NE571 coupling caps

[Dave Eason]

Hi there,

I'm building seperate compressor and expander circuits as part of a larger wireless project; can anyone help as to recommend the type of coupling caps to be used.  Phillips suggest electrolytic 2.2 uF for inputs, and 10 uF on the output, and a 1 uF attached to the rectifier in the old data sheets.  They also suggest putting a 22uF in the DC feedback path, to short out any AC feeding back.  Are there any 571 pro's out there!?

Could I get away with smaller, non-electrolytics caps for i/o, bearing in mind the circuit is DC biased at half the supply?  What affect does changing the rectifier cap have? smaller = shorter attack/decay of the compressor/expander? 

Dave

[Dave Eason]

bump

[Paul Perry (Frostwave)]

Could I get away with smaller, non-electrolytics caps for i/o, bearing in mind the circuit is DC biased at half the supply?  What affect does changing the rectifier cap have? smaller = shorter attack/decay of the compressor/expander? 

Yes and yes, I think. Say .1 for coupling. All compressors are subject to personal judgment, so be prepared to experiment before finalising it.

[Dave Eason]

thanks paul

even as small as 0.1 on the output?  The compressor will have a buffer before it, to stop the guitar from being loaded down and provide a good low impedance load to drive the compressor circuit.

http://www.muzique.com/editor.htm - I found that on the AMZ site, interesting stuff there.  Oddly an article in a guitar mag about upgrading ts808's recommended swapping the electrolytics for tantalum or other "hi fi" equivalents, and so on, a big mistake according to this.

[jrc4558]

I am by far not the best expert here, but as far as coupling capacitors go, the impedance of the following stage has by far the largest effect on the corner frequency of your high-pass filter, which the output of any stage essentially is. If you have the device with greater than 100 kohm input impedance after the capacitor, 0.22 µF is essentially an all-pass stage (audio range).
In the rectifier case - yes, shorter attack-decay.

[Dave Eason]

thank you! yeah, I understand that