[pikkashoe]

Ok im running into more and more instances where the stock amp turns off, cutting my subs. Ive tried removing the cover, but its still not getting enough ventilation or air i'm guessing. Anyone run into this and had any remedies?

Im thinking about hooking up a 120 mm high speed computer fan to keep constant air flow over the amp. Any ideas where i would tap for power? Just need a power and ground.

[solefald]

there has to be a power going to the amp. you can buy a power probe at an auto parts store. they are about $5-10 (for a basic one, that is)

[pikkashoe]

Hmm, will a volt meter also work?

[solefald]

Originally Posted by pikkashoe

Hmm, will a volt meter also work?

yep

[VP Electricity]

If the stock amp is shutting off, and both subs are cutting out, it sounds like a bad amp more than anything (assuming you have no mods to the audio...)

[noire07]

Originally Posted by VP Electricity

If the stock amp is shutting off, and both subs are cutting out, it sounds like a bad amp more than anything (assuming you have no mods to the audio...)

Yeah and if thats the case, you should probably take it to the dealership and try to get it replaced.

[tintivilus]

Hopefully you can get it replaced under warranty, but this is a classic symptom of long-term amp abuse. After you've overheated good and proper a few times, the transistors start to break down and get hotter faster. If you're not really careful you wind up in a heat death-spiral. You can usually prolong the life of the unit by upping fan power to compensate for the extra heat output.

I ran my last stereo receiver with a box fan on top for the last couple years of its life

edit: don't take the word "abuse" personally btw; I meant running the amp hotter than spec through any combination of high volume and airflow restriction.

[pikkashoe]

Well, its only done it 2 times in the last 6 months, im just afraid as we get deeper into the summer months and the temps start creeping up to the 100's I will run into it more.
I dont really abuse the system, but I do know what you mean, there is a lack of ventilation back there, and the fans only turn on once the amps has overheated. I just want to be proactive and eliminate any potential future amp failures.

[VP Electricity]

See, my objection is that I don't believe you can overheat the OEM amp. Just because you can overheat an aftermarket amp with big subs on it doesn't mean you can overheat the OEM amp. I could be wrong, but until someone proves otherwise to me, I expect any OEM amp shutoff to be due to something else. Most OEM amps lack the protection circuits for overcurrent out and thermal that aftermarket amps have, because the OEM amp has a defined and consistent load - but aftermarket makers never know just what we're going to do with their babies.

Unless you KNOW that overheating is the issue, all you know is that the subs cut out intermittently, and the rest is assumption.

BTW, tint, I'm not convinced that transistors get hotter faster in a death spiral. I suspect it has more to do with other parts off the board - possibly even the thermistor. Remember, transistors don't shut down when they get hot - there is other circuitry in there to handle that. Alternately, you could have had capacitors changing values over time - common in olde - I mean classic gear - that messes up the entire circuit.

I would make an appointment to have the system looked at.

[Technic]

Originally Posted by pikkashoe

Ok im running into more and more instances where the stock amp turns off, cutting my subs. Ive tried removing the cover, but its still not getting enough ventilation or air i'm guessing. Anyone run into this and had any remedies?

Im thinking about hooking up a 120 mm high speed computer fan to keep constant air flow over the amp. Any ideas where i would tap for power? Just need a power and ground.

Is this system 100% stock?

[tintivilus]

Originally Posted by VP Electricity

BTW, tint, I'm not convinced that transistors get hotter faster in a death spiral. I suspect it has more to do with other parts off the board - possibly even the thermistor. Remember, transistors don't shut down when they get hot - there is other circuitry in there to handle that. Alternately, you could have had capacitors changing values over time - common in olde - I mean classic gear - that messes up the entire circuit.

It may have been more accurate to say that the amps get hotter faster rather than transistors specifically. It's been a few years since my semiconductor physics course, but I'm fairly certain that prolonged application of heat causes the doping agents to get wonky (to use a technical term) leading to reduced power efficiency of the semiconductor, leading to increased heat production (wasted energy) for the same output level. This is more pronounced in the comparatively fragile integrated amp circuitry that an OEM-style amp used than in more professional kit with big-ass discrete BJT's or FET's.

If we're talking about MOSFETs or CMOS parts, then heat breaks down the oxide layer leading to increased current leakage. That's a relatively simple process.

I did observe that the amp I mentioned above did actually run hotter, not just shut down at a lower temperature.

Capacitors changing values over time is a whole different ball game, but could indeed play a role depending on what's going on inside the box. I'm not too familiar with the details of production amplifier design.

Regardless of our armchair troubleshooting results it should be the dealer's problem

[pikkashoe]

VP electricity, you do make a valid point, stock amp probably doesnt have any thermal shutdown protection. But the issue is so intermittent, and it happens to coincide when the fans are running full blast and the amp is very hot to the touch. What also leads me to believe that its a thermal issue is that if you restart the car, the amp will not work, you have to literally let it cool down for 10 minutes. So it might have some type of protection, just nothing as fancy as aftermarket amps. Any BMW techs in here???
I guess by adding the aftermarket computer fan, I will be able to see if it is actually a thermal issue, or something else like you indicate vp electricity.

