An alternative approach
Sorry, slightly OT but related to these discussions. I found this patent describing a single stereo matrix loudspeaker with dual horizontal dipole mounted on a flat battle extending outwards in front of a mono loudspeaker.
Patent US3637938 - Stereo speaker arrangement and circuit - Google Patents
Sorry, slightly OT but related to these discussions. I found this patent describing a single stereo matrix loudspeaker with dual horizontal dipole mounted on a flat battle extending outwards in front of a mono loudspeaker.
Patent US3637938 - Stereo speaker arrangement and circuit - Google Patents
The RC across the center speaker not only rolls off treble to that speaker, but simultaneously increases the treble on the L and R speakers. It just re-positions it. Because we listen "binaurally", that may help reduce combing of the treble from the center speaker treble.
Wow - beautiful job! Now I know where all the SOLs went and why no longer available 🙂
Looking forward to listening impressions. Cool you are able to implement with class D amp.
Why do thou drive left and right driver with the difference signal, Sharpie? M/S means, that there is a cardiod recording or playing back L+R, and a dipole recording or playing back L-R. While thy center drivers have a somewhat cardiod radiation pattern, thy side drivers have no dipole radiation pattern. The essence of M/S stereophony, coincidence, all signals originating in the same point, can become put out into a living room, tho.
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Having some issues with noise/hum. The line level mid side matrix works and I'm getting a stereo effect from the MX-1. I've played with ground connections, swapped the EI core for a toroid and then an smps. I can kill the hum but not the buzz. It's not deafening, and not audible with music from >1m, but it's not good enough. Mulling things over right now. Wondering if the mid side transformer matrix needs to be working with a full line level signal before being attenuated with a volume control, rather than at the inputs to the amp. Any ideas...?
Since you are using the balanced inputs - are you certain that the matrix coming out of the input trafo is balanced? Balanced means opposite phase. If the matrix setup unbalances that / you could be picking up EMI hum since the balanced subtraction to achieve high CMRR is not working properly.
Try grounding the negative input and test each signal path for hum independently. Maybe a class AB amp may be needed?
Try grounding the negative input and test each signal path for hum independently. Maybe a class AB amp may be needed?
There is one series connection from each amp input + to - travelling through one secondary on each transformer. For the sum channel the two transformer secondaries are in phase (+ to - to + to -). For the difference channel the polarity of one secondary is reversed. As a result the inputs are by necessity balanced.
The centre two drivers replay the sum channel directed forward. The two side drivers replay the difference channel out of phase. This means that the sound to the front left of the speaker is sum + difference, and the sound to the front right is sum - difference. This recreates the left and right separation.
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Final(?) setup with BBC LL/252-H12 repeater coil transformers doing the input stereo > sum + difference encoding. I had to connect the input ground to amp star ground to avoid hum/buzzing with portable sources. Using my Fiio X3 I can pan left to right and the sound 'moves' smoothly from one side to the other as it should.
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Nice work Sharpi! Trafos for input passive blending is really cool and probably ultimate for SQ.
Did you show schematic already?
Did you show schematic already?
