Can this be done?

Wombat2 · 31st May 2006, 02:56 AM

Would this arrangement cause any problems? Car radio/cassette player and a separate CD player feeding into the same set of speakers. Both units are power up when the ignition is on but only one playing at any one time.

Reason I ask is this arrangment has been working OK for about 6 mths but recently playing a tape and the CD player let out the magic smoke.

lndm · 31st May 2006, 06:31 AM

I once tried to bridge both channels of a stereo amp by soldering their outputs together. They died before I could even connect a source. I would definately use a line level connect from one component to the main component, or use a buffer amp.

Just guessing, there may have been a tiny DC offset between the channels, but with almost zero resistance between them, they would have passed current until they passed out.

sreten · 31st May 2006, 08:38 AM

Hi,

Simple answer is no it should not be done.
Something will rapidly or eventually blow.
The active amplifier is driving the inactive amplifier as a virtual short.
Power output for both amplifiers will be poor.

/sreten.

Wombat2 · 31st May 2006, 12:53 PM

Thanks - not what I wanted to hear but what I needed to hear

Stocker · 31st May 2006, 06:49 PM

easy solution, not cheap but easy, is to buy a head unit with tape and CD

or get a portable CD player and put it to the line level input of the tape headunit

Perry Babin · 1st June 2006, 04:14 AM

You can use relays to switch between sources. If you use common Bosch relays, you will need to use 1 relay per speaker wire.

Pin 30 - speaker terminal
Pin 87a - the default source unit
Pin 87 - the alternate source unit

85/86 switched power/ground to the relays. You may be able to use the remote turn on of the alternate source to switch the relays but 4 relay coils may burn out the remote driver transistor. You could switch the relays with a toggle switch or use a 5th relay to buffer the remote output of the alternate source.

IMPALAMAN1 · 1st June 2006, 02:56 PM

very nice Perry. Is there a limit on the amount of power you can put through the relay?

ocool_15 · 10th June 2006, 06:21 PM

yes, but they are marked on them and a regular 12V 30A relay is more then enough. A 12V relay at 3A or larger is adequate

31st May 2006, 02:56 AM	#1
Wombat2 diyAudio Member Join Date: Nov 2003 Location: Brisbane	Can this be done? Would this arrangement cause any problems? Car radio/cassette player and a separate CD player feeding into the same set of speakers. Both units are power up when the ignition is on but only one playing at any one time. Reason I ask is this arrangment has been working OK for about 6 mths but recently playing a tape and the CD player let out the magic smoke. __________________ David L

31st May 2006, 12:53 PM	#4
Wombat2 diyAudio Member Join Date: Nov 2003 Location: Brisbane	Thanks - not what I wanted to hear but what I needed to hear __________________ David L

31st May 2006, 06:49 PM	#5
Stocker diyAudio Member Join Date: Dec 2003 Location: Austin	easy solution, not cheap but easy, is to buy a head unit with tape and CD or get a portable CD player and put it to the line level input of the tape headunit __________________ Jesus loves you.

1st June 2006, 04:14 AM	#6
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	You can use relays to switch between sources. If you use common Bosch relays, you will need to use 1 relay per speaker wire. Pin 30 - speaker terminal Pin 87a - the default source unit Pin 87 - the alternate source unit 85/86 switched power/ground to the relays. You may be able to use the remote turn on of the alternate source to switch the relays but 4 relay coils may burn out the remote driver transistor. You could switch the relays with a toggle switch or use a 5th relay to buffer the remote output of the alternate source. __________________ Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links

1st June 2006, 02:56 PM	#7
IMPALAMAN1 diyAudio Member Join Date: Jun 2005 Location: BAY AREA, CA.	very nice Perry. Is there a limit on the amount of power you can put through the relay? __________________ linear power/ oz audio/ clarion


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31st May 2006, 06:31 AM	#2
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	I once tried to bridge both channels of a stereo amp by soldering their outputs together. They died before I could even connect a source. I would definately use a line level connect from one component to the main component, or use a buffer amp. Just guessing, there may have been a tiny DC offset between the channels, but with almost zero resistance between them, they would have passed current until they passed out.

31st May 2006, 08:38 AM	#3
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, Simple answer is no it should not be done. Something will rapidly or eventually blow. The active amplifier is driving the inactive amplifier as a virtual short. Power output for both amplifiers will be poor. /sreten.

10th June 2006, 06:21 PM	#8
ocool_15 diyAudio Member Join Date: Nov 2004 Location: sk	yes, but they are marked on them and a regular 12V 30A relay is more then enough. A 12V relay at 3A or larger is adequate

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