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Old 26th December 2011, 11:02 AM   #41
AndrewT is offline AndrewT  Scotland
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D,
why are you not including in your recommendations for single amplifiers driving single speaker drivers?
For instance. You mention MTM and suggest that the paralleled M//M be driven by a paralleled chipamp.
What about omitting the extra 0r22 and the potential risks of the paralleled chipamps misbehaving and simply use dedicated chipamps to drive each of the M Drivers? This uses fewer components. It can tolerate a wider tolerance range of component values. It uses the same number of chipamps and uses the same number of M drivers and finally it allows the chipamp to drive the M driver without that intervening 0r22
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Old 26th December 2011, 12:22 PM   #42
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Quote:
Originally Posted by AndrewT View Post
D,
why are you not including in your recommendations for single amplifiers driving single speaker drivers?
For instance. You mention MTM and suggest that the paralleled M//M be driven by a paralleled chipamp.
What about omitting the extra 0r22 and the potential risks of the paralleled chipamps misbehaving and simply use dedicated chipamps to drive each of the M Drivers? This uses fewer components. It can tolerate a wider tolerance range of component values. It uses the same number of chipamps and uses the same number of M drivers and finally it allows the chipamp to drive the M driver without that intervening 0r22
Thank you sir!

The designs are different between the two options. I think it just comes down to whichever speaker design that you're more comfortable with and the necessary topics of parts availability and costs.

For the MTM bi-amp that you mention, I could apply some favorite 1" dome tweeters or favorite 2" paper tweeters to get the crossover point down a bit and then I could buy 2 inductors sized for the 2 8 ohm woofers. Of course that works fine and it may be more efficient. I didn't mention it because in comparison there is doubled voice coil inductance and four times the amount of copper to buy for the crossover.

Probably, it is a simple matter of cost.
Personally, I'd rather apply that single low cost inductor example as with a much larger inductor so as to adopt 3-way design supporting the wonderful little miniature full range products for mid range, electrostatic for tweeter and a design that is far easier than it looks. In this case electronic dampening has been increased for the 8 ohm woofer pair via the much larger capacitors directly across their terminals, ultimately inspiring them both to identical mad fast action, meanwhile the mid range driver carries the voice band unshaken. It is the highly caffeinated version.

This is inexpensively expandable to array sizes for larger coverage or more power. It is this particular case when I was thinking about decreasing crossover inductor expense. Crossover inductor expense could be decreased further by choosing better matching drivers and employing the hybrid 1st order series crossover, since it uses a smaller number of inductors.

The main thing that I like about all of these examples, and yours too, is that no single speaker driver is stressed--Whatever high fidelity result is available with the smallest example also scales up to the largest example, fidelity intact.

If made into a low cost (or at least easily doable) modular system, with 2 speaker drivers and 2 Lm1875 per each box, this could be stacked or arranged wherever and however you'd like. For example, utilizing the odd corner between wall and ceiling for zero consumption of floor space, stacked up high at either side of the TV, or stretched out long across a bookshelf are just some of the possibilities of a cute little modular system. By the time there is six woofers and chips per each channel, the copper costs of this little chip system is much higher than a competitive large discrete system, and that's why I've been designing for decreased copper costs. And, I wanted to show what the innocent looking tiny little thing from post 18 can really do with a scale up boost and some acoustic coupling fun with woofers. How much power is that anyway?

Last edited by danielwritesbac; 26th December 2011 at 12:28 PM.
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Old 26th December 2011, 12:24 PM   #43
AndrewT is offline AndrewT  Scotland
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I never mentioned bi-amp.
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Old 27th December 2011, 03:24 PM   #44
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Default LM1875 Parallel with. . . Cake Flattening Power!!! and a weird center amp

Looking a lot like a Cmoy with a wiring problem, I'm trying to work out a center channel preamp with a lot better performance than a retail product would have.

