Pioneer GM-600 Car Amp Problem

[dricker]

I've got a question about a small car amp that I was wanting to use for an amp in my garage. A link to the schematic is posted below:
http://elektrotanya.com/pioneer_gm-600_sch.pdf/download.html
Trying to see if this thing still worked, I had my phone plugged into the audio in, hooked up a speaker, and powered up the amp.........nothing. I opened it up and started checking voltages. Everything was looking good until I got to the "Isolator Power" and "Isolator Circuit". Voltages were way off and audio ground to power supply ground was about 12V. When I went to hook up a scope to the input signal coming in, as soon as I hooked the probe ground to amp (power) ground, the thing starts working. All voltages looking good. At this time, I had my laptop (which was plugged into the wall) hooked up to the audio and the amp running off a 12v power supply (also plugged into the wall). I got the same positive results when I unhooked the probe and connected the 12v supply ground to earth ground on the wall plug. When I switched the audio supply back to my phone, I got same problem again. Audio ground is floating around 12V. I'm not 100% sure how the isolator and isolator power circuit works and how it deals with the grounds at 2 separate potentials. Do you have to have what is supplying the audio have the same ground as the amplifier to work, or do I have something weird going on? Thanks!

 

[Ecki]

did you come any further with amp? im asking because i have the same amp and want to connect it to my tablet pc in the car. so far all the wiring is done, speaker connected, +12,ground and ACC, also 3,5mm plug from pad to the two cinch on the amp.the amp seems to work, at least some tiny humming from speaker when its switching on. but...no sound coming from speakers. after googeling a lot, i came several times across the issue on pioneer amp, the they need same ground as ???. i never understood exactly which same ground and from where. and i would rather ask before connecting my tablet minus to battery minus hey...as you can see, im not a car hifi geek but would love just to get it working. so please, if you can explain which minus/grounds need to be connected...thanks a million

 

[dricker]

I'll have to check.....

The best I can remember, I had to tie the audio ground to the power ground. I did this inside the amp, but you should be able to do it outside as well. I will warn while this worked in my situation, no guarantees it won't smoke your amp or audio source! There are two grounds going into this amp. You have an audio ground (Left +, Right+, and gnd for audio) and then you have your car battery (or other power source) ground (Power+ and gnd). In order for my setup to function, I had to connect audio ground and power source ground together. (Never hook up the 12V+ to either ground or you will create sparks and possibly damage everything!) I'll check tonight and let you know. But again, I can't explain why this is necessary (it may be a bad idea) and your situation might be different, BUT IT COULD POSSIBLY DAMAGE YOUR SYSTEM! All I know is that it fixed my issue.

 

[dricker]

see above

 

[Ecki]

thanks a million! i will try that over weekend. i found out that pioneers have so called pico fuse on board. some advice to "pop" a drop of solder on it if its blown. if i get them right its same like connecting the rca shield with the chassis from amp??? hey let me try, got nothing to loose. im sitting in the middle of africa surrounded only from chinese crap shops selling china crap amps. just want to get my ipod or tablet playing music over amp... by the way, is connecting the illum pin of any importance for it to function?
will keep you also updated. thanks a million for answer!!!

 

[Ecki]

will also try to connect car charger to tablet while testing as soon as i get one. that should also bring grounds together. so far tablet was only connected via 3,5mm to rca adapter to amp...