Audio Interconnect cable Performance - is Return Wire Diameter a Factor?

On 11/12/2020 11:29 pm, Peter Wieck wrote:
> The Dynaco PAT-5 biFet makes 15V @ 50MA +/- 5%

**Umm, not quite. The specs for the LF357 indicates significantly lower
numbers than that. At 25 degrees C:

* Maximum output Voltage (god, I forgot just how primitive that old
things was - zener regulation!?), with a +/- 15 Volt supply - 25 Volts
p-p = 8.8 Volts RMS (theoretically).
* Maximum output current @ 25 V p-p (dunno what the value of the output
series resistor is, as that will change the final figure somewhat) - +ve
20ma and (wait for it) -ve 5ma.

> There is an Aktika (sp?) pre-amp that makes 20V @ 50MA +/- 5%
> And there is a mod for the PAT-5 to get it to 42V @ 20MA +/- 5%
>
> The reasoning for those superficially absurd voltages is headroom. And that is a long, difficult, and very nearly futile discussion mostly based on revealed religion.

**Well, once the input Voltage limits of the power amp are exceeded,
it's all over red rover.

>
> And, that is AC voltage. Not DC - so those electrons are flying back and forth at whatever the audio frequency might be. Not departing for parts-unknown and in only one direction.

**Of course.


--
Trevor Wilson
www.rageaudio.com.au

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On Friday, December 11, 2020 at 10:19:54 AM UTC-5, Peter Wieck wrote:
> The Dynaco PAT-5 biFet makes 15V @ 50MA +/- 5%

How is that relevant to the domaine?

> There is an Aktika (sp?) pre-amp that makes 20V @ 50MA +/- 5%

How is that relevant to the domain?

> And there is a mod for the PAT-5 to get it to 42V @ 20MA +/- 5%

How is that relevant to the domain?

> The reasoning for those superficially absurd voltages is headroom.

And that reasoning is itself provably absurd.

> And that is a long, difficult, and very nearly futile discussion mostly
> based on revealed religion.

Sir, it is you spouting religion and absurdity.

Let's go, once again, to the issue of what follows the preamp: a power amp.
Since these preamp do NOT have balanced outputs, we can safely assume
that they are intended for power amps with unbalanced inputs.

And what is the input voltage for these amps required to drive them to
full rated power? Well, it ranges from 0.5V to 2.0V RMS.

So, REGARDLESS of the headroom of the preamp, what is the result of
driving a power amp whose input sensitivity is, say, 2.0V when driven by
20V?

(Subtle hint: the power amp will be driven FAR into clipping).

Can you guess what the result will be?

Do you need another hint?

Let's be generous and assume the amp is very conservatively spec'ed and can
put out TWICE its rated power (and let's, in fact, NOT deal with revealed religion,
like "headroom", let's deal with physicqal facts, like the MAXIMUM instantaneous
output power of an amp is limited by the unloaded rail voltage minus the voltage
drop of the output devices. That's it, regardless of which religion you buy into,
THAT is the limit. Doesn't matter HOW the power supply is design, doesn't matter
if the PS has bazillion microfarad caps in it: what's the maximum rail voltage?
THAT's what defines the maximum output power. Period.

Let's say we got ourselves a power amp nominally ratede at 200 watts continuous
into 8 ohms, that's 40 VRMS, meaning the nominal rail voltage is in the realm of
+-60V. Let's just pretend and say it's +-75V and ther are ginormous capacitors sitting
in it.

And lets say that an input voltage of 2.0V is required to get the amp to put out 200
watts continuous into 8 ohms. At that point, the amp is swinging +-56V peak.

And since our rails are limited, in our example above, to +-75 volts, putting ANY
more than 2.5V into the amp will result in clipping: that +-75 volts DEFINES
the headroom of the power amp under ALL conditions.

Now, stuff in your 20V from your magic preamp. That means the amp will be asked
to swing +-560V peak. And where is that +-560 volts supposed to come from?

Expain to me, now, how that 20V output voltage is in any way relevant to the
domain at hand?

Given the choice between YOUR revealed religion of "headroom" and "20V
preamps) and the like vs physical reality, what do you think my choice would
be?

Need a hint?

> And, that is AC voltage. Not DC - so those electrons are flying back and forth

No, they are NOT "flying back and forth": they are imperceptively jigging about
with a small net movement in one direction than another, with an average net
velocity measured in some small fraction of centimeters per hour.

Dick Pierce