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Decker 3rd December 2012 07:36 PM

BOZ distortion problem
This is a semi-lengthy inquiry. Bear with me. I recently modified my BOZ by taking out the stepped attenuator at the input in parallel with R107 (100k load resistor) and putting a 5 k dual pot on the output, as is recommended in the original article. The BOZ was working fine before the change, i just wanted to try it as designed by Mr. Pass. I checked the bias before putting it in the rack: 40 ma. per channel. I now have distortion when using both CD and tuner as inputs. After checking the usual suspects, I began to suspect that the input was being overloaded. Putting a 5:1 step down transformer temporarily between the CD player and BOZ, and then between the tuner and the BOZ eliminated the distortion that I was hearing. So I tried a voltage divider consisting of a 100k series resistor before R107 (also 100k). Still distorts. So... Anybody else notice this with their BOZ? Does this sound like the BOZ is getting too high an input signal? Is there a way to increase the overload resistance of the BOZ? (other than going back to an input attenuator) All answers and general musings appreciated.

Decker 3rd December 2012 08:44 PM


Michael Rothacher 3rd December 2012 08:59 PM


Originally Posted by Nelson Pass (
It would be 3V (0.03A * 100 = 3).

Actually the more probable issue is input overload, and higher bias
raises the input overload figure.

If overload is an issue, then I suggest some input attenuation. Many
have found that using both input and output pots is useful. A 10K
pot can be adjusted so that the maximum volume that you will actually
use is achieved when the output pot is at max, and thereafter the
output pots becomes your volume control.

Decker 3rd December 2012 09:43 PM


Decker 3rd December 2012 09:51 PM

This is EXACTLY the info I need! Thanks again.

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