any circuit components.

In this context (well soldered or cold joint), it is 0 ohms if continuous. Now, in real life any conductor will have a tiny amount of resistance but it will be less than the resolution of any DMM. In fact, most DMMs will read a fraction of an ohm across a well soldered joint, but that's besides the point.

I should also mention that many DMMs have a continuity tester mode where it would "beep" when it thinks that you have continuity. This is not a good use of that function because one doesn't know what the beep threshold is. Is it 10 ohms? 100 ohms? Just because it beeped doesn't guarantee a good solder joint.

 

[chews89]

Hey amb, from my problems stated before, how do I know which opamp needs to be replaced? U4 or U5? Or both? Or I just can't know for sure?

 

[amb]

Whichever that has a high DC offset problem. U4 is for G, U5 for L and R. You could have looked at the schematic diagram and saw this for yourself.

 

[chews89]

I actually have no idea how to read a schematic diagram but I think I have an idea of what you're talking about. Thanks

 

[dhp]

general question about the mini3 - can the LM6172/6171 opamps be used in lieu of the ad8397? I know there are only 2 recommended opamp combos at the moment.

 

[nsx_23]

Chews, got the mini3 working?

 

[amb]

Quote:

Originally Posted by dhp /img/forum/go_quote.gif general question about the mini3 - can the LM6172/6171 opamps be used in lieu of the ad8397? I know there are only 2 recommended opamp combos at the moment.

The answer is it would sort of "work", but you will suffer major performance loss. Its specified minimum supply voltage is 10V, but we have only about that much after the battery is just freshly charged, and will drop to around 8V-8.5V over most of the operating life of the charge.

The LM6172 is not rail-to-rail, it will give you no more than about 1.3Vrms output voltage swing into a mid-Z load (100 ohms) before clipping, and it gets worse into lower Zs. Contrast this to the AD8397, which will give you 3.2Vrms (mostly load invariant). With 10V supply voltage, the LM6172's maximum output current is about 25mA into 100 ohms (not specified at anything lower than that), whereas AD8397 can deliver up to 10x that (rated down to 25 ohms load).

Given this, the LM6172 won't drive high-Z or low-Z headphones effectively in the Mini³.

 

[chews89]

Quote:

Originally Posted by nsx_23 /img/forum/go_quote.gif Chews, got the mini3 working?

Haha well yes and no.

I actually completed my 2nd mini3! I was extremely careful with going through all steps thoroughly especially the testing stage after making dreadful mistakes by rushing through it and taking some very good advice from amb, and it works! It is definitely a step up from my cmoy.

As for my first mini3, I'm waiting for the opamps to come in to try and fix it up. But until then, I'm pretty happy with my working mini3

Thanks for asking, nsx

 

[nsx_23]

It's a brilliant little amplifier isn't it

I'm looking for something to build actually, but damn uni work has kept me extremely busy. Maybe the CTH, but it'll have to be during the mid-year break

The urge to build is strong.

 

[chews89]

Yes it is, indeed

Yeah, same here. Mid semester exams are coming up as well, so there isn't much time for anything else. CTH? Ohyeah there's a kit available right? Making one would be pretty sweet. Do you know how much it would cost all up though?

How about a Starving Student? Did you see the one that fred_fred put together? I guess it is possible to source components in Australia

 

[nsx_23]

The problem is that I suck at reading schematic, so it'll be a bitch to put together for me.....