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Steve Gonzales
01-28-2005, 01:02 PM
I have a friend who is interested in hooking up a third speaker (4660 JBL) into his stereo system. I told him that I remembered a technique for this very thing that was done in the old days. I don't remember what it is called or how to do it. All I remember is that the third speaker is powered by taking the + from one channel and the - from another. Does this sound familiar to anyone? Please let me know if you can help. Thank you, Steve G

andywin
01-28-2005, 01:10 PM
I have a friend who is interested in hooking up a third speaker (4660 JBL) into his stereo system. I told him that I remembered a technique for this very thing that was done in the old days. I don't remember what it is called or how to do it. All I remember is that the third speaker is powered by taking the + from one channel and the - from another. Does this sound familiar to anyone? Please let me know if you can help. Thank you, Steve G

Its called a Haffler array... Ive got some details on it somewhere

Steve Gonzales
01-28-2005, 01:13 PM
I await the details:applaud:

andywin
01-29-2005, 01:38 AM
The first step is to link the two negatives of the outer pair of speakers and provide the negative return to the amps via a third centre speaker (in series) thus achieving a mono centre.

The problem with this setup it crosstalk degrading the stereo image. David Hafler of Dynaco came up with a solution that resolves a lot of the problems.

His solution was to bridge the positive chanels from the pre-amps to the power amps with 22k resistors on the outputs and bridging with a 20K variable resistor

The idea is then to use a feed from one channel only with a mono source and adjust the pot to gain minimum output from the opposite chanels loudspeaker. Swapping the input to the other channel should achieve the same results. If not then either the gain of the amps are not identical or tone/balance controls may be at fault. Next step is to connect both inputs an give it a go.

Perhaps one of the more tehically minded members can calculate what this does to impedances etc. :dont-know

I've attached a pic of an article from August 1965 of the Gramophone magazine to illustrate the schematics...hope you have 20/20 vision

Steve Gonzales
01-29-2005, 09:41 AM
Very good Sir, much appreciated!

Zilch
01-29-2005, 09:52 AM
Hmmm. Sounds like just summing to create a center channel, which would narrow the sound field.

A better contemporary approach would be to use a matrix stereo chip and summing to create three channels.

Matrix chip attenuates program material identical on L & R, creating a "hole" in the middle. It's the basis of SRS stereo in TV's, for example, broadening the sound field.

It's also why you can't hear the singer sometimes. :p

It may be that one or more of them already provides the summed center.

National Semi, I think. May take me a day or two to dig it up, if anybody's interested....

subwoof
01-29-2005, 10:56 AM
Look around for one of the carver "sonic hologram" stand alone processors or any of their recievers that has it built in.

It did a bunch of L-R, L+R, etc summing ( and subtracting ) tricks - simply add one of these to your preamp outputs and feed some combination to your center channel amplifier ( always recommended ).

Possibly using the L+R outputs to a balanced input would *leave* the vocalist !

BTW that is one BIG center channel - it requires good technique to aim it at a couch rather than 200 pews...

:cheers:

sub

andywin
01-29-2005, 11:23 AM
[QUOTE=Zilch]Hmmm. Sounds like just summing to create a center channel, which would narrow the sound field.QUOTE]

The reverse is actually true, I've read a couple of articles of people who have tried the Hafler system and all say soundstage broadens but at the expense of pinpoint stereo imaging. Apparently it's supposedly something to do with "psychoacoustics". An Italian profesor (can't remember his name) has written a lot on this subject.

Zilch
01-29-2005, 11:37 AM
ENHANCED STEREO


The LMC1982 has an enhanced stereo effect that can be


achieved by cross-coupling reverse phase information between


the left and right stereo channels. This feature can


help improve the apparent stereo channel separation when,


because of cabinet or equipment limitations, the left and right


speakers are closer to each other than optimum.


Enhanced stereo is created by connecting an external frequency


shaping RC network between the OUTPUT operational


amplifiers’ inverting inputs through an internal CMOS


switch (see Figure 6). The external network couples 60% of


each channel’s output to the opposite channel’s inverting input.


This cancels a portion of the signal common to both


channels.


