What's really nice about the Cirrus Logic CS4398 is that it's a voltage output DAC with balanced outputs. This avoids possible slew rate issues in the I/V stage that current output DACs require and it also makes it really easy to implement what a lot of people regard as the best analog output stage possible for this DAC which is transformer coupling. Offsetting the cost of the transformers is the fact that all you have to do to the analog stage is remove four capacitors.

You don't need to do anything to the analog power supplies or fret about what op-amps or discrete modules to use because you're using none of it. This saves a lot of parts as detailed above and more importantly time which if you're paying someone to mod your player is mostly what you're paying. Even though the current active setup is sounding pretty nice it's no doubt something to consider in the future but it would of course depend on being able to source some suitable transformers.

That day came and went because when I tried to source those suitable transformers from a local designer of some note I was told that he couldn't possibly sell them to me unless I had a full mod package installed on my machine because there wasn't enough profit margin on just the transformers. Sort of like walking into a green grocer to buy an apple and being told that you can't have the apple unless you also buy a banana and a pineapple. I explained that I'd already modded the player and only wanted the transformers and was happy to pay what he considered a fair price for them, including a fair profit, but no go. This left me slightly perplexed to say the least and the project got put on hold for some time.

Time passed and then one day with renewed vigor I set out once again to source some suitable transformers. Apart from being made in Sweden I'd been hearing very good things about Lundahl line transformers when used with the CS4398. So when a mate mentioned that a mutual friend had obtained Lundahl's from a local supplier I thought why not.

Why not indeed but sadly when I contacted this local supplier I found their delivery time frame, not to mention their draconian terms and conditions to be totally unsuitable. What is it with Australian retailers and their inability to sell you what you want and yet they complain that things are hard and sales are down. So then I tracked down the Australia importer and distributor for Lundahl and they were happy to supply them but quoted a three week delivery time Ex Sweden as they didn't have stock. They also quoted a price that was 33% more than the first offer I'd had. I did reply to their quote and point this out. I was polite, I was just trying to negotiate a more reasonable price but I never heard back from them.

Time to turn to the InterWeb where I found the USA distributor for Lundahl, K&K Audio. Exchanged a few emails and for the cheapest price I'd been quoted so far, by far, including freight they arrived here within seven days. Talk about friendly, prompt and efficient service. Australian distributors and retailers could certainly learn a thing or two from them. So if you're in Australia or anywhere else for that matter and you want some Lundahl transformers I can highly recommend that you get them from K&K Audio. Okay, enough whinging about the inablilty of Australians to do business and moving onto building stuff, yay.

Due to the fact that I've used the space at the front of the player to the left of the transport to house a low noise power supply for the DAC, power supply for the clock and the clock itself, I had a slight problem. Because this is where most other modders put the transformers as there isn't any room anywhere else.

Thinking laterally and being a firm believer in function over form, substance over style et al. I took what some would regard as a radical approach. Rather than house the transformers inside the case I'd put them outside of it. And to keep lead lengths to a bare minimum the obvious place outside the case was on top of the case directly above the DAC chip.

Yes that involves drilling a hole in the top case of the player. It is only a small hole of 10mm in diameter and there is only one. I do understand that some will find this rather distressing so if you feel the need for a calming beverage and a lie down before reading further please do so. Be reassured though that I haven't included photo's of this barbaric act of vandalism, just the finished product.

The circuit is the standard serial connected primary and secondary as suggested by Lundahl. I've also used their suggested, or close to them loading and filter values on the output consisting of a 39k resistor in parallel with a series 7k and 390pf. The primary side is simply fed via 1k resistors from both the Out + and Out - from the CS4398 chip.

Designation	Description	Replaced with
CE7, CE8, CE9, CE10	100uf/16V TK	Remove
KTTran1, KTTran2	Additional component	Lundahl LL1690 1:1 transformer Lundahl LL1690 data sheet
KTR1, KTR2, KTR3, KTR4	Additional component	1k Takman Carbon Film
KTC1, KTC2	Additional component	390pf Polystyrene
KTR5, KTR6	Additional component	39k Takman Carbon Film
KTR7, KTR8	Additional component	6.8k Takman Carbon Film
KTR9, KTR10	Additional component	200 ohm Takman Carbon Film
KTC3, KTC4	Additional component	390pf Silver Mica

The Lundahl LL1690 transformers are mounted in a small die case box which provides excellent shielding. They sit on strips of Blu-Tack to both fix and provide damping. The filtering and loading components are mounted directly on the transformers.

