Little gem mkII problems please help!

[fredy]

the tip of my iron has crumbled away. I have a power supply for my weller 50w FE iron, but i hear that 50w is a lot for what i will be using it for, hence i have not used it.
Thanks for the sites, will check them out.

[fredy]

you know what, i think i will start again, this time, on a little gem MK1. Are the cap values in nano farads or something else? also, if i do not want a master volume, do i just leave out the 25ohm pot to ground or should it be replaced with a suitable sized resistor? One last thing, what ype of caps should i use? ceramic, multi layer, tantalum bead?

Thanks.

[fredy]

can't seem to find any 1w resistors, anyone know of a good internet supplier? also, could i wire 2 half watt resistors in series (or should it be parrallel if at all?) to handle 1w?

[slacker]

If you wire 2 half watt resistors of the same value in parallel you'll get a 1 watt resistor. The value will be half of the original values.

Before you abandon your original build are you sure there are no shorts between the pins of LM386s. On the photo of the underside of the board there don't appear to be very good trace cuts between the pins and there's a lot of solder around there. Get something like a 4mm drill bit and completely remove the copper from the traces to make sure there's no shorts.

[fredy]

i am fairly sure that there are no shorts but there is no harm done in making sure. i will give it a go. Thanks!

[mdh]

Ah, OK, you were still talking about the soldering iron situation.  I'm still unclear on exactly what you have... a complete 50W Weller soldering station?  If it's temperature adjustable and has a small enough tip (or if you can change the tip), you should be able to use it for just about anything.  If it's just a simple plug it in and go type of thing, then it may not be suitable, but it may become perfectly suitable at some point down the road, when you get a bit more skilled at soldering.  By the way, you may be able to replace the tip of your old soldering iron.  Have you looked into that?

Now, about the Little Gem.

All of the cap values in the Little Gem schematic are given in microfarads (often abbreviated uF).  To convert from uF to nF, just move the decimal point three places to the right.  So 0.01uF = 10nF, 0.047uF = 47nF, etc.  You can use ceramic or polyester film for the smaller caps, and for the larger caps (the 100uF and 220uF) you'll use electrolytics.  I would just use aluminum electrolytics.  Be sure to pay attention to polarity with electrolytic caps.

If you want to leave out the master volume, just take the output from the negative end of the 220uF cap.

As for the 10 ohm resistor in the Zobel network, I actually don't know how much power to expect it to dissipate, as I said before, so I'm not sure if you really need a higher power resistor there.  If you want to try to replace it with multiple resistors of a lower power rating, you need to put them in parallel.  The reason for this is that if you have a series circuit of resistors, the current flowing through each of them is equal, and power dissipation in a resistive circuit is P = I^2 R.  If you put them in parallel, then the voltages across them will be equal, but the current through each resistor will be proportional to the inverse of its resistance.  This is just a way of saying that parallel resistors split current, and therefore, power dissipation.  If you're having trouble following this, go read about Ohm's Law and the properties of series and parallel circuits of resistors.  Then, try to figure out for yourself how much current it would take to make a 10 ohm resistor dissipate 1W, and maybe even what parallel arrangement of lower power resistors would "look like" a 10 ohm, 1W resistor.

[fredy]

ah i see, thank you very much. Just went to check the current through the resistor, and guess what, no voltage oh, and yes, its a dull 50w soldering station with no variable temp. I cant change the tip on my current iron, partly because the screw has crumbled away and also because the iron is cheaper than the tip.

[fredy]

EUREKA! i had the 10 and 10k resistors in each others places and now i need a new 10k resistor, sods law i find this out just as i get the components for the little gem MK1.
Regarding the MK1, where do i connet the other speaker cable to? i know one will conect to the pin 5 ut what about the other?

[fredy]

just found out that the other speaker cable goes to ground. I have made it all up and guess what.... it doesn't work again! will take photos and voltages again but i can not see the problem with this one at all even with the wealth of experience gained.

[fredy]

tell a lie, it works! however, the switch doesn't dangnabit. Here are some photos of the new build.




Thanks you everyone who has helped, i really needed it cand i appreciate it muchly! thank you.