And yes the system is completely stock. This is such minor issue and so intermittent that i would never be able to replicate it to a dealer. You know how that goes!!!

[Technic]

Originally Posted by pikkashoe

VP electricity, you do make a valid point, stock amp probably doesnt have any thermal shutdown protection. But the issue is so intermittent, and it happens to coincide when the fans are running full blast and the amp is very hot to the touch. What also leads me to believe that its a thermal issue is that if you restart the car, the amp will not work, you have to literally let it cool down for 10 minutes. So it might have some type of protection, just nothing as fancy as aftermarket amps. Any BMW techs in here???
I guess by adding the aftermarket computer fan, I will be able to see if it is actually a thermal issue, or something else like you indicate vp electricity.

And yes the system is completely stock. This is such minor issue and so intermittent that i would never be able to replicate it to a dealer. You know how that goes!!!

The risk in adding any aftermarket equipment to your OEM system is that you will be voiding any warranty that you may claim if in fact the OEM Amp is defective.

My suggestion is, instead of experimenting with a fan, simply try to replicate the steps required to induce an OEM amp shut down. It is irrelevant for you to find the cause (from the warranty perspective, although you may want to know because it is you car after all); that's the tech's job. However, by finding the steps you will be helping the tech in replicating the fault and submitting a valid and prompt warranty claim.

It seems that you have some idea of what's going on, so well, structure that idea into a logic step by step procedure. Only you can do that because you have more time and invested interest than any tech would have in such intermittent fault.

[pikkashoe]

Hey technic, thanks for the advice.

I really dont like dealing with dealers and warranty work. I have the worst luck when it comes to taking my car to dealers. They usually just cause more headaches and problems than what its worth.

The problem with my amp is so intermittent, that i dont even think i can replicate it if I tried. It happened about 2 weeks ago on a saturday night, and the time before that would of been a couple months ago. In total its only happened 3 times since ive had the car, that being april 07.

I only plan to put a 120 mm computer fan to blow air over the amp, so its not a very invasive modification, at most i am just tapping one power wire.

My theory is that the stock cooling on the amp is not enough to keep up with the heat being generated, especially since its in an enclosed space which I would assume does not get any airflow.

I will keep you guys posted.

[VP Electricity]

I think radio shack has a digital thermometer with a remote pickup - I would tape the pickup to my amp and next time it stops working, I'd look at it.

Only way to verify your theory.

BTW, your theory requires BMW and Harman to be about as ignorant of thermodynamics as I could imagine...

[pikkashoe]

I hope im right about the heat theory, and bMw and harman just overlooked it, but the more i think about it the more im starting to believe i have another issue as you guys have mentioned. Others would of been experiencing this as well. Ive only seen like 2 people on these forums with the issue.

I will swing by radio shack today and pick up one up.

By the way guys, i appreciate all your help and insight and suggestions.
So how hard would it be to remove that amp and get a decent amp in there. Im sure the wiring is proprietary.

[Kozmo86]

Iv had the exact problem!! It generally happens when i turn up the volume to highest and in the summer due to hot and damp weather... But from what iv heard...the amp automatically shuts down when it overheats to protect it from being damaged!! I sent it in to BMW service but they told me that they tested it out and the subs or amp didnt shut down when in highest volume?? Thats sounds like bull ... i havent had it shutdown in a while since it hasnt been hot here in NYC nor have i been blasting the radio lately!?! So if someone can come up with a solution..id like to hear it!!

[pikkashoe]

See, there you go, number 4. Kozmo, thanks for chiming in.

To be honest, the last incident I had, the volume was cranked up. I had been driving for about 40 minutes at moderate sound volume, then picked up some friends and the radio got cranked up. Not full volume, but higher than I normally have it at. About 5 minutes of that caused the amp to go into that state. The other two previous times, it wasnt cranked up.

So the amp does have thermal shutdown, so my little fan idea might work. That area back where the amp sits has to be a dead spot in terms of airflow.

So Logic 7 upgraded system cant even handle loud volume levels. Not much of an upgraded system if you ask me. And before you guys jump on me, I do like the system, i just think for it being their high level system, it should not shut off like that.

[tintivilus]

Originally Posted by pikkashoe

So how hard would it be to remove that amp and get a decent amp in there. Im sure the wiring is proprietary.

Since I think you mentioned having Logic7, it's basically impossible. The Logic7 amp has an optical digital input from the head unit and does the EQ and "surround" effects with its onboard DSP. You need at very least the front end (everything but the power amplification) to get analog outputs to do anything with.

That said, if you're using the L7 outputs to drive an outboard amp you'll be sourcing next to no current compared to the speakers, so you shouldn't have any heat problems.

[pikkashoe]

Well that little amp does get hot, pretty hot actually.

I figured swapping out the amp would be difficult.

[VP Electricity]

t seriously sounds like a bad amp...

[pikkashoe]

I hope not!!!!! Im going to work on my project this weekend. One 120 mm computer fan. one tapped power wire, one ground. Should take 15 minutes. Going to have it blowing air over the amp. Ill take some pictures.