The block diagram is probably a good place to start. The 1073 is basically a series of similar, three transistor fixed gain blocks, each with their own function.
The first amplifier block brings the mic signal up. It's only used when you need very high gain. Otherwise, it's bypassed.
The second amplifier block accepts a now-higher mic signal or a line input signal.
The sensitivity switch controls resistor pads before the second amplifier block, and a little bit of gain control of the second amplifier, to get the desired gain.
The third and fourth are part of the EQ.
The fifth is a line amp.
The signal flow is something like:
- Mic input transformer
- Sensitivity / gain switch part 1
- BA284 amplifier #1
((- Line input transformer))
- Sensitivity / gain switch part 2
- BA283 amplifier #1
- Low and high shelf EQ using BA284 amplifier #2
- Mid EQ using BA284 amplifier #3
-High pass filter
-BA283 amplifier #2
- Line output transformer
When you're talking about filters you're using something that has a different impedance at different frequencies. One way to filter is by connecting the filter to ground - when it has very high impedance, those frequencies pass it by. Frequencies where the filter has low impedance pass easily to ground and are subtracted from the rest.
If you can imagine taking this same filter and connecting the input of it to the signal coming in, the center of it to the input of an amplifier, and another part to the output of the amplifier, using a potentiometer to control this connection, you are now thinking of one way to make an active filter. By moving the potentiometer, you adjust the balance of the filter that is between the output and input of the gain stage. Anything connected between the output and input is feedback. By controlling the feedback, you control how much of the filter is subtracted or added, net, to the signal.
This loosely is how the 1073 EQ works. The BA284s by themselves have fixed gain, around 50 dB. This gain is used for feedback, with the filters, to change the frequency response of the signal.
July 16, 2005, 03:07:19 AM