convert Quad44 radio input to CD input - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 20th September 2004, 05:11 PM   #1
jives11 is offline jives11  Europe
diyAudio Member
 
jives11's Avatar
 
Join Date: Mar 2004
Location: Hampshire
Default convert Quad44 radio input to CD input

Greetings. My Quad 44 has a radio module which appears to be very similar to the Aux module, though much more sensitive, based on the schematic at http://iquebec.ifrance.com/quadfranc...schemas44.html

Q. By changing the resistors before the opamp I should be able to change the Radio input into a useful additional CD/DVD player input.

Anyone done this or can suggest optimum values for the potential dividers, I know some Aux inputs can be overloaded by CD-level output.

many thanks
  Reply With Quote
Old 20th September 2004, 09:37 PM   #2
diyAudio Member
 
Join Date: Jun 2004
Location: Knoxville
If the input device is an op-amp, then the impeadence is high. Just make a voltage divider with two resistors that of which both in series equals the output impeadence of the CD player. Probably about 2KOhms or so.
  Reply With Quote
Old 20th September 2004, 09:52 PM   #3
Steven is offline Steven  Netherlands
diyAudio Member
 
Steven's Avatar
 
Join Date: Oct 2003
Location: The Netherlands
Outputs of CD players can have a very low output impedance, often just 100 Ohm. Loading with an equal value resistor to divide the output voltage by 2 (-6dB) is not a good option, because the CD output is forced to deliver a lot of current.

If I look at the schematic of the Quad 44 aux input, it has a series resistor of 390k (R600/601) and a shunt resistor of 100k (R602/603), so it already has an input voltage divider. CD players often have an output voltage that is 6..10dB more than tuners. So if you change R602/603 (or the equivalent in your tuner input module) from 100k to 47k or 33k, you get a nice CD input. This will have a negligible influence on the low cut off corner frequency. That frequency is mainly determined by the 390k resistor and the 100n input capacitor.

Steven
__________________
The Analog Art shows no sign of yielding to the Dodo's fate. The emergence and maturation of monolithic processing finesse has perhaps lagged a bit behind the growth of the Binary Business. But whereas digital precision is forever bounded by bits, there is no limit excepting Universal Hiss to the ultimate accuracy and functional variety of simple analog circuits. - Barry Gilbert, 1973
  Reply With Quote
Old 20th September 2004, 10:09 PM   #4
diyAudio Member
 
Join Date: Aug 2003
Location: Prague,Czech Republic
Steven is correct. Change also this bloody TL's .
  Reply With Quote
Old 20th September 2004, 10:17 PM   #5
diyAudio Member
 
Join Date: Mar 2001
Location: Brazil
Quote:
Originally posted by Steven
If I look at the schematic of the Quad 44 aux input, it has a series resistor of 390k (R600/601) and a shunt resistor of 100k (R602/603), so it already has an input voltage divider. CD players often have an output voltage that is 6..10dB more than tuners. So if you change R602/603 (or the equivalent in your tuner input module) from 100k to 47k or 33k, you get a nice CD input. This will have a negligible influence on the low cut off corner frequency. That frequency is mainly determined by the 390k resistor and the 100n input capacitor.
IMO both the resistor and the capacitor should be wire bypassed and leave just the 100K shunt.

The TLO71 is working as a buffer, with no amplification, and every CD player already has an output cap. The 2 volt CDP standard output should be fine for the IC and for the +/-15v supply.


Carlos
  Reply With Quote
Old 20th September 2004, 10:19 PM   #6
diyAudio Member
 
Join Date: Mar 2001
Location: Brazil
Quote:
Originally posted by Upupa Epops
Change also this bloody TL's .

Indeed that might be a good move. Being singles you can use better chips, like OPA627 or similar.



