![]() As someone once said, tubes are forgiving. If the DC voltage is not right don't worry. A few power amplifiers have auxiliary power sockets for just this purpose. The ac requirement is 6.3 volts at 600 mA at most. The current required is small ranging from 1 mA for the least to 7 mA for the maximum at a voltage of 250 volts DC. There are alternatives to building a standalone power supply. I have concluded that it is advisable to include a power supply schematic on this page. The recall notice does not apply to this section or any of the schematics in it.īefore we get to the tone controls themselves a question arises "how to power the electronics in a tone control circuit?" I often receive emailed questions on this subject. This page will attempt to rectify that situation. Although I have covered this topic under the heading of "Audio Amplifiers, How they Work" the circuits on that page are not intended to be duplicated by the reader and there is virtually no information on how and where to insert them into an amplifier. It's beginning to seem as if 2/3 of the earth's surface is covered by water and the remaining 1/3 is covered with diagrams of tone controls. I have lately found that there is a lot of interest in tone control circuits. New material has been added to this page. If you take it directly from the cathode follower output there will be some serious low frequency peaks in the frequency response. Take the output from the point shown in the schematic. The simulated circuit has been scanned down to 0.01 Hz to check for infrasonic peaks. DC blocking capacitors have been added where they should have been in the first place. But I don't recommend taking chances with an expensive amplifier or even a cheap one. This could damage the power amplifier in the system although some amplifiers do have protection circuitry built in. In addition to the expected safety hazard the circuit produced a large pulse of voltage when the bass control was rotated. The problem was caused by allowing B+ voltage to appear on the tone pots. Ones that I could not render safe continue to be posted for historical interest and are clearly labeled DO NOT USE. If you accessed this page after Mathe circuits have undergone some additional testing and most of them are safe to use. A flaw in the circuit design surfaced on the above date. If you accessed this page prior to Maand built or planned to build one of the circuits into a preamp there may be trouble ahead.
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