[Steve Eddy]

just as an example... i spend a lot of time with equipment... different one... and as far as sources go... i think that i have heared that ideea that if something is louder brain gets it better... but...

Yes, playing something a bit louder not only sounds a bit louder, but because of psychoacoustics, the perceived quality is higher. This was sometimes used by unscrupulous audio sales people. They would make sure to play the system they wanted to sell slightly louder than the one they didn't,

i cannot go above a certain level with entry level equipment without distortion... everything cheap produces diistortion on high volumes of listening... expensive products have no distortion at loud listening levels... this is why... i think that there are a pleathora of differences being heared... i cannot hear cheap things loud. without clipping..

Not sure exactly what you mean by "cheap," but yeah, if you're wanting to keep costs down, you're going to have to cut some corners somewhere.

se

 

[bigshot]

Any time you try to make things louder than they were designed for, they will clip and distort. You just need enough power and headphones or speakers capable of performing well at loud volumes. Cheap transducers are much more of a problem than cheap electronics. As a general rule of thumb, a cheap player with expensive headphones is a lot better than the other way around.

 

[limpidglitch]

This seems like a good a place for this as any:

How does differential come into all of this?

Words like balanced, anti-phase, bridged and common-mode gets bandied about, and I vaguely understand the goal of applying techniques like these (more driving power with a limited supply voltage, reduction of noise in some way, and/or marketing), but it all sort of blends together for me.

 

[Steve Eddy]

This seems like a good a place for this as any:

How does differential come into all of this?

Words like balanced, anti-phase, bridged and common-mode gets bandied about, and I vaguely understand the goal of applying techniques like these (more driving power with a limited supply voltage, reduction of noise in some way, and/or marketing), but it all sort of blends together for me.

Differential is pretty much the underpinning of balanced interfaces. And I'm talking about balanced, not bridged.

As I've said before, balanced is all about the rejection of common-mode noise. Common-mode means that the noise impinges equally in both magnitude and polarity on both the "positive" line and the "negative" line. For example, let's say you have a simple twisted pair of wires running from point A to point B. And then you have a noise source, such as a fluorescent light fixture at point C. Because of the twisting of the wire, the electromagnetic waves that are being produced by that noise source will impinge on the two wires more or less equally.

And now here's where the differential input comes in.

An amplifier with a differential input has two inputs and the amplifier is designed in such a way that it will only amplify the difference that it sees between those two inputs. In other words, what's seen on one input gets subtracted from what's on the other input.

So now let's say we have a signal on one input that is at +1 volt, and at the other input, -1 volt. If we do a simple subtraction (and remember that the result of a subtraction operation is called the "difference," which is where we get the term "differential"), we get (+1) - (-1) = 2. And just to illustrate my earlier point that common-mode rejection doesn't have anything to do with anti-phase signals, let's say the signal is single-ended so we have +1 volt at one input and 0 volts on the other. 1 - 0 = 1.

Getting back to our noise, as I said it will tend to impinge on each line equally in both magnitude and phase. So our noise ends up being say, +1 volt on one line and +1 volt on the other. Perform our subtraction and you get (+1) - (+1) = 0. And that's known as common-mode rejection.

That help?

se

 

[Steve Eddy]

By the way, in its proper context, "balanced" refers to the balance of impedances between one line and ground and the other line and ground. If the two impedances are identical, then the voltage drop across those impedances due to noise will be equal. Otherwise, they won't be. So let's say the imbalance of impedances are such that due to the difference in voltage drops you end up with there being one line with +1 volt across it and the other line has +0.95 volts across it. Do your subtraction and now you get (+1) - (+0.95) = 0.05. And that represents noise that has managed to get through the system.

Impedance balance is most important on the output impedance side. And some professional gear has trimmable components on the output in order to precisely balance impedances due to such things as simple manufacturing tolerances of the cables being used, and this helps improve the common-mode rejection of the system.

se

 

[charleski]

I don't see how you get cancellation of even-order distortion from bridging.

se

Because the two amplifiers are effectively in push-pull configuration. This assumes the amps are properly matched, but you'd have to be insane to bridge two amps that weren't symmetrical. The same effect is seen in Class-B amplifiers.
 
Common-mode noise cancellation really isn't an issue with 1-2m headphone leads carrying ~1V signals, just as it isn't an issue with the short-length line-level interconnects used to hook up hifi gear (it is an issue with long microphone leads, but the signals there are a few millivolts). Most manufacturers peddling 'balanced' headphone amps are smart enough not to claim this to be a reason to buy them. As I explained, 'balanced' headphone outputs are simply bridged amplifiers that produce more power without having to uprate the supply rails. There are some vairiations, like the Mjolnir which is run completely in differential mode, but they all have essentially similar output stages. The use of the word 'balanced' rather than 'bridged' is a result of historical factors within the hifi market, that's all.

 

[limpidglitch]

What's the difference between differential and bridged amplifiers?
The way Steve puts it, with a differential amplifier being an amplifier that amplifies the difference between two symmetric signals, I can't see how a design like this can "run completely in differential mode".

 

[Steve Eddy]

Because the two amplifiers are effectively in push-pull configuration.

No, simple bridging doesn't put them in push-pull. At least not in the same way that a complimentary push-pull output stage is, which does have even order distortion cancellation. Bridging just ties the load across the outputs of a pair of identical single-ended amplifier channels. Now, if there's anything common on both outputs, it will cancel at a differential input, but there's no cancellation in the bridged pairs like you get in a complimentary push-pull output stage.

Common-mode noise cancellation really isn't an issue with 1-2m headphone leads carrying ~1V signals, just as it isn't an issue with the short-length line-level interconnects used to hook up hifi gear (it is an issue with long microphone leads, but the signals there are a few millivolts). Most manufacturers peddling 'balanced' headphone amps are smart enough not to claim this to be a reason to buy them.

Yes. But there are a couple that I'm aware of that do.

The use of the word 'balanced' rather than 'bridged' is a result of historical factors within the hifi market, that's all.

No, not historical factors. Unless you intend historical factors to mean that the so-called "high-end" audio industry has a history not quite understanding what they're doing and use terms based on those misunderstandings.

se

 

[Steve Eddy]

What's the difference between differential and bridged amplifiers?
The way Steve puts it, with a differential amplifier being an amplifier that amplifies the difference between two symmetric signals, I can't see how a design like this can "run completely in differential mode".

Hmmm... How to explain this.

Put very simply, a differential amplifier is designed such that each of its two inputs are able to see and react each other. When you simply bridge together two identical amplifier channels, they only see what is on their respective inputs. This means that the input is not differential and anything that is common to both inputs will just be amplified and passed along as if it were a signal instead of rejecting it.

se