NEC's mysterious digital filter and DAC chips

[thatsright]

It's hard to find much info on NEC's brief plunge into digital audio (roughly 1986-91). NEC did put out some very interesting CDP's including a flagship from 1986:

NEC CD-903 Monster High End Vintage CDP | audioaddicts: Everything HiFi, Music and More!

Only recently learned about these and from what I know, not a lot of people were or are aware of them, I certainly wasn't, in fact NEC hifi in general slipped my radar - This thing from what I do

audioaddictsforum.com

NEC 903 TRUE AUDIOPHILE CD PLAYER

Item Condition: Good Shipping Options: Pickup available but audition is not available. Suburb or Town: Cronulla State: NSW Payment Method: Cash eft Reason for selling: Too much stuff This is one of the finest CD players ever made! It is built like a tank, as soon as you go to lift it you realise ...

www.stereonet.com

The Dutch list shows several models from NEC and CDPs from various manuf. that use "µPD" series chips. Maybe the final IC was the UPD6376 (2-ch, 16-bit from 1991; readily and cheaply avail from Ali in SOIC form factor)

UPD6376 Datasheet - AUDIO 2-CHANNEL 16-BIT D/A CONVERTER

NEC, Stock #:369047, Datasheet, equivalent, pinout, replacement, pdf, complementary.

datasheetspdf.com

Back around 86/87, NEC put out some interesting models, incl. model CD-810, using the PCM56 BB chipset and NEC's own DIP-size digital filter chip. I can't find any info on the uPD6352ACA IC, with bunch of 74-series logic chips around it (reclocking, buffering ???)

Some photos here: https://www.diyaudio.com/community/threads/nec-cd-810-revival-and-mods.338152/

Any help with more info on the NEC µPD6352ACA -- or any other NEC digital product -- is much appreciated!

About that flagship NEC903 ... I have no idea what's inside that mysterious device. The Dutch list says PCM56, but those stereone photos indicate some sort of custom R2R job. Not sure the stereone player is a "real" 903 or some kind of mod job???
In any case, NEC is a serious designer of semi chips themselves. This is unlike many Japanese brands that used other manufs' chips. Give NEC stature ...

wikipedia:
NEC was the world's fourth-largest PC manufacturer by 1990.[5] Its semiconductors business unit was the world's largest semiconductor company by annual revenue from 1985 to 1992, the second largest in 1995, one of the top three in 2000, and one of the top 10 in 2006.

... they may indeed have some magical powers when it comes to DACs (even basic consumer-grade models).
When companies, like NEC, have deep pockets, they can afford to create "loss lead" products -- show-off, cost-no-object projects that will never recoup development costs in sales. But will sell to certain CEOs and govt officials ... and are political showpieces, too.
In the 70s and 80s, Japanese companies put out many flagship products such as this.

 

[AnalogSteph]

NEC's semiconductor business must have been absolutely massive in the '80s, the first half in particular. They made a ton of audio ICs, even stereo decoders for FM tuners and power amplifiers for radios. In those days having an IC production was quite common among electronics giants in general - SONY, NEC, Pioneer, Toshiba, OKI, Mitsubishi, Fujitsu, Philips, Siemens, Motorola, ... (Even Kyocera I think.)

Datasheets for µPD6355, µPD6372 and µPD6376 seem to be readily available (search for uPD instead of µPD). No dice re: µPD6352 though. I may need to add some of them to the list, they seem to be the oldest 2-channel DACs I've seen so far. (Well, except for CX20017, and its single-page excuse for a datasheet isn't very informative.)

That's a better datasheet situation compared to mid-late 1990s SONY DACs, or any Pioneer ICs ever.

About that flagship NEC903 ... I have no idea what's inside that mysterious device. The Dutch list says PCM56, but those stereone photos indicate some sort of custom R2R job. Not sure the stereone player is a "real" 903 or some kind of mod job???

There are two NEC-branded 14-pin jobs which could be DACs, judging by what appears to be HP optical cables coming in near them (that couldn't have been cheap). PCM56 is a decidedly 16-pin affair and would have had an opamp close by, so these must be something else.

Or wait, these might just be coax, and they're going to this board with the bunch of resistors and transistors... could be kind of a discrete DAC implementation indeed.

 

[Doodski]

NEC's semiconductor business must have been absolutely massive in the '80s, the first half in particular. They made a ton of audio ICs, even stereo decoders for FM tuners and power amplifiers for radios. In those days having an IC production was quite common among electronics giants in general - SONY, NEC, Pioneer, Toshiba, OKI, Mitsubishi, Fujitsu, Philips, Siemens, Motorola, ... (Even Kyocera I think.)

