Thanks!
desol said:
Any chance we could get a 'quick debriefing on how the circuit operates?
Well, I've opted for the cinemag input transformer and glad I did. Sounds nice. The circuity is all very simple class A transistors...very nice tone to the unit. Transistors are so inexpensive and simple. Makes me want to build more stuff without opamps...
So the gain is controlled by a fader pot on the input and a fader pot on the output. Its a feedback compressor so the signal splits off before the make-up gain stage and is sent through a step-up transformer to some germanium diodes and the sidechain. I think this is what makes this compressor very unique... It has a very musical release circuit. I'm not quite sure HOW it does it exactly, only that it is very cool! Along with the PWM gain control it hands the peaks of the signals very well.
So moving on, the rectification ends of with a DC signal that tracks the audio and added with the release time that is chosen. It is then used to control the PWM signal. And the PWM signal is in turn used to control the gain of the audio. Its the same idea behind light dimmers and switching power supplies...turn a signal on and off extremely fast and how long you leave it off or how long you leave it on can control how much RMS energy gets through.
So Enter:
The oscillator. It oscillates at 250khz. To get a good stereo matched pair, you must make sure that they are as close to the same oscillating frequency as possible. Easy in theory, not as easy in practice with toroids with wires and capacitors as the timing reference, as these all drift with temp and humidity...but can be used and obviously worked excellent. The oscillator sends out a "ping" every 250khz. This ping is then turned into a version of a triangle wave. This is then combined with the DC control signal the sidechain spits out and walla! A pulse width modulation. This gets sent to the base of a switching transistor and it chops up the audio.
The 555 timer chip can be set up in a pinging oscillator type configuration, and you can adjust the frequency with a screwdriver! (yay!) also stable and uses less current than the toroid and less chance of noise getting into things it shouldn't. The ping from the 555 timer gets sent to the circuitry that creates the triangle wave.
Is Dan doing a new front panel design for the unit? (I noticed the meter...)
yes Dan has some cases
And lastly, pro's/con's involved in using the different oscillators?
Well the impedance changes when you use the different circuitry, so a cap has to be changed to get the correct value of triangle wave. In practice I can not tell the difference and in theory it shouldn't affect the audio in anyway.