Carlos
  Reply With Quote
Old 26th September 2004, 09:08 AM   #7
diyAudio Member
 
Jan Dupont's Avatar
 
Join Date: Apr 2003
Location: Copenhagen, Denmark
Send a message via MSN to Jan Dupont
I have modified my QUAD 34 some time ago.
One of the things done was removing (shorting) all DC blocking caps in the signal path, and changing orther caps to new and better types.....
The result: The was expanded to go from DC to app. 300.000 Hz +/- 0.5 dB, and a all new clear and dynamic sound
__________________
Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com
  Reply With Quote
Old 26th September 2004, 12:05 PM   #8
Zombie is offline Zombie  Sweden
diyAudio Member
 
Join Date: Feb 2003
Location: At home
Rip out C36/37 and C48/54 and put a wire from the front leg of the first to the back leg of the other performs a little miracle.

I am considering putting a switch on the back for bypassing the tone controls and/or to find better caps (14 of them) for them...

If you do the same, let me know what you think...
  Reply With Quote
Old 29th September 2004, 09:05 PM   #9
jives11 is offline jives11  Europe
diyAudio Member
 
jives11's Avatar
 
Join Date: Mar 2004
Location: Hampshire
well I took out the CD/Aux board to see what it looked like. This is a 300mv/500K later model which is explicitly titled CD/Aux.

unlike the AUx circuit on the schematic there is no 390K R600 resistor at all. R602 (the shunt) is 470K.

OK,


however the feedback resistors are slightly different values also (based on the colour codes)

R604 on the output from the Buffer is 1K5 rather than 2K2 (R604). R606 from the feedback to ground is 820 Ohm rather than 3K3.

I understand the change in the shunt but I wonder why Quad changed the feedback arrangement ? Is it becuase they moved from 2 single TL071 to a single dual TL072 ?
  Reply With Quote
Old 30th September 2004, 07:33 PM   #10
Steven is offline Steven  Netherlands
diyAudio Member
 
Steven's Avatar
 
Join Date: Oct 2003
Location: The Netherlands
Hi jives11,

Appearantly there was no need anymore to have the voltage divider at the input, maybe the level diagram for the whole unit has been changed. This had nothing to do with a change from 2x TL071 to TL072. That is probably just a price or availability issue.

The change of the output resistor values didn't do anything with the gain of that stage. Gain of the opamp is still unity. Don't get confused because it looks like feedback resistors to determine the gain. They are not. It is just a clipper! The ouput is taken from the voltage divider R604/R606 and not from the opamp output. Because of feedback the output impedance of that stage is still close to zero. Gain is one because the output of the stage is directly going to the inverting input of the opamp. These resistors are used to fix the maximum output voltage of the stage. While the opamp itself may clip at around 13V peak (for 15V supply), the maximum output is 820/(820+1500)*13V = 4.6V peak. I haven't looked at the rest of the circuit but this has probably been done to protect some CMOS switches that are used for source selection or tone control against too high input voltages. Of course this is a "dirty" clipper, since the opamp may be driven very hard into saturation with subsequent sticking to the supply lines. Well, it is allowed if you are quite sure that the input voltage will never exceed 4.6V peak or approx 3Vrms.

Steven
__________________
The Analog Art shows no sign of yielding to the Dodo's fate. The emergence and maturation of monolithic processing finesse has perhaps lagged a bit behind the growth of the Binary Business. But whereas digital precision is forever bounded by bits, there is no limit excepting Universal Hiss to the ultimate accuracy and functional variety of simple analog circuits. - Barry Gilbert, 1973
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Convert 110v to 230v input ? istari knight Digital Line Level 6 1st January 2009 07:41 PM
current bias j-fet input 2sk170 ,2sj74 at input stage YUTK Solid State 11 2nd June 2005 03:34 AM
Want to convert amplifier output to input level rkc7 Everything Else 1 16th May 2004 10:19 AM
Transformer at input of SOZ to convert unbalanced->balanced? psarin Pass Labs 29 29th December 2003 05:13 AM
How to convert Unbalance -> Balance Input ? Minh Solid State 21 19th September 2002 11:09 AM


New To Site? Need Help?

All times are GMT. The time now is 09:07 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2