Hi all,
In an amp I am experimenting with ( see schematic) I have removed the 47K NFB resistor connected to the presence pot and made a direct connection.
Why does this amp still makes noise? Is it because the 5K presence pot is always shunting some signal to ground?
When applying the B+ after warmup there is some low level hum for a short period that could be motorboating. It disappears after a minute. Can this be an effect of all the NFB I am using?
In an amp I am experimenting with ( see schematic) I have removed the 47K NFB resistor connected to the presence pot and made a direct connection.
Why does this amp still makes noise? Is it because the 5K presence pot is always shunting some signal to ground?
When applying the B+ after warmup there is some low level hum for a short period that could be motorboating. It disappears after a minute. Can this be an effect of all the NFB I am using?
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So you havent removed the resistor youve just made it vey small. This has increased the feedback signal to full output. You need to study a little feedback theory, easiest to look at opamp circuits. The easiest way to look at it: the amp will try to keep the voltage at the - input the same as the + input ( or close, input /gain = output, so with lots of gain the input is very small so - almost equals the +. ). Since youve shorted the output to the negative input the 2 will have the same voltage, and since the - input follows the + input ( or close) the output = + input, or gain of 1.
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