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Old 18th March 2004, 05:35 PM   #1
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Default Simple subwoofer/pre-out question

I have an older Pioneer VSX-D503S amp (ca. 1992) that works great but does not have a subwoofer pre-out. I am thinking there a piece of equipment out there that could take the data from the right & left channels and split it out to R & L plus a subwoofer pre-out. Am I thinking correctly? If so, what are they called? My amplified subwoofer is also older and is fairly basic. It only has a single RCA jack type input and no additional input plugs like my newer one has. I figure this is a simple question for some of you out there.

As I think more about it here at the end of my post, it would need to be line-level and the speakers-out signal wouldn't be. Any suggestions would be great.

Thanks,
RHH
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Old 18th March 2004, 06:51 PM   #2
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Hi thb,

The back of your amp should have line level outputs (full range). These are your Tape 1 monitor outputs (Rec). A lot of subwoofer outputs are full range also. The crossover is in the sub. I am guessing that you are able to get a Y connector and split the two tape rec outs to your one input on your old woofer.

Your second left and right channels can come off of Tape 2 Rec if you are using a second amp. If not then use your speaker outputs on your Pioneer. The Rec outputs on your amp are constant "hot" meaning always active, constant level ie: not affected by the volume control.

Hope this has answered your questions.

Cheers,
Cal
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Old 18th March 2004, 07:29 PM   #3
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DO NOT DO THIS!

Unfortunately you cannot simply use a Y-lead to join a left and right signal, by using one of these leads you are shorting the left and right outputs together = bad.

I can't say I've ever seen a full range sub out, if it were full range it would just be a pre out! Using tape loops is no good either because they don't follow the volume control. OK if you never change the volume I guess...

You need to make a summing and filter unit that accepts either line-level (if your amp has pre-outs) or speaker-level signals, then sends out a single line-level signal. Have a look on the net for op-amp summer circuits and filters. The summer is dead simple and is made from an inverting amplifier.

If you are on about trying to get a 'black box' to work with Dolby Digital and give you an LFE out, sorry but no.
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Old 18th March 2004, 07:31 PM   #4
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Cal,
I don't know if THB's receiver has pre-outs, but using monitor- outs is a royal pain. As you suggested, they are fixed level. Thus, everytime the volume is changed, you need to go fiddle with the subwoofer level. Not an acceptable solution in my opinion.

Quote:
get a Y connector and split the two tape rec outs to your one input on your old woofer.
Don't do this! You cannot just "y" left and right outputs to form a single output to the subwoofer. At best, it won't work since the left and right outputs will be driving each other. At worst, it will destroy the line drivers in the receiver. You've got to sum these signals with an active device (an op amp will do). If you're just experimenting on the cheap, you can just connect to left or right --since a fair amount of bass information is mono.

This all assumes, of course, that the "older" sub has a built-in crossover. Since it doesn't even have L-R line-ins, I'd start to wonder.

THB, there are devices to do what you are looking for - assuming your receiver has pre-outs. The Outlaw ICBM is one of the most popular. However, if your receiver doesn't have pre-outs, I'd say upgrade the receiver or stick to subs with speaker-level inputs.
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Old 18th March 2004, 08:51 PM   #5
Luke123 is offline Luke123  Canada
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Default ...THEHOLMBOY

OK. You have an amp that does not have a preamp output and you want to drive an amplified subwoofer from L/R channels of your amp. I've done this several times.

The way to go is to get the L/R signals coming from the wipers of your main volume control.

First thing to know is to watch in a scope if what is coming out from your control volume's wipers is an analog signal! Naturally. I say this 'cause I don't know your amp at all. And this signal could be a digital signal or something else. Anyway.

If it is analog, just take a signal split from the 2 wipers of this volume control and send them at the positive input of a good opamp. Build your gain structure on this opamp to get a sensitivity of , let's say, 1 Vrms at the output of this opamp for your amp's full power at 8 ohms. Now you have a stereo preamp output. If you want a mono one, instead take these two wipers output and send them on a inverting summing configuration on one channel of this opamp. Use the other channel of this opamp as an inverting buffer with your needed gain structure. So now you will be back as a non-inverting.

Power supply : use a pair of 12 or 15 volt regulators to feed this opamp or split from a decent ±voltage not more than 18 volts.

Luke123
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Old 18th March 2004, 09:11 PM   #6
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Sorry THB,

Thank you to all who recognized the error in my ways. I just headed out for lunch and got a sick feeling in my stomach while eating.

I was trying to relate what I have to what you want to do. Just a couple of parts missing ie: pre-amps between the original outputs and the secondary amps. Therefore I have the ability to control the input signal.

I am very sorry to have caused this confusion. I agree with the others Do not Y the two together. I do a Y connect from one into two not two into one.

I was trying to be helpful but really should have thought it through before posting. I really hope this has not caused you problems.

Tail between my legs,
Cal

Humblist of apologies
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Old 19th March 2004, 12:08 AM   #7
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Quote:
Originally posted by richie00boy

I can't say I've ever seen a full range sub out, if it were full range it would just be a pre out!
My Harman Kardon has full range Sub outputs, I am running an amp of each of them
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Old 19th March 2004, 12:11 AM   #8
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Post External active xover.

Heres what you need an external active xover with speaker level inputs.
I use the Pardaigm X-30 (line level) between pre-amp & power-amp.

In your case you need the speaker level input, take your speaker outputs from your receiver & connect to the xover, then the high-pass to your speakers & low-pass to your sub. (If the sub has an active xover seto it to highest frequency)

I'm pretty sure these units sum mono as well.

http://www.paradigm.com/Website/Site...Unit_Specs.htm
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Old 7th January 2007, 11:23 PM   #9
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Supposing one were to connect an amplified subwoofer to an older receiver with no subwoofer outputs, using the tape line out jacks. For those of us on a budget. Assuming this not-yet-purchased subwoofer had l and r line level inputs. Other than the need to manually adjust volume on the subwoofer whenever the main volume were changed (maybe I'd only use the subwoofer occasionally, like when we're playing a movie, etc.), are there any other issues?
Thanks,
John
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Old 7th January 2007, 11:42 PM   #10
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No issue, other than the volume problem.
Just remember to set the subwoofer volume to minimum as the tape out is full level. If your receiver has a separate record selector, set it it the apropriate source, turn up your main volume to listening level, then bring the sub up to match. A lot of subs have an automatic turn on/off feature, that way if you had a record selector set to the dvd input you could leave the sub on & level set, it would turn itself on whenever you started playing a dvd.
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