Questions for the student No. 141
 

Peter Wieck wrote:
On Nov 7, 4:54 pm, Andre Jute wrote:
A STAX 252A amp, same as the 2050 sold in anglo markets, has parallel-
connected input ports, called "through ports". With both sets of
inputs connected, one to a CD player, one to a computer output, the
sound is muted, dulled. With the computer leads pulled, the sound is
louder and brighter.

Is this report what we would expect? What is the key mechanism at work
here? Suggest some ballpark values.

Newbies especially welcome.

Andre Jute
Invigilator

So, you tried this by accident, got results that are utterly
predictable as no competent design would permit this to happen. That
second "port" is to drive a speaker amp as the amp you describe is for
headphones.

What are you, some kind of idiot that would attempt to look "smart" by
posing a stupid question?

He usually asks these questions through West so as not to appear stupid
himself.
His next question will be how to put the magic smoke back in after doing
the same with power amps.

The best answer is a switch box.
Another method would be to put a 10k resistor in each cable; then if both
sources are powered up, they would see a 20k load and the amp would see
aproximately a 5k source resistance. With only one source powered,
results are unpredictable.

--
Eiron.

Questions for the student No. 141
 

Andre Jute wrote:
A STAX 252A amp, same as the 2050 sold in anglo markets, has parallel-
connected input ports, called "through ports". With both sets of
inputs connected, one to a CD player, one to a computer output, the
sound is muted, dulled. With the computer leads pulled, the sound is
louder and brighter.

Is this report what we would expect? What is the key mechanism at work
here? Suggest some ballpark values.


"This is left as an exercise for the student" :-)

For more fun, consider when one of the sources isn't even powered up.

The typical op-amp output stage has ESD protection diodes connected to
the power rails. So anything exceeding about 0.7V above or below the
respective positive or negative supplies will get clamped. And from 0.4
to 0.7 it's gonna be rather nonlinear. So it's still gonna sound really
bad...

Questions for the student No. 141
 

E

You must have just discovered the word "PORT" it seems.

The word 'port' is only used by people who haven't a clue what it really is and
what to really call it.


No, it's used by people who prefer port to vermouth... :-)

Questions for the student No. 141
 

Another method would be to put a 10k resistor in each cable; then if both
sources are powered up, they would see a 20k load and the amp would see
aproximately a 5k source resistance. With only one source powered,
results are unpredictable.


I've done that back in my distant past...

Works fine if both sources are powered up, and one outputting silence,
but if one source is not powered up, the ESD diodes in its output op-amp
will start to conduct at above and below 0.7V (as the supplies are at
zero volts), and that will make for horrid non-linear clipping or sorts.

Questions for the student No. 141
 

On 8 nov, 01:48, Andre Jute wrote:
"Where is that wonderful Andre Jute? The world just doesn't rotate without him...'" -- John
Mayberry, Emmaco

"Apprenez que tout flatteur Vit aux dépens de celui qui l'écoute" Jean
de La Fontaine.

Questions for the student No. 141
 

On Nov 8, 8:05 pm, robert casey wrote:
Eeyore wrote:

You must have just discovered the word "PORT" it seems.

The word 'port' is only used by people who haven't a clue what it really is and
what to really call it.

No, it's used by people who prefer port to vermouth... :-)

And by the gin-and-pink drinkers too, as in POSH -- port out,
starboard home...

....out being India, home being England, and the side of the ship being
important because it will be in the shade.

Andre Jute

Questions for the student No. 141
 

Andre Jute wrote:
On Nov 8, 8:05 pm, robert casey wrote:
Eeyore wrote:

You must have just discovered the word "PORT" it seems.
The word 'port' is only used by people who haven't a clue what it really is and
what to really call it.
No, it's used by people who prefer port to vermouth... :-)

And by the gin-and-pink drinkers too, as in POSH -- port out,
starboard home...

...out being India, home being England, and the side of the ship being
important because it will be in the shade.

False etymology.
And before the opening of the Suez Canal it would have been SOPH.

--
Eiron.