Coupling Caps
All transformerless mike amps require input blocking capacitors to keep P48 out of the front end. I had previously replaced the input phantom blocking capacitors with 10uF/100V metallized polypropylene capacitors, but there are problems that can result from this modification. The physical size of the replacement capacitors forced me to mount the caps for channel two above the output stage, and this caused some undesirable ultrasonic coupling and resultant instability.
While film caps do sound cleaner than electrolytics, their size can cause input - output coupling problems, especially once you have extended the bandwidth of the amplifier, so I feel that replacing the stock caps with new, high quality replacement electrolytic caps is a better way to go with the SX202. I chose 22uF 63V Panasonic HFQ radial electrolytics and they work well.
Unfortunately, the HFQ series is no longer available, so try to choose a capacitor that is designed to have low leakage and low impedance. Also note that if you choose a higher capacitance value, leakage will increase, and this can upset the balance of the first stage, so it's probably wise to stick to a cap in the 22-47uF range. Low leakage is a very important parameter to optimize here, as well as any other dielectric losses. In practice, very little signal voltage will develop across these caps, so the nonlinearities of aluminum electrolytics should not be a problem if you use a fresh, high quality capacitor. Since the SX202 is an older unit, a few of your input caps are probably starting to leak anyway, and need to be replaced.
There is a set of coupling capacitors after the output buffer amplifiers that can be jumpered if the output amplifier and interstage coupling mods are done. They are 100uF 35V polarized electrolytics located near the output jacks. The output offset of the modified preamp should be very low, less than a millivolt, so unless you have special requirements, these caps can be removed and jumpered. See the page on for details on these mods.
There are also some 4.7uF non-polar coupling caps after the polarity switch and pad, and these too can be jumpered if you don't mind hearing ticks or pops when the pad or polarity switches are used, which is hopefully not while you're recording! I decided to remove them just so I would not have another set of electrolytic caps that would need to be replaced over time.