Help me understanding this opamp circuitry

SmellOfPoo · 9th June 2006, 09:53 PM

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)

I´m 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 !

traderbam · 9th June 2006, 10:04 PM

The NJM4580 has pnp bipolar inputs.

SmellOfPoo · 9th June 2006, 10:24 PM

I´m as wise as before ...

sawreyrw · 9th June 2006, 10:31 PM

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.

BobEllis · 9th June 2006, 10:39 PM

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.

SmellOfPoo · 9th June 2006, 10:42 PM

I´ve changed a 4580 in a cdp for a 2134 before by advice, and it really sounds better. So I´d 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 ...

SmellOfPoo · 9th June 2006, 10:50 PM

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 I´ll just give it a try and if it doesn´t work I´ll 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 !

9th June 2006, 09:53 PM	#1
SmellOfPoo diyAudio Member Join Date: May 2004 Location: Hamburg / Northern Germany	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) I´m 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 !

9th June 2006, 10:04 PM	#2
traderbam diyAudio Member Join Date: Jan 2002 Location: Earth	hint The NJM4580 has pnp bipolar inputs.

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9th June 2006, 10:24 PM	#3
SmellOfPoo diyAudio Member Join Date: May 2004 Location: Hamburg / Northern Germany	I´m as wise as before ...

9th June 2006, 10:31 PM	#4
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	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.

9th June 2006, 10:39 PM	#5
BobEllis diyAudio Member Join Date: Sep 2003 Location: PA and CT	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.

9th June 2006, 10:42 PM	#6
SmellOfPoo diyAudio Member Join Date: May 2004 Location: Hamburg / Northern Germany	I´ve changed a 4580 in a cdp for a 2134 before by advice, and it really sounds better. So I´d 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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