RCA 1972 Basic amplifier MODS

[jaycee]

This wasn't a particularly heavy duty PA amp by the looks. It was also designed to run from a car battery, so the power supply was 13.8V and the speaker connected via a transformer (with 8 ohm and 100V taps), and a feedback winding! Rather odd... I'd have thought it cheaper to use an SMPS than an output transformer!

Anyway, 30W should be adequate for me. I have a 2xLM3886 based amp which is on 25V rails, and that produces plenty of sound The only reason Im building this, is because I want to build a discrete amp

[jaycee]

I might have a better case candidate now. I got a Technics SU-Z55 from freecycle. The original owner said it wouldn't power on. Well, it powered on but the right channel was heavily distorted. After a poke about and investigating a quite warm 2SD592A - no sound at all

[anatech]

Hi jaycee,
Wow, I didn't realize that 60 W PA amp .... wasn't.

Still, I imagine you would be doing no worse than most of the commercial product out there. I don't read you as a head banger either.

Allow me one comment though. Joy may be found with systems around 150 wpc (+3 dB headroom also) and a pair of large speakers. This is an occasional thing, but satisfying. Puts a grin on one's face when the music is up to the job. I'll admit that most times, a 30 ~ 50 wpc system would do very well.

I would suggest that you also build a SymAsym at some point. That is one very good sounding little amplifier. I used MJW0281A and MJW0302A for outputs and Japanese transistors for everything else. My bias current for lowest THD ended up lower than most. There are several variants of that basic circuit now, my next build will use J-Fets for the diff pair. It will work well anywhere from 25 to 35 volt supplies. I would recommend tending towards the 35 V end as that was what it was really designed for.

Check out the threads for this amplifier if you have time. Poke around past the middle and closer to the ends.

-Chris