The Regulated 25 W Power Amplifier

We noted early that the power supply had a significant effect on the sound.  We decided to implement regulated power supplies for the amplifier.  I'm not quite sure about when we did this, but it might have been sometime in 76, possible 77.  We did it straightforward, no switching, no nonsense, only linear regulators.  Hot ?   Yes, indeed !!!

I've had some trouble locating the schematics for the regulators, but I believe I've found them.  It might be that the ones shown here are prelimenary schematics, but the design never made it into production, so I'm not quite sure if there ever existed any other.

There were only made a couple of these amplifiers, and one of these was returned to me for service a couple of years ago.  Sadly, it was now beyond repair :-(

The amplifier have two set of supplies, one for the prestages, and one for the output stages, so two sets of regulators was needed..

Note the Q27 emitter, it should be coupled to the unregulated prestage power supply.   Q27 acts as a current generator and needs some voltage space.  Note also that there are no current limiters, so if the regulated output was shorted to gnd, blue smoke was the result !

The transistors are listed with only numbers. 139/140/203/204 are BD, and 413 are BC.

All BD transistors was heatsinked.  In fact, they were mounted onto the bottom plate of the amplifier !