help me analyze the Philosopher's tone compressor?

[Eddododo]

curious about a few 'key' features... what is up with the strange power setup...

http://1.bp.blogspot.com/-TRdHJssdmJ8/T-DF1m6lbdI/AAAAAAAABg4/nOMrqz2HNOI/s1600/PigtronixPhilosophersToneSchematic_1.0_20111214.png

--why is it 18+V in, 15+ as the positive 'supply' of the Ic's, and then biased to +9?


--What is the function of  LM741 in  the lower-left-hand side?

thanks for any insight!

[armdnrdy]

The schematic that you posted is a bit misleading.

The manual states that EHX supplies a 15VDC adapter with the unit but...you can use up to 18VDC for higher headroom.

With the input at 15VDC the reference voltage isn't actually 9 volts as written on the schematic. It would be more along the lines of 7.5v volts as you would expect.

The 741 is doing nothing more than buffering the voltage for the rectifier.

[Eddododo]

A little confused still.

The vref was obvious I  just didn't look at values. ..

But the 741... from what is it Buffering the rectifier? Or is the rectifier getting a bias voltage from the 741? I hope I'm not being confusing..

[Eddododo]

oh hm... does the 741 kind of... give the complementary diodes (D 13 and D16) something to "push" and "pull" on to create pseudo full rectification?

[merlinb]

oh hm... does the 741 kind of... give the complementary diodes (D 13 and D16) something to "push" and "pull" on to create pseudo full rectification?

It buffers Vref, providing a rock-steady reference voltage for the bridge rectifier circuit. If it wasn't buffered, U1B would be trying to dump several milliamps (for the LED) into the Vref supply (R11), which would change Vref. The 741 provides a way of sinking that current rather than let it go into R11.