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Old 8th Apr 2009, 6:10 pm   #1
vintage4ever
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Default Does anybody have an idea how to build a quadraphonic amplifier?

I am a compleate electronics amature, my knowlage of electronics goes as far as GCSE at a C grade level, i can read a basic diagram, do basic programing and solder, quite well, anyway i've been after a quadrophnic system for a while, but with no luck, and an idea dawned on me, would it be possible to build a quadraphonic amplifier? if enyone know's, im shore i will find you here im guessing it would have to be a some kind of matrixing cicuit connected to two seperate stereo amps? (im am actually useless at this stuff, unless someone tells me in plain english). There's hundreds of mono and stereo amplifier kits about but i thought it would be fun to work out how to design a quadrophonic one and hopefully build it!

Thought this would be a nice challenge for some of you. Any idea's are appreciated

cheers
Ben

Just to warn you, eny thing really technical go's over my head,for exsample, its either a 40k resistor, or a 0.1uf capacitor, so if i reply saying 'Wha' its my fault for being stupid
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Old 8th Apr 2009, 7:41 pm   #2
'LIVEWIRE?'
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Default Re: Dose anybody have an idea how to build a quadraphonic amplifier?

If you are thinking of the quadraphonic systems that were being promoted about 25- 30 years ago, Practical Wireless published a design for home construction. I still have the relevant issues somewhere if you're interested, Ben. As I recall there were four competing quadraphonic systems (SQ, RM, QS and ??) none of which were compatible with each other, but the PW amp. could decode them all. There were LPs issued in most formats, but, at least in the UK, AFAIK, no other sources of 4-channel sound.
On the other hand, a simple 4-channel system could be built by making two stereo amplifiers and feeding signals to their inputs via Balance(Left to Right) and Fader(Front to Rear) Controls. Any normal stereo or mono signal from radio, Tape, CD, Records, MP3, etc., could be played via such an amplifier, this system being used in most modern Car Stereos.

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Old 8th Apr 2009, 7:44 pm   #3
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Default Re: Dose anybody have an idea how to build a quadraphonic amplifier?

There are two different issues. A quadraphonic amplifier is exactly that, an amplifier with four channels instead of the two used in a conventional stereophonic amplifier.

The second issue is where the quadraphonic signal is to come from. There are various historic quadrophonic disc systems, which require a demultiplexing circuit, and professional quad used 4 tracks of a tape deck.

All in all it would be better to use a current multichannel system such as 5:1 or 7:1 unless you have a particular reason to pursue this.

Best regards, Paul
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Old 8th Apr 2009, 7:54 pm   #4
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Default Re: Dose anybody have an idea how to build a quadraphonic amplifier?

Paul, you beat me to it in regard to 5:1 & 7:1 surround sound systems. However, I don't know of, and certainly wouldn't attempt to design such an item for home construction.
Maybe someone more au fait with modern electronic circuitry than I will produce a suitable design!
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Old 8th Apr 2009, 8:04 pm   #5
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Default Re: Dose anybody have an idea how to build a quadraphonic amplifier?

Hi Ben, I wonder if you've tried the simplest of simulation system (called Haffler or some-such). Wire your stereo in the normal way and put a second set of speakers at the rear, wired between the live terminals of the front speakers. Wire one phased +/- and the other phased -/+ if you see what I mean.
Try it - at least it's cheap!
Graham
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Old 8th Apr 2009, 9:37 pm   #6
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Default Re: Dose anybody have an idea how to build a quadraphonic amplifier?

Thanks guys, great advice!, SQ would be the one i would go for, as i have a few pinkfloyd SQ vinyls that i cant play plus sq records are the easyist to get hold of, I am very interested in the Practical Wireless issue, as llong as its not to difficult,
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Old 8th Apr 2009, 9:41 pm   #7
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Default Re: Dose anybody have an idea how to build a quadraphonic amplifier?

Quote:
Originally Posted by llama View Post
Hi Ben, I wonder if you've tried the simplest of simulation system (called Haffler or some-such). Wire your stereo in the normal way and put a second set of speakers at the rear, wired between the live terminals of the front speakers. Wire one phased +/- and the other phased -/+ if you see what I mean.
Try it - at least it's cheap!
Graham
My current amplifier has outputs for 2 sets of speakers, i used to have a system like that a few years ago, ended up killing my amp, tryed it on another one, did work but after what happend last time i opted for an amp capable of powering 4 separate speakers, good idea tho
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Old 8th Apr 2009, 10:59 pm   #8
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Default Re: Dose anybody have an idea how to build a quadraphonic amplifier?

The system was the PE Rondo running from the September 1973 to February 1974 issues. It is primarily an SQ system using the Motorola MC1312 SQ decoder although it does mention the JVC CD4 and the Sansui QS systems. The first 2 articles detail the decoder, pre amp and power amps followed by the power supply, wiring, speakers and turntables.

The MC1312 was only available as part of a complete kit due to licensing restrictions imposed by CBS who developed the system and is by now obsolete so this may be a major issue to building one of these systems.

