can someone with an MS2250 do me a quick favour?

[marko]

..or any ms amp really, what should the resistance between rca shield and heatsink be? i'm getting almost a dead short and this doesn't seam right!

the strange thing n with these amps also is the negative speaker cable is connected to the heatsink!

[The Golden One]

i will but i need you to be a little more specific what do you mean like you need the resistance of the rca ground connector to the outer part of the heat sink or what?

[marko]

what i need to know is the resistance between rca shield and heatsink, i'm showing an almost dead short and this doesn't seam righht as non of my other brands of amps i have lying around do this

i have bad alternator whine and 99% convinced it's the amp(s)..

[The Golden One]

well ok i checked my mps2500 from the rca ground the outer part of the rca to the heatsink and its dead short i even took the rca off of the faceplate and still no resistance straight zeros on the meter on both rca's .

[Eric D]

Last I knew you should have a dead short with the switch on the amp in the "ground" position, and some measure of resistance with the switch in the "float" position. The switch either ties the input section to ground or floats it with regard to the rest of the amp.

Also, like many other amps, one speaker (+) will be tied to ground and the opposite channel's (-) will be tied to ground. There are amps which have a completely isolated chassis, but these are not.

[Eric D]

Take a look at this attached photo. In it you can see one speaker terminal, and next to it the screw to mount the board which will thread directly into the chassis. There is plenty of trace material connecting the two. So, the speaker outputs have one terminal tied to the chassis of the amplifier. The center tap of both transformers is also connected to this (as it is the negative speaker connection as well).

[The Golden One]

Last I knew you should have a dead short with the switch on the amp in the "ground" position, and some measure of resistance with the switch in the "float" position. The switch either ties the input section to ground or floats it with regard to the rest of the amp.

Also, like many other amps, one speaker (+) will be tied to ground and the opposite channel's (-) will be tied to ground. There are amps which have a completely isolated chassis, but these are not.

Eric D my amp doesnt have a floating ground switch i thought only the zpa's have it, but i did switch both the stereo bridged switch and the master slave switch and still read dead short on rca ground.

[Eric D]

Your are right, my MS2250 has just the stereo bridge switch. I was thinking of the MS275 I guess.

Either way, the larger ms amps are tied to ground.

[The Golden One]

Your are right, my MS2250 has just the stereo bridge switch. I was thinking of the MS275 I guess.

Either way, the larger ms amps are tied to ground.

yea my 2125 doesnt have a switch but the mq430 does so i guess maybe the bigger amps dont have the floating ground.

[marko]

very strange design! if i uncouple those 2 board screws near the speakers then that takes the dead short out

so my amps may be ok after all, seamed odd that all 3 ms2250's in my system exhibited the same results

[The Golden One]

very strange design! if i uncouple those 2 board screws near the speakers then that takes the dead short out

so my amps may be ok after all, seamed odd that all 3 ms2250's in my system exhibited the same results

have you figured out the reason your having alternator whine? some things like pinched rca's or rca's ran along side the power wire and leaking spark plug wires can cause this noise amongst other things.

[marko]

guaranteed not spark plug wires (diesel)..

with muting plugs in the amps and speaker wiring disconected i have whine on all 3 amps, 2 are noisier than 1, the quitetest is on my mids/tweeters and it's hardly audible just bugging me a bit

[longboard]

marko have you got the amps and or any proccesors isolated from the chassis of the car thats one of the most common alt wine causes

[marko]

marko have you got the amps and or any proccesors isolated from the chassis of the car thats one of the most common alt wine causes

i shall check this although everything is mounted to wood/mdf but you never know, something could be touching a bracket/chassis somewhere..

[longboard]

we had a simalr issue and found one of the bolts holding a line driver down had rubbed through the back side of the mount and had rubbed the paint of the chasis and earthed! that was a pita to find!

[The Golden One]

we had a similar issue and found one of the bolts holding a line driver down had rubbed through the back side of the mount and had rubbed the paint of the chassis and earthed! that was a pita to find!

yep i had this happen on a zx450 one of the screws went past the plastic mounting feet and it actually sparked, i just used some left over ground wire insulation to keep the screw from touching the chassis of the amp and it worked good.

[marko]

alternator whine is almost gone now but is more noticable for the 1st few moments then goes away (always done this even with different amp!)

...but something more worrying is happening, after i completely turn the system off i hear static on the left channel for anything up to 30 seconds after, no idea what this can be??

[ttocs]

we had a simalr issue and found one of the bolts holding a line driver down had rubbed through the back side of the mount and had rubbed the paint of the chasis and earthed! that was a pita to find!

aahhhh that brings back memories. "How come when I tap on the time driver I hear it though the speakers?" how often have you said that?????

[gridracer]

Take a look at this attached photo. In it you can see one speaker terminal, and next to it the screw to mount the board which will thread directly into the chassis. There is plenty of trace material connecting the two. So, the speaker outputs have one terminal tied to the chassis of the amplifier. The center tap of both transformers is also connected to this (as it is the negative speaker connection as well).

Like Eric explained and thats why PG amps all had whine if the amp chassis was grounded to the vehicle chassis creating a ground loop. At least any that came in our shop with a whine that was usually the cause. If that's not the problem let us know I am sure someone will come up with a valid reason and it'll get fixed. Could be as simple as a stray wire, or a screw got put through a cable?

[Eric D]

alternator whine is almost gone now but is more noticable for the 1st few moments then goes away (always done this even with different amp!)

...but something more worrying is happening, after i completely turn the system off i hear static on the left channel for anything up to 30 seconds after, no idea what this can be??

That is probably the one channel slowly discharging its rail capacitance. I just found this out as well with an amp I was working on. One channel discharges fast, the other does not. Yet the amp seems to work fine.

[marko]

so what's the fix Eric, new rail caps? this static discharge can go on for anything up to a minute, very strange! i had this amp on my midbass through a passive before i swapped things round so i never picked up on it it's frustrating as i've already stripped all 3 amps down for psu cap swaps and didn't fancy stripping them down any time soon