The finished product with both transformers mounted and wired. Additional Blu-Tack to the sides and on the top of the transformers helps hold them firmly. White blobby things are packing foam. A small amount of silicone holds the die cast box to the top cover of the player. The very short input wiring enters via the hole at the front of the box. Both the transformers and the box are earthed via the players chassis earth. Please note that the layout differs from the previous photo in that the .0047uf capacitors have been replaced by 390pf.

There's not much you can do around the DAC chip except upgrade the storage caps for the 3.3V and 5.0V supply rails and perhaps add some decoupling caps. There's also some voltage reference caps, CE1, CE93 and CE95 that I replaced with some better ones.

* The 100uf coupling caps on the balanced outputs of the DAC are replaced with pairs of 47uf/6.3V Black Gate NX Hi-Q in Super E-Cap configuration. Four on one side of the board and the other half of the pairs on the other side of the board as are the additional decoupling caps, KTC7 and KTC8 which are mounted directly on the pins of C23 and C97.

The Blu-Tak is to damp vibrations.

As a DAC is only as good as it's power supply it's time to beef that up with better storage/filter and decoupling caps.

Designation	Description	Replaced with
CE27, CE29, CE128, CE129	470uf/25V TK	470uf/35V Rubycon ZL
CE32, CE34	220uf/25V TK	220uf/25V Rubycon ZLG
C28, C30, C31, C32, (C42)	684J63	.01uf/400V Vishay 1839
U13	7805	+5V low noise regulator

+5V low noise regulator, as well as the +12V regulated supply for the clock and the Dexa D-Clock which is mounted in a shielded enclosure. The red, green and blue LEDs light up this corner of the chassis rather well. Very colourful at night, pity the top cover hides it all.

Low jitter clock

As is usually the case with players that spin silver disks the master clock in the Oppo is just a crystal and two capacitors variety. As such it has very high jitter and unless it's replaced then all the other mods being done will amount to not very much at all. After removing X1, C194 and C197 the new clock signal feeds into the vacated pad closest to the heatsink. For the earth connection I've simply scrapped the lacquer from the board underneath where the crystal used to be and soldered the lead there. The clock signal required is 3.3V at 27Mhz.

Running the lead from the centre of the player keeps it away from the analog board.

Designation	Description	Replaced with
X1	27Mhz crystal	Remove
C194, C197	Probably 33pf	Remove
Additional component	KTXO1	27Mhz Dexa D-Clock

Clock power supply

Even though the Dexa D-Clock has the whole ground loop isolation thing going for it I still prefer to power it with a completely independent supply with it's own mains transformer. There's a convenient place to locate this in the front left (from the front) corner of the chassis which is also as far away from the analog sections of the player as possible.

A small Block transformer, some ultra fast diodes, the usual RC snubbers and an initial 6600 uf (8 x 820 Rubycon ZL) storage/filter caps. The supply leads then run under the drive to the other side of the chassis and via a low noise regulator to the clock.

The clock supply is powered directly from the mains via a fuse and switched with a 5V/240V switching solid state relay activated by the main +5V rail on the power supply board. I've also replaced the IEC power socket with a better one which also includes an earth terminal which connects with the power supply low voltage side earth and hence to the chassis. Possible ground loop problems in the future will decide if this was a good idea or not.

Main power supply board

A switch mode supply is what it is and other than replacing all of it with an analog supply about all you can do is upgrade the main diodes to ultra fast soft recovery types and improve the storage/filter caps on all the supply rails.

Some of the new caps are just a tad big so they need to be offset a bit and then stabilized with some Blu-Tack. I didn't bother replacing the initial 68uf/450V CapXon filter caps because I'm not sure there's much to be gained by fitting only slightly better ones.

Designation	Description	Replaced with
D1, D3, D4, D5	IN4007	UF4007
CE9, CE14, CE16, CE18	2200uf/16V Acon	2200uf/25V Panasonic FM
CE10, CE17, CE19	1000uf/10V Acon	1000uf/10V Rubycon ZL
CE11, CE15, CE20	1000uf/25V Mtdcon	1000uf/25V Rubycon ZL
CE21	470uf/25V Acon	470uf/35V Rubycon ZL
CE22	220uf/16V Acon	220uf/25V Rubycon ZLG
CE12, CE13	470uf/25V Acon	470uf/25V Rubycon ZL
CE7	470uf/10V Acon	470uf/25V Rubycon ZL

Drive damping

Now I have no idea if covering just about the entire top cover of the drive with Blu-Tack is actually improving the audio but it used to sound very "tinny" and resonant before. It's certainly very dead now (and not just when you tap on the Blu-Tack) and the Blu-Tack layer makes a nice connection with the now shielded and damped top cover of the player. I've also treated the plastic housing where I can and also the underside of the cup holder at the front of it as well as the underside of the fold down of the front of the chassis. There is less drive noise now and far less buzzing from other parts of the player as the laser seeks which on this player it does a lot.

