How to set the DPA 330


The starting and setting up is similar to the one described by the DPA220 amp, only the bias current is not set according to transient distortion - I hope you call it so -, because it's not visible on an oscilloscope. Also, contrary to the bjt-types' setup procedure, the bias-current setting trimpot (R38 in this case) has to be set to maximum resistance.
It is simply set to 200mA +/- 10mA, without the need to heat the amp - these types of FETs are perfectly temperature stable: the 200mA set at 20 degrees centi grade change to 198mA when heated to 80C.
If you have problems reaching 200mA, you can change R48 to 27 or 39 ohms - in 99% of cases you won't have to do it.
One more change: two resistors were added- R60, R61 - for better security during wiring. If you use the securing block described above with this amp, as you should, you must replace resistors R25, R26 on the securing block PCB with 47k ones.

My own advice: when you start and set the amp for the first time - or any other circuit - be absolutely careful. When changing configuration of signal generator, oscilloscope, meters and load, ALWAYS switch off the power supply. I even unplug it ever since I burned a TDA2040.

In general, it cost me about a handful of transistors to gain this knowledge.
Note that the frequency response is a full graph and measured 1 dB under limitation (=maximum sinus power) - when measuring voltage, value in decibels = 20 log (amplification) - 6 dB means amplification 2x.





You can Email Rysanek Frantisek who sent me this info.


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You can Email Stefan Wieman (for HTML comments) at s.wieman@tudent.utwente.nl