The desired 60% cross-coupling is accomplished through


the internal 6.5 kW feedback resistor and an external 10 kW


resistor. Bass frequency cancellation is prevented by using a


0.047 µF coupling capacitor to couple only frequencies


above 330 Hz. Switching noise is eliminated by using a


680 kW resistor across the 0.047 µF. R3, R4 and C6 can be


eliminated if enhanced stereo is not desired.

John Y.
01-30-2005, 12:10 PM
The first step is to link the two negatives of the outer pair of speakers and provide the negative return to the amps via a third centre speaker (in series) thus achieving a mono centre.

The problem with this setup it crosstalk degrading the stereo image. David Hafler of Dynaco came up with a solution that resolves a lot of the problems.

His solution was to bridge the positive chanels from the pre-amps to the power amps with 22k resistors on the outputs and bridging with a 20K variable resistor

I've attached a pic of an article from August 1965 of the Gramophone magazine to illustrate the schematics...hope you have 20/20 vision

The three channel system derived from two stereo amplifier channels was originally championed by Paul Klipsch obviosly in considedration of having two corner horns that may have been located alomg the long wall of the listening room. Using 1933 demonstrations by Bell labs as a reference, Klipsch derived the center channel by connecting the center across the 4 Ohm taps of the L & R amplifiers and connecting the amplifier commons together. In Klipsch's case, the main channels were connected in the usual manner to the 16 Ohm taps.

Early on, Hafler chose to use the three speaker setup where the center is placed in series with the L & R channel returns, the L & R being connected to the taps representing twice the impedance of the individual speakers - all speakers of the same impedance. Thus, each side saw a series impedance mated to the proper amplifier taps. Hafler admitted that stereo imaging was reduced by crosstalk from the opposite channel and recommended moving the L & R farther apart than normal and the use of a blend control to assist in reducing the crosstalk to regain proper imaging.

In a letter from Dynaco, dated July 21, 1961, Mr. William Phillips states "It is not possible, under any circumstances, to derive a third channel from the preamplifier alone, no matter by what means". Pretty strong conclusion to my inquiry at that time of bridging the preamp channels with two 33K Ohms and the derived signal from the center of this bridge feeding a center amplifier. Their proposed solution was to have the L & R 16 Ohm taps bridged by two 500 Ohm resisters, the center of which would connect to ground through a 100 Ohm audio pot, providing the adjustable source to the center amplifier. This became their documented solution to the problem of derived center channel.

Later on, Dynaco produced a low cost Quad device providing for L & R rear matrixed signals without, as claimed, degradation of the stereo signal. This was around the time that SQ, QS and other four channel schemes were proposed. It was also the time that I obtained my four JBL L100's, which I have to this day. I mostly used the Sony SQ system with a Crown D150 on the fronts and a Crown D75 on the rears. I never bought a Dyna Quadaptor, but I wish I had gotten the schematic just to see how they derived their rear signals.

John Y.

Zilch
01-30-2005, 12:32 PM
In a letter from Dynaco, dated July 21, 1961, Mr. William Phillips states "It is not possible, under any circumstances, to derive a third channel from the preamplifier alone, no matter by what means."Yeah, well, no op-amps back then, and he probably never heard of a unity-gain buffer, either. :p

Seems like once you derive a Matrix subtraction signal, you can feed it to a center channel.

Gonna watch for that Carver hologram thingy, I am. Could be fun....

Flodstroem
01-30-2005, 03:02 PM
Hi Steve

In Sweden in the sexties and seveties this idea was called "ambiophoni". The idea was to try to get som new information from the tracs of common stereo vinyl LP´s

There was a common belief at that time when using the stereo-headphones there was allways thougt the stereo-image was much better than when using the common stereo loudspeakers. The bad image was probable due to some cancellations of the program materials when reproducing the "L" and "R" program in the same room.

The effect of cancellation could be compensated in a way by adding a third or even a fourth channel as described by member John Y, Zilch etc. Most famus for "ambiophoni" in the USA at that time was probable "Carver" with their model C-4000.

My own practical solution at that time was to use a balansed input line amp (without balaced output) or a balanced input power amp (a mono-block). I connected (bridged)one of the "R" outputs fro the pre-amp to one of the balanced "hot" input and connected the other "L" outputs from the pre-amp to the reminding "hot" balanced input. What was amplified in the third amp was the electrical differensies between the two channels (you can get "two" different "differencies", positive or negative depending on whitch way you put the "R" and "L" outputs from pre-amp to the two balanced inputs.

