I wanted to share an anecdote about this subject. I modified an amplifier’s op amp stage in a way that causes the op amp to output a small positive DC voltage that varies slightly with signal level. This was causing problems downstream, as the stage did not have a coupling capacitor at the output.
So I decided to insert a cap to block DC, but it needed to be rather large to maintain decent low end response because the load was relatively heavy. I decided I needed 10uF. I decided to go with an electrolytic for size, and non-polar because the DC offset was hanging around 200mV (less than the swing of the AC signal).
I didn’t have a non-polar cap handy, so I wired up two 22uF caps in anti-series, with cathode to cathode, resulting in a makeshift non-polar 11uF cap, and wired it into the circuit.
Here’s the interesting part. I played the amp and was greeted with a slight crackling distortion that followed along with my playing. I wasn’t sure if I had a bad solder joint, or if the capacitors themselves were causing the distortion.
After walking away from it for a bit, I decided to try biasing the makeshift non-polar capacitor arrangement. I ran a 470k resistor from the cathodes to the -15V supply, buttoned her up and played. The distortion was gone!
TLDR; Makeshift non-polar capacitors made from two polar electrolytics can introduce unpleasant distortion into audio. Try biasing the capacitors with a modest amount of DC to see if this eliminates the distortion.
So I decided to insert a cap to block DC, but it needed to be rather large to maintain decent low end response because the load was relatively heavy. I decided I needed 10uF. I decided to go with an electrolytic for size, and non-polar because the DC offset was hanging around 200mV (less than the swing of the AC signal).
I didn’t have a non-polar cap handy, so I wired up two 22uF caps in anti-series, with cathode to cathode, resulting in a makeshift non-polar 11uF cap, and wired it into the circuit.
Here’s the interesting part. I played the amp and was greeted with a slight crackling distortion that followed along with my playing. I wasn’t sure if I had a bad solder joint, or if the capacitors themselves were causing the distortion.
After walking away from it for a bit, I decided to try biasing the makeshift non-polar capacitor arrangement. I ran a 470k resistor from the cathodes to the -15V supply, buttoned her up and played. The distortion was gone!
TLDR; Makeshift non-polar capacitors made from two polar electrolytics can introduce unpleasant distortion into audio. Try biasing the capacitors with a modest amount of DC to see if this eliminates the distortion.
