QUAD 44 Aux/Radio input for CD/DVD ?
 

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.

QUAD 44 Aux/Radio input for CD/DVD ?
 

"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.
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

Mike

QUAD 44 Aux/Radio input for CD/DVD ?
 

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

--
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

QUAD 44 Aux/Radio input for CD/DVD ?
 

"Mike Coatham" wrote in message ...
"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.
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

Mike

Many thanks Mike,

Hmmm, maybe I got the 202/204 & 203/205 the wrong way round but I
tried this as this is the arrangement on the CD/Aux TL072 300mv/500K
input. I found I was getting very little volume range i.e it was too
lund at 4 on the Quad 44 dial. This was worse than I was getting on
the CD/Aux input which I have left alone

Maybe my CD player (ISOmagic DAC) or Sony DVD player sources are too
high ? I know some peak at 2.4v in order to sound "better" in an A-B
comparison in your average retailer. How much volume range do you have
using the Radio as a CD input ? I'm using the 1.5v outputs (as opposed
0.5 or 5v) into a Radford STA15 with very inefficient LS3/5a speakers.

QUAD 44 Aux/Radio input for CD/DVD ?
 

In article , Jonathan
Ives
wrote:
"Mike Coatham" wrote in message
...
"Jonathan Ives" wrote in message

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


Hmmm, maybe I got the 202/204 & 203/205 the wrong way round but I tried
this as this is the arrangement on the CD/Aux TL072 300mv/500K input. I
found I was getting very little volume range i.e it was too lund at 4 on
the Quad 44 dial. This was worse than I was getting on the CD/Aux input
which I have left alone

The 'radio' board I have the circuit for is M12511 - ISS1. This shows a
feeback pair of 2k2 and 3k3. The voltage gain of the actual op-amp stage is
therefore 5.5/3.3 = 1.66 (4.4 dB). If you changed the 2k2 to a 0 resistor
(wire link) and took out the 3k3 (open circuit) the voltage gain would fall
to 1.0 (0dB). For a non-inverting amp of this type this is the lowest gain
you can get from the op-amp stage.

Most of the steps on the 44's detent pot are 2dB apart. However below '7'
the steps rise and you start to lose the ability to set the loudness you
want with good precision. Hence you'd need to alter the gain overall of the
44 to get the same output from settings around '8' to '10' as you now get
from '4'.

Setting '9' corresponds to a volume pot attenuation of -26dB.

Setting '4' corresponds to a volume pot attenuation of -42dB

i.e. You probably need to reduce the total gain by about 14dB. About 10dB
more than you can expect to get by altering the feedback resistors.

I'd say that you best bet was a mix of:

1) altering the *input* resistors and perhaps caps, leaving the feedback
ones alone.

2) Altering the *output* resistors of the preamp.


So, for example, with 'radio' board M12511 ISS1 you could change C200/C202
into a couple of 22K resistors, and R200/R201 into a couple of 10K
resistors. These would drop the board gain by 10/32 = 0.31 (10dB).

The above would mean you'd have to ensure no d.c. input, but the board also
has a d.c. break cap on its output, so a small level of d.c. would not
matter. The input impedance would be 32K, but I doubt most sources would
care about this value.

Changing the input as above (i.e. method (1)) may mean you can then hear
some background noise. So (2) might be better if this is the case.


Maybe my CD player (ISOmagic DAC) or Sony DVD player sources are too
high ? I know some peak at 2.4v in order to sound "better" in an A-B
comparison in your average retailer.

2.4V is nominally only 1.5 dB bigger than 2.0V. Hence it would mean less
than one step on the 44's volume control even in its 2dB-per-step regions
above '9'.

How much volume range do you have using the Radio as a CD input ? I'm
using the 1.5v outputs (as opposed 0.5 or 5v) into a Radford STA15 with
very inefficient LS3/5a speakers.

Ah. Have you tried the 0.5V outputs? :-)

Using the 0.5V outputs instead of the 1.5V outputs would drop the level by
about 10dB. i.e mean you could use volume settings around '8' rather than
around '4'.

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