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Old 28th July 2012, 11:06 PM   #1
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Default DIY Passive Stereo=>LCR=>Quad=>LCRS Switch box.

I have a yamaha rx-496 with A-B monitoring options. Both can be selected at the same time. Would the wiring array depicted in the following diagram work to somewhat exhibit a "faux surround" similar to what was going on in the DIY home theater community in the late 80s? Excluding speaker impedance and exact values of components described in the diagram and what needs to be added still, would this work?

I have four bookshelf speakers (bought from mother in law during a move) impedance unknown at the moment, 2 Klipsch SF-2 floors and an active sub on the way. I believe that if the speakers impedance are all the same or similar I can make it work with a few transformers.

Probably wont sound great but it's essentially free to me at this point, and I just want to have something until I can finish my DIY Pro Logic Decoder.

Click the image to open in full size.

I'm no design engineer so it ain't pretty, but I think I get my point across. Discrete Left and Right front channels, an LR summed center, a phase inverted LR summed mono surround pair, pots to calibrate both the rear channel and the center, and a couple switches to change from true stereo=> LCR=>(what I call)'Quasi-Quad'=>'LCRS'.

My only concern is changing the load impedance in real time, I'm sure I'll need to throw in some L-pads to balance everything out. Hell, I might refit the whole lot with TRS and balance the **** outta that ****!...Probably not though...

Let me know what you guys think!

tbuckner
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Old 29th July 2012, 06:36 AM   #2
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Anybody have any advice to lend?
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Old 29th July 2012, 08:19 AM   #3
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The Hafler-Dynaco faux surround audio system from the 70's is probably what you refer to. From personal experience, with unmatched speakers in several homes, it's simple phase inversion delay systems was (is) a flop. Actually, I should rather say that my implementations with a single stereo amplifier and guided by then current magazine articles, projects and suggestions were a flop.

In the early and very expensive period of Dolby surround sound, many manufacturers saw an opportunity and experimented with pseudo-surround sound processors that just added a couple of extra channels to your system with adjustable analog or digital delays. These were cheap and worked well enough, IMO, to give enjoyable surround sound from stereo sources. I dusted my 30W p/ch. add-on unit from 1990, about six months ago and it still does what is expected.

Given that fully working 5.1 receivers are now just kerbside clutter and plenty of "home entertainment centre" compact audio systems have routinely had 5 channel digital sound processing in any flavour you like (also free now), is it worth the effort of resurrecting a system which never really did much?
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Old 29th July 2012, 08:38 PM   #4
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I hold it to be true that to really understand the growth of technology is to appreciate its current state. Being an Audio Engineer my feelings towards understanding the foundations of what most people take for granted these days is extremely important solely for the purposes of appreciating what is possible. That is not to say that I do not want to own a surround receiver. I just A) cant afford it right now and B) well that's it really...

I appreciate your response but my main objective was to get feedback as to whether this design would work or not. Now I know that all of the speakers are 8 ohms. So unless my receiver can handle a four ohm load I may not be able to do this at all (unless I get crafty with series and parallel decisions while preserving the current signal flow).

Anyone able to shed some objective light on my question?
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Old 29th July 2012, 11:32 PM   #5
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Quote:
Originally Posted by tbuckner View Post
I hold it to be true that to really understand the growth of technology is to appreciate its current state. Being an Audio Engineer my feelings towards understanding the foundations of what most people take for granted these days is extremely important solely for the purposes of appreciating what is possible. That is not to say that I do not want to own a surround receiver. I just A) cant afford it right now and B) well that's it really...

I appreciate your response but my main objective was to get feedback as to whether this design would work or not. Now I know that all of the speakers are 8 ohms. So unless my receiver can handle a four ohm load I may not be able to do this at all (unless I get crafty with series and parallel decisions while preserving the current signal flow).

