First Lm3886

[AndrewT]

if the lightbulb does not light up, nor glow dimly, then that confirms that only a tiny mains current is flowing =good.

[Ted205]

you may see it glow slightly then dim when you first power up due to inrush current.


keep up the good work

[PJPro]

Thanks guys. It's good to know that I'm interpeting the results correctly and things seem to be working.

I have taken a step backwards, however, and am in the process of doing a more complete job on the testing front as recommended by AndrewT. I am building the whole lot (semi-permanently) on a wooden board and will add components to it over time until I have one complete channel in place...there's too many bits to do it in one hit and I cannot face building the rig and then tearing it down only to put it back together again to test the next bit on a subsequent night.

Oh, and I bought some 8ohm test speakers the other day. £1 each from a car boot sale. Never been used and still in box. Plastic cabinets. Nice.

[akis]

To be honest everything you bought has been built and tested before so the chances of complete meltdown or some other failure are very limited. :-)

Some practical tips for soldering. Soldering affects the characteristics of devices, especially smaller items like transistors and small electrolytic capacitors. I usually start by placing on the board same size items in a batch, starting from the smallest, so that there is the option when you turn the board upside down all the small items are held against the desk. Aslo bulky items make working on the board more difficult, so it is better to leave them for last. They say start with big items first but that is pants advice, unless you have to solder a bulky item perilously close to some small item and the heat may affect the smaller item.

When soldering I move from item to item and come back to the other pins of the same item later, so that I do not attack the same device twice in a row. My PCB arrived with silver mask which made soldering so much easier as the solder took immediately, I had very few stubborn joints. If plain copper try rubbing it clean (I use some special semi-hard material) the solder will take very much easier then.

Every time you apply the iron start counting and if you reach 3 and the solder has not yet melted uniformly, completely covered the pin on all sides and the flux escaping from the middle, then stop, pull the iron and come back to that pin later. If you are counting to 5 or more you are cooking the item, some items can only take 2 seconds at 250C and in my opinion this is when they get destroyed, not when their parameters change. For small items like transistors I keep the heat to about 180C and sometimes use tweezers to absorb the heat. For connecting terminal posts or other bulky items I go up to 280C even.

When you apply the iron it needs to make good contact to transfer the heat, so you may have to move it (I rotate mine usually) to allow it to transfer the heat while holding the item in place and with the other hand applying the solder, 3 hands definitely would come handy there, not sure how humans have evolved with only two. I use "helping hands" at all times, and sometimes teeth :-)

If the board is two sided then you need to pay attention to the top side - if there are pads on the top that have traces then you have to solder on the top (as well). If there are no traces, just pads then you do not need to, but you can for extra firmness on say pots etc. If you have pads on top you can also place a quick solder to hold the item in place for when you turn the board upside down so everything does not fall off.

If there are vias I usually put a pin and solder it both ends better safe than sorry.

In general I think the most likely problem you might encounter is hum

[PJPro]

Thanks for the advice akis. As it turns out I'm quite an accomplished solderer (so I am told).

I disagreed with your comments regarding how long you should heat an item. In my experience (admittedly limited) it depends on the amount of heat the component can absorb and the size of the trace you are trying to solder it to.

When building my SSMH headphone amp, some of the components took one hell of a time to heat. I was worried that I'd over done it. I usually avoid placing the solder on the iron and prefer to place it on the lead of the component or the pad. On some of the pads, the ground plane was sooo massive I had to heat up the whole lot before the solder would flow, i.e. more than ten seconds. Other builders had the same experience, so I was not alone.

For me, I'd rather get a good joint rather than end up with cold joints...so am prepared to risk messing up the component. I suspect my problems are exacerbated by using a cheap, fixed, low powered soldering iron.

[Stuey]

I have a temp controlled iron, but for those odd occasions when the ground plane is massive, I actually use a cheapy 60w fixed temp iron for as brief contact as possible. The mass of the tip is the key. (I have larger tips for the other iron, but can't be bothered changing them).

Stuey

[PJPro]

Agreed. I use fairly fine tips and have 12w and 25w fixed irons. I need to get something more....satisfying ;-)

[Stuey]

Actually, I used to use a 25w cheapy (with a half decent tip, though) and I found it pretty good. The temp controlled iron wasn't the leap I expected! 'tis good, though.

Stu

[wintermute]

Hi PJ, I have a Hakko 936 soldering station. Probably the best investment (in tools) I have made for DIY stuff. It cost me around $200 AU, but man was it worth it. I kicked myself I hadn't bought a decent soldering station years before. I started off with a cheapy 15W iron, then got a temp controled 25W and when it blew, finally got the Hakko, it is like chalk and cheese... it is a 60W and temp controlled. I normally use it around the 350C mark (though as I don't have a thermometer for calibrating it I can't be sure that really is the temp) cranking it up to 480 if I need to solder something that sinks a lot of heat, though I might have to try stueys tip (no pun intended) of using a bigger tip! I use a chisel point for most work and a fine conical tip of any extra fine stuff or temp sensitive. I tend to prefer to use a higher temp for a short time rather than a lower temp for a longer time. I suspect it does need calibrating though because it won't even melt 60/40 solder at anything under 300C on the temp scale...

Tony.

[PJPro]

Anyone tried one of these? Seem to share a lot of the Hakko features and I understand there are a lot of Hakko clones out there.