About that heat our friend have measured..if not a assemble trouble, then we can fix
producing a resistor replacement as explained below:
People that feel these 2 small vertical heatsinks too much hot can reduce VAS current in order to reduce heat there.... i have simulated and i found the original schematic fine... with the modification you will have changes in performance, but not that huge.
The 22 ohms resistor that sets the CCS current can be increased to 47ohms in order to reduce current...then you will have these transistors mounted into vertical heatsinks (CCS to VAS and VAS transistor) less hot.
I found power there not that big...the left one is the CCS transistor, CCS to feed VAS (Voltage Amplifier Stage) and it is dissipating 1.65 watt.... the rigth side one is the VAS transistor, the second stage, the most active unit, following the buffer and the power there, dinamic power, will be around 1 watt....not that huge power and the small heatsinks should fit in most of the cases... exception is when people is using higher supply voltage... say... really higher voltage.
You can replace the 22 ohms resistor by a 27 ohms, 33 ohms, 39 ohms or 47 ohms.... i suggest you to go to 47 ohms because will really cool down in order to work fine with tiny vertical heatsinks... with this resistor replaced, the performance when using low impedance output loads will clip earlier.... some loss in power...not that huge, not that important.
Some high current, high voltage and high speed diodes installed into the output, in the power transistors, from colector to emitter, can be used too as we gonna face some back EMF there.... so, if you intend to push the amplifier hard, then search for high speed, high current diodes used to fly back purposes there...what model to use i cannot suggest you as i do not use them, so they are not familiar to me... search for high power amplifiers and copy the diode model to apply to yours....this is to play heavy metal, full power, distorted sound and connected to 2 ohms loads... an extra protection if you intend to operate your amplifier above the limits, entering distortion and draining huge ammounts of current and generating enormous output having a lot of back EMF in your output line.... normal civilized use will not need these diodes.
If you intend to use your amplifier under the dB competition of bass...then for sure you gonna need these diodes as you will operate in clipping mode and speaker will generate back EMF high voltage spikes that may destroy your output...diodes will "eat" these spikes helping you a lot.
These diodes usually are in the output, nearby the power transistors..from positive line to output line and another one to the negative line to the output line..... or from power transistor colector to emitter, one to each rail, one up and other down...both with arrows pointing up when schematic is draw standard, input at left, output at right side, positive is up and negative is down..this is standard position to draw and show and read schematics.
Enjoy your amplifier boys...sound is awesome and you will perceive that instantaneously.
regards,
Carlos