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More SCD-1/777ES Power Supply Mods

12.209.231.80

Posted by jhietbrink on October 26, 2003 at 17:58:32

"I just want to say one word to you -- just one word -- ceramics."
(A slight recasting of advice from a businessman in “The Graduate”).

In the end, the most significant cap change I made in the Audio Board digital power supplies was adding ceramic bypass caps – BIG ceramic bypass caps. I have to admit, I’ve suffered from a fear of ceramics – perhaps arising from experiences in the analog world. It was a little counseling from Alan Wright and the discovery of a couple of diyAudio threads on large ceramic caps started by ftorres that helped me to overcome my fear.

ftrores performed a interesting experiment in which he used various combinations of ceramic and electrolytic caps to tame the power supply noise emanating from a 50 Mhz oscillator. Conventional wisdom calls for .01 or .1 uF ceramic bypass caps at the power pins of high speed digital components, but ftorres found that these small caps had only a modest effect on power supply noise. However, BIG ceramic caps – 1 uF or more soaked up noise like magic. Check out the following URL in that other forum:

http://www.diyaudio.com/forums/showthread.php?postid=42786#post42786

In his Level 2 Upgrade, Alan Wright adds large value surface-mount ceramic caps around the VC24 filter and S-TACT chips. Surface mount caps probably are the best choice since they minimize problems with lead inductance, but I didn’t really feel like doing microsurgery on the circuit board traces. Fortunately, Sony provided plenty of mounting locations for thru-hole ceramic caps. The VC24 and S-TACT chips are bypassed by both 220 uF and 100 uF electrolytic caps followed by .1 uF ceramic caps on the VC24 chip and .1 uF stacked film caps on the S-TACT chip. The 220 uF electrolytics are way large enough to support the chips on their own. Moreover, the 100 uF electolytics are really too close in size to the 220 uF caps to be ideal bypass caps – so I just replaced the four 100 uF caps (C309, C313, C330, C334) with 2.2 uF Kemet X7R ceramic caps. And for those of you who still have stock oscillators, I replaced the .1 uF film cap bypass (C326) with a 4.7 uF ceramic.

Sony’s choice of .1 uF ceramic bypass caps for the VC24 is fine since this chip operates at about 22.6 Mhz – definitely ceramics territory. Much of the S-TACT chip operates at the frequency of DSD (2.8Mhz) and this is a better frequency for the stacked films Sony provided. However, this chip is a mixed frequency chip with at least the clock buffer running at 45.1 Mhz. C-328 should have really been a ceramic – but I’m too lazy to change it – at least for now.

The current-pulse DACs also operate at 2.8 Mhz and Sony’s choice of Vishay MKT1826 stacked film bypass caps is probably o.k. – so I left them alone. I didn’t consider ceramics here because 2.8 Mhz is a little on the low side of the frequency spectrum for ceramics.

The current-pulse DACs are also bypassed with big black United Chemi-Con DTD mylar bypass caps, one on each chip. Sony doesn’t really provide enough information to determine exactly what these caps do – but replacing them with caps with better high frequency performance improves the sound. I used Panasonic ECHS caps because the PPS caps have the high frequency performance of polypropylenes in the size of a mylars.

I started modifying the digital power supplies by changing the Elna Silmic electrolytic caps on the Audio Board digital power supplies to Sanyo Oscons. The Elnas are excellent caps for analog applications, but organic polymer caps like the Oscons are a better choice for digital applications. Inmate phopson started with a change to Oscons followed by a change to BlackGates and reported a preference for the BlackGates. At several times the cost, one would hope for these results.

All of the cap changes produce more or less the same kinds of improvements: better dynamics, a more articulate and driving bass response, more body at all frequencies, more fluidity, a smoother treble response and more resolution overall. Adding the ceramic caps was the most effective change, followed by the Oscons and the PPS caps.

All of the caps are thru-hole components and their locations are polarities are clearly marked, so swapping them out is relatively straightforward. But do use ESD precautions including an ESD safe iron. The mods have no downside and collectively, the effect is quite significant. There is a bit of a break-in period for the Oscons (during which there will be less body rather than more), but the ceramics sound good from the get go. And just a warning to those of you who have filled the digital power supplies with BlackGates – there are reports of BlackGates and ceramic bypass caps not mixing well.

There is another important digital power supply tweak – but I’m going to write it up with what may be my last analog tweak. The two mods are synergistic so writing about them together seems to be the best thing to do.

AC Board Mod, Part II

Sony high-end SACD players have custom AC power filters with discrete components, making upgrades possible. Many months ago, I posted a simple mod that removes the choke in the AC filter before the “analog” transformer, improving dynamics. But there’s more that can be done – like upgrading key capacitors.

I finally got around to replacing the .01uF ceramic caps across the “analog” (C482) and “digital” (C484) transformers with .1uF film caps. To be totally safe, these caps should be replaced with Type X capacitors rated for continuous duty across the AC line. Vishay F1772 and F1773 caps (Mouser) are examples Type X metalized film caps. However, I used a .1uF REL PPMF-X MultiCap rated at 400V. I’ve had good luck with these caps on power lines, and they sound great – but you’re responsible for your own choice.

Be careful when installing the caps to keep the leads of one cap from interfering with the leads of the other. I used a little Teflon tubing to make sure that the leads weren’t going to drift into each other – spacing is a bit tight since the film caps are larger than the stock ceramic caps.

A unique thing about the AC Board is that there are separate filters for the “analog” and “digital” transformers. This helps to prevent “self pollution” where noise from one internal power supply migrates to the other. Increasing the size the filter caps and improving their quality enhances the isolating effect of the twin filters. The primary purpose of these filters is to prevent noise from moving out of the SACD player to the power line. However, the larger caps are effective in filtering incoming noise on the power line as well.

This is a mod I’ve done before and its effects can vary somewhat with the equipment. On the SCD-1/777ES the most noticeable effect is a more natural treble presentation. A bit of digital sizzle goes away. And there is a small improvement in detail retrieval and soundstaging. This is a minor mod, but is relatively easy and inexpensive.

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 capacitors on Audio Board digital power supplies, revised capacitors on AC Board – this post

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
http://www.audioasylum.com/forums/hirez/messages/137033.html

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

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