It is a very simple amplifier with Darlington obsolete outputs, if the offset is fine just enjoy it.
For that you will need at least an oscilloscope and a signal generator. Nothing fancy, But I would say, only if you are interested in servicing/evaluating gear. Otherwise just compare it with what you have access and have fun.
Is a starting point... he could look for crossover distortion, HF oscillations, etc etc and will be better than a multimeter, but I'm agree that if he needs more, he can go from a DAC+interface and REW, a QA-403, a Panasonic VP7725D to ASR aficionados favorite; AP gear.
AP gear is not cheap. Usually, companies buy that, not hobbyists who aren't wealthy. That means this chicken! Bedawk!
Terribly expensive I would say. I said it as a little bit of humor (unsuccessfully).
That is good enough comparison when everything seems OK, because only electrolytic capacitors were replaced and that approximately restores original distortion specifications of the manual. Measure AC/DC with the multimeter on amps for accurate sine wave comparison.
This is a widely accepted opinion, however wrong. It applies only to low order harmonic distortion, and the limit is rather about 2%. Talking about clipping and crossover distortion, the scope screen may show distortion as low as of 0.01% order. In a technical discussion, I would recommend to spread only facts based on deep personal experience and knowledge.
REW and a cheap interface then (and some resistors for a divider to drop speaker output level to something the interface can handle)
Good? Peerless!! And a mind-blowing up-grade.
Then HP became Agilent, which later became Keysight.Thanks for the input. Most measurement instruments mentioned are new to me. I cut my teeth on an HP VNA 8409 in a university lab in the 1980s:
View attachment 454215
And on HP and Techtronics TDRs (Time Domain Reflectometers).
Is capacitor degradation the only ageing mechanism to consider in audio amplifiers like the X-A2? In my old line of trade we struggled with parametric drift in RF transistors causing a shift in bias current. Anything like that for audio amplifiers?
/Martin
PS Before I left university we had up-graded to the then brand new 8510 VNA: https://hpmemoryproject.org/technics/bench/8510/bench_8510_home.htm Expensive? You bet!! HP stands for High Price
Not really, feedback tends to iron out such issues pretty well. You might find yourself with a blown-up power stage and output devices that have gone EOL years earlier one day. Last time at the repair café there was a dead Kenwood KA-770D which uses relatively low power 16A Sanken MT-200 case devices (2SC2921 and complementary)... good luck trying to find spares for those in this day and age.
Love the HP-150 PC!Thanks for the input. Most measurement instruments mentioned are new to me. I cut my teeth on an HP VNA 8409 in a university lab in the 1980s:
View attachment 454215
And on HP and Techtronics TDRs (Time Domain Reflectometers).
Is capacitor degradation the only ageing mechanism to consider in audio amplifiers like the X-A2? In my old line of trade we struggled with parametric drift in RF transistors causing a shift in bias current. Anything like that for audio amplifiers?
/Martin
PS Before I left university we had up-graded to the then brand new 8510 VNA: https://hpmemoryproject.org/technics/bench/8510/bench_8510_home.htm Expensive? You bet!! HP stands for High Price
Re-capping done.
What do you mean by reference? Specifications for THD are 0.7% at 6 ohms and 0.08% at 8 ohms nominal.
What I had in mind was that all testing has been relying on my highly calibrated ears and all they tell me is that the obvious issue (distortion) that made me start this project is 'gone'. But to know if I brought the amplifier up to 'new status' standards I would have to compare with an amplifier I know is of that status. (And do proper blind testing...)
That is what I thought, but you do not technically need listening testing here. Electronic test equipment was used to make the amp specifications. That amp is close to the absolute threshold of the ears.
