Posted on Feb 5, 2014

By now many audio DIYers would be familiar with `What Compressor `, a project that apparently had its origins in one man`s dissatisfaction with Alesis` 3630 compressor and his fascination with a friend`s Joe Meek device. DeeT, as he calls himself, generously shared his story and schematic but not his printed circuit board design. That`s a shame b

Click here to download the full size of the above Circuit.

ecause the complexity of the circuit precludes easy wiring on a Veroboard. Still, not many people would have enough skill or patience to deal with surface mount devices that he apparently used in the 10 prototypes he mentions on his page. To say little about gaining access to these SMDs in the first place. I`m aware of one other site that deals with this intriguing design and has a PCB layout but was somewhat dismayed with that author`s choice of opamps for his version. DeeT specifically mentions that substitutions to the MC33178 opamp should be a low noise device "able to drive 600 ohm(s)" loads. The obvious choice is the bipolar NE5532 with its extremely low noise and very low distortion at 600 ohms. Unfortunately 1176neve site`s printed circuit board is designed around JFET TL074 quad devices which, aside from not fulfilling the above requirement as well as the NE5532, is not pin for pin compatible with any device meeting DeeT`s basic specification (there is the MC33179, a quad version and even harder-to-find part than the MC33178 though). Therefore if you want to use dual opamps ” even the MC33178 device originally specified (which can be obtained in a ordinary DIP as well as SO-8 surface mount package) ” the layout is useless without extensive modification. Curiously, according to data sheets from Motorola and On Semi, the distortion from the MC3317* family at 600 ohms isn`t all that great ” despite their first bullet...

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