Anyone able to shed some objective light on my question?

ok maybe this will help you a little bit in your decision, I found this post somewhere else. I am sure your receiver will not have enough juice to drive all those speakers in A+B speakers.
Yamaha RX-496 Receiver won't power speakers - Audioholics Home Theater Forums
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Old 30th July 2012, 02:28 AM   #6
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True, there is only 75w per channel in stereo A mode, and I remember that in A+B the output power drops a little. So yes, this will certainly under-drive my speakers. In fact, the receiver is already under-driving my Klipsch which are rated 100w RMS min @ 8ohms.

I had a feeling that this might be the case which, so I'm not too surprised to have gotten a response like lanchile has given.


Perhaps I should have worded my question a little differently:

Does this signal flow make sense and, excluding all nominal values, impedance values and power ratings, would wiring diagram accomplish the channel separation that I have attempted?

I'm getting the feeling that I may never get my question answered and will only be told that it's silly to try an old fad, or that I would not have enough power to drive the speakers sufficiently. I had hoped that lurking somewhere on this forum there would be an electrical engineer of some sort or even a weekend DIY'er that has a better grasp on this sort of thing than I do. I just want to know if the theory behind my idea makes sense.
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Old 30th July 2012, 03:22 AM   #7
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Quote:
Originally Posted by tbuckner View Post
True, there is only 75w per channel in stereo A mode, and I remember that in A+B the output power drops a little. So yes, this will certainly under-drive my speakers. In fact, the receiver is already under-driving my Klipsch which are rated 100w RMS min @ 8ohms.

I had a feeling that this might be the case which, so I'm not too surprised to have gotten a response like lanchile has given.


Perhaps I should have worded my question a little differently:

Does this signal flow make sense and, excluding all nominal values, impedance values and power ratings, would wiring diagram accomplish the channel separation that I have attempted?

I'm getting the feeling that I may never get my question answered and will only be told that it's silly to try an old fad, or that I would not have enough power to drive the speakers sufficiently. I had hoped that lurking somewhere on this forum there would be an electrical engineer of some sort or even a weekend DIY'er that has a better grasp on this sort of thing than I do. I just want to know if the theory behind my idea makes sense.
OK, first you will need TWO DPST switches to keep the chain in stereo and YES they will work! But make sure the "end" of terminals do not short out as it is now. why don't you get an speaker selector with impedance compensator?. anyways, to drive all those speakers is a waist of time!
Too many speakers...too little power
http://www.nilesaudio.com/product.ph...cordID=Speaker Selectors with Volume Controls&categoryID=Speaker Selectors&catcdID=7&prdcdID=FG01043
For what I can see here is maybe you just want to be able to add and regulate volume in different speakers. if that is the case look here.

PS: There are better and simpler ways to add all of those speakers and "still" have it in stereo mode! http://www.nilesaudio.com/product_de...cordID=Speaker Selectors with Volume Controls&categoryID=Speaker Selectors&catcdID=7

Last edited by lanchile; 30th July 2012 at 03:52 AM.
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Old 30th July 2012, 03:56 AM   #8
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is this what you want to do? http://www.google.cl/url?q=http://ww...dDZp4myNpw4fZw
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Old 30th July 2012, 04:15 AM   #9
Ron E is offline Ron E  United States
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You want this for passive surround and center with a stereo amplifier:
http://members.tripod.com/martin_lee...lerCircuit.txt

Whether it works or not depends on your receiver - if it places A and B in series it probably won't work, like a couple friends' JVC and Sony receivers. I had an onkyo (A and B in parallel) that this worked fine on. High sensitivity speakers (klipsch) will reduce load on your amp, but remember to be sensible with the volume control. I put the rears on channel B and could switch in and out (I didn't have a center that could keep up at the time)
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Last edited by Ron E; 30th July 2012 at 04:21 AM.
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Old 30th July 2012, 04:34 AM   #10
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I see now what He wants!!! I thought He wanted to just "add" more speakers to his receiver. I would measure the impedance before connecting that circuit to the receiver for sure. that pot "will" change the impedance seen by amp as it is turned and amp will be pushed even harder to drive all those speakers
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