Audio… (Amps, THD, channel separation) with analog equipment (scopes, etc.)

[Coordonnée_chromatique]

10dB of headroom for today's musical peaks weird comment by a previous poster "10db headroom set by amplifier gain"

Thanks i've got my answer, i'm really happy with the clarification.
Sorry but you are all hard to follow when you speak to others EE

[Alex Nikitin]

2) New capacitors need at the very least 24h under power before you could listen to the amplifier, some caps need a week or more. Nothing esoteric, just forming the isolation layer, with measurable changes. 

Do you mean measurable changes that you can observe (measure, with instruments) during amplifier operation or measurable changes if you had the capacitor isolated and were testing with an LCR meter or similar?  I'd be very suprised if you could tell the difference between a capacitor that has been "formed" for 1 minute vs 72 hours in either case, but causing gross changes in amplifier operation seems very unlikely.

Either is possible, the second is obviously much simpler. A good indication of the capacitor changes with time after a DC voltage applied to a capacitor freshly from storage is the "leakage current" which would decrease steadily in time for most capacitors (at a constant temperature).

On the need to "run-in" an amplifier after replacing capacitors (especially power supply ones) I speak from personal experience * . That requirement also makes it difficult if not impossible to do a quick comparison when swapping various capacitors in the same circuit.

Cheers

Alex

* - I did design Hi-Fi amplifiers professionally for many years and was heavily involved in production and quality control, including listening tests. So I had many opportunities to compare a fresh from the assembly line amplifier with a well run-in unit of the same model. You have to be completely deaf not to hear the difference a 24h run-in makes. At that company we ended up running every amp for 48 hours at 1/4 output power before shipping (which incidentally helped also to catch occasional quality problems).

[bdunham7]

Either is possible, the second is obviously much simpler. A good indication of the capacitor changes with time after a DC voltage applied to a capacitor freshly from storage is the "leakage current" which would decrease steadily in time for most capacitors (at a constant temperature).

In order to cause a measurable difference in the output of the amplifer there would have to be some observable difference in the power supply rail voltage...or something.  How is the leakage current going from 5mA to 5µA going to affect the power rail voltages?  I'm asking how I could observe this with test instruments, not whether you or I can hear the difference.

[Alex Nikitin]

The “leakage current” is only an indicator of changes, not the reason for change in the sound*. In a common “traditional” power supply (iron core transformer, split secondary winding, rectifier and a pair of reservoir capacitors) the dynamic of what is happening when it is used with an audio amplifier, especially class AB/B, is quite complicated and every component can affect the sound. A possible approximation would be a diode mixer producing a complex interference pattern by mixing the pulsed mains frequency current with a distorted amplified signal current and all that goes through reservoir capacitors (which are not completely linear and nonlinearity changes in time during run-in. The simplest way to observe the difference is to look at the intermodulation products for an amplified multi tonal signal.

Cheers

Alex

* - however it is a useful parameter as the speed of the “leakage current “ changes is a good indicator of how fast a particular capacitor could settle .