NEWER Aleph-X calculationsheet AXE-1.2

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yldouright,

This is friendly advice, use it as you wish. I am by no means attacking you. I am simply trying to help you understand so things do not get out of hand. The reason why your posts are viewed a confrontational is as follows. There are alot users here who know alot more about audio circuitry than you do. You are wise to use the forum to gain insight into the project you are trying to build, but with that said, a bit of respect must be used when tapping on this source of free information. It's an easy trade, information for respect. When you ask a question, accept the fact that nobody here owes it to you to answer anything. They provide you an answer of their own free will. If you do get a reply do not make your next reply a challenge of the validity of the answer you recieved. Remember, it makes you look very bad when you ask a question and immediately challenge the answer. That just make you look like a troublemaker. If you do not understand the answer say so. Don't challenge the answer because you do not understand it. Also show that you are willing to do some research on your own instead of just firing questions. This lends credibility to you and your quest to have your questions answered. It looks fishy sometimes when someone keeps firing off questions. It gives people the perception that you could be just looking to start trouble. Perception is reality, not truth. Lastly, be nice. It is ok to point out something that is wrong, but make sure when you do, that your objection is based on fact and not speculation and when pointing out an error try to do it with decorum. I think the largest problem is not what you are asking, but the tone in which you ask it. Remember, we are all human beings with different feelings and egos. This is not a courtroom. That behavior has a time and a place, but this forum is not that time and place. Try it, you have nothing to loose and alot of knowledge to gain.
 
yldouright,

I think the only way we will ever resolve this is to go right back to basics and make sure you correctly understand 1 concept at a time.

You need to understand,

* Single ended Class A operation
* Bridged Amplifier operation
* Aleph Current Source

Then and only then I think will we all be able to put this issue to rest.
 
originally posted by yldouright
Why is the 4A of bias considered peak if the Aleph-X is a Class A current drive amplifier? As I understand it, the 4A are sustainable output, so why wouldn't I²R be a fair rms power representation?

OK, a simple view of pure Class A is that the output devices are always on and conducting the bias current, and produce an output to the speakers by modulating how much of that current is shunted out of the circuit to the speakers. Now picture a sinewave, lets for the moment say 60Hz, with 4 amps corresponding to the maximum current peak. If we try to drive higher than 4 amps, the circuit clips the signal introducing distortion. If we look at the maximum output without clipping, the average current delivered is 4/sqrt(2)=2.83 A(RMS).

You ask about the fact that the 4A ouput can be sustained continuously with this circuit, so let's look at what that really means. It means that the amp can output 4 amps DC!, or in other words, the bias scheme will happily live with frequencies down to fractions of a Hz where many amps run out of steam, or alternatively, will happily drive low impedance speakers, or for that matter will happily drive a dead short. However, if you feed the amp a waveform, no matter what the amp will clip if you try to draw more than 4 amps, limiting you to a max RMS output of 2.83A without distorting.

What is misleading you is a common approach class AB amplifier designers use where a large capacitive reservoir is made available to the output devices that can deliver extra current, but for a limited period of time, allowing transient signals to output more current than the power supply can deliver on a continuous basis. This is where the "40W/Ch but capable of 120W/ch on transients" comes from. For the Aleph amps, the max current is the max current, limited by the circuitry that sets the bias point of the active current sources. No matter what you do, that max bias peaks at 4 amps and will go no higher.

To understand this properly, I suggest you read all the Zen articles about 20 times each. That's about what it took for me to wrap my head around it.

As to the accuracy of wuffwaff and BobEllis, you can pretty much accept what they say as gospel. They both know this circuit inside out, backwards and forwards. Also, if there were significant errors in the Aleph-X spreadsheet, you can be guarunteed that Nelson and Grey would have pointed them out, and I'm pretty certain that Grey vetted wuffwaffs original spreadsheet for correctness.

My last suggestion to you is find a copy of SPICE, and simulate the circuit you are proposing, and it will confirm what wuffwaff and BobEllis are telling you, and you'll learn a great deal in the process.

Cheers, Terry
 
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If you can keep the junction temperatures to 70C in an AX, your heat sink dealer will love you!

Keeping them under 100C is generally considered good for reliablility. Most seem rated for 150C these days, so you can go a little hotter if you are willing to sacrifice reliability and have hot sinks.

The spreadsheet calculates the junction temperatures for you. you input rail voltage, bias, nuimber of fets, heat sink and insulator themal properties and it's right there in the last section of the page.
 
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