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klitgt 28th October 2004 02:35 PM

Neede help identifying details in a diagram
2 Attachment(s)
Hi there

I need help indentifying some detalis in my Denon DCD3300 CD player.

The attached gif file shows the first steps (Super Linear Converters of L and R channel) that follow immediately after the outputs pins from the DAC chips (lead 3 in CB702 and CB752).
Then comes the Low Pass Filter (3 coils and C123,124,125) of the L channel and then the L channel output buffer opamp (IC106 = NE5532, pin 7 goes directly to the RCA out socket L channel. R channel not shown).
The opamps in each of the blocks 2U1435 are in fact also NE5532 (only of each is used).

I would like to know what is the purpose of the NE5532 in the two blocks 2U1435?

My guess is that it is I/V converting circuits between the DAC chips and the Low Pass Filter (3 coils and C123,124,125) but I am not sure.

I have read that replacing the NE5532 opamps in the buffer stage (IC106) by e.g. AD825 modules should be a good idea.

But if the opamps in each of the blocks 2U1435 are also NE5532, should they also be replaced by AD825 modules or is the quality of the opamps here of no importance?

dangus 31st October 2004 05:11 AM

I'd guess that those opamps in 2U1435 are even more critical, since they're handling higher-bandwidth signals, right?

Is this CD player from the 80's? I seem to remember that the Japanese decks were into high-order passive filters back then, which tended to ring when reproducing square waves. Whether that was supposed to have any audible consequences, I don't remember. Anyway, the pictures of square waves from oversampling decks like Philips looked a lot cleaner.

klitgt 31st October 2004 08:29 PM

The Denon DCD3300 is from 1987. What makes this deck so remarkable is the transport mechanism which is rock solid and contributes to the sound of this machine. I put a new reference clock (LC Audio LClock XO 3) in it and replaced the IC106=NE5532 with LC Audio's AD825 based opamp module (same as the product) and it sounds great! Much more fine grained sound and remarkably better soundstage.
I wonder whether replacement of the NE5532 in the 2U1435 circuits with some other opamp would be beneficial.

hjelm 2nd November 2004 11:39 AM

As i read it it is a voltage buffer, provided that the opamp is a voltage feedback opamp. A high quality discrete buffer here would be nice.
My guess is that it is there to isolate the DAC from the varying load of the filter.
Selection criteria for the OPAMP would be ultra high bandwidth and low settling time since it is coupled before the LPF filter.

Do you know if it is a current output dac?

klitgt 3rd November 2004 07:43 AM

2 Attachment(s)
It is a BurrBrown PCM56KP DAC (one for each channel) see diagram. As far as I can read from the diagram it is a voltage out and not a current out DAC.
Then I am probably wrong in assuming that the 2U1435 circuits are I/V converters?

klitgt 3rd November 2004 07:58 AM

2 Attachment(s)
And further from the datasheet:

92dB MAX THD: FS Input, K Grade
74dB MAX THD: 20dB Input, K Grade
1.5ms SETTLING TIME, TYP: Voltage Out

The PCM56 is a state-of-the-art, fully monotonic,
digital-to-analog converter that is designed and
specified for digital audio applications. This device
employs ultra-stable nichrome (NiCr) thin-film
resistors to provide monotonicity, low distortion, and
low differential linearity error (especially around
bipolar zero) over long periods of time and over the
full operating temperature.
This converter is completely self-contained with a
stable, low noise, internal zener voltage reference;
high speed current switches; a resistor ladder network;
and a fast settling, low noise output operational
amplifier all on a single monolithic chip. The
converters are operated using two power supplies that
can range from 5V to 12V. Power dissipation with
5V supplies is typically less than 200mW. Also
included is a provision for external adjustment of the
MSB error (differential linearity error at bipolar zero)
to further improve total harmonic distortion (THD)
specifications if desired. Few external components
are necessary for operation, and all critical
specifications are 100% tested. This helps assure the
user of high system reliability and outstanding overall
system performance.

Now I think I understand something:
There is a I out option (PIN 13) and a low noise output operational amplifier (input PIN 13, output PIN 9).
I assume that the I/V conversion is taken care of internally by the "noise output operational amplifier ".
Or am I still wrong here?

My question is still whether there is a better opamp than NE5532P for the 2U1435 circuit.
A NE5534 (single opamp) would require a different pin connection scheme, and maybe other component values (R701, R702 and R703).

hjelm 3rd November 2004 09:46 AM

The IV conversion is done by the internal opamp yes.
Question is if that isn't where you should put your effort if you want to upgrade the quality of the device. I.e pull the current out signal instead and forget the internal opamp.

Yes there are better opamps for the buffer, it is a buffer nothing else.
The question on which is the best one is a religious one.
Some say AD797 is the one others AD8610 (8620 for double).
Some like the BB(2)604 BB(2)134 and so on.

Personally i would build a discrete buffer for this application.

klitgt 3rd November 2004 10:40 AM

hjelm, you wrote. Yes there are better opamps for the buffer, it is a buffer nothing else.

By buffer do you mean the IC106 in my diagram in firts post?

hjelm 3rd November 2004 02:34 PM

Nope i mean the 2U1435. If i read the diagram right it is a opamp coupled as a buffer (GAIN=1). Is it on a separate board?

klitgt 3rd November 2004 03:22 PM

First of all thank you Hjelm for helping me!
Yes Hjelm, the 2U-1435 "modules" are mounted on one separate PCB with wires for +/- 15 V power supply (CB701/CB751 connectors) and wires for signal from DAC chips and wires for output from 2U-1435 to LPF (CB702/CB752 connectors). The opamps in the 2U-1435 are NE5532P of which only are used (strange, why not use NE5534).

Are you able to tell why the 2U-1435 "modules" are mounted separately in stead of just putting all the components directly on the main board?

OK, so the NE5532P in the 2U-1435 "modules" are gain=1 buffers.
Then the following NE5532P (IC106) is another buffer for connection directly to the output RCA socket (left ch, right ch similar).

I may ask stupid questions but try nevertheless: Why is the signal going through IC106 before it goes to the RCA output socket? Why not directly from NE5532 in the 2U-1435 modules to the RCA output sockets?

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