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Old 5th January 2010, 11:28 AM   #1
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Default Philips cd850 MKII Audio Circuit

Hi

i just started looking deeper at my Philips CD850 MKII.
In the Audio Circiut Schematic i came across transistors 7308/7309/7310.
What's the exact purpose of those circuits ?
In similar designs, like Marantz CD52 MKII, those can't be found.

have a look at the attached schematic.

thanks a lot
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File Type: png cd850mkII-audio-circuit.png (170.0 KB, 187 views)
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Old 5th January 2010, 02:28 PM   #2
UV101 is offline UV101  England
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They look like they could be part of the De emphasis circuit. They aren't really required on pretty much all recordings.

What are you/ have you done so far with this player? I had one from new until just over a year ago. Had a few bits done, clock caps etc. Also all the muting was removed and the DC blocking caps!!
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Old 5th January 2010, 02:43 PM   #3
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Regarding Emphasis; then the Marantz CD52 MKII does not have Emphasis circuit at all ?

Actually, i'm in the planning phase with the CD850 MKII.
i have bought it back in 1992.
First i will re-Cap the Power Supply and swap the 78xx/79xx.
On the D/A Board i will change some Caps, Restistors and OpAmps.

Need to get all together to place an order for all the parts.

Will update as soon is any progress ...
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Old 5th January 2010, 03:31 PM   #4
UV101 is offline UV101  England
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its a bit tight for space near the psu!!! those bracing bars get right in the way!!
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Old 5th January 2010, 04:49 PM   #5
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Ok, will cut-off the De-Emphasis circuits, right ?

Resistors 3322/3324 and 3323/3325 will be swapped out and replaced by a single 5k6 on each channel.

thanks so far
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Old 5th January 2010, 05:08 PM   #6
brianco is offline brianco  Ireland
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My 850 11 is still in use but I found the analogue output stage to be poor, sosome months ago I bought one of the CS DACs from ebay (China: arrived in Scotland on third day!!!) and fitted a Transformer output stage, totally ignoring the on-board audio stage. I now run this from the digital output of the 850 and it is light years better than a friends Theta ever was! [The tray is beginning to click though.]
Experience with this DIY DAC ?

You could probably fit this board inside the 850! Good luck.
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Old 5th January 2010, 05:18 PM   #7
UV101 is offline UV101  England
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Quote:
Originally Posted by Alpha-Linux View Post
Ok, will cut-off the De-Emphasis circuits, right ?

Resistors 3322/3324 and 3323/3325 will be swapped out and replaced by a single 5k6 on each channel.

thanks so far
I'd look at the whole output stage! you can remove those muting (7304 & 7306) transistors without too much of an issue and def loose the elco (2338). If there is no DC accross them (2338), link them out. It will be a very big improvement just removing the caps. If there is DC present, look at something like mundorf MKP's or poss better if your budget allows. If you need to buy caps, go for something like 4.7uF Mundorf MKP smaller will kill the bass bigger will sound poor! If you are using a commercial amp, the chances are there will be DC blocking caps on the input stage in anycase!

Also, you may want to try taking point "92" direct as the output (via caps if there is DC) I've often found that the more simple you make the output stage, the better it sounds. You should only need the 2nd stage as a buffer if you are driving long interconnects or a difficult amp! IMHO!!!
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Last edited by UV101; 5th January 2010 at 05:21 PM.
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Old 5th January 2010, 05:25 PM   #8
UV101 is offline UV101  England
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Quote:
Originally Posted by brianco View Post
My 850 11 is still in use but I found the analogue output stage to be poor, sosome months ago I bought one of the CS DACs from ebay (China: arrived in Scotland on third day!!!) and fitted a Transformer output stage, totally ignoring the on-board audio stage. I now run this from the digital output of the 850 and it is light years better than a friends Theta ever was! [The tray is beginning to click though.]
Experience with this DIY DAC ?

You could probably fit this board inside the 850! Good luck.
With the right voltage regulation on the 850's DAC and much playing with the opamp output stage, you will get a very good smooth sound from this player.

I do however agree (having a TDA1541A Chineese DAC kit for my media centre stuff), those chineese DAC's will kill most CDP's DAC and output stage dead. They represent excellent value for money!!!
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When Bitstream came out, I thought, “my God, what are we going to do...?” Ken Ishiwata http://www.hifisounds.co.uk
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Old 20th December 2011, 12:15 PM   #9
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Hi

i have restarted the CD850-II modding project. Since this player nearly 20 years old, i will first bring all the Caps to "Stage 0". So replacing them with Panasonic FC series, replace the rectifier diodes with Schottky. In the Output Stage i will try some other Opamps. A Tentlabs XO with dedicated Power Supply has already been ordered.

What types of Bypass Capacitors do you recommend in place of C2344/C2348 ?
Philips used Ceramic SMD. Can they be swapped against WIMA MKS2 caps ?
Do you recommend an additional cap betweend the Opamp power supply, Pin4+8 ?

thanks for feedback

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Old 20th December 2011, 12:26 PM   #10
UV101 is offline UV101  England
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Personally, I'd use Rubycon ZA or ZLH 220uF - 470uF (unless you have access to BG) in place of 2344 and 2348. You dont need anything between 8&4 bevuase you are shunting noise to gnd with 2346 and 2342. You dont really want to shunt noise from 1 rail to another!

I would poss use 100nF PPS or COG's for 2346 and 2342. Try with and without the 100n. sometimes it sounds better without!!!
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