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Old 23rd July 2004, 07:11 PM   #1
ronardi is offline ronardi  Hong Kong
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Unhappy What happened to my cdp?? help!!

I changed the opamp, signal coupling caps and output caps of my cdp, but when I thought all is done, I found that there is no sound but some "hum" in the left channel!! What happened? I tried to use my dmm to find out the problem, but I don't know how...plz help, I am deeply frustrated
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Old 23rd July 2004, 08:02 PM   #2
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You'll need to supply more details; CD player? Which op-amps were replaced and what were they replaced with? etc.
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Old 23rd July 2004, 09:19 PM   #3
ronardi is offline ronardi  Hong Kong
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It was my cd player.

I changed the opa604 to opa627 and opa2134 to opa637 and the signal output caps are 2 2.2uf ero mkp caps and the signal caps are 2 axon 33uf film cap.

I think the opamps are ok as I got sound from the right channel, and the DCV of the coupling caps in left channel is higher then that in the right, is it the culprit? the problem may seem stupid as i am just a rookie to DIY, plz help
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Old 23rd July 2004, 11:44 PM   #4
sek is offline sek  Germany
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Quote:
You'll need to supply more details; CD player?
Quote:
It was my cd player.
*LOOOL*

Sorry Ronardi, which CD player type was it exactly. Please supply a link to the schematics and datasheet or (if those aren't available) make a scan of the schematics and load the pictures up. You were using schematics, were you?

Quote:
I changed the opa604 to opa627
Why?

Quote:
and opa2134 to opa637
The OPA2134 is a dual opamp. The OPA 637 is not. How and why should that work?

Please make a comparison between your left and right channel: check every single solder joint, the orientation of every polarized component, check for solder residue that could produce shorts between copper traces, damaged components, etc.

Sebastian.
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Old 24th July 2004, 06:31 AM   #5
ronardi is offline ronardi  Hong Kong
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It was my cd player.

I changed the opa604 to opa627 and opa2134 to opa637 and the signal output caps are 2 2.2uf ero mkp caps and the signal caps are 2 axon 33uf film cap.

I think the opamps are ok as I got sound from the right channel, and the DCV of the coupling caps in left channel is higher then that in the right, is it the culprit? the problem may seem stupid as i am just a rookie to DIY, plz help
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Old 24th July 2004, 07:19 AM   #6
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Hi Ronardi,
You cannot use a single opamp in a socket for a dual opamp! You will need two OPA637's and an adapter board. Also the OPA637 is not unity gain stable as the OPA2134 is. If this is all abakadabra for you first read a book about opamps or Horowitz and Hill, The Art of Electronics, Cambridge University Press.
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Old 24th July 2004, 12:02 PM   #7
ronardi is offline ronardi  Hong Kong
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Thanks you all,

just forgot to provide some more detail of my case. I know opa2134 is a dual opamp, so i substituted it with two opa637 on an adapter board. Thus I think the opamp part is ok. Do you think the problem came from the caps? the voltage readin of the two channels are different!
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Old 24th July 2004, 12:25 PM   #8
sek is offline sek  Germany
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Hi Ronardi,

well, now that you answer my questions for details with a simple double post (?!), I'll just ask other questions.

Quote:
It was my cd player.
If that means that you've built the player completely by yourself, I understood you right now. Otherwise, please write down, which brand and type or model it exactly is.

Secondly, please point on a schematic or provide one yourself. We can't help you out as long as we don't know what you're talking about.

Quote:
the DCV of the coupling caps in left channel is higher then that in the right
...
the voltage readin of the two channels are different
What does that mean, Ronaldi?

Where do those coupling caps sit (schematic-wise, not when you look at the board)? Directly before the output? Or inside the I/V or buffer stages?

How much voltage do you measure (mv or V) and where exactly? Across the cap or between one of the cap's pins and ground, or where (across) exactly?

I assume: across the cap's pins. Did you do all the tests I suggested (solder joints, polarity)? Can you test the components for failures (caps, opamps, everything around them in the circuit)?

Quote:
so i substituted it with two opa637 on an adapter board
That may already be the explanation. As Elso pointed out, the opa637 isn't stable in the same environment as the opa(2)134! Why (exactly) did you choose the opa637, and why do you expect it to work (e.g. circuit gain is >5, compensation/bypassing provided etc.)?

Quote:
just forgot to provide some more detail of my case
Yeah! Sorry,
Sebastian.
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Old 24th July 2004, 04:10 PM   #9
ronardi is offline ronardi  Hong Kong
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Quote:
Originally posted by sek
Hi Ronardi,

well, now that you answer my questions for details with a simple double post (?!), I'll just ask other questions.



If that means that you've built the player completely by yourself, I understood you right now. Otherwise, please write down, which brand and type or model it exactly is.

Secondly, please point on a schematic or provide one yourself. We can't help you out as long as we don't know what you're talking about.

My CD player is a Original(Made in China) A9.8 or "DaVinci", maybe you don't know much about this...

What does that mean, Ronaldi?

Where do those coupling caps sit (schematic-wise, not when you look at the board)? Directly before the output? Or inside the I/V or buffer stages?

two of them sits right before the dac chip and the other two sits before before the RCA anologue output

How much voltage do you measure (mv or V) and where exactly? Across the cap or between one of the cap's pins and ground, or where (across) exactly?

I assume: across the cap's pins. Did you do all the tests I suggested (solder joints, polarity)? Can you test the components for failures (caps, opamps, everything around them in the circuit)?

In fact, I do hope providing more details by, I just can't....My electronics knowledge(may not beyond the level of "common sense" much)is very limited. I modified the CD player by following someone's experience in other forum....and they say it's easy..so I did it..

That may already be the explanation. As Elso pointed out, the opa637 isn't stable in the same environment as the opa(2)134! Why (exactly) did you choose the opa637, and why do you expect it to work (e.g. circuit gain is >5, compensation/bypassing provided etc.)?

I chose the opa637 because someone using the same player changed the stock one to this and work well. I just follow...

Yeah! Sorry,
Sebastian.

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Old 25th July 2004, 06:53 PM   #10
ronardi is offline ronardi  Hong Kong
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My CD player is a Original(Made in China) A9.8 or "DaVinci", maybe you don't know much about this...

two of them sits right before the dac chip and the other two sits before before the RCA anologue output

In fact, I do hope providing more details by, I just can't....My electronics knowledge(may not beyond the level of "common sense" much)is very limited. I modified the CD player by following someone's experience in other forum....and they say it's easy..so I did it..

I chose the opa637 because someone using the same player changed the stock one to this and work well. I just follow...
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