In 2017, I built this amplifier for my brother's audio system. It is a single common grounded collector amplifier based on RMX series of QSC.
Supplied with +/-80V, I added five pairs of transistors for output stage. It is very stable once the bias adjustment is set properly. The input opamp is very important to be good quality and check +/-15V rail supply to be as simetrical as possible. I wanted to keep the same subsonic filter to cut off frequencies under 30Hz and 50Hz.
The sound is very good however I was designing a PCB with smaller size. Thanks
Supplied with +/-80V, I added five pairs of transistors for output stage. It is very stable once the bias adjustment is set properly. The input opamp is very important to be good quality and check +/-15V rail supply to be as simetrical as possible. I wanted to keep the same subsonic filter to cut off frequencies under 30Hz and 50Hz.
The sound is very good however I was designing a PCB with smaller size. Thanks
Attachments
Yes.. the power supply has no GND reference.. for the first time I hear it: "a special transformer with low capacitance is required" well, I did not know it but I have supplied several amplifiers of this topology with any transformer and it works very ok.. but I will bear it in mind.
Sajti, I respect your opinion, but I love how it sounds; of course maybe it is not an extreme Hi Fi circuit but it works OK 😀
The “special transformer” requires separate windings for each channel. That is non-negotiable as the power supply can’t be shared. Inter winding capacitance is an issue, but all that does is degrade channel separation. Primary-secondary is usually good enough, but between secondaries it’s not. On PA amplifiers at that price point, it’s a don’t care. If you wanted the highest possible fidelity from the topology, build it dual mono with totally separate transformers.
Two Antek transformers is almost ALWAYS cheaper than a custom wind job. A surplus core (where you save the original primary) and wind both secondaries yourself can be cheaper, if you can easily source full 10 pound rolls of magnet wire. And are willing to put in the work necessary. Amplifiers that are one channel obviously have no issue with off the shelf trafos.
Two Antek transformers is almost ALWAYS cheaper than a custom wind job. A surplus core (where you save the original primary) and wind both secondaries yourself can be cheaper, if you can easily source full 10 pound rolls of magnet wire. And are willing to put in the work necessary. Amplifiers that are one channel obviously have no issue with off the shelf trafos.