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Old 21st Aug 2013, 1:21 pm   #10
ukcol
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Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
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Default Re: Roberts R200- Distorted Output

Hi Chris,

Perhaps there would not be enough voltage across R21 to use a silicon diode? Using the emitter voltages given in the Trader sheet, Ohms law calculations suggest there is only 5mA flowing in the previous stages which gives only 0.5volts across R21.

The approx 0.18volts Josh is reading across the germanium device seems a fraction low to me.

Josh

What is the distortion like? Low Q-current causes crossover distortion which sound worse at low volume and difficult to hear at high volumes. If it’s not crossover distortion one possibility is that you have low current in the driver stage due to a bias fault or a faulty transistor and that is this that is causing the distortion. The low Q-current in the output stage being a red herring. If this is the case you will, of course have to set up the output stage bias (quiescent current) when you have fixed the driver fault.



Colin M
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