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“PAB autobias” versus “Adaptive autobias”


adaptive_autobiasThose of you who know the famous dutch brand PRIMA LUNA, with their tube amplifiers manufactured by Cayin Ltd. in Zuhai, China, have probably heard that they also offer a feature called “Adaptive autobias”. Their amplifiers have been awarded by Hifi magazines in the years 2008 to 2010, but are now less popular.

Regarding friendly using, the PrimaLuna Adaptive Autobias is superior to our PAB autobias because there is not even one single button to press, it is a kind of “plug and play” autobias. Our PAB autobias has one button to press and need around 30 second to have our microprocessor to reset the bias settings.

However if we have a button to press on contrary of Adaptive Autobias, it is because the way their autobias works is not the proper way to run an autobias. The main reason is that it works in real time and this it is not a proper technology to set the bias, whereas our PAB autobias put the amplifier in mute mode during the bias reset. And any expert will tell you that bias has to be set once, without signal and after that, it should only be checked once or twice per year, depending how many hours you use your amp per day. That’s all.

Having the bias settings in real time increase the distortion and don’t reduce it has stated by P.L and we consider as nothing else than a marketing argument, to make potential buyers feel safe they won’t need to do any setting. About this last statement, we think they are right, in the 21st century, a user should not need tools to set the bias, that is the reason we launch as well our PAB autobias in 2011.

Probably because P.L wanted to make it cheap to produce by avoiding to use a real adaptive-autobiasmicroprocessor and engineering research fees like our PAB autobias, they chose a basic technology with a cheap OPA plus 6 transistors. A sarcastic alternative name for it could be “Marketing Autobias”. Those interested by technique can click on the picture on the right to have a look to their schematics and will see that there is nothing magic and that they just use a cheap OPA ref. TL084 at $0.20 per piece. The total cost of this Adaptive auto-bias is then less than a $2 including all components and any DIY’er can duplicate it.

This said, we think the PRIMA LUNA are good amplifiers, not totally our taste, but they are among what we consider as good tube amplifiers BUT only because they use good components and good output transformers and certainly NOT because of their cheap odd “Adaptive Autobias”. It is also interesting to see that despite its very cheap production cost, not any other company has chosen to use this real time autobias in their amplifiers, especially knowing that such simple schematics can’t be patented, so any tube amp manufacturer could use it in their amplifiers for just $2.

Our PAB auto-bias on the contrary combines all advantage of manual bias and the advantage of friendly user interface.

It could be described as a manual bias managed by computer. Our PAB autobias has a more expensive cost as we use a real microprocessor and a few other processors (but none of them is in the signal path of course !).  So we would be foolish not to have done the same autobias than Prima Luna if the result was so good and so cheap to produce.

The reason we choose an alternative much more complex technology, having taken one year development in partnership with digital department of South-West Central university of China, was really aimed with the core idea that the bias should be set WITHOUT signal and NOT in real time.