CD740 47uf in signal path!? - diyAudio
Go Back   Home > Forums > Source & Line > Digital Source
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Digital Source Digital Players and Recorders: CD , SACD , Tape, Memory Card, etc.

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
Thread Tools Search this Thread
Old 27th October 2012, 04:54 PM   #1
wheijke is offline wheijke  Netherlands
diyAudio Member
Join Date: Oct 2005
Default CD740 47uf in signal path!?

Im modding a CD740 and it sounds a lot better after work around the DAC and PS and removing muting transistors, really like this player!
Only it seems different from other Philips players beacuse of the 47uF / 25v in the signal path right after the TDA1549 dac and before the opamp.
So my question, can I remove it, or what shall i do to it?

I've included the piece of the service manual (CD751 which is the same) and marked the spots.

Attached Images
File Type: jpg cd740.jpg (41.2 KB, 71 views)
__________________ and my websites dedicated to Cassette Decks!
  Reply With Quote
Old 27th October 2012, 05:26 PM   #2
diyAudio Member
Frank Berry's Avatar
Join Date: Sep 2003
Location: Midland, Michigan
I wouldn't remove the capacitors. It appears that the DAC is powered by a + supply only. If that is the case, the output of the DAC is sitting at 1/2 the + voltage.
The capacitors are necessary to block the d.c. from the opamps.
Enjoy the player.
  Reply With Quote
Old 27th October 2012, 05:29 PM   #3
wheijke is offline wheijke  Netherlands
diyAudio Member
Join Date: Oct 2005
Yes only + voltage to the dac, thanks for the explanation!
__________________ and my websites dedicated to Cassette Decks!
  Reply With Quote
Old 27th October 2012, 07:23 PM   #4
diyAudio Member
Join Date: Oct 2006
Actually, you could eliminate the blocking caps if you "bias" the grounded input of each opamp channel to the same dc level as the dac output. You just need to add a trimpot, of I'd say 10K-100K to each channel, connecting CW pot terminal to 5V line, CCW pin to ground, and wiper pin to pin 3 of one channel, and other pot's wiper to pin 5. I would think you should also add a cap to ground from each of those pins, such as the 47u you will be removing from signal path. Once installed, trim each pot to get 0volts on each opamp channel's output pin, which then means you can eliminate the 4.7uf caps on those lines. Only potential problem is the question of whether or not the 2.5VDC offset of the opamp's input stage, versus the +/-10V supply, will cause the input stage to run out of headroom on the positive end of the waveform, but I don't think this can happen, as the peak-to-peak amplitude of a 2VRMS signal is around 6V, and you should have 7.5V positive peak headroom available.
  Reply With Quote


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
Signal Path Components patfont Analog Line Level 15 17th September 2011 01:07 PM
Determine the signal path ? lordvader Solid State 12 20th November 2006 09:25 AM
How does this sound for a signal path? Fryguy Digital Source 0 25th May 2004 08:15 PM
Help identifying the signal path Eric Solid State 7 24th August 2001 08:10 AM

New To Site? Need Help?

All times are GMT. The time now is 10:20 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2