NAD 5420 CDP opamps

[parrot]

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]

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]

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]

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]

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]

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

 

[parrot]

and a little more .......

parrot

 

[Mooly]

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

 

[parrot]

four ... 🙂

 

[Mooly]

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 ?

 

[Tube_Dude]

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

Q202 and Q204 are both in the same chip ( the dual NE5532), so pin 4 an 8 are the supply pins common to both channels.

The same happens with Q201/203.

In any doubt, consult the NE5532 data sheet... 😉

 

[parrot]

and a little more .......

parrot

 

[parrot]

Thanks for all the help/wonderment so far.

I can't check underneath at the moment but I'll get back to you with that as soon as I can ... as in tomorrow Aus. time.

parrot

 

[parrot]

sorry, a rogue reply slipped in there ...

I've checked the data sheet, the complete parts list and looked in the box and there are four [4] chips.

parrot

 

[Tube_Dude]

I've checked the data sheet, the complete parts list and looked in the box and there are four [4] chips.

parrot

4 chips, because there are 2 for each channel, but what I have told you in my previous post ( #11 ), totally apply ...

 

[Mooly]

4 Chips (5532's) is 8 Opamps. I would have agreed with Tube Dude, but the circuit does show otherwise. You need to physically look at the board.
Regards Karl

 

[parrot]

ok ... one last one and I'm not sure how clear this view of the pcb will be but yes, I'll have a close look at the board tomorrow, thanks

parrot

 

[Mooly]

Getting brain ache looking at that, don't wait up 😉 Will try and puzzle it out.

 

[Tube_Dude]

Effectively, Parrot is right.

There are 8 opamps (4 dual NE5532 ) in the output of the NAD CD player.

 

[Mooly]

Going crosseyed looking at that . They are 5532,s not 5534 in the player. Pin 5 does not look connected on the layout.

Edit, If they are 5532 then there are 8 individual OpAmps in there, the filter for the player shows 4. So how are they connected. The image is not really clear enough.