I was retailing NEC home audio in the mid'ish 80s and the customers accepted the gear, it sounded very good and the quality was good too. Then suddenly the NEC service depot closed, they sold off all the test gear and stuff and then NEC stopped selling home audio gear. It was all very sudden.

 

[AnalogSteph]

There was a big semiconductor depression in 1985 which may have had an influence on this. NEC made a ton of computer chips, too.

 

[JustJones]

I don't think the PCM 56P J needed OP Amps
Old Burr Brown chips

https://www.ti.com/lit/gpn/pcm56

Figures 9 and 10 show a circuit and timing diagram for a
single PCM56 used to obtain both left- and right-channel
output in a typical digital audio system. The audio output of
the PCM56 is alternately time-shared between the left and
right channels. The design is greatly simplified because the
PCM56 is a complete D/A converter requiring no external
reference or output op amp.

 

[thatsright]

Datasheets for µPD6355, µPD6372 and µPD6376 seem to be readily available (search for uPD instead of µPD). No dice re: µPD6352 though. I may need to add some of them to the list, they seem to be the oldest 2-channel DACs I've seen so far. (Well, except for CX20017, and its single-page excuse for a datasheet isn't very informative.)

Only the 6376 has a datasheet that I could find. And that DAC is readily -- and cheaply -- avail. on Ali, as I noted in the OP.
What "list" are you referring to?

BTW: If anyone has PDF serv manuals for the NEC CD-810, NEC CD-710, or NEC CD-650, please share! I have seen print copies going for hefty change on eBay.

 

[AnalogSteph]

Only the 6376 has a datasheet that I could find.

Datasheet Archive: UPD6372CX datasheets

View results and find upd6372cx datasheets and circuit and application notes in pdf format.

www.datasheetarchive.com

Datasheet Archive: UPD6355 datasheets

View results and find upd6355 datasheets and circuit and application notes in pdf format.

www.datasheetarchive.com

What "list" are you referring to?

Search hint: It's in my signature...

 

[restorer-john]

Love this:

That machine has been messed with. New Panasonic caps, poorly mounted Nichicon Muse, sockets and opamp rolling etc.

 

[thatsright]

Love this:

View attachment 319401

That machine has been messed with. New Panasonic caps, poorly mounted Nichicon Muse, sockets and opamp rolling etc.

As I noted in the OP, that image came from a thread at DIYAudio.com. Experimental mods and at-home upgrades don't have to play by any rules of cleanliness-is-next-to-Godliness.

What's more noteworthy is number of chips -- front and rear of this PCB -- that are NEC branded. Indeed, NEC, being largely a semi and IC designer, manuf and fab house, could have made very high-performance ASICs for digital audio, even in very low batches (which would be cost prohibitive for, say, better-selling Kenwood or Sherwood or even Yamaha) ... and which is why I am curious about that uPD6532ACA.

Reading the magazine reviews -- in Audio, High Fidelity -- from mid 80s, notable journalists like Len Feldman had overwhelming praise for CDPs of this era. This was a few years before CDs overtook the sales metrics (1988) .And these early CDPs were hardly cheap. And there were very fine TTs and cartridges (as good as 2023 vinyl playback that get so much attn), and Nakamichi Dragon cassette decks, at the same time, competing in a death race. Yes, these 16-bit 2x oversampling jobs sounded great (ahem, cont. to sound great, even today). Maybe it's because in R&D facilities and listening rooms at Sony and Philips and NEC, folks were not just measuring, but listening and "voicing" and tuning by ear. The good old days.
Not sure how and why early digital gets such a bad rap. Even on the A/D side, Denon (PCM) delivered the goods in early 1970s:

 

[audio_tony]

Nakamichi and Shure also made players with the 6352 chip.

CD player DAC and transport database - home page.

CD player DAC list, list of CD players, DACs and transports.

daclist.dnsbits.net

 

[thatsright]

Nakamichi and Shure also made players with the 6352 chip.

Right, but what's under the hood? 2x, 4x

 

[audio_tony]

Right, but what's under the hood? 2x, 4x

I don't know - but I thought it might be useful to mention those other makes, as perhaps the service manuals for those might have more detailed information?

Assuming service manuals are available of course.

 

[tcli]

About that flagship NEC903 ... I have no idea what's inside that mysterious device. The Dutch list says PCM56, but those stereone photos indicate some sort of custom R2R job.

From this front photo :https://audioaddictsforum.com/thread/1845/nec-903-monster-high-vintage
It seems that the NEC 903 have a "remote controled attenuator system" . I guess it's what you take for a R2R DAC .

I think that the four DACs are here :

https://audio-heritage.jp/NEC/player/cd-903.html

 

[AnalogSteph]

Good catch! The metal bar thing might be for thermal coupling then, so that the chips don't drift apart once adjusted.

 

[thatsright]

I don't know - but I thought it might be useful to mention those other makes, as perhaps the service manuals for those might have more detailed information?