Keith
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Old 9th Apr 2009, 12:03 pm   #9
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Default Re: Dose anybody have an idea how to build a quadraphonic amplifier?

There were several mutually incompatible standards for quadraphonic sound on stereo-compatible discs. All were ultimately killed off by various combinations of expense, incompatibility with existing systems, greed on the part of patent holders and not actually being very good. Any patents governing them will have long-since expired; so, assuming you can get hold of some source material, you should be able to knock up a decoder using just a few op-amps. The outputs can then be fed to a pair of stereo amplifiers (or four TDA2030s).

SQ, QS and RM all used variants of adding the rear signals, phase-shifted by 90 degrees, to the front signals. The decoding circuit is similar in each case, only the proportions of signals used in each case are varied. You could easily make a switchable decoder for any of these formats, since the only differences are resistor values. Any record encoded with one of these systems will be labelled "manufactured under licence" with the relevant patent numbers, which you can look up.

CD4 used a 30kHz carrier on each stereo channel, SSB-modulated with the rear signal on that side; while the main audio signal consisted of the sum of front and rear on that side. (Sort of like the old German TV sound system, where the sum [mono] and right signals used to be broadcast on different carriers.) You will need a very good cartridge and stylus to pick up the high-frequency carrier.
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Old 9th Apr 2009, 12:04 pm   #10
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Default Re: Does anybody have an idea how to build a quadraphonic amplifier?

For reference, here's David Hafler's system.
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Old 10th Apr 2009, 2:22 pm   #11
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Default Re: Does anybody have an idea how to build a quadraphonic amplifier?

I have had a thought, it reqires 2 amps, with 4 channels, place the 4 left and right channels of one amp in the four corners of the room i.e. fornt L-R and back L-R, then place the second set L-R inbetween the front and back, the only part that will be a problem is the 2 set on the second amp, they will have to go in the center, (front and back) but they will be L-R channels which will mess it all up.

This quick diagram i made will describe it better than i can

http://i488.photobucket.com/albums/r...akerdigram.jpg
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Old 10th Apr 2009, 10:58 pm   #12
vintage4ever
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Default Re: Does anybody have an idea how to build a quadraphonic amplifier?

Anybody have an idea of how to slove the problem?
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Old 11th Apr 2009, 11:46 am   #13
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Default Re: Does anybody have an idea how to build a quadraphonic amplifier?

Asumin that the amplifier outputs are not either floating or have bridged outputs, ie they have a common 0V, I'd connect the rear centre speaker between the left and right 'hot' output terminals, so it will effectively respond to the difference signal (if L=R there'll be no output from this speaker).

At the front, I'd connect two 10 ohm resistors, one lead to each 'hot' output terminal, then connect the remaining two resistor leads together. Then I'd connect the front centre speaker between this junction and the common 0V of he front amplifier. This will make the front speaker respond to the L and R sum signal.

The phasing of the rear speaker will be non-ideal for this, but it will be fun trying it to see what it sounds like!
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Old 11th Apr 2009, 12:12 pm   #14
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Could connecting L-R channels together damage the amplifier? i have done this before to see what would happen (morbid curiosity on a rainy sunday) and the amp started to hum and crackle and cut out, although it recovered quickly, im a little dobious, i will give it a try if its the only solution

Mind you i didnt use any resistors when i did it i will definatly try it, gotta dig up another set of speakers now
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Old 14th Apr 2009, 6:29 pm   #15
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Default Re: Dose anybody have an idea how to build a quadraphonic amplifier?

Quote:
Originally Posted by vintage4ever View Post
...Thanks guys, great advice!, SQ would be the one i would go for...
If you're patient an option is to get a standalaone SQ decoder on EBay, although it'll probably be from the US. For SQ you just need a standard tutntable and stylus with the decoder giving you four phono outs (LF, RF, LR, RR). The phonos could then go to a 4-channel amp or 2 stero amps.

In the last six months I've picked up Pioneer QD-210 and a Sony SQ-2010. The Pioneer is as described above with phono input. The Sony is a bit different in that it doesn't have a phono input but instead sits on a tape loop on a stereo amp, with the turntable connected to the stereo amp. The Sony receives the un-decoded SQ from the tape loop, and sends back the decoded LF/RF. It then sends the decoded LR/RR to a rear stereo amp.

The guys over at www.quadraphonicquad.com call the Sony a 'door stop' which I think is a bit unfair - any Sony kit from the 70s with a 4 VU meters can join my collection any time. They rave about the Fosgate Tate II 101A as the best standalone SQ decoder ever - but the next one that comes up on EBay won't sell for less than US$1,000 and could be loads more.

Once you've got the SQ decoding and 4 channel amplification sorted you've got to get a quad. reel-to-reel and start chasing the few commercial tapes on EBay. To pick things in perspective on a typical EBay day worldwide the items available are:

CD albums: ~6,000,000
Vinyl albums: ~ 1,000,000
Quad. reel-to-reel
albums: < 10

PC
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