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Old 05-20-2005, 07:33 AM   #1
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Sub-woofer needs delay circuit

Help, every time I turn on, off, change channel, or source I get a bump through the newly installed bazooka sub-woofer. I've called Crutchfield and they told me it was caused by the momentary drop in power when switching which causes the amp to discharge its capicitors. I disconnected it from the remote turn-on and it still happened when I turned on and off a light. I unplugged the RCAs and it stopped.

I called Crutchfield tech support and this is what they suggested, sending me to this site http://www.crutchfield.com/S-1Crd0pm...ech/kb327.html Will this work even though it pops when its not hooked up to the remote but plugged into the RCAs? Where can I get this stuff? Can you talk me through the fuse, I haven't seen one in a circuit diagram before.

I'd appreciate any help, diagrams or play by play you can give to the hook-up extra.
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Old 05-20-2005, 08:24 AM   #2
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Quote:
Originally Posted by Crutchfield
Occasionally, after installing a new component in your car stereo system, you will notice a 'pop' when you turn the receiver On or Off.
Crutchfield's circuit is addressing what are commonly referred to as "turn-on transients" or "turn-off transients". While their circuit will alleviate some of your problems, I do not believe it will help when changing channels or sources.
Quote:
Originally Posted by M&M
...and it still happened when I turned on and off a light...
Which light is this? One of your Airstream's lights? While I do not have a solution yet, I am working on a suggestion. I don't won't to offer it until I completely understand what's wrong.

Tom
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Old 05-20-2005, 09:58 AM   #3
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The lights over the couch

Quote:
Originally Posted by TomW
Which light is this? One of your Airstream's lights?Tom
Tom,
It was the two reading lights and the flourescent light over the couch, all Airstream installed lights. I did not try any other lights at the time. The radio was not on at the time I turned on the lights and the remote switch wire was disconnected. It was not as loud a pop as it was when the radio was on. I'm going out to the trailer and see if it makes a difference if I switch the RCAs (the ones for the sub are identical) maybe it's a polarity thing. I will also see if the pop happens when I try a corded light. Thanks for your continued help.
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Old 05-20-2005, 10:38 AM   #4
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It sounds like you are using a 'powered' bazooka (built-in amplifier).

If it happens when radio is off you may want try running the ground wire direct to the battery. Grounding problems can be quite evil in the audio/video world.
There are filters made that can be installed, but I wouldn't use them unless all else fails. Filters tend to mask the problem -- it's best to FIX the problem if you can. As a quick test, run an adequate sized ground wire and attach directly to the (-) post on the battery and see what happens.

I did home/mobile audio-video installations for years, everything is 'fixable', but can be frustrating and time-consuming.
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Old 05-20-2005, 02:08 PM   #5
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I believe you have separate issues working against your listening enjoyment. While all are overcomable, the amount of money, level of effort, or a combination of both may cause you to reconsider if the problem can be lived with.

The bump heard when turning either the head unit or subwoofer on or off is a design issue, and can be alleviated with the “soft start” solution outlined by Crutchfield. BTW, Crutchfield’s solution is what should have already been designed into a given piece of equipment.

The noise heard when flipping a light switch on or off is a power quality issue, and could be lessened by a noise filter at the head unit. This device is not a big honking electrolytic capacitor, but rather one or more smaller bandpass variety capacitors and maybe a choke. Ideally, your head unit would have already had this device incorporated, but it does not appear that it does.

The issue of bumps heard when switching channels or sources can not really be fixed. My perception is that the bumps were not designed out of the head unit probably because the manufacturer did not think anyone was ever going to hook up a subwoofer. The bump may not be noticeable with stock (non-subwoofer) speakers.

So where do you start? If it was me, I would test drive some new head units connected to good speakers & go from there.

Good luck,
Tom
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Old 05-21-2005, 11:02 AM   #6
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This is m&m's son. The bazooka had a loop which could be disconnected. This loop allows the amp to turn on if it detects music. The RCAs were pretty close to some positive power lines running from the batteries. I think the change in current in the power wires to the trailer by turning on the light created a change in magnetic flux which created a current in the rcas, turning on the amp (pop).
I moved the rcas and the problem was solved. We still have the problem with a hiccup in the remote line from the head unit. I understand what every component in the circuit crutchfield suggests is doing except for the transistor. I assume the voltage in the remote line is too small to flip the relay so they're increasing that. I can't find that transistor locally, and mouser.com doesn't carry it, newark.com charges a minimum of about 10 dollars shipping and handling for a 80 cent transistor . Could I just use an op amp with some resistors instead (1+R1/R2=gain)? Also, what type of relay should I buy? A 5v reed relay? Thanks.
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Old 05-22-2005, 04:23 AM   #7
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Quote:
Originally Posted by M&M CAPECOD
...I understand what every component in the circuit crutchfield suggests is doing except for the transistor. I assume the voltage in the remote line is too small to flip the relay so they're increasing that...
My take on their circuit is that the transistor is being used as a switch. When the base is at near the potential of the collector, the transistor conducts, and 12 volts is available at the emitter. Using the transistor ensures the circuit will either be ON or OFF. In effect, the whole circuit is just a solid state relay with delay.

If only Dr. J. were here...

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Old 05-22-2005, 10:31 AM   #8
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Quote:
Originally Posted by TomW
My take on their circuit is that the transistor is being used as a switch. When the base is at near the potential of the collector, the transistor conducts, and 12 volts is available at the emitter. Using the transistor ensures the circuit will either be ON or OFF. In effect, the whole circuit is just a solid state relay with delay.

If only Dr. J. were here...

Tom
Tom
You are correct, the time it takes the capacitor to charge is the delay time.
This could be done much easier by using a time delay relay. They can be expensive but I have seen them on Ebay for cheap. They are available in 12vdc and you can set the delay time to what ever you like.
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Old 05-22-2005, 11:41 AM   #9
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It seems like any npn power transistor would work, it's just being used as a switch so any specs except for the power to feed the relay aren't too critical.

John
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Old 05-22-2005, 02:52 PM   #10
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I purchased two pieces of electronic equipment from Crutchfield that had feedback making the units unpleasant to listen to. Crurchfield told me that is how the system worked and there was nothing wrong. Since I already had one of these units that I purchased from the manufacturer years earlier that worked like it should without this problem, I figured something about the really low Crutchfield price had something to do with the problem. It was a manufacturer's second. I returned the merchandise to Crutchfield and found replacements at a local retailer. There was no feedback in the local purchased machines, which did cost more.
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