Hello everyone. I made a BOZ preamplifier. I am very satisfied with the performance, but it has a small problem, at least I hope it is small, ie that the input signal goes into distortion when it is high level.
Looking here and there on the net I found a forum where even another owner of Boz had the same problem. He solved it by setting a bias current to around 0.3A, in this way symmetrical clipping occurs, measuring with the oscilloscope, and the input signal was no longer distorted.
I don't have an oscilloscope, so "by eye" I set a voltage on the Irf610 of 3V, instead of 4V as the project foresees (with 3V the current should approach about 0.3A, instead of the original 0.4A). The distortion has decreased a lot, but unfortunately there are still some impulsive peaks that go into distortion.
The Dac has a fairly strong output, while with old sources with low output there is no distortion.
If I put an input potentiometer (obviously eliminating the resistance R107) we create a mass noise (like 50hz of the network) that I can't eliminate with various mass tests, moreover we could create an audio band limitation since there is a 1uf capacitor in input.
I kindly ask you for a suggestion on how to eliminate the bias in input to Boz.
Tank, Giovanni!
Looking here and there on the net I found a forum where even another owner of Boz had the same problem. He solved it by setting a bias current to around 0.3A, in this way symmetrical clipping occurs, measuring with the oscilloscope, and the input signal was no longer distorted.
I don't have an oscilloscope, so "by eye" I set a voltage on the Irf610 of 3V, instead of 4V as the project foresees (with 3V the current should approach about 0.3A, instead of the original 0.4A). The distortion has decreased a lot, but unfortunately there are still some impulsive peaks that go into distortion.
The Dac has a fairly strong output, while with old sources with low output there is no distortion.
If I put an input potentiometer (obviously eliminating the resistance R107) we create a mass noise (like 50hz of the network) that I can't eliminate with various mass tests, moreover we could create an audio band limitation since there is a 1uf capacitor in input.
I kindly ask you for a suggestion on how to eliminate the bias in input to Boz.
Tank, Giovanni!
post exact schmtc and explanation what you have in front (source) and what are your needs , regarding output swing
I have made the BOZ, and found that the amplifier due to its high gain could easily clip on output. This is when the potmeter on the output is used af volume control.
Moving volume control to input solves this problem...
Moving volume control to input solves this problem...
What about simply changing r100 from 100 ohms to 200 ohms and adjust for 8v across it instead of 4 v so to maintain the 40ma bias. That cut the gain thus lowered the miller capacitence while introduced a little more local feedback.
after having set the voltage to 3.5v you did not have more distortion in input?
And were you distorted before this setting?
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