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Studio Channel Tube Drive Issue

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asked May 16 in PreAmps, Signal Processors and Monitoring Hardware by martincohen1 (120 points)

I would like to draw attention to a fault recently repaired on one of my two Studio Channel units. It was found that increasing Tube Drive gain on one unit produced popping and noise and the VU meter swung hard over into the red, tripping the connected power amp protection circuit. When measured, the voltage at the output was in excess of 5 volts DC when the expected reading should have been a fraction of 1 volt or less.

The source was traced to a coupling capacitor after the tube circuit which was replaced with one of a of a different rating that dissipated the unwanted voltage correctly. However, when tested off the unit the capacitor was found to be in good order. The engineer remarked that the original capacitor had an unusually high rating for the function intended and replaced it with one of a much lower farad rating. My second unit functions normally although when turning the Tube Drive pot the movement of the VU meter is greater than the now repaired unit. The modified unit functions perfectly with no alteration in frequency response. I would be very grateful for any comments you may have.

Both units are used as pre-amps for bass guitar feeding power amps in live performance. They produce the most brilliantly detailed sound I have experienced in my forty five years as a professional musician using many different types of amplifier combinations.

Many thanks.


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