Re: Headphone amp / mixer

Posted by MAO on
URL: http://guitar-fx-layouts.238.s1.nabble.com/Headphone-amp-mixer-tp44796p46153.html

That sounds like the dreaded charge pump high frequency whine.

There were a lot of bad ICL7660SCPA selling on ebay. The bad ones were most likely the noisy ICL7660CPA but labeled as the quiet ICL7660SCPA.

If you have two 9v batteries, you can find out fairly easily.

Test: Disconnect your dc adapter and remove the charge pump.
Attach the + terminal from Battery 1 to the top rail, at the top right corner of the board is fine. (Pin 8 of the charge pump socket)
Attach the (-) terminal from Battery 2 to rail 4, again at the right side of the charge pump socket (pin 5 charge pump socket)
So both are attached to the right most column.(or pin 8 and pin 5 on the charge pump socket)
Then connect the (-) of Battery 1 and  (+) of Battery 2 to ground.
This will supply the circuit with Clean +/- 9v.

If the whining goes away, the charge pump is the issue.