[jules]

I'm planning on swapping the NE 5532 opamps on my NAD CDP for a pair of Burson's discrete component "HDAM" modules. Both the NE 5532 N and the Burson opamps have an eight pin base so in situations where there is only a single output opamp a simple swap works ok.

With the NAD, the output uses 4 NE5532Ns, two per side. As I read the circuit diagram below, each one does part of the work. So Q202 uses pins 5,6 & 7 while Q 204 uses pins 2,3,4, 8 & 1. The NAD is therefore only using half of each of the NE5532Ns [they are dual opamps].

Shown here is one side only of the NAD with Q202 & Q204 being a pair of dual NE5532N opamps:

 

I'm enthusiastic about Burson products but the Burson people haven't been much help here in that they seem to think there is only one opamp per side. If I replace Q204 I think I might get some improvement without causing smoke but I will only be using half the [dual] burson opamp.

What I think I have to do if I want to replace both Q202 & Q204, is to mount the Burson modules off board and make wire connections based on the pin numbers. Hence, I would connect board points 5,6 & 7 (these are on the Q202 base) to one side of the [dual] Burson opamp and board points 1,2,3 & 4 (Q204) to the other side of the opamp. The slightly tricky one is board point 8. This corresponds to pin 8 of the opamp which is "V+". It looks to me as though I will have to cross wire this one so that point 8 on Q204 is connected to the same side of the opamp as points 5,6 & 7.

Q202 does not use V+ or V-. This looks significant to me though I don't know understand it.
 *Are V+ & V- power inputs? Is Q202 a less significant "amp" than Q204?
 *Could it be that replacing a microcircuit like Q202 with a discrete component circuit might not work or might require changes?
 *Why did NAD use duals when they could have used  5524 singles?
 *Could I split a dual Burson [it looks possible physically] and just use half as a plug in replacement for Q204 only?

Aaagh, putting it in words looks horribly hard to understand but I hope the diagrams help.

Is there an expert out there who can advise me on this one please and secondary question, is it ok to mount a dual opamp like this off-board from a functional point of view?

jules

ps This might help ...

[peranders]

I think it's a much better idea to use some high performance IC instead. LME49720 for instance. AD8620 is not so bad either.

[jules]

Thanks Peranders ...

are the two types you suggest interchangeable with the NE5532 opamps?

jules

[Davey]

The other halves of Q202 and Q204 are used elsewhere in the circuit, are they not?  You're not showing the whole schematic.  Or is that schematic mislabeled?
I think you better investigate further.

I'm not sure I would bother anyways.  NE5532's are excellent op-amps.

Dave.

[jules]

Davey,

no, interestingly enough, the other halves aren't used elsewhere. The other channel of the CDP uses two completely separate NE5532s. I don't think the schematic is mislabeled. You'll notice that above "Q202" it has the fraction 1/2 and likewise with Q204.

The other thing that seems odd about Q202 is that there are no connections to pins 4 & 8. These are V+ and V-, the power supply. Now I realize that sometimes convention ignores these but given they are shown in Q204, what does this mean?

Thanks for confirming my view that they are only using half of each. There might be a really mundane reason why they didn't use a couple of 5534. Perhaps the duals actually cost less because they manufacture more?

Yes, I realize the 5532s are an ok op-amp though a number of people who've tried the Bursons in their place seem to think there's a big improvement. I'm planning on replacing the clock in the NAD so it wouldn't be a huge job to do the op-amps at the same time. I'm tentative about using a chip, drop in op-amp replacement here unless I know that it's safe, or been tried in this CDP and will not cause problems.

My current thinking is that if I do try the Bursons, they should be single rather than dual or else I'll be wasting half the op-amp. After doing a little reading [I'm now dangerous, I know more than 99% of the general population about op-amps but about 1% of what any half decent EE would know  ] it appears that "off-board" mounting could be problematic in that short lead lengths are important, particularly where some of the caps are concerned.

jules

[whubbard]

Jules,

I don't know much about this, but maybe a fresh pair of eyes could help. I understand why the Burson people might think it is just one chip, because first off, it could be one chip, so I believe any good designer would only use one chip. Also, because the schematic uses all the pins 1-8, and Q202 doesn't use pins 4 or 8. Basically it seems they labeled it to be one chip. If it was two chips, I feel like it would be labeled 1-3,4,8 for all of them, and 5-7 wouldn't appear anywhere. I would actually say that in my opinion...it is just one chip, or that’s at least as it appears in the schematic.

Do you have any photos of the inside where there are two chips? Are you sure this is the correct schematic?

-West

[jules]

Thanks West,

I appreciate your reply and the logic. I've checked inside the real thing and there definitely are a total of four chips [two per side]. I haven't got a camera with me at the moment so I can't add that to the mix. The parts list for the CDP also states that it uses 4 x NE5534N and the full circuit diag shows the other channel identically to this one. I suspect the reason they've chosen the left side of one [1 to 3] and the right side of the other [5 to 7] is simply because it works from a layout point of view.

Another reason they might have chosen two chips instead of one could be heat. The 5534s apparently develop a reasonable amount of it and again, if they happen to be cheaper than the single 5532s it might make sense.

I think the Burson people might have assumed that this CDP [5420] is the same as the 542 and not looked too closely at the diag.

jules

[whubbard]

Jules,

I guess it is two chips, which is weird, but thats how it goes. The only reason why I still question the schematic is that since it is two chips...where are pins 4 and 8 on Q202. I know it could just be that they 'forgot', but I find that very hard to believe. Have you contacted NAD about this?

Also, like you said, you can just use the single version and it should be no problem. Let us all know how it sounds if you end up doing this!

-West

[jules]

West,

yes, pins 4 & 8 looks odd and it's the same on the other side. Maybe it's just assumed?? Maybe that chip really isn't using 4 & 8 though that's beyond my knowledge.

NAD, hmmm ... might be possible  .

It looks to me as though the single version would work but I'd like to be reasonably sure before applying the hot iron.

I promise to report back. I'm pretty sure the clock upgrade will be worth while but unfortunately I'll probably do both at once which isn't good from the point of view of evaluating each change.

jules

[peranders]

Thanks Peranders ...

are the two types you suggest interchangeable with the NE5532 opamps?

jules

Yes and they are also rather compatible when it comes to speed and other things but they were only a suggestion from many possible types.

[jules]

Thanks Peranders ... the suggestions are most appreciated and I'm now tending to think that might be the better way to go. This doesn't seem to be a mod that's likely to make a huge difference and with advice not available from Burson, I'm doubtful about taking a plunge with their op-amps when the NAD layout is slightly unusual.

jules