[ginettaman]

I have built a cmoy with a gain of 11 as standard. I get a slight amount of hiss at approx 2/3 and higher volume with nothing connected, and the hiss is slightly louder with mp3 player connected on pause, still only top third of volume, which is to loud to listen to anyway.
Is this ok or should it be hiss free all the way through the volume range?

 

[jnewman]

Quote:

Originally Posted by ginettaman I have built a cmoy with a gain of 11 as standard. I get a slight amount of hiss at approx 2/3 and higher volume with nothing connected, and the hiss is slightly louder with mp3 player connected on pause, still only top third of volume, which is to loud to listen to anyway. Is this ok or should it be hiss free all the way through the volume range?

That happens a lot with gain that high and low impedance headphones - you can try putting a small resistor (nothing higher than 200ohm, and try starting with something around 50) on the output. A gain between 3 and 6 is much more common than anything above 10. Really high gain is only useful with extremely high impedence headphones.

 

[silvervarg]

Getting hiss with no input connected and high volume on a high gain amp is quite normal. The hiss often comes from disturbances at the input. There are a few ways to fix this if you feel that this is a problem.
One is to put resistors from input to GND (before input capacitor).
Another is to put a small capacitor between + and - input on the OP-amp.
Most sources will give you something similar to the grounding resistor when they are not sending out any signal.