Repairing a line 6 low down studio 100 amp

[electricity440]

I have this nice amp that I got a few years ago. I was going to put it on a bicycle trailer with a 12v10ah battery and an inverter. The inverter is square though, so when I connected it the transformer made a very annoying buzzing sound. I was messing around and I put a 3.3uf 400v aerovox capacitor in series with the amp and that seemed to make the noise to go away- atleast for the first time. When I connected power again, the cap must have had a big charge and I heard a big BOOM, and the amp started drawing enough current for my wires hooking up to the battery to get very very hot. I then connected it to a light bulb limiter, and sure enough, the light turned on. The amp also had a burning component smell coming from it. Well the first thing I tested was the speaker. The speaker seemed to be fine. I then tested the transformer by disconnecting it from the power supply board. When I did that, the amp stopped drawing tremendous amounts of current and I realized there must be something wrong here. I also found this component on that board called TDA7293 (looks like the audio amp IC) which seemed to be the source of where the bad smell was coming from and was getting hot. When I removed that component, the current draw went back to normal and everything seemed OK. I ordered a new one from digi-key. Does what I am doing seem to be okay and is this how I should repair it? is there any other tests I should do? I really liked this amp and I want to be able to fix it!!!

[phatt]

Hi E440,
You may have done other damage but you have the light bulb limiter sorted so you will know soon enough if the new power amp chip fixes the issue.

As long as you have learned your lesson of using dodgy inverters then things should run just fine.  8|
Phil.

[Roly]

Hi electricity440.

Generally speaking you can't use a square wave inverter to power a device with a transformer power supply.  These require sinewave power.  Square wave inverters are intended to run small appliances with universal motors such as electric shavers, not electronics.

I'm not sure what you were trying to do by connecting a cap in series with the supply, but what appears to have happened is excessive internal supply voltage which has damaged the main chip amp.  Hopefully that is the only damage.

[Roly]

Hi @PhyllisReynolds and welcome.

Perhaps you could give us some indication of your intended application.

Generally:

The TDA7293 is a 100 watt chip amp and seems to be serious overkill for a busking amp.

A 10 amp/hour battery will deliver 1 amp for 10 hours, but a 100 watt output amp will draw about 200 watts flat out and this will imply a current of at least;

P = E * I

200 = 12 * I or
200/12 = 16.7 amps

In practical terms this will flatten a 10 amp/hour battery in about half an hour (if the high rate of discharge doesn't actually damage it).

So, either, a much bigger battery and higher powered sine wave inverter is needed, or for busking a much smaller amp preferably running directly from a battery to avoid the inefficiency and losses from converting 12 volts up to mains, then back down to the amp power supply.

Practically speaking I wouldn't attempt to run such a high power amp from anything less than a few kilowatts of motor-generator.

For busking only a few watts can make quite a racket and 10 watts would normally be quite sufficient.