I've owned at LEAST a dozen of these amps. I cycle them thru my system and sell'em to friends. A truly great little amp with the ability to drive low/complex impedance loads. You should hear a pair of them driving my electronicly bi-amped Apogee Stages & Duetta Signatures.
Anyway, the basic difference, besides minor face plate cosmetic differences, is that the 4a has a set of balanced inputs while the 4 does not. Pretty much end of story. There were some minor parts differences as the production line aged but I've found little if any sonic differences even between samples with large gaps in the serial numbers.
There is one tweak I can recommend though and that is to get the 4a and bypass the input selector switch & balanced inputs. Run it with just the single ended inputs. I have noticed a slightly more open sound (even over the 4) running it this way. The tweak is easy & reversible.
In general, avoid the balanced inputs as they have an input impedance that is just south of 1K ohm, which is a very difficult load for most pre-amps (certainly tubed ones).
Voltage gain is 26 DB and they actually work quite well into an Adcom Ace 515 line conditioner, most other conditioning flattens the amp dynamically (and this amp DOES boogie). A Wire World Aurora power cord is a nice upgrade as well.
Good Luck, you have a fine amp!!
Anyway, the basic difference, besides minor face plate cosmetic differences, is that the 4a has a set of balanced inputs while the 4 does not. Pretty much end of story. There were some minor parts differences as the production line aged but I've found little if any sonic differences even between samples with large gaps in the serial numbers.
There is one tweak I can recommend though and that is to get the 4a and bypass the input selector switch & balanced inputs. Run it with just the single ended inputs. I have noticed a slightly more open sound (even over the 4) running it this way. The tweak is easy & reversible.
In general, avoid the balanced inputs as they have an input impedance that is just south of 1K ohm, which is a very difficult load for most pre-amps (certainly tubed ones).
Voltage gain is 26 DB and they actually work quite well into an Adcom Ace 515 line conditioner, most other conditioning flattens the amp dynamically (and this amp DOES boogie). A Wire World Aurora power cord is a nice upgrade as well.
Good Luck, you have a fine amp!!