The upshot is this...the Piccolo amp uses +/- DC supplies and no capacitors in the output signal path to filter out any DC which may be present...'DC coupled' or 'DC coupling' meaning, in general, a straight-wire path using no capacitors to block the flow of DC currents. Because Jim designed the Piccolo to be DC coupled at the output, the possibility exists that the output of the Piccolo may not be sitting at 0.000VDC, which is the ideal since we're interested in listening to audio frequencies and DC is kinda boring.
DC coupling is preferred in most cases, but it does mean that more care is needed in the design to ensure that the output is 'centered' with regard to DC. In the case of my own Piccolo, I had about 12mV (0.012V) of DC on one channel, and about 22mV (0.022V) of DC on the other, which I felt was excessive.
Whether this matters or not depends somewhat on what you're feeding the output of the Piccolo to. If the Piccolo is feeding a tube RIAA phono stage, it's no big deal. Similarly, if it is feeding a solid-state phono stage using bipolar transistors for its input stage, this is also not usually a problem, since bipolar transistor input stages nearly
always have an input capacitor to de-couple any possible DC that might try to flow to the cartridge.
DC coupled solid-state phono amplifiers which use FET's are another story (and most of my own RIAA phono stages are DC coupled FETs)...these type of FET RIAA phono stages are DC coupled directly to the cartridge, and if you put the Piccolo between the FET input phono stage and the cartridge (which is, of course, how it is intended to be used), then the DC present at the output of the Piccolo is presented directly to the gate of the FET at the input of your phono stage. This can and will affect the DC biasing of the first stage of your phono amplifier, and since the gate to source junction on the FET is essentially a diode, the DC can even forward-bias this diode with destructive results (but the DC present at the output of the Piccolo is a long way from doing anything like that...at least until you power it down*). Still, a fully-DC coupled FET-input phono stage is not such an unusual item, and that 20mV of DC coming from the Piccolo can easily be an issue. If it's possible to get rid if it, then doing so is a desirable thing.
To check the offset, just measure the DC with a DMM (set to read DC millivolts) at the output of the Piccolo (there should be no input to the Piccolo, BTW. I unplug the input cables and use RCA shorting plugs). Jim posted a solution (in the thread referred to above) which will reduce any DC offset at the output of the Piccolo, and I also showed my own solution (which is more of a PITA, but will eliminate any DC altogether).
*(As a side note to using the Piccolo with a DC coupled FET RIAA phono amplifier, I noted in my original thread that the Piccolo isn't terribly well-behaved at power-down time and the output likes to jump to nearly 600mV and sit there till the filter caps bleed off. If you're using the Piccolo with a FET phono stage, flip your input selector to something other than phono when you're ready to power it all down, as that 600mV is nearly enough to do some real damage.)
Dat's da story. Sorry you asked?
