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Old 28th September 2007, 05:50 PM   #1
ddutch is offline ddutch  Netherlands
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Default Problems with LM4562 Opamp in Tjoeb '99 cd-player

I tried the new Lm4562 Opamp in a Tjoeb '99 cd-player as a replacement for the standard BB OPA2604. It works but not as good as it should, i guess. The sound is rather thin and hard and there is some kind of distortion in the higher frequencies even after more than 70 hours of burning in.

I think its not suited as a direct swap in this configuration, although it sounds very promissing in some ways. There is already much more detail and separation in the soundstage than before.

Does anyone understand what goes wrong and what can be done to make it work properly?
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Old 28th September 2007, 06:45 PM   #2
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Did you break it in?
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Old 28th September 2007, 07:37 PM   #3
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What local power supply decoupling do you have on the opamp ?
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Old 29th September 2007, 01:10 PM   #4
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What voltage are they operating at? The OPA is good to 24V, the LM only to 17V.
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Old 30th September 2007, 08:09 PM   #5
ddutch is offline ddutch  Netherlands
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Thanks for your respond!

Yes, i broke it in for about 70 hours or so.

I haven't put any decoupling on the opamp. If this is necessary, could you please do some suggestions how to do this? Do you think this could solve the problem?

I don't know what the operatingvoltage is but it is on the print of a Tjoeb '99, based on a Marantz CD38.
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Old 30th September 2007, 09:09 PM   #6
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Hi,

What is the output of the opamp connected to, is it connected directly to a capacitor ? If so, try connecting a small resistor in series with the output of the opamp - it won't like driving more than a few 10's of pF directly.

For decoupling start with 100nF soldered directly between the + and - supply pins on the opamp. There should also be 10-47uF between the supply pins and gnd within a few cms of the opamp.

Hope that helps.

Cheers,

Jon
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Old 30th September 2007, 09:17 PM   #7
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Do you have a link maybe?
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Old 3rd October 2007, 09:10 PM   #8
ddutch is offline ddutch  Netherlands
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Thank you all,

I am not sure if the opamp is directly coupled to a capacitor but I ll try the decoupling. Should there be 10-47uF between the supply pins and ground within a few cms of the opamp on both (+ and -) pins?

Unfortunately i don't have a schematic of the player.
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Old 3rd October 2007, 09:27 PM   #9
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Yes, 100nF between the + and - supply pins directly on the opamp. Then one 10-47uF between + and gnd and another between - and gnd (mind the polarity!) close by the opamp.

I've looked at other Marantz players produced around the same time and you may find the output of the opamp connected directly to a coupling cap to block DC at the output, probably bipolar (unless there is a deliberate DC bias) and between say 10 and 100uF in value.

With inadequate supply bypassing you may find that the opamp is oscillating at high frequency and this is the cause of your problems. Adding the 100nF may just do the trick.
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Old 19th November 2007, 02:23 PM   #10
ddutch is offline ddutch  Netherlands
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Sorry for this delayed reaction. Finally i got my hands on a working soldertool.
I haven't soldered a ceramic capacitor (0,001uF) right across the power supply leads but soldered it underneath an 8 pin dip socket in wich i put the opamp itself. Could this have a bad influence on the functioning of the the capacitor?

Now it works and sounds(!) better than before because the sound is more natural and relaxed but there still is a bit of hardness to the sound, especially in high frequencies. Because of my limited soldering skills i don't like to solder on the print itself so the suggestions of putting caps from the chip to ground are not an option immediatly.
What else can be done? If i use a 0,01uF cap instead of the 0,001uF, could it make a difference?
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