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Omega Help Area => Omega Electrical and Audio Help => Topic started by: Dazzler on 11 May 2008, 21:15:52

Title: Line input amp for sub
Post by: Dazzler on 11 May 2008, 21:15:52
I have an Elite with Bose and was wandering if i can use an extra amp that takes speaker line inputs into it to drive another sub?

If i can can i piggy back onto the existing wire that feeds the Bose sub and use the Bose sub as well?

Or will i need to disconnect the Bose sub and use only the new amp?

All feedback gratefully recieved :)
Title: Re: Line input amp for sub
Post by: Dave DND on 11 May 2008, 23:11:58
Possible on anything except the BOSE system.

If you use the High level inputs to the BOSE amp, the voltages are all wrong and will not drive a line unput adaptoe sufficiently, and I would advise not to connect anything else to the speaker outputs of the BOSE amp, as being 2 ohms, the amp could be damaged with the additional loading placed upon it.

Bottom line, if you don`t like the BOSE system - rip it all out, speakers and all.
Title: Re: Line input amp for sub
Post by: Marks DTM Calib on 12 May 2008, 08:31:05
I cant see a problem with connecting an amp with speaker level inputs across the Bose amp sub outputs.

The speaker level inputs on the amps tend to be in the order of Kohm so wont present any significant load to the BOSE unit.

In fact, if you wished to retain the Bose subs this would be by far the best route to follow as the sub should (in theory) then be truely in phase (or much easier to get in phase) with the rear shelf speakers.
Title: Re: Line input amp for sub
Post by: Dave DND on 12 May 2008, 08:55:25
There is no problem in theory about connecting across the inputs to the BOSE amp, the only problem is that you will end up with a signal that cannot be used effectively.

The signal you end up with will need to be converted to RCA using one of the aftermarket convertors.

The standard Non adjustable RCA convertors will probably not have enough of a signal to make the output useable, and the preferred fully adjustable RCA converters will not generally cover the range of voltages offered by the BOSE line levels used.

Not yet found an accoustically satisfying solution to that one.

But whatever you do, do not connect across the speaker outputs to get the signal.
Title: Re: Line input amp for sub
Post by: Dazzler on 12 May 2008, 09:11:05
The amp i was thinking of (Alpine) can use RCA or Just speaker line inputs so i don't have to convert to RCA and i thought the amp was configured in such a way as to accept whatever voltage is supplied by the speaker line inputs :-/

But i am no expert hence the post ;)
Title: Re: Line input amp for sub
Post by: Marks DTM Calib on 12 May 2008, 09:27:12
Quote
There is no problem in theory about connecting across the inputs to the BOSE amp, the only problem is that you will end up with a signal that cannot be used effectively.

The signal you end up with will need to be converted to RCA using one of the aftermarket convertors.

The standard Non adjustable RCA convertors will probably not have enough of a signal to make the output useable, and the preferred fully adjustable RCA converters will not generally cover the range of voltages offered by the BOSE line levels used.

Not yet found an accoustically satisfying solution to that one.

But whatever you do, do not connect across the speaker outputs to get the signal.

I was sudgesting connecting to the output......
Title: Re: Line input amp for sub
Post by: Dave DND on 12 May 2008, 09:28:40
If you had RCA or ordinary speaker level signals to play around with, you would have no problems whatsoever.

In their infinate wisdom, BOSE screwed everything up when they adopted their own range of signals. There will be no harm in taking the input levels from the BOSE amp and connecting to the High level speaker input on the Alpine amp.

It may work, and as you are only driving a sub, you probably may not notice the shortfalls of the poor signal - an alpine amp will also have a wider degree of adjustment than most others - worth a go
Title: Re: Line input amp for sub
Post by: Dave DND on 12 May 2008, 09:31:50
Quote
I was sudgesting connecting to the output......

Definately not. The output of the BOSE system runs at 2 Ohms, and unless the resultant load is exactly 2O hms after you have finished playing around, you will overload the amp and almost certainly blow the output stage.

the BOSE amp is exceptionally fragile and does not like being played around with, so be carefull.
Title: Re: Line input amp for sub
Post by: Marks DTM Calib on 12 May 2008, 09:33:43
Quote
Quote
I was sudgesting connecting to the output......

Definately not. The output of the BOSE system runs at 2 Ohms, and unless the resultant load is exactly 2O hms after you have finished playing around, you will overload the amp and almost certainly blow the output stage.

the BOSE amp is exceptionally fragile and does not like being played around with, so be carefull.

But, your amp output will now be seeing 2ohms (rear shelf speakers) in parralel with say 2Kohm (amp speaker level input).........so still basicaly 2ohms!
Title: Re: Line input amp for sub
Post by: Dazzler on 12 May 2008, 09:42:46
Im confused now, as to wether to use the input to the amp or its output to the speakers.
Two highly respected experts saying the opposite. :-/

I don't want to damage the Bose system or the new amp and sub. :(
Title: Re: Line input amp for sub
Post by: Dave DND on 12 May 2008, 10:02:07
Quote
But, your amp output will now be seeing 2ohms (rear shelf speakers) in parralel with say 2Kohm (amp speaker level input).........so still basicaly 2ohms!

I understand what you are saying . . .

I have around a dozen amps here in the workshop that have been blown to pices by others who went down this route !!

Quote
Im confused now, as to wether to use the input to the amp or its output to the speakers.
Two highly respected experts saying the opposite.

I don't want to damage the Bose system or the new amp and sub.  

I would use the input signal to the BOSE amp if I had to,

BUT ! . . . I am one of the few on here who thinks the BOSE system is awfull (yes, I`ve been spoilt by the systems I sell and install) and the first thing I would do is to rip the whole lot out as if you do not like the way it sounds, then it is not a system that takes lightly to "modification"
Title: Re: Line input amp for sub
Post by: Dazzler on 12 May 2008, 21:24:47
The Alpine amps can handle about 0.2-4.0v on its input, is this good enough for the Bose input signal to the sub amp??

Thinking of this one or similar...
http://www.cel-direct.com/p/Alpine-MRP-M500/Alpine-MRP-M500.asp
Title: Re: Line input amp for sub
Post by: Dave DND on 12 May 2008, 21:28:57
Quote
The Alpine amps can handle about 0.2-4.0v on its input, is this good enough for the Bose input signal to the sub amp??

No, thats an adjustable low level RCA input and not the high level speaker inputs that you were talking of earlier.

 :'(
Title: Re: Line input amp for sub
Post by: Dazzler on 12 May 2008, 21:33:33
Do you have an example by chance Dave please so i know what to look for ;)

TIA