I've had many commercial amplifiers which were unstable on my bench. Some inexpensive, some expensive tweeter-cooking, high performance, ultra low distortion amplifiers from the past where hunting down the problems proved to be fruitless as the designs themselves were flawed. ie you had to slow them down to stop oscillations/instability or change output devices. Much time was spent scratching my head trying to work out exactly what the designers had in mind. Usually it was pressure to have better numbers on their brochure than their competition at the expense of ultimate stability.
It was the direct result of the specmanship games of the 70s and 80s, where bandwidths were pushed and THD numbers were the headline acts. Now we are in the same situation, with power outputs and THD specs (how many zeroes have we got today) as key selling points. Trouble is, they are quoting one without respect to the other- a clear violation of FTC amplifier rules (which incidentally are still in force) Feedback is wound right up again, compensation networks are numerous, an onboard PIC/uP monitors and controls everything, with tentacles into parts of the amplifier in order keep the thing stable. All talk of difficult/reactive loads is banished as it doesn't fit the core message, which is "trust us, we know what we are doing".
My old analogue oscillator sits on my bench as it has done for over 35 years. It's on all day until I turn off the power. Pretty much the first test on amplifiers and preamplifiers is feeding sines and squares through them at various frequencies to determine channel related imbalances/responses, low end coupling cap/feedback network issues, tone control functionality and high frequency stability/performance. Virtually every functional part of a typical integrated amplifier can be quickly and visually confirmed with just an analog oscillator and a 'scope. The sine/square switch is instant.
As Don mentioned, it's the vitriol that spews forth like a foul-smelling geyser when decades old established amplifier testing procedures are dismissed as being unimportant, that I do not like one bit. I'm not screwing pre-built off the shelf modules into a box, I'm chasing down mysteries with each and every item I restore/rebuild/repair. I do it because it's my passion, not to make money, as that's not really important to me.
Allowing commercially driven narratives and thought policing is not a good look. In fact, it serves to gradually and slowly poison the entire premise of ASR. In my opinion, there is already creeping evidence of it in the review threads.
Amir can't be bothered with extensive amplifier testing- that is quite clear. He sees little 'value' to the membership. Fair enough, he's only got so much time in retirement
, but that doesn't mean we can't test and characterize amplifiers for others to see and comment on, without being shouted down.
And just remember, this entire thread is posted in the DIY forum, not the Desperate Dealers forum for anyone who hadn't noticed.