Assuming service manuals are available of course.

Yes, I've been digging up those SM's for a few weeks now. The only one I found a PDF of was the Nak. OMS-4/40. It's quite a thorough serv. manual, and shows indiv. datasheet for every IC except, weirdly, that 6352 chip! Obfuscation? Interference from the Simulation ??

From the CDP reviews I've read of units using that NEC IC, I'm fairly sure it is a 2x over-sampler [but it may need ancillary logic devices attached to it as well].

Below images from OMS 4/40 SM. [elektrotanya.com]

Also see:

Nakamichi OMS-40 Specifications Nakamichi

And can anyone here can translate the Japanese captions to the infographic?

 

[thatsright]

From this front photo :https://audioaddictsforum.com/thread/1845/nec-903-monster-high-vintage
It seems that the NEC 903 have a "remote controled attenuator system" . I guess it's what you take for a R2R DAC .

I think that the four DACs are here :

https://audio-heritage.jp/NEC/player/cd-903.html

NEC was doing discrete R2R in the mid-1980s. There may have been other manufs then, too. Or even hobbyists. Or private corporate skunk-work or pet projects. You know ... stuff that CEOs and Executives of major corps get to take home. The 903 was likely a "loss lead' product. Meant for CES shows. It made NEC's other audio products -- cheap receivers , etc. -- sound very nice at the shows.

I wonder whether MSB and other johnny-come-latelys like Soekris and Denafrips weren't ... ahem ... inspired by ... ahem ... thrift store finds?

 

[AnalogSteph]

The only one I found a PDF of was the Nak. OMS-4/40. It's quite a thorough serv. manual, and shows indiv. datasheet for every IC except, weirdly, that 6352 chip! Obfuscation? Interference from the Simulation ??

There may only have been a Japanese datasheet available, and/or it was under NDA.

From the CDP reviews I've read of units using that NEC IC, I'm fairly sure it is a 2x over-sampler [but it may need ancillary logic devices attached to it as well].

Looks like a 2X oversampling digital filter indeed. You can tell how ancient everything is by the fact that they needed extra logic to split the data stream for a second DAC chip, looks like it was originally designed with just one in mind (and external analog switching, still a very common arrangement in 1986 but all but gone by 1989).

 

[thatsright]

Looks like a 2X oversampling digital filter indeed. You can tell how ancient everything is by the fact that they needed extra logic to split the data stream for a second DAC chip, looks like it was originally designed with just one in mind (and external analog switching, still a very common arrangement in 1986 but all but gone by 1989).

I have the Nak OMS-4/40 SM. It uses two 74-series ICs to split the data signal for the two PCM54s.

And yes: The PCM54/55/56 do indeed require:
"A Sample/Hold Amplifier (Deglitcher) is Required at the Digital-to-Analog Output for Both Left and Right Channels."
From:

https://www.ti.com/lit/ds/symlink/pcm56.pdf

The Nak seem to do this purely discretely (see schematic, p. 36).
Not sure about NEC (no schematics or SM to be found). Those photos of the innards of the NEC cd-810 do show some opa's and discrete yo-92's before the output filter stage.
In some models, I have seen a dedicated Sample/Hold chip, also.

About external switching not being used after 1989. It did see some use in mid-1990s with the Philips tda-1305 stereo dac chip. In certain models, such as Cambridge Audio DAC Magic, Micromega and Rotel [do a search for "2 x TDA1305" at https://www.dutchaudioclassics.nl/the_complete_d_a_dac_converter_list -- you'll get 9 hits] . I've played around with this topology myself as a diyer -- create a "splitter" of sorts. The tda1305 is stereo dac and has no way to select a "mono" mode like you can with, say, PCM1792 or even the classic tda1541. It's messy glue logic but for dacs like the tda1305, it's likely worth it.

 

[audio_tony]

do a search for "2 x TDA1305"

I get 13 hits on this site:

CD player DAC and transport database - home page.

CD player DAC list, list of CD players, DACs and transports.

daclist.dnsbits.net

 

[thatsright]

I get 13 hits on this site:

That Philips CDR765 [a cd recorder with analog inputs] uses two tda1305's, but one for the cd player (tradit. stereo analog output) , and the other from the analog input to adc to dac (the other 1305). This works like a cutting lathe DDL (digital delay line) or a 3-head cassette deck, so that you can listen to what you're recording "live".

There is a newer dual tda1305 piece of kit that some Ali diyers may have encountered.
The Fever dac."Dual TDA1305 DAC chip + CS8412 Digital reception + CM108 USB Fever Class HIFI DAC Decoder board with usb fiber coaxial input"
Avail on Ali for this (about $38 usd total).
It is a 2 x tda1305 device but it stacks them (parallel); and not one per channel.