In article ,
Mike Coatham wrote:

"Jonathan Ives" wrote in message
m...
Hi,


has anyone modified either the Aux (100mv) or CD/Aux (300mv) input
modules on a CD input for better results with highish outputs from
CD/DVD ?

I don't have a low output radio and so replaced the 1M shunt with
470K, but still not too much control. Before dropping to 100K or even
47K I thought I'd see if anyone has found the best balance. I also
noticed that the potential divider on the TL072 output on the aux and
CD/Aux are different ? Anyone experimented. I have 2 CD players and a
DVD player, but there output levels appear to differ considerably.

BTW I *know* the current religon is to replacxe the OpAmps, but I'm
sticking with the originals as they sound fine to me, just want a bit
more control on volume.

First, apologies Jonathan for not having replied as yet to your email.
Temporary shortage of 'round tuits'. :-)

Yes, I have converted an early Radio module to the CD module. I had a
genuine CD/Aux module from Quad and just changed the older module components
to suit. The component changes a
Reduce R200 & R201 from 1M to 470K (you've done this already).
Reduce R202 & R203 from 2K2 to 1K5
Reduce R204 & R205 from 3K3 to 820R

The following comments may be useful. however note that I don't have a 44,
just a couple of 34's that I have modified, so what I say is based upon
modding the 34's and just looking at the service data for the 44.

You can adjust the gain/overload in various ways. However with the circuit
diagrams I have there is one distinction between the 'radio' and 'aux'
cards. The 'radio' ones don't have an input series resistor, just an input
d.c. block cap. If you change the input shunt resistor on the boards with
no input series resistor you will alter the LF response, but unless the
signal source has a high impedance you won't change the level very much.

You can adjust the gain and overload of the boards by changing the feedback
resistor pair's ratio. However the scope for this is limited as the amp is
non-inverting, so you can only wind the gain down to unity.

To get a significant change in gain/overload I tend to prefer to alter the
input resistor pair. Given that most sources don't have much d.c. output I
am personally quite happy with inputs that don't have a series resistor to
take out the series cap and use the holes for a new resistor. Given this,
you can drop the gain by as much as you like. I'd tend to keep the sum of
the chosen resistors around 20k as most sources will be perfectly happy
with this.

I agree with you about the op-amps. Despite what may be the fashionable
view, the TL's seem fine to me, and I haven't bothered to change them. The
34's sound fine to me, so I'd guess much the same will be the case with the
44.

I doubt that in practice you will have an overload clipping problem.
However I certainly found that the factory sensitivies for the 34's are
such that I'd end up with the volume control down near minimum where the
detent steps are awkwardly large. Hence I dropped the gain a fair bit to be
able to use the gain around the '10' mark. However to do this I also
altered the output attenuation resistors.

When changing input resistor values where there is a cap in series I'd
recommend also checking the effect of the RC on the LF response. Otherwise
you may be adding an unintended LF filter. :-)

FWIW I do tend to remove the input series caps and replace them with a
resistor or a link as I'm fairly sure there is no significant input d.c.
However for obvious reasons I'd recommend you only do this if you are sure
this is OK for the sources you have.

Slainte,

Jim

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