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RE: Help with troubleshooting Ming Da MC34-AII

Posted by JKT (A) on July 4, 2015 at 10:49:07

In Reply to: RE: Help with troubleshooting Ming Da MC34-AII posted by Sidewinder on July 4, 2015 at 01:23:00:

" Given the info what would happen if the 100k ohm load was increased to 210k ohms? Will this harm the amp in the long term?"

Problem here is you need more info. The two stages are interconnected. Changes to one affect the other. To start with: measure the plate voltages of each stage and measure the voltage drop across the cathode resistors to determine the bias currents of each stage. Then plot out the operating points on the two sets of plate curves. Doubling the load on the first stage will change the gain and the plate voltage with no changes to the cathode resistor. This plate voltage needs to by compatible with the operation of the driver/phase splitter stage.

If it was up to me I would replace the cathode resistor of the 2nd stage with an active CCS. That way the 2nd stage would be properly biased for whatever plate voltage the 1st stage presents to it (as long as the CCS isn't starved for voltage).

Another approach is very empirical. Try the 100K resistors and listen to familiar music and measure voltages and bias currents. Compare to results with 210K resistors. Go with what sounds best.


"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln

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