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).
Any one have a schematic that they may scan for me. It seems that the
tactile switches drive a row of 8 transistors that probably do the
switching part...

would appreciated any help.

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

nicolas

In article ,
nicolas wrote:
It seems that the
tactile switches drive a row of 8 transistors that probably do the
switching part...

IIRC, they're CMOS switches. And IIRC again were replaced with a better
type at some stage in the amp's production.

--
*When companies ship Styrofoam, what do they pack it in? *

Dave Plowman London SW 12
RIP Acorn

In article ,
nicolas wrote:
It seems that the
tactile switches drive a row of 8 transistors that probably do the
switching part...

IIRC, they're CMOS switches. And IIRC again were replaced with a better
type at some stage in the amp's production.

--
*When companies ship Styrofoam, what do they pack it in? *

Dave Plowman London SW 12
RIP Acorn

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


Hi Nicolas

Lucky inheritance.

From recent experience (although these things change!) Quad themselves will
offer good advice either by e-mail or by 'phone and there first tack doesn't
seem to be "send us a blank cheque and we'll fix it" Might even send you a
copy of the relevant circuit?

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

Sound is OK - a wee bit noisy compared to recent designs but a v. good phono
stage if my memory is intact. Not sure about the tweekability - in my
experience it almost always results in a worse sound than the original.

Have fun with it

David

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


Hi Nicolas

Lucky inheritance.

From recent experience (although these things change!) Quad themselves will
offer good advice either by e-mail or by 'phone and there first tack doesn't
seem to be "send us a blank cheque and we'll fix it" Might even send you a
copy of the relevant circuit?

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

Sound is OK - a wee bit noisy compared to recent designs but a v. good phono
stage if my memory is intact. Not sure about the tweekability - in my
experience it almost always results in a worse sound than the original.

Have fun with it

David

In message , nicolas
writes
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).
Any one have a schematic that they may scan for me. It seems that the
tactile switches drive a row of 8 transistors that probably do the
switching part...

would appreciated any help.

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

nicolas


I replaced those with OPA604s in my 34. It lowered the noise level but
that's about all.

I have the service manual for the original DIN socket version. I don't
have a scanner but my brother has one. I could scan the schematic in a
weeks time or so for you.
--
Chris Morriss

In message , nicolas
writes
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).
Any one have a schematic that they may scan for me. It seems that the
tactile switches drive a row of 8 transistors that probably do the
switching part...

would appreciated any help.

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

nicolas


I replaced those with OPA604s in my 34. It lowered the noise level but
that's about all.

I have the service manual for the original DIN socket version. I don't
have a scanner but my brother has one. I could scan the schematic in a
weeks time or so for you.
--
Chris Morriss

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

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

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

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Jim Lesurf wrote:



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.
Thanx,
I'll check this....

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.
Thanx for the reply,
I tested the transistors and they seem ok, and yes I think they are
drivers for the leds. I will next replace the 4066, as I see thats next
in line. As for "some other logic" controlling the inputs, I am at a
loss here......

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.)
Thanx, a schematic would be great. I found a 44 schematic on the web,
and trying to cross reference that to get an idea as how this thing
works, but it's a pain....I dont even know how similar they are...

I can tell you the serial number tomorrow...

thanx again..

regards,
nicolas


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