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Old 9th June 2006, 08:53 PM   #1
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Question Help me understanding this opamp circuitry

These are the partial pre and output sections of a Technics SU-C1010 preamp. I wonder for what the big elytic caps in the signal path are. (signal path is marked with arrows)

Im thinking of replacing the NJM4580s with OPA2134; would it be wise to take the said caps out ? Or what else is advisable to change ?

Thanks !

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Old 9th June 2006, 09:04 PM   #2
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Default hint

The NJM4580 has pnp bipolar inputs.
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Old 9th June 2006, 09:24 PM   #3
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Im as wise as before ...
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Old 9th June 2006, 09:31 PM   #4
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I don't know why you would want to replace the op amps with a different type. The big caps are AC coupling caps. I can't tell from the schematic you posted whether you need them, but I would leave them in.
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Old 9th June 2006, 09:39 PM   #5
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You definitely need them in the second part where the opamp runs single rail. That would not be the best place to drop in an OPA2134. You also need the left two in the first part, since that blocks the DC from the second. The output caps depend on what you are driving - if it is another single rail stage they MUST stay.

In the first part you could use an OPA2134, but again why? What are you trying to accomplish and what is the rest of your system? Whether it would make a difference depends on the board layout and other factors.

You'd probably get more bang for your buck bypassing the electrolytics with an MKP of 0.47 to 1 uf or so. Just solder them to the electro's pins on the bottom of the board.
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Old 9th June 2006, 09:42 PM   #6
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Ive changed a 4580 in a cdp for a 2134 before by advice, and it really sounds better. So Id like to try this in my pre.

My knowledge in electroncs is very limited; doing not much more than soldering by numbers but all that went fine ...
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Old 9th June 2006, 09:50 PM   #7
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Quote:
Originally posted by BobEllis
You definitely need them in the second part where the opamp runs single rail. That would not be the best place to drop in an OPA2134. You also need the left two in the first part, since that blocks the DC from the second. The output caps depend on what you are driving - if it is another single rail stage they MUST stay.
Roger that !

Quote:
Originally posted by BobEllis
In the first part you could use an OPA2134, but again why? What are you trying to accomplish and what is the rest of your system? Whether it would make a difference depends on the board layout and other factors.
So maybe here Ill just give it a try and if it doesnt work Ill change it back.

Quote:
Originally posted by BobEllis
You'd probably get more bang for your buck bypassing the electrolytics with an MKP of 0.47 to 1 uf or so. Just solder them to the electro's pins on the bottom of the board.
Thats what I will do in the second part and with the left two in the first part.

Thank you very much !
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