[dokebi]

I finished building my first cmoy. It worked perfectly the first time and I left it naked for a day playing. I then added a power switch and put it inside a case. The problem is that the battery becomes very warm as soon as I turn it on and a fresh 9volt dies very quickly. I suspect it is how I attached the power switch or a grounding issue. I also tried my rechargable 9volt and I think I destroyed it. It actually bulged out as if was going to explode. The switch is mounted on the project box and I attached both the battery leads and the power leads of the amp to the switch pins of which there are 2. Shorter one is fo negative yes? Does this problem sound familiar to anyone?

 

[ServinginEcuador]

Sounds like something is shorted internally, causing the battery to discharge very rapidly. Be careful of damaging the amp. Try to take some readings with a multimeter and see if you cna find a short somewhere near where you were working. It sounds like you introduces some short in there when you put in the switch. Look for any solder blobs that might be shorted.

Also, check to see if anything else gets hot when the battery gets hot. Like the new switch, wires, part of the case, etc. These are all clues to help you find out which component is shorted. If the wire gets hot, trace it to wherever it goes, and keep following hot/too warm items until you don't find any more and you can isolate down to a component that is bad.

You may also want to just remove the switch again and see if the problem goes away. Remember, whatever you last did is where to start!!

 

[dokebi]

Could a faulty switch cause these symptoms?

 

[gdahl]

A faulty switch? Measure the resistance from each switch terminal to ground, with the battery disconnected. You should get a high reading in both places. If you get something close to zero ohms, you've found the problem.

The other possible symptom of a faulty switch would be if it you got a reading close to zero ohms across the switch in the "off" position as well as "on". But that is probably not your problem because that wouldn't cause the circuit to draw excess current when on; it would simply be on all the time.

 

[ServinginEcuador]

Could also be that the switch was installed incorrectly and when switched on is creating the short??????

 

[gdahl]

Okay, I'm going to assume that the power supply is a single 9-volt battery, split into +4.5 and -4.5 volt rails by a pair of resistors. I am also assuming that there is an LED and resistor across the rails, and a capacitor across each rail. The switch connects the + terminal of the battery to the + rail. I am looking at the power supply schematic on the CMOY project page on Headwize. com.

Things to check, without the battery installed:

1. Measure the resistance of the rail-splitting resistors. Make sure their value is correct. If you are supposed to have something in the K-ohm range and it is really just ohms, that would explain your excess current draw.

2. Measure from the negative battery connector terminal to ground. You should get the value of one rail split resistor. It might be a little less if you have a bit of current flowing through the LED.

3. Measure from the positive battery connector terminal to ground. With the switch off, you should get infinity. With the switch on, you should get the value of one rail split resistor.

4. Make sure your battery clip has the correct + and - orientation.

5. Make sure your electrolytic caps are oriented properly. For the positive rail, + goes to the positive rail and - goes to ground. For the negative rail, + goes to ground and - goes to the negative rail.

Find any problems yet?

 

[gdahl]

After reading your initial post again, I think I know what went wrong. You wrote that you connected the battery and the switch to the same two terminals, right?

If you connect the battery to the two terminals, and the switch to the same two terminals, that is the problem. The result would be:

1. With the switch in the off position, the unit is actually on, for as long as the battery lasts.

2. With the switch in the on position, the battery is shorted, until it dies its torturous death.

The proper way to connect the switch:

1. One terminal of the switch goes to the positive terminal of the battery.

2. The other terminal of the switch goes to the positive power input of the circuit.

3. The negative lead of the battery goes to the negative power input of the circuit.

This way, when the switch is off, current can't flow through the battery because the positive lead dead-ends at the open switch. Turning the switch on allows the current to pass from the battery through the switch to the positive power input of the circuit (conventional current flow, + to - ... actually the electrons travel the opposite direction!)

 

[ServinginEcuador]

[size=small]Any word dokebi????[/size]

 

[dokebi]

Hi, Yes it was mis-wiring the switch just as gdahl said on his last post. ::repeatedly smacks head::

A newbie should not try to do these things during finals week. A lot of confusion was due to not thinking things out in a slow logical manner. However, I am very happy with my first results and the fact that it works.

I will probably build another during the weekend as I bought enough parts from mouser and such for 2 more and try to build the meta42 during my winter break. Is it worth using bigger power capacitors for the cmoy?

On a side note, I am also interested in distortion/fuzz pedals for electric guitars. Is this more consuming compared to headphone amps such as the meta42?

 

[ServinginEcuador]

Thanks for the update dakobi!! Glad to hear you found the problem and got it fixed.

 

[PinkFloyd]

Try a different battery and if that fails ....... scream

Pinkie