[sdiy] my first schematic - please critique

[Oren Leavitt]

eat-it at new.rr.com wrote:
> hello all,
> 
> with some help i've designed my first schematic and i'm looking for
> critiques on what could be done better.  please keep in mind that
> simplicity is key and i just want it to work right.  this is designed to
> accept two stereo inputs, mix the two allowing crossfade, and amplify
> the output.  please let me know what you think.
> 
> http://www.sub-version.net/images/crossfading_headphone_amp.gif
> 
> drew
> 
> 
> 

Hi Drew,
Congrats on your first schematic!
In addition to advice others have offered,
The LT1013 is not a good choice for audio (too slow - better for DC 
applications). Use a TL072 for the dual op-amp or a TL062 (low power 
version - good for battery op) instead.

As mentioned, C1 and C2 will need to be much bigger.
With the gain control in the feedback loop, input impedence seen by C1 
and C2 will vary from 10K (min gain) to 60K (R2+R4a) and (R3+R4b) at max 
gain.

At 10K (min gain), with 0.001µf you are cutting off all frequencies 
below 16KHz!

f = 1 / (2*pi*R*C)

where
R = (R2 + R4a) in Ohms - (10,000 - 60,000)
C = C2 in Farads (0.000000001)

Make C1 and C2 1µf - you'll be good down to 16Hz.

My 2db,
- Oren