So far, a quad op-amp as a buffer
Half of it as a normal non inverting stereo buffer. #1, right, #2 left
Anti-mixer via CapDiv from the outputs of #1 and #2.
Half of it as inverting buffers, #3 left tilt and #4 right tilt
The outputs of #3 and #4 fused by resistor mixer input to inverted power amp.

Out of the stereo buffer like this.
#1 right 22nF to #3
#2 left 47nF to #3
both of the above into inverting op amp #3, left tilt

AND Out of the stereo buffer like this too
#1 right 47nF to #4
#2 left 22nF to #4
both of the above into inverting op amp #4, right tilt

And then pair of 1k resistors out of the op amps #3 and #4 as resistor mixer for unified center channel Power amp input. The power amp in this case seems to be a Decibel Dungeon inverting gainclone or other inverting amplifier. Little green polyester dip caps are used for the capdiv section, and in such a thing, the pin of a small cap touches the pin of a large cap directly at the stage output, as indicated above.

This circuit that I just invented doesn't look like the smartest thing ever, but it should at least prove different from an ordinary resistor mixer.
Possible caveats:
Unfortunately it seems that resistor matching is critical and that you will have to hand voice the center speaker rather than use a convenient off the shelf speaker.

For some applications, regular stereo is ideal. Probably that ideal arrangement is stuck in there with the TV while a family member has blocked off your music with reality TV, noisy news or sitcoms.
Other areas in the home, such as dining room or kitchen may not be arranged for compatibility with the proper function of a stereo pair and lopsided noise results depending on where you sit or stand. For the dining room the center can be placed at the opposite end of the room, pulling the stereo image out to the middle of the room. Sometimes is is needful to roll off the extra low bass of the center with a series capacitor and then invert polarity of the speaker cable. Anyway, for the dining room or pub, a greater number of chairs now faces a speaker. This, which is Triad format, with an on-stage sound, may be better than the cheap seats effect of sitting in the wrong spot. You do have options to explore.

Darned TV! So, the living room is blocked. No problem. [fanfare]Little hi-fi utility amplifiers to the rescue![/fanfare] Rock out the kitchen, the laundry room, the garage, whatever!
Exhibit: The kitchen: One pair of 40 watt stereo mains above the cabinets, one center speaker on the opposite side of the room, for triad format. Surprise! You're standing on the stage with a hundred watts of power at point blank range. This is probably able to drown out that TV, especially when you are standing in the middle of your music at the same location as the musicians stand within the sound field on stage.

I think that you should be able to do stuff while also listening to high quality music, rather than a mutually exclusive approach. This is a great party but it mash your cake completely flat. So, please be conservative if you're baking breads. LM1875 might not have plaster crashing power; however, it does have cake flattening power.

For some applications monophonic is appropriate and it is the only option that isn't actually multi-channel; but, dull monophonic is inappropriate for center channel and inappropriate for table radio. So the very first step for either is mixing down to mono without the typically dull caveat. The circuit above (in addition to a customized speaker) is only one possibility. Maybe we can look at more options?

Last edited by danielwritesbac; 27th December 2011 at 03:46 PM.
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Old 1st January 2012, 05:56 PM   #45
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Default Transmitter heatsink

With my LM1875's there were some conductivity problems with a transmitter heatsink. It seemed that the hole in the middle of the shoulder washer was too large and the precision of my drilling was lacking slightly. This combination was a point of failure.

This was solved by taking a drill bit same external dimensions as a shoulder washer and chamfering the existing hole on the back side of the LM1875 to make a divot (like extremely shallow miniature crater). Next I slightly lapped the back of the LM1875 by sanding it with #600 sandpaper to gain smoother edges. Finally, I filled the chamfered spot with Arctic Ceramique. The back of LM1875 cannot now make contact with minor drilling errors.

This fix was just barely sufficient.
Although the transmitter heatsink (thick black non-conductive coating) is the highest performance option, it is also the most difficult and thus least safe. Hopefully this chamfer trick will help keep somebody safer. Again, please verify total non-conductivity with ohmmeter.
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