Car audio

[Mustang]

I recently bought a used car with the factory sound system still intact. Unfortunately there was a lot of snaps, pops and distortion with the volume cranked up. Being curious, I disassembled the power amp and saw quite a few caps inside They looked fine, all Nichicons RS, VX and VP series. Since I had a few low esr caps and a "so what if it doesn't work cuz it sounds like crap anyway" attitude I replaced the 2 2200uf 16v RS series caps with 3300uf 16V panny FM's. The snapping and popping disappeared! Still distorting though. Pulled the head unit out and replaced the chemicon 2700uf 16v SXE with the same value panny in the amp. No more distortion! I know this isn't a very scientific approach and no idea if low esr caps are even recommended for this type of application but so far the results have been heartening. The system will probably blow up next week though..

After reading Pete S's post about metal foil resistors, I may try to replace the existing one's in the power amp with those. I just need to know if there's an easy way to determine the wattage rating of the resistors.

[stretch0069]

Re: Car audio

Well...as long as the fuses haven't been messed with, you shouldn't have to worry about a fire.

What kind of car is it??

[davmax]

Re: Car audio

Hi Mustang. It may be difficult to visually identify the rating of an installed resistor. If you are going to replace, try to measure the voltage drop across the resistor, most will have a DC current flowing through them that will be disipating heat. Armed with the value of voltage and the resistance value calculate the wattage dissipation (voltage squared/ resistance). With the wattage known typically install a resistor rated at > twice that value. ie measured 400mW install a 1 watt resistor. There is usually some adjustment based on the ambient temperature within the equipment but the suggested rating estimate is a good starting point.

If there is little dissipation go for 250 mW rating.

Hope this helps

[Mustang]

Re: Car audio

It's a Contour SVT and I can't wait to start doing a few performance mods This pc stuff just keeps the fingernails clean when it's too damn cold to be wrenching
Dav, thanks for the advice and I'll test a few according to your principles. They look to be the standard type resistors so I would assume 1/2 watt or less. If this proves to be the case, would the readily available .6 watt metal foil resistors be ok on this project? Is it like caps where going from a 6.3v cap to a 16v cap just gives you extra breathing room..ie..can't hurt.. ?

[kc8adu]

Re: Car audio

nichicon had some junk caps in the early 90's.
i am still fixing lots of delco/bose stuff with leakers in them.
the caps in some of the speaker mounted amps were responsible for many car fires.