It's a '96 with a stock Bose Gold system. I was going to hook up a Bazooka sub for a little more low end. I connected the Bazooka speaker wires at the + and - terminals of the Bose rear speakers. Polarity was correct, no apparent shorts and I had not yet switched on the Bazooka. I turn the radio on and instant garbage from the rear speakers. Seconds later, I smell smoke from the rear speaker amps. Front speakers were fine. Disconnected all the Bazooka wiring, but rears are fried.
Now, I will be getting a complete aftermarket system, but I was wondering what I did wrong.
Thanks. :mad
Wrong ohm ratings. You can't hook anything up to a bose system. Its totally incompatable with anything without expensive poorly made voltage adapters. It must all be removed. Time to sell the crappy stuff and get a real system. To bad you won't be able to sell them now.
Wrong ohm ratings. You can't hook anything up to a bose system. Its totally incompatable with anything without expensive poorly made voltage adapters. It must all be removed. Time to sell the crappy stuff and get a real system. To bad you won't be able to sell them now.
An amp burning up after improperly connecting to it has nothing to do with the ohm rating.
An amp burning up after improperly connecting to it has nothing to do with the ohm rating.
[Modified by 99HT, 11:14 AM 1/27/2002]
Actually, it has everything to do with blowing up an amp. The Bose amps have no "protection" to an overload. If the Bose speakers were to short, it would blow the amp. I suspect that when the Bazooka amp was connected, it presented a lower impedence to the Bose amp and cooked it. We are very used to "real" amplifiers (aftermarket) which have a very good protection system against low inpedence loads or short circuits. We can make a mistake wiring the amp and it would simply go into protection... the Bose amps just go into smoke mode.
The Bose amplifier is a class D switching amp. It's "ohm" rating has nothing to do with having output short circuit protection. If you screw up connecting to the amp, you can blow it. It has nothing to do with the "ohm" rating.
The power rating of any amplifier is based on the power supply voltage, in this case 13.8 volts, the size of the power output transistors and the heatsinking capability of the amp. The Bose amp is a class D design whose ouput devices are power Mosfet's in a full bridge configuration. A class D amp's output devices operate as switches that are either OFF or ON, they never operate in the linear region. The ON resistance of these FET's is very low, and when they turn on, they dissipate very little heat. The use of low ON resistance output FET's, gives the Bose amp it's ability to drive low resistance loads.
Ok, so you are telling me that my Infinity Beta Digital 300 amp can drive a near zero impedence load (even though the manual explicitly says not to connect a load of less than 1 ohm)?!?! Yes, I understand the principals of pure class D amplifiers, but it is still very possible to blow the output devices if they have to sink too much current. Now, the Bazooka itself probably didn't introduce a zero load, but if there was any mistake in wiring, the Bose didn't protect itself and released the magic smoke.
A Bose amp is considered "special" because it is capable of driving custom Bose speakers that are 2 ohms OR less. This is a very unusual feature you will find in only the largest aftermarket power amps.
The dealer who "commented" on why the amps blew up, alluded to the fact that the low Z drive capability was the reason the amp blew up. This had zero to do with the problem. A short is a short.
If you take one of your "special" expensive amps and put a short on their output for long enought time, they would burn up also. Having short circuit protection does not always protect an amplifier, if the short occurs for a long period of time.
A Bose amp is considered "special" because it is capable of driving custom Bose speakers that are 2 ohms OR less. This is a very unusual feature you will find in only the largest aftermarket power amps.
The dealer who "commented" on why the amps blew up, alluded to the fact that the low Z drive capability was the reason the amp blew up. This had zero to do with the problem. A short is a short.
Good points.... I think the Bose speakers are less than an ohm to begin with, therefore, the amp may be at its impedence with little more load added to it. I still think there is an inherent problem with the amps and loads considering all of the problems that are reported with blown amps.
If you take one of your "special" expensive amps and put a short on their output for long enought time, they would burn up also. Having short circuit protection does not always protect an amplifier, if the short occurs for a long period of time.
As a previous post stated, the Bose amp has a bridge output. That means neither side of the amp is grounded. If you connect a speaker (I'm not familiar with the speakers you connected) that has one side grounded, you will probably blow the amp -- it depends how well the amp is protected.
The amps that were in the C4s are prone to cooking very easily. I don't know if they had any protections built in to them like later models. They have a two ohm output. Adding the woofer can lower the ohm rating and fry the amps quite easily. Unfortunately I don't know exactly how it was wired but I suspect this is the case. BTW, the auto standard is 4 ohm and the home 8 ohm. Most quality aftermarket amps will go down to 2 or even 1 ohm so adding extra speakers and lowering your resistance is ok. In fact, Carver made a home amp that was rated to be able to withstand 0 ohms or have the + plugged into the - and still operate. One reviewer said you could weld with it if you took the time. Don't think I'll b e welding with the bose amps anytime soon.
I don't know about any safety features in the amps but I do know that they fry on a regular basis when people try to switch speakers or decks. I suspect that any safetys that were put in were minimal and designed to resist problems presented to them by the stock equipment and not able to withstand aftermarket equipment changes. This would be inline with the rest of the C4 sterio design which is make it just good enough so it works but don't do any more that would add any expenses to the system's production. (i.e. very cheaply made and constructed) :rolleyes:
There is come confusing statments in this posting that I would like to clarify.
