Monday, January 2, 2012

Enhanced Hafler Matrix Surround Sound Decoder

Enhanced Hafler Matrix Surround Sound Decoder circuit diagram

This is the circuit diagram of enhanced Hafler Matrix surround sound decoder. The above schematic can be a basic technique to attain exactly the same factor (with some extra rewards) at line level (i.e. prior to the signal reaches the power amplifiers - in a bi-amped method, this circuit should be in between the preamp along with the electronic crossover). The extras obtainable are readily apparent:
  • Wiring is simplified (despite the fact that extra power amplifiers are necessary)
  • We now have a centre channel signal accessible
  • Provision for a mono signal to a sub-woofer is simple

Though there have been comparable circuits published more than the years, this can be slightly unique in several locations. I wanted to prevent getting any active electronics inside the key Left and Right channels, due to the fact this eliminates any possibility of sound degradation because of the introduction with the op-amps. The input impedance of 50k won't pose an issue for any pre-amp (such as valve sorts), as well as the principal signal is merely in parallel using the extra circuitry.

No volume control has been integrated, due to the fact you already have one inside the pre-amp circuit. It would just turn into one more component to fiddle with, and due to the fact it could be hardly ever applied, would most likely develop into noisy as time passes.

How the Circuit Works
Opamp U1A is connected as a subtracting amplifier. Really should exactly the same signal be applied to each inputs, the output is zero. Because of this, it'll eliminate all popular data from the stereo signal, and reproduce only the distinction signal - in specifically exactly the same way as the original Hafler style.

U1B is actually a straightforward summing amplifier, along with the output consists of all of the info from each the left and appropriate channels. A possibility that springs to thoughts is the fact that we could then subtract the distinction information and facts from this output, to ensure that only material that's definitely typical to each channels will be reproduced. Would this enhance the efficiency for the extent that the added circuitry is warranted? I have a tendency to doubt it, but will appear into this additional.

Centre Channel Control
The pot (VR1) would be to set the centre channel level. This may be a trimpot, or perhaps a standard pot mounted in the rear (to assist stop "fiddlers" from mucking up the settings you like). I've observed circuits which don't involve this, which appears generally a poor concept. When the two channels are summed, the centre channel will ordinarily have a degree of -3dB relative for the left and right channels - supplied the signal isn't mono. Centre channel speech (for instance) will probably be mono, so the level will probably be equal to that of every single from the most important speakers. Given that the centre channel amp and speakers are hardly ever as strong as the primary Left and Right channels, there is certainly a distinct possibility of overload with the amp, the speaker or each.

Due to the fact the centre channel is supposed only to fill the "hole" and offer a stable centre sound image, it will not must be as loud - particularly because it'll practically undoubtedly have inferior sound superior towards the principal speakers and will thus degrade the overall sound excellent. The level manage will permit you to set the level to just adequate to supply the stable sound image, and no much more.

The capacitor (C1) is optional. It gives a nominal 8kHz roll-off frequency (that is apparently rather regular for "real" surround-sound processors). This assists to minimise any disturbance towards the most important stereo signal, but really feel free of charge to leave it out, given that most centre channel speakers almost certainly will not be capable of reproduce considerably above this frequency anyway.

Sub-Woofer Output
The sub-woofer output is merely taken directly from the centre channel mixer, and I integrated no low-pass filter simply because I do not know of any sub which doesn't have a filter already. Adding a different one basically adds unnecessary complexity, and will introduce phase shift in the output that a phase compensation circuit (usually integrated in sub woofers) may possibly not have the ability to cope with.

The 100 Ohm resistors inside the outputs are to stop the capacitance in the signal leads causing the opamps to oscillate. At this value, they are going to lead to no high frequency loss, unless you insist on 100m lengthy signal leads (in my expertise, these are uncommon).

It'll also be noticed that you will discover two outputs for the rear speakers, merely in parallel. I integrated this simply because it can be less difficult to wire if the user is connecting a stereo amp for the rear speakers. Naturally, a mono amp will do just fine, so long as it's capable of driving the two rear speakers in parallel. This could not be probable if the speakers are 4 Ohm forms (these are becoming a lot more popular in hi-fi, so its not that silly).

The enhanced Hafler Matrix surround sound decoder circuit source page:

About Audio Amplifier
An audio amplifier is an electronic amplifier that amplifies low-power audio signals (signals composed primarily of frequencies between 20 - 20 000 Hz, the human range of hearing) to a level suitable for driving loudspeakers and is the final stage in a typical audio playback chain.

The preceding stages in such a chain are low power audio amplifiers which perform tasks like pre-amplification, equalization, tone control, mixing/effects, or audio sources like record players, CD players, and cassette players. Most audio amplifiers require these low-level inputs to adhere to line levels.

While the input signal to an audio amplifier may measure only a few hundred microwatts, its output may be tens, hundreds, or thousands of watts. More explanation about power audio amplifier can be found at

This is a video tutorial about how to a very simple audio amplifier based on the LM386 amplifier chip. It can be built for less than $20 (or might be less than $8 in some countries) and used to amplify any low level audio signal including a guitar, bass or mp3 player.

Watch the video:

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