NAD 5420 CDP opamps

parrot · 26th May 2008, 08:37 AM

My electronic knowledge is limited so this might be a basic question ...

The attached section of circuit diagram is one channel of the output stage of a NAD 5420 CDP.

Q202 and Q204 are both NE5532 dual opamps but as you can see Q202 is using only pins 5,6 & 7 while Q204 is using pins 1,2,3, 4 & 8.

It appears to me that only half of each of these dual opamps is being used. Is this correct?

Secondly, Q202 appears not to be using the V+ & V- power supply connections. Are they omitted by convention or if not, what's the role of this opamp?

I ask these questions because I had been planning to replace the NE5532 opamps in my CDP with a set of Burson's discrete component dual opamps but it doesn't look logical to just replace both [or all 4] of the NE5532s with 4 x dual Burson opamps.

parrot

glennb · 26th May 2008, 10:07 AM

I'd hazard a guess and say the other half of Q202 is used in the other channel of the stereo pair, and pins 4 & 8 will be shown on that.

Likewise, the other half of Q204 is in used in the other channel, and doesn't have pins 4 & 8 shown.

parrot · 26th May 2008, 10:56 PM

Yes, there's logic behind that suggestion but the other side uses a completely separate pair and that's clear from the full circuit diagram [as well as by looking inside the box :-)].

parrot

glennb · 27th May 2008, 08:35 AM

Quote:

Originally posted by parrot
Yes, there's logic behind that suggestion but the other side uses a completely separate pair and that's clear from the full circuit diagram [as well as by looking inside the box :-)].
parrot

Really? Can you post a complete schematic of all the audio stages and/or the PCB track layout. I can't believe that half of dual opamp part would be wasted in a commercial design, when a single opamp part could be used.

parrot · 27th May 2008, 11:04 AM

Hope this is clear enough ...

If I try to fit any more in it could get blurred perhaps?

If it is as it appears to be, what's happening with opamps Q201 & Q202, which don't seem to have a power supply?

parrot

Mooly · 27th May 2008, 11:18 AM

Hi,
Very intriguing. Have a look at the underside of the PCB !

parrot · 27th May 2008, 11:18 AM

and a little more .......

parrot

Mooly · 27th May 2008, 11:19 AM

How many actual 5532 are in that area of the board ?

parrot · 27th May 2008, 11:20 AM

four ... :-)

Mooly · 27th May 2008, 11:24 AM

Look at the underside, see if one half really is unused !
Sounds a bit bizzare to me. Cost is everything to a manufacturer, they won't waste half an I/C. Is there a headphone amp ?

26th May 2008, 10:07 AM	#2
glennb diyAudio Member Join Date: May 2004 Location: Melbourne	I'd hazard a guess and say the other half of Q202 is used in the other channel of the stereo pair, and pins 4 & 8 will be shown on that. Likewise, the other half of Q204 is in used in the other channel, and doesn't have pins 4 & 8 shown. __________________ Glenn.

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26th May 2008, 10:56 PM	#3
parrot diyAudio Member Join Date: Aug 2004 Location: NSW	Yes, there's logic behind that suggestion but the other side uses a completely separate pair and that's clear from the full circuit diagram [as well as by looking inside the box :-)]. parrot

27th May 2008, 11:18 AM	#6
Mooly diyAudio Member Join Date: Sep 2007	Hi, Very intriguing. Have a look at the underside of the PCB !

27th May 2008, 11:19 AM	#8
Mooly diyAudio Member Join Date: Sep 2007	How many actual 5532 are in that area of the board ?

27th May 2008, 11:20 AM	#9
parrot diyAudio Member Join Date: Aug 2004 Location: NSW	four ... :-)

27th May 2008, 11:24 AM	#10
Mooly diyAudio Member Join Date: Sep 2007	Look at the underside, see if one half really is unused ! Sounds a bit bizzare to me. Cost is everything to a manufacturer, they won't waste half an I/C. Is there a headphone amp ?

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