My CMoy has the hiss

[espire]

So I've had my CMoy hissing for the longest time, and I've decided that I want to fix it. My first thought was to put a 33Ω resistor in each of the R5 spaces on Tangent's layout. However, the hissing is not so terrible that I don't prefer using the CMoy already. Would lowering the gain from the default 11 get rid of the his without having to use an R5? I'm in fact rather confused on what the feedback loop is, exactly, but my specific question answered would be more helpful

 

[amb]

Your headphones are probably low impedance and much too sensitive for the default cmoy gain of 11. The amp's intrinsic noise is amplified and thus you hear the hiss.

Reducing the gain is the better approach than attenuating the output with R5. The feedback loop on the cmoy is R4 and R3. If you reduce the value of R4, or increase the value of R3, you will reduce the gain. The gain is set with the following formula:

Gain = (R4 / R3) + 1

 

[espire]

The problem is that I'm using the 50Ω HD-555. Is this still what you consider to be too low an impedance?

 

[amb]

It is low impedance. But "too low" is a value judgement.

 

[espire]

Well then, I'll set my gain down to 5 or 6, I suppose whatever my 2.2 KΩ resistors can do for me.

Thanks

 

[Joshatdot]

- reflow the solder joints
- try another op-amp, maybe you got a funky one

 

[D_Tinnitus]

Most likely excessive gain for low impedance cans, however always a possibility it's oscillation (especially if using a socketed opamp).