In the 1980’s Mitsubishi made a series of amplifiers that are somewhat unknown, however they are really standouts in the their class. The DA 30 is a plain looking 105w RMS per channel power amp. It is not till you open the case does the design reveal itself.
The amp is basically a dual mono design, with two transformers and separate power supply for each channel, and unlike others of this vintage (NAD, APT etc) this unit can only be operated in Stereo. The power supplies are completely independent, with 2 10kuf caps per channel. The input/voltage amp and bias sections have their own independent regulated power supply which is tapped off each transformer separately form the output stage power supply.
The front end of the amp uses a dual FET for the input stage (2SK109) which then feeds the voltage amp stage. There are two inputs marked AC and DC. The AC input has a cap (non polar) across the input whilst the DC input does not. There is a volume control on the back panel- though generally this is set and full open.
There are no capacitors in the audio path through out the whole amp. The main outputs are the well respected Sanken 2SC2837/2SA1186. There is an over power detection circuit and a protection circuit with independent relays for reach channel. The two front panel leds indicate power and protection status.
The other unique feature is the heatsinks which use a copper “heat pipe” coupled to a set of fins, which appears to do a very fine job of handling the thermal energy from the amp.
So having examined the amp, of course this looked like a great amp to upgrade! So all the electrolytic caps have been replaced with low impedance types, Nichicon PW and HE, as the are all associated with some form of power delivery. Where appropriate some values were increased, though the original design provided adequate capacity.
The outcome is a very good sounding amplifier, neutral and quiet and transparent- in fact so much so that I use one as my “reference” in the lab- connected to a modded APT pre amp and B&W speakers. The sound is simply whatever the music is delivering, the bass is tight the mids and highs neutral, with plenty of power for transients and excellent dynamics.
This amplifier is certainly underrated and deserves its place with the other stand outs form that period , the NAD 2200 and APT 1.