newbie solder question

Sometimes the DC levels can tell you a lot. No signal - since without a scope it wouldn't do much good. Check input output ground and Vcc - don't assume it is connected check it at the solder joint or component leads. Assume nothing. Believe the voltmeter not your eyes when it comes to connections.

I don't know if I buy the no output caps and single supply . . .

With class AB (which is your amp) the output of the amp running on a single supply HAS to be one half the supply voltage with no signal present. That means the speaker would be driven close to its travel in one direction at all times if the circuit doesn't have a transformer or cap to take the DC from the speaker.

The choice is a coupling cap (high value like 400 to 4,000 ufd) in series with the speaker - or two amps per channel with the speaker between the outputs. Both amps sitting at 1/2 half the total supply so the speaker has no voltage differential across it - the amps when driven are working out of phase to one another - one side becomes more positive the other more negative. (a technique used in car radios)

The other choice is a plus and minus supply with one side of the speaker to ground.

It does matter, to the capacitor in particular. Electrolytics don't tolerate over-voltage or reversed polarity very well. There are non-polar electrolytic caps, but they aren't common.

The data sheet suggests you use a one or two microfarad cap for input coupling. A .1 may also work but give some tinny sound quality.

You can "make" a non-polar cap from two polar caps. Take two caps with the same specs - preferably from the same maker and batch. Tie either both plus terminals together, or both minus terminals together

- use as you would a normal un polarized cap.

The voltage rating will be the rating of one cap and the capacity will be 1/2 the value of each cap. (2 X 4 ufd / 25 volts = 1 X 2 ufd / 25 volts)

An electrolytic is usually specified at something like a tolerance of

Likewise if you have a 2,000 ufd speaker coupling cap (as shown in the data sheet) a working 100 ufd may sound a lot better than a non working 2,000 . . .

Bridge pin one on one amp to pin one on the other with a non-polar cap (to be safe). You could just touch the terminals with the cap but that may cause some output noise and it would be safer to clip the cap in then apply power.

On Thu, 19 Jan 2006 22:04:09 GMT, "Dave" wrote: PS turn on thump is almost always a sign of a DC offset in the output. It may suggest a DC offset in the input to the amp and carrying that logic further - the built in protection is saving the speakers from frying.

Some amps do thump when nothing is wrong - the design just comes up in an unbalance condition and straightens out after a millisecond or two as caps charge in the input stages.

Check the voltages . . .

I haven't kept up with this thread, but I have been using lead free solder for over 5 years now. I had to jack up the tip tmeperatures to 700 degrees in order to get good flow. A touch of standard external flux helps a lot. I use smaller guage solder also, flows better. I do keep standard solder on the bench. I once, early on, did an amplifier repair and the customer who picked it up returned it sayng that the side I had repaired sounded so much better he wanted me to fix the other side. I had used the lead free solder on the repair. I replaced the lead free with standard solder and both sider were equal and he was happy. I do admit, I hated the lead free in the beginning, but I've become used to it and can work around it's mlimitations. I do cheap a bit and sometimes tin old joints with leaded solder before applying lead fee.

Stu

Not all lead free solder is the same, though even the best that I have used is not as good in terms of flow as leaded. The best formulation that I have found is Sn 96.5, Ag 3.0, Cu 0.5 that I got from Mitsubishi. It only requires a slightly higher temp than normal, about 30 degrees.

Leonard