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Old 20th December 2011, 03:07 AM   #1
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Default Help for Kenwood dp-7050 mod

I have a cd player named Kenwood dp-7050. The problem is that I see at the cdp's ended output stage two many things (transistors, resistors...) that i think might affect the signal quality. Could anyone help me to optimize it for better sound?
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Old 20th December 2011, 07:02 PM   #2
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Hello! For many examples of taking audio feeds before op amps and transistor stages ( either amplification or muting) I'd recommend you look in on the Lampizator ( Lukasz Fikus Lampizator). I've worked on a few Kenwood players but always DP-xx90's. Looking at the board it's a certainty that you have both muting transistors and capacitors in the audio signal path. Might be worth lifting the lead from the board and taking your L&R direct from there? The DAC is a Philips TDA1547 - I know Lukasz did some work on this chip in one of his projects. Good luck!
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Old 20th December 2011, 09:46 PM   #3
UV101 is offline UV101  England
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There's a fair bit about the DAC7 (TDA1547) as its a nice sounding chip. It should be possible to take the output from the dac via a single opamp stage and DC blocking caps straight to the output. Could do with a manual really ;-)

If you wanted to go mad, you could bypass the built in opamp I/V on the DAC and build a separate I/V ;-)
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Old 20th December 2011, 10:22 PM   #4
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Just leave everything there in place (it won't make a difference) and replace the OpAmps with something decent. You might need to add decoupling caps between OpAmp power pins and ground.
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Old 20th December 2011, 10:50 PM   #5
UV101 is offline UV101  England
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That's probably the best advice to be fair. Decent Opamps with their local decoupling caps will significantly help. Also check for dc blocking caps after the opamps but before the muting circuit. Swapping these for mkp type will help. If you take a picture of the pcb with the dac and opamps, we should be able to point out the candidates for upgrade ;-)
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Old 21st December 2011, 01:24 AM   #6
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Hi, UV101
I attach herein more photos of the player for your reference. My player uses two output opamps named njm4565l, one for left channel and one for right channel. output capacitors are 47uF/50V brown elna ones as you can see in the previously attached photos. filter chip is NPC sm5840cp.
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Old 21st December 2011, 01:39 AM   #7
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Hello
I also has a nice highly rated Kenwood DP3300D about 20Lb but sound awful.
Built very nice inside, I'll open up and take some pictures.
If is possible to improve the sound that would be great.
Greetings Gabor
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Old 21st December 2011, 01:40 AM   #8
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Which opamps should i use to replace the old ones and what capacitance for the decoupling caps? As the current opamps are sip8 type, so i will have to make two adaptor sockets for new ones. I have fortunately found a schematics for such adaptor on the internet.
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By the way, should i remove the mute transistors?

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Old 21st December 2011, 02:55 AM   #9
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Dear SoNic_real_one ,
Which opamps should i use to replace the old ones and what capacitance for decoupling caps? By the way, should i remove mute transistors?
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Old 21st December 2011, 05:31 PM   #10
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I've used Burr Brown OPA627BP's - big improvement over the normal ones used in CD players, but there is plenty of choice. For the minimum effort, Sonic's input is fine. Marantz used the TDA1547 with their HDAM system in the CD-17, which turned out to be a discrete transistor stage and sounds great. This is closer to UV101's suggestion, but involves more reading & work!
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