In article , nicolas
wrote:
Hi,

I inherited a Quad 34 pre that weirds out now and then. The preamp comes
on, with the default source selected. Either by itself, or when
selecting another source, all the selector leds light up dimly, and the
sources are lost (pre does not work).

if this is intermittent, then I'd suspect that there is an unreliable power
or reference level connection. Possibly to the board at the front of the
set that holds the switches, etc.

The actual signal switching is done using 4066 CMOS switches (at least in
issues 1 - 3 of the amp). However some other logic is used to control this
and (when working correctly) ensure only one non-tape input can be selected
at any time. That would probably be the failure point as the LEDs are also
driven from this. The transistors here are simply to give enough boot to
light the LEDs, I think.

If no-one else has a diagram to hand, ask again and I'll see if I can
produce a scan. Do you know what issue of board you have? (Or can say the
serial number.)

BTW, does this thing sound ok? I am a bit put off by all the tl071
opamps that populate this thing. Aby recommended mods?

I find the 071's work fine and would not personally change them.
Replacement with a different IC might lead to other problems. However I do
change some other components to alter the action of the 'tone controls' a
little. You can also easily change which input is selected by default by
moving a capacitor. :-)

Slainte,

Jim

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