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Scott Dorsey Scott Dorsey is offline
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Default Questions About the Event TR5 Schematic

In article , Paul wrote:
https://www.gearslutz.com/board/atta..._schematic.pdf

Ok first off, the TR5 is similar to the TR8 on the front end, with
the TL072 Opamp configured as an inverting, unity-gain buffer amp.

So it's normal to NOT see any signal on the input differential pins 2
and 3, right? I remember reading about the virtual ground on the input
pins of this topology.


If it's being driven by a transformer, you will see signal between them but
not necessarily signal between one of them and ground. Because the signal is
floating and has no ground reference.

If it's being driven by a modern differential output, you will see signal
on them because both sides are being driven with respect to ground.

If it's being driven by an unbalanced output or an impedance balanced output,
you'll see signal on only one of them.

Secondly, on all these models, the so-called "power" switch only
turns on the LED, and turns off the mute on the two power amps,
which means the rail voltages are ALWAYS ON the Opamp and the final
amp, no matter the state of the switch, as long as the 3 prong AC
cord is plugged into the unit. This means the leakage currents in
the ICs are always there, which would explain why the back plates
of these units stayed warm, even when I turned them "Off."

Is this what they typically do with these smaller reference speakers
to maybe save money for the bean counters? Why not put a switch
with more poles, so you can turn the rail voltages off too?


It saves money, and it also means "instant on" operation so that you just
touch the switch and there is the signal. This allows people to be able to
use the power switch as a mute button too.

In a perfect world you'd have a mute button like that AND a big switch on
the primary of the power transformer. You might also have some filtering
and input protection on the primary side of the transformer too. But you
will notice that there is a price difference between the Event and the Tannoy.
It has to come from somewhere, and I'd rather them cheap out on stuff like
this than on stuff that will affect the sound.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."