The positive effect of using balanced inputs was it did´t ad any extra crosstalk. you could allso balance the volume of this third channel to not to be to loud regardles of the two front speakers ("L" and "R").

The image of a third channel is strongly dependent of the recording of the original program material and most of the "studio-recordings" are useless.
Absolutely the best effect to demonstrate the "ambiophoni" is with live-recordings.

I should never forget a very special occasion when hearing the public clapping there hands and whistling in rear of me when the "band" was in the "L" and "R" in the front of me when listening to a live recording by Rolling Stones. It was like a live experience at that time.

Best Regards :D

andywin
01-30-2005, 03:24 PM
This link should explain all... and no more mentioning nasty things such as Op-Amps and other new fangled devices that have no heaters and don't glow in the dark.

Seriously though the only true stereo + centre mono would be if Mercury released some of their early 3 track recordings on DVD without any mixdown. It still does'nt guarantee it will sound good though.

http://www.dai.ed.ac.uk/homes/cam/gadgets/hifi.html

Michael
01-31-2005, 12:48 AM
Its really not that complicated. Any amp that can be bridged can run like this.

Its also referred to as 'tri mode' and 'phantom mode'. You connect your two main speakers to the amp as per normal, but connect the third as though it is running in bridge mode of the amp.

However there is one catch. If the two main speakers are 8ohm, then the third must be 4ohm. Or the other way around, if the two main speakers are 4ohm, the third must be 8ohm.

I've found that tougher amps can run 8ohm loads all round, or even 8ohm stereo loads with a 2ohm bridge load. But to play it safe follow the method in the 3rd paragraph :D

Steve Gonzales
01-31-2005, 01:26 PM
Thank you to EACH and EVERYONE that responded to my question!! I think I have a grip on what to do now. MUCH appreciated!:applaud:

analogman
01-31-2005, 07:18 PM
This may help:

http://forums.klipsch.com/idealbb/files/Klipsch2ph311.pdf


Analogman

analogman
01-31-2005, 07:31 PM
Hello again,
I have the Dynaco QD-I from Pancor. You can still buy them new for under $50.00. Seems to work well and is a lot of fun to play around with. The current versions are marketed as an alternative to "suround" but make for an inexpensive way to obtain a "derived" center channel. Doesn't seem to affect the sound in any negative way (subjective) and makes for a VERY full presentation. The level is adjustable. The last time I was at the Dynaco site they were still selling them, you can buy them new from on line sellers for even less. Got mine from J&R for $20.00. The latest version is the QD-II, same circuit as the I nicer box. Some pictures on a French site:http://80.236.77.152/qd-1.htm
Analogman

speakerdave
02-03-2005, 07:40 PM
Seriously though the only true stereo + centre mono would be if Mercury released some of their early 3 track recordings on DVD without any mixdown. It still does'nt guarantee it will sound good though.

http://www.dai.ed.ac.uk/homes/cam/gadgets/hifi.html


You may be referring to the recordings in the RCA Living Stereo series that were originally made in 3 channel. These are being made available now on SACD reissues.

David

andywin
02-04-2005, 11:56 AM
You may be referring to the recordings in the RCA Living Stereo series that were originally made in 3 channel. These are being made available now on SACD reissues.

David

I was referring to the Mercury Living Presence Stereo SR series that were recorded on ampex 3 track machines.
I thought that most of the RCA LSC series were recorded on 2 track machines and only a few on 3 track, but I may be wrong.

Good to see them being isued though.

Andy

JBLROCKS
02-07-2005, 04:19 PM
One thing I have experiminted with using an old reciever is simply hooking the "Center" to L+ and R+....Dont know if this is good practice or not...it worked though!



Also I am doing more experimintaion...Can I "Bridge" a standard reciever amp?

IE I want to use a seperate amp to drive a single channel Sub and was wondering if I can use both channels or will that let the smoke out of something?

I am using two 32-ohm woofers wired in parallel through a single crossover for a 16 ohm load. I had them blasting all weekend on the amp that I intend to use and it did not even get warm

:cheers:

p.s. It was a thrift store amp so it doesnt much matter if I let the smoke out of it:wave: