memphis mc-500d @1 Ohm

lincolntc

Member
2008-03-31 1:37 pm
i have a memphis mc-500d that i have driven at 1 .3 or so ohms (a dual 2 ohm kicker L7 wired at "1"), it worked great until i upgraded my alt to 160 amps.

sounded great, till one day it just dropped out, after turning down for a few seconds, it will go back up for a sec. then att. again. cant see any thing burnt, any ideas?

thanks ahead of time to any and all that can help!



ps can i bypass the protection circuit?
 

lincolntc

Member
2008-03-31 1:37 pm
the amp is not rated at 1 ohm btw, the 1000d is but... the speaker tested good on the meter, i dont think it was the wiring, unless it was coming loose at the speaker.

i dont have it in the house w\ me at the moment and its raining here in ohio, so i cant get the voltage reading right now, but when the opportunity comes......

thanks again
 

shagone

Member
2007-04-11 9:42 pm
if it is not rated for 1 ohm then you just answered your own question. if you disable the protection circuit you are just asking for more problems.

i would try to wire the sub coils in series just to verify that the amp is still running fine. you may find that you don't need to run it at 1 ohm to sound good and it will save your amp from overheating.

or you could try adding some outboard cooling fans and running your sub at 1 ohm for an hour or so at a time and letting it rest in between. but it may already be too late:hot:
 

lincolntc

Member
2008-03-31 1:37 pm
shag, the thing is it never got hot,i went and got a plexiglass peice cut for the bottom cover and put a fan in but it never got hot, so i never put it on. i need a bigger amp, thats y ive been pushin this one so hard. if i wire it at 4 ohms, the amp is only rated at 250 watts.

im a noob at this but since it never got even remotely hot, idk whats up!

thanks
 

shagone

Member
2007-04-11 9:42 pm
you can still wire it to 4ohms just to see if it cuts out still or not. is your gain set properly? do you have adequate sized power, ground and speaker wires with a good ground to a bare metal spot on the chassis that is tightly connected? are all of your connections tight at the battery and behind the head unit?
 

lincolntc

Member
2008-03-31 1:37 pm
shag, when i said noob i meant at internal fixing, not install. thanks for that tho, i just figured id save you some typing:)

i no why its cutting out(1 ohm load) but why now after 5 months of use. just putting it out there to give an idea to what im looking to fix.

dont take this the wrong way i appreciate the help i just want to give an idea about what i know, to save the extra steps.
i thought about trying it on a 4 ohm load, but i have to put it back in to test it.

i asked about bypassing the pro. circuit because the next use will be spl use, so any one no how i can mke a "cheater" amp out of this??

mr. babin do you have any general ideas about what components go wrong in this situation?? and is there a way to make those parts "beefier"?

i have looked around in these forums you two are great contributors to strangers with a common interest, my hats of to you
 

shagone

Member
2007-04-11 9:42 pm
interresting! i just did a sytem repair last night where the guy had simmilar issues. he had a rockford 4002 wired mono at 2 ohms to 2 10" jl W1's and it worked fine for a couple months unless it was turned up too loud and it would blow the 30 amp fuse by the battery. recently it would start cutting out after an hour or so without blowing the fuse.

problem 1: the amp has 60 amps worth of fuses and only 30 at the battery with a tiny cheap inline fuse holder.

problem 2: the amp is only rated at 4ohms stable in bridged mode.

problem 3: the wires to the subs were about 18 gauge (the free stuff you get with cheap coaxials)

Solution: I upgraded the fuse holder up front and installed the appropriate size fuse, rewired the subs to stereo 4 ohms per side, replaced the speaker wire with much larger cable and re-adjusted all amp settings.

i think after the parts are stressed at too low of an ohm load the solder joints and parts themselves become less stable or get bad connections as Perry stated so it goes into protection earlier without overheating from the outside.
 

jol50

Member
2007-11-08 2:14 am
I just sold a couple 1kw class d for ~$100 each, unless you are in a class for SPL. I see 900-1,000rms class D on ebay all the time for that sometimes less, and maybe not great but not no-names.

I just read a thing elsewhere of a guy saying you need lots of power to make an amp run with too low a load. He said low voltage will burn it up and since you are potentially doubling current at half its rated load you need much larger electrical. Said you have to keep the B+ up to do that. Now, I don't think that is going to keep every amp alive...what do you guys think? I think some amps can do it they are underrated, more amps can do it briefly...but it is still abusive to the amp if it is not up to the task (underrated) and eventually the smoke will come out.

From what I see the SPL guys run right at impedance rise so real ohm load is not that low, they are very careful what frequencies get into the amp to keep it that way and they only burp. Obviously that does not work well at all for music.
 
lincolntc said:
i no why its cutting out(1 ohm load) but why now after 5 months of use. just putting it out there to give an idea to what im looking to fix.


that's because, when you first used it at 1ohm, you had a lower amperage alt so the voltage sags and prevents the overcurrent protect in the amp to trip. when you got a HO alt, the stiffer 12V supply means more power going to the amp and gives it enough current to trip the protection ckt.