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SCD-1/777ES Alternative Clock Mod

12.247.43.125

Posted by jhietbrink on May 12, 2003 at 18:53:50

O.K. – so your first question is “Why?”

There are a number of add-in clock upgrades available including the Audiocom Superclock II, LC Audio LClock XO2, Tent Engineering XO2 and – if you want to build your own, the Kwak Clock. I had decided to use a Superclock after reading glowing reviews on this board -- and I even bought one. But then I started looking at Sony’s clock implementation and realized that maybe it just needed a little fixing.

This post applies only to the SCD-1/777ES. Other Sony players use gate oscillators constructed with discrete parts (crystal, capacitors, resistor). But on the SCD-1/777ES, Sony used a KDS packaged oscillator – and a rather good one apparently. Although the jitter spec is not published for the DSO751S series oscillator, I talked with a KDS engineer and learned that the spec is 5 picoseconds. This isn’t quite state of the art – but damn close. Packaged oscillators are more expensive than the typical gate oscillators constructed of discrete parts, but they offer a number of advantages including laser-trimmed frequency of the complete oscillator circuit and very short signal paths – which can lead to high accuracy and very low jitter if a good crystal is used.

Physically, the design of the clock is excellent. The oscillator is within an inch of the S-TACT DAC, right where it belongs. The clock is buffered and the buffer is integrated into the DAC rather than existing as a separate component. This ideal layout can’t be duplicated by an add-in clock connected to the oscillator mounting pads by an umbilical.

Sony also provided separate power supplies for the VC24 chip, S-TACT chip and oscillator/buffer. The single-regulated power supply for the VC24 chip is located on the Power Supply Board. The double-regulated supplies for the S-TACT chip and oscillator/buffer consist of a rectifier and regulator on the Power Supply Board and a second set of regulators on the Audio Board.

But Sony took a misstep on the design of the oscillator/clock power supply. It’s just a 3-pin regulator– and it’s a really noisy little SOT-92 type. One of the big advantages of add-in clocks is low-noise power supplies and this thing is anything but low noise at 70mV! (For those of you with add-in clocks, this noisy regulator is still feeding the input buffer in the S-TACT chip to which your clock is connected.)

I replaced the SOT-92 regulator with an Audiocom Super Regulator. The stock regulator is glued to the underside of the board – so I sought help in removing it. I then used silicone to glue the Super Regulator to a blank spot on the underside of the board near the regulator pads (spaced off the board about 1/16”).

I also replaced the 5V regulator feeding the S-TACT chip with an Audiocom Super Regulator. The S-TACT chip contains the clock generator and appears to reclock and amplify the pulse train from the VC24 chip. If upgrading regulators is going to make a difference, upgrading the oscillator/buffer and S-TACT regulators will have the most effect. If I were going to replace another regulator, it would be the 5V regulator on the Power Supply Board that feeds the VC24 chip. This chip distributes the clock signal from the S-TACT chip to the DSD decoder and ARP chips on the Main Board.

The caps on the regulator outputs are also less than great. Sony used 25V Elna Silmics which are very good caps for analog – but not the best choice for digital. So I replaced the Silmics with Sanyo Oscons. The bypass cap straddling the oscillator is a .1 uF, 250V mylar cap. This is a really bad choice for a 45 Mhz component – so I replaced it with a Panasonic ECHS PPS film cap which has the same lead spacing.

Changing the regulators and caps is a BIG upgrade and I attribute most of the effect to changing the oscillator/buffer regulator and caps. David Robinson described changing the S-TACT regulator along with the current pulse DAC regulators and OPA2604 op amps as no big whoop (Positive Feedback Online, Issue 4) – but this mod is a big whoop. The results correspond with the descriptions of replacing Sony’s clock with add-in clocks. There are many eloquent descriptions out there of what add-in clocks can do – so here’s just a quick summary of what you get from this mod: much better articulation resulting in much better soundstaging, better overall coherence, increased body, more extended AND smoother treble, cleaner and more articulate bass and a better sense of pace. Yes, it’s almost too good to be true.

Besides the suboptimal power supplies, there are grounding problems around the oscillator and S-TACT chip. I believe that one of the reasons that add-in clocks are effective on the SCD-1/777ES is that they get the clock off the noisy ground plane. However, it’s better to leave the clock in an ideal position and fix the ground plane.

The Audio Board ground plane has three ground connections to the three power supplies coming from the Power Supply Board (5V, 9V and 18V). These ground connections are literally distributed from one end of the Audio Board to the other. This makes for a noisy ground plane in the vicinity of the oscillator and S-TACT chip as the different ground potentials of the three power supplies attempt to equalize themselves. In a previous mod (see power supplies, revised grounding below link below), I created a star ground for these three power supplies on the Power Supply Board. The effects of this mod were substantial – and correspond to the effects described for jitter reducing mods.

So are these clock mods as good or better than an add-in clock? The answer will never be known unless both approaches are taken in identical players and the players are compared. All I can say is that this mod sounds great!

Break-in: I did this mod in multiple parts – and learned that both the regulators and caps need at least 50 hours of operation to break in.

Other SCD-1/777ES Mods and Information

Analog Signal Path

Replaced RCA jacks with Vampire OFC jacks
Replaced output wire with Kimber AGSS
Revised grounding creating a star ground for audio board
http://www.audioasylum.com/forums/hirez/messages/41691.html

Replaced AD712s in the output buffer stage with hi-spec OPA2132s
http://www.audioasylum.com/forums/hirez/messages/78259.html

Replaced resistors and capacitors in I/V conversion stage
http://www.audioasylum.com/forums/hirez/messages/93363.html

Set filters to “custom”

Power Supplies

Revised grounding, AC polarity, analog supply bypassing
http://www.audioasylum.com/forums/hirez/messages/107304.html

Removed choke on analog power supply
http://www.audioasylum.com/forums/hirez/messages/32357.html

Transport

Added capacitance to the “Digital” (Transport) Power Supplies
http://www.audioasylum.com/forums/hirez/messages/133431.html

Clock

Improved power supplies to oscillator and S-TACT chip and quieted ground plane
This post

General Description

Analog Signal Path
http://www.audioasylum.com/forums/hirez/messages/33130.html

Accessories

Electraglide Reference Glide power cord
Chang Lightspeed HT1000 power conditioner (w/upgraded capacitors)
AudioDesk Systeme CD Lathe
Aurio Pro Media Isolation Bearings w/optional tungsten carbide balls

This post is made possible by the generous support of people like you and our sponsors:

Sonic Craft

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