Unitra ws 442
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Hi i have this amplifier for more than 20 years. It works perfectly.
I checked the dc offset at speaker terminals and on left i get 64mv and right 45mv. Is that ok? Can I reduce this? Amplifier is in factory state every part is original.
In my opinion dc offset below 100 mV is correct, however 64mv … is too high . I think is able to gain dc offset below 50 mV. Darkwood gave you a solution so try to match differential pair > T501 and T503.
Ok so I transfered bc307 from another working amp just for the experiment and the voltage dropped on right channel to 10mv but on the left still remains the same 64mv. Also one thing I noticed is when i turn the volume poti the voltage rises in peaks on left channel ro 130mvand gets back to 64mv. On right channel it doesnt change when i turn the volume poti. Could it be a fault capacitor somewhere?
Did you check the HFE for pair of transistors before you put them on board of amplifier (difference between two transistor should be less than 20%)? It's very important if you want to get low DC offset.
Congratulations :)
You achieved very good result.
Is there diference in sound when dc offset is low?
I don't think so, but low dc offset is better for speakers.
Hi.
Such difference is common in those amplifiers.
You can improve it by closely matching Hfe of the differential pair.