Newbie needs help upgrading CD Player

[Stew]

I have an old Yamaha CDC-745 that I'm trying to upgrade. I ordered two AD826 opamps and then discovered that there are two more opamps in the signal path, presumably for the volume control. Do I need to upgrade those as well? I have a very limited understanding of all this and would appreciate any advice.

[Stocker]

Probably couldn't hurt. Be sure to replace them with compatible opamps though, or sound quality will suffer due to smoke infusion to the ambient air.

[Francis_Vaughan]

Can you get the schematics? This will help greatly, and give you clues about what to do in other places other than just op-amp rolling. Plus, as a learing experience it is hard to beat.

One place that has the service manual is here:
http://tigerdirect.partsearch.com/Pr...oductType=ACCS

For $10 it is money well spent.

[Stew]

Thanks for the replies! I need to get a schematic but here's what I know so far:

1) There are two JRC 55320 8-pin chips and two JRC 2068DD 8-pin chips that all use +/- 5v.

2) I have a sales brochure that gives a sketch of the DAC and output circuit. It shows a YAC514LSI chip which contains Pro-Bit, S-Bit Plus, etc. Then there is a "Twin Balanced Processing Circuit", followed by a 3rd order LPF, followed by an output buffer amp, for each channel. The brochure states that in the Twin Balanced Processing Circuit, "The normal (+) and reverse (-) phase signals from the left and right channel DAC outputs are combined before passing through the filters."

I'm fairly sure that the 2068DD's are the "Twin Balanced Processing Circuit" and the 55320's are the output buffer amps. Any thoughts on how critical the 2068DD's are? Any idea where I can find specs for both opamps?

[Stew]

oops, 5532D rather than 55320.

[Francis_Vaughan]

Don't worry, that JRC 5532 is well known about these parts, and a liitle typo won't disguse him for long.

Datasheets. Easy answer is www.datasheetarchives.com for most things.
http://www.datasheetarchive.com/semi...asheet=1559987

Google is also often your friend. But the YAC514LSI is a Yamaha proprietory part and information doesn't seem to have leaked out about it. But it is a single bit DAC, so most of what you need to know is already known, for better or worse.

I'm going to bet that the 2068DD (which is a dual op-amp) implements two transimedance amplfiers - one each for the + and - DAC outputs. These two signals then pass to the first of the op-amps in the 5532 which implements a simple balanced to single ended conversion, thence to the second op-amp in the package which buffers it to the output. If there is a volume control - it would sit before the output buffer.

This is a very generic circuit. Much fun, and probably some significant gains should be realised by op-amp rolling. The 5532 garners some pretty vitriolic opinions, despite its ubiquity in hifi gear. The 2068DD is not all that shabby a device, and having a bipolar input has nice low noise. But other specs are beaten by the AD826, noteably gain bandwidth and slew rate - things that are important for the transimpedance amp. But nothing is ever clear cut. That is why it is fun :-)

[Stew]

Francis - Thanks for all your help! This will be fun; much more so with your good advice! I think I'll try four AD826's. I also need sockets. I'm looking at the following 8-pin, open frame, 30ì gold plated DIP sockets with solder tails:

Assmann AR08-HZL/07-TT .93/ea Digikey# AE7313-ND
Mill-Max 110-93-308-41-001000 .42/ea Digikey# ED3308-ND

Are these good choices or would you recommend something else?

[Stew]

I ordered four AD826AN-ND opamps and four Mill-Max 110-99-308-41-001000 8-pin, 4-finger, Sn/Pb sockets. I got worried about using gold plated sockets because of dissimilar metals and corrosion. Don't know if this is an issue or not. Looking forward to the upgrade!

[Stew]

Hey Francis - Four sockets and AD826's are installed. Sounds great! Much cleaner, more open, and more detailed - top to bottom. The only complaints I found when researching the AD826 were that some found it too bright and/or the midband too recessed. My system needed the additional brightness and vocals were in your face. Now it sounds much better and vocals are back on stage with the rest of the band. Thanks again for the help!

[sunyata]

Hi,
I'm new here. I have a Yamaha CDC-635, and would like to improve its sound and dynamics. In the output stage there are four 2068JRC's (I don't have any schematic)
After looking through some threads, it seems like the OP275 or the OPA2134 are "safe" replacement opamps. The AD826 seems a bit more risky, regarding oscillation.
I would appreciate any help on this.

Best regards

Sunyata