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Old 26th May 2008, 07:37 AM   #1
parrot is offline parrot  Australia
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Default NAD 5420 CDP opamps

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.

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Old 26th May 2008, 09:07 AM   #2
glennb is offline glennb  Australia
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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.
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Old 26th May 2008, 09:56 PM   #3
parrot is offline parrot  Australia
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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 :-)].


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Old 27th May 2008, 07:35 AM   #4
glennb is offline glennb  Australia
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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.
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Old 27th May 2008, 10:04 AM   #5
parrot is offline parrot  Australia
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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?

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Old 27th May 2008, 10:18 AM   #6
Mooly is offline Mooly  United Kingdom
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Hi,
Very intriguing. Have a look at the underside of the PCB !
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Old 27th May 2008, 10:18 AM   #7
parrot is offline parrot  Australia
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and a little more .......

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Old 27th May 2008, 10:19 AM   #8
Mooly is offline Mooly  United Kingdom
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How many actual 5532 are in that area of the board ?
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Old 27th May 2008, 10:20 AM   #9
parrot is offline parrot  Australia
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four ... :-)
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Old 27th May 2008, 10:24 AM   #10
Mooly is offline Mooly  United Kingdom
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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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