ALL audio power amps have a VERY low output impedance. You can consider it almost ZERO ohms at low frequencies or DC. The "ohms" rating of the amplifier has almost nothing to do with it's own internal output impedance. The output current rating of the amp, it's design class, A,AB,D..etc, heatsink capability, power supply voltage..etc, unconditional stability in driving reactive and resistive loads, determine the "ohms" rating.
A VERY low power OPAMP circuit can also have an output impedance of ZERO ohms at low frequencies, but yet can only drive a 600 ohm load.
A balanced or bridged output amplifier design is used to provide 2x the voltage swing to a speaker. 2x the voltage is 4x the power. For an amp running off 13.8 volts, a single ended amp driving a grounded speaker will only put out about 5 wrms into 4 ohms. A bridged output will put out about 20 wrms into a 4 ohm floating load. A bridged output class A or AB amplifier utilizes TWO seperate amplifiers. One of the amps is driven 180 degrees out of phase from the other.
A class D design is more similar to switching regulator power supply. It can also be a single ended or bridged design like a class A or AB design. What class D offers is much lower heat dissipation and efficiency than an AB design. A bridged class D design will supply 2x the voltage swing of a single ended. A class D full bridge output design utilizes 4 switches driving the speaker. The switches can be Mosfets or transistors.
There are two reasons the Bose amps did not have short circuit protection, first is cost and complexity, the second is the extra parasitic losses in the resistors used to sense current. Older gen power Mosfets had high ON resistance, adding current sense resistors made things worse. Modern class D amps are based on new integrated circuit designs that have lowered the cost tremendously. These new IC's only need VERY low resistance current sense resistors for short circuit protection. New generation Mosfets are much faster and have VERY low ON resistance, lowering parasitic losses even further.
The initial posting said "I had not yet switched on the Bazooka" which implies to me it was an amplified version; the passive units wouldn't have switches. It's my guess that the amplified bazooka needs a common ground system, and maybe the (-) side of the high-level inputs was grounded. That would certainly make the push-pull output stage of the Bose amps unhappy trying to drive -12v into ground!
Or if it was a passive 4 ohm; connecting it in parallel with a 2 ohm Bose would have yielded a 1.3 ohm load which was probably just too much for the amps. As pointed out above, they have no current limiting.
Maybe you could clarify what type of Bazooka it was and exactly how you connected it?
Since the Bose amp uses "balanced" full bridge output design, if the input impedance of the Bazooka was too low, it could unbalance the Bose output when the Bazooka + input was connected to the Bose + output, causing a DC offset in the output. This would cause a big problem. This could happen if the installer set the input on the Bazooka to high level and connected the Bazooka - input to chassis or power ground. Some amps use have a very low input impedance when set for high level inputs.
If the Bazooka - input, which is normally connected to the Bazooka power ground, was connected to the - Bose output, this would definitely blow the Bose amp. This would then provide a direct short from the Bose - output to chassis or power ground. This is a common mistake by inexperienced hi-fi installers who don't know crap.
Sounds like that could have been the problem. Like I said I never saw what happened so its all theory right now. He also didn't have it installed but did it himself which makes me think you're right on that 99.
This is a common mistake by inexperienced hi-fi installers who don't know crap.
That describes me perfectly! :D
The Bazooka is an amplified version. I had it in another vehicle and it worked fine.
Seven wires were connected:
1. Power - Directly to the battery.
2. Remote power - Tapped into power antenna wire. Toggle switch off. No power.
3. Chassis ground
4. & 5. Right side + and - inputs. I contacted SAS Bazooka prior to the installation. Their website (as well as a tech I spoke with) advised that, due to the low output of the Bose amps, I needed to tap into the speaker wires AFTER they came out of the Bose amp. I did this by using a "T" adapter on the + and - terminal posts of the speaker itself. The tech also advised that these wires should be tied into the LOW LEVEL input of the Bazooka as opposed to the line level inputs. I did this also.
6. & 7. Left side. Same as above.
I wire it up, turn on the radio (no power to Bazooka) and immediate garbage from the speakers. Both rear Bose amps cooked.
Today, I connected everything back up the way it was. I figured that since the amps are shot, why not? There was still garbage from the rear speakers, but the Bazooka sounded good. Go figure.
BTW, thanks for all of the responses. You guys might as well be talking rocket science from the small amount of terminology that I understand.
Bottom line: Can an amplified subwoofer be connected to a Bose system in a C4? IF so, how? If not, don't burn up $150 worth of amps trying.
You can connect to the HU outputs that feed the Bose amp ONLY if your Bazooka low level input does not load down the HU output or shift any DC level that may be on the wires. The Bazooka input impedance must be high and have a capacitor on it's input to block the DC that may be on the wires. You should not tap the signal at the Bose amp input, you may cause a ground loop in the audio, causing noise. Connect to the back of the HU or main module that feeds the Bose amplifier/speaker.
I am not an expert on a C4 system, I have NEVER played with one or even SEEN one. If your system is a two piece system, then connect to the main module, not the control head.
What do you mean when you say "tied into the LOW LEVEL input of the Bazooka as opposed to the line level inputs."
Usually low or line level are the same thing (< 1 Vrms) which interconnect components; as opposed to high level (> 12 V) which generally drive speakers.
The low-level inputs would normally connect to preamp-outs and have very high input impedance. But like I said above, I bet that (-) side is grounded! Especially since they're summing the L/R inputs to mono, the channels need a common-ground. You can check easily with an ohmmeter; and if that's the case, Crutchfield and others sell an isolator/adapter for this purpose.
Of course considering the Blose sucks sooooo bad, you now have a good excuse to install a real system......
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Why did my Bose amps burn up?