Isn't Blu-Tack great, but here's an idea for Bostik. Coloured-Tack. Then we could get really creative.

Chassis damping and shielding

The Oppo's chassis could at best be described as "flimsy" and from day one the folded top cover of my Oppo "buzzed" whenever a disk was playing and in the short term I solved this little problem with a small bag of lead shot. As copper shielding is very popular with makers of high end audio gear and as I shield everything else I mod or make I thought why not kill two birds etc. So I attached some single sided PCB offcuts to the top cover with some neutral cure silicone. Certainly damps the panel and when earthed via the copper braid earth strap no doubt shields as well which is probably a good thing as my passive pre sits on the next shelf up.

The purpose of the additional 0.7mm thick copper plate strips will be explained shortly. The earthing strap mates with a similar one on the clock/power supply board sub assembly which is earthed to the chassis.

The bottom of the player is also a bit flimsy even though it has several stamped dimple sections to help strengthen it. I filled these with yet more Blu-Tack as I also did for the four feet but the centre section underneath the drive was still a bit "tinny" so I stuck a piece of 15kg/m² lead sheet onto it with yet more neutral cure silicone. It's certainly dead now. The piece of lead weighs in at 900g and it and everything else that's been added have pushed the weight of the player up from it's intial 5.1kg to a now quality inspiring 7.7kg (17lbs).

Yeah it looks unsightly but when are you ever going to see it.

And that's about it, for now...

But I do plan to change the DAC chip power supply caps and the +/- 12V supply caps (after the regulators and maybe replace them with Linear Technologies LT's) with Elna Silmic II's, perhaps also explore the transformer coupled output option and a few other things. Which only leaves the question of how good is this Oppo as a stereo CD and SACD player? The short answer to which is that once you improve a few, well quite a few parts of it, it's very good indeed, staggeringly good in fact. So why is this Oppo so good as a CD/SACD player? Well for a start it's a Blu-ray player and as way of further explanation (in a round about way) on this point...

A couple of years ago I attended a demonstration by a couple of guys who came all the way from Linn in Scotland of their Linn Klimax DS audio streaming technology. According to Linn, all CD/SACD players have a fundamental flaw in that they cannot in real time (as the disk is playing) read the contents of the disk accurately. So you get read errors and if the source or in this case the players interpretation of the source is flawed then it doesn't matter what you do afterwards because you're only trying to cover up the errors. They are serious about this and have since boldly announced the death of CD players and have stopped making them.

One reason perhaps that a CD/SACD player has trouble accurately reading a disk is because of limitations in the laser, the size of the beam compared to the pits and the servo tracking system that moves it. A CD only contains 700mb, a SACD 4.7gb (SACD total content only on one layer) and a Blu-ray disk contains on one layer 25gb. So a Blu-ray player has to be capable of reading much smaller pits packed much closer together so it uses a shorter wavelength laser (half that of a CD player). Not much of a leap to say that it will make easy and more accurate work of reading the bigger pits of a SACD and the much bigger pits of a CD.

Back to the Oppo and you do have to remember here that this is a US$499 machine and to be honest a rather cheaply built one at that. Don't get me wrong here, it's a great design and implementation of the various chips, some very nice firmware, well put together but just using the cheapest parts and construction methods possible. The fact that several companies in the USA who specialise in "modding" players for superior 2CH audio performance are offering "mod packages" for this player costing up to US$3000 speaks volumes about what this machine is capable of. That and a few other companies who are taking the guts of the Oppo, keeping most of it (or all of it in the case of Lexicon), putting a better chassis around it and their badge, and then selling them for many many times what the Oppo costs.

You might have gathered by now that I'm as impressed by this beast as others seem to be. There is a massive improvement in audio quailty over the stock machine and I now find it hard to find fault with it so for CD/SACD playback it has replaced my Marantz. It also plays DVD-Audio disks which is a bonus, not that I have many of them. I may have to buy another one though for Blu-Ray/DVD usage, either that or put up with future drive replacements as I wear them out as this will be getting a lot of use.