My understanding is the first generation of transistors amps they were trying to make them sound like a tube amp. For some reason they changed that as time went on to a brighter cleaner sound. You can’t beat that warm tube sound, especially if listening fatigue is something you suffer from like I do. Great video. Thanks
At age 18 (now 71) I found that the power supply components have a huge bearing on the sound. A 6 W/Ch quasi complementary amplifier was brought back for repair the the shop where I worked. The power supply consisting of four diodes arranged as a bridge rectifier was faulty so I replaced the diodes with 1N4002s. A week later mum & dad and daughter called in to the shop, daughter was beaming and full of thanks for making her amplifier sound so much better, to this day I can't figure out why changing the rectifier diode could make such a difference. Since then I have built (not designed, I'm not that good) dozens of amplifiers and have always tried to make the PSU as stiff as possible so as to maintain a good transient response. Doing so usually means employing a mains transformer that's twice the rating of the amplifier's output and using a large amount of capacitance that's spread over several smaller value capacitors. Large value capacitors have a significant inductance because they consist of a rolled up sheet of aluminium and inductors resist change in current flow, connecting inductances in parallel reduces the overall value of the inductance. Also a 1 uF film capacitor wired in parallel immediately across the large capacitor's terminals will help remove the inductance and reduce noise. To this day when friends call and hear my stereo they often comment on how good my amplifiers sound :). Thanks for the video, i get it that an amplifier doesn't have to measure great so as to sound great.
The best thing about these low power units is that they are cheap. Build yourself a collection and then play around with some efficient speakers. I love testing various 10-20 wpc solid state amps with my Cornwalls.
I just restored one of these. New electrolytic caps and transistors and all voltages adjusted to spec. It sounds amazing driving a pair of vintage advents (also restored). I cannot believe these are 50+ years old amp. The one problem is the thump on start up and an even louder one on shut off. I understand that this is common in these units. Is there a way to alleviate this some? The woofer pumping is alarming to see.
There are ways to get around the "thump". One is to install a relay circuit to delay the speaker connection another is to "mute" the pre-amp and bring up bias slowly on the output transistors. If you compare schematics for the Kenwood KA-2000 and KA-2002a you will see what they changed to allow a softstart. I also noticed in my restoration work that upsizing the 1000uf speaker coupling capacitors makes the thump worse and setting the bias to a slightly lower value as measured across an emitter resistor (14mv to 10mv) lessens the thump. Maybe I should do a video.
Thanks for the suggestions. I did increase the output caps to 1500uf. I'll play around with that and the biasing and see if it helps. For now I am just leaving it on. They run remarkably cool even when playing!
I think this construction was developed by so famous brand and shpuld be used with original or "special design" for it speakers. . In past s market offered speakers were very different than today and surely that amplifier is now not matched with them In past was frierce competition. - not like today. with a low prices. .The capacitor 1000 uF could be best for such speaskers which apparently were much more effective than modern having much more max power. and poor lows. With effectiveness is directly conected sounding of each amplifier with loudness correction. - you cant't get the same. good but now I am afraid you will stick to modifications. which will exclude any amaze.
