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Old June 15th 21, 07:25 PM posted to uk.d-i-y
Fredxx[_4_] Fredxx[_4_] is offline
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First recorded activity by DIYBanter: Dec 2020
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Default An electronic question.

On 15/06/2021 10:35, Peter Able wrote:
On 15/06/2021 00:17, Dave Plowman (News) wrote:
Shame you can't point us to the circuits.* Even with your extra notes,
above, there are still many questions arising - not least if your notes
are incorrect. (It does happen!)


Most Op Amps applications are inherently PSU-ripple insensitive.


They are a design from Elliot Sound Products. But the published schematic
doesn't show the supply rail side of the design. You have to buy the PCB
to see it.


Assuming that Fredxx has the right link, I think that you should take it
with a little pinch of salt.* An article originated 2000, referring to a
50+ year old Op Amp design (great advance though it was) is the first
hint.


I'm struggling to see this phrase. A word search finds 3 'year's as part
of 2 'many years" and one "over the years". A search of '50' finds 4,
none of which pertain to time.

FAOD the article was revamped in 2021. Perhaps they frequent this
newsgroup and updated it in the past day or so? Rod? No, he claims to be
a chemist.

Concerns about supply impedance at audio frequencies is another.


Many op-amps are effective Class B outputs, where pulses in current
occur when the output is changing.

If the guy was writing about designing with Dynamic Memory, then he'd be
closer to the mark.


DRAM is relatively simple to decouple. There are models that predict
voltage dips and resonant behaviour for multiple decoupling capacitors
on power pins with multiple value.

A bit OTT for audio.


The design voltage ripply for DRAMS would be somewhat higher than levels
preferred for audio.

Incidentally, you attack power supply noise at the power supply.* I
wonder if the last components in your proposed PSU are - electrolytic
and / or other capacitors across the outputs.


What outputs? I would hope regulator outputs. It's normal to use a mix
of types, though high value ceramic is sometimes used alone.

At least he isn't trying to argue that no semiconductor device will beat
a 12AX7 ;-}


That would be difficult to argue. I note on some equipment the valve is
there for pure show, and while the heater is glowing all they are
producing is heat.