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SCD-1/777ES Op Amp Mods

12.209.231.80

Posted by jhietbrink on November 3, 2003 at 18:49:55

After many other mods, I finally felt compelled to ditch the OPA2604 op amps in the I/V conversion stage of the Analog Board. These are the only thu-hole op amps on the board (although there are many others) and are typically the op amps that are changed out by modifiers. The OPA2604 is a reasonably well-respected FET input op amp – but it’s on the slow side for I/V conversion in a 1-bit player.

The most common replacement is an add-in board with dual OPA627’s. This is certainly a safe choice since it sounds very much like the OPA2604. Most people say they prefer the 627 because it’s quieter and more articulate. However, in this application, others find it to be a hi-fi, less musical version of the 2604. But then, the OPA627 is still a relatively slow op amp better suited to purely analog applications – and the faster OPA637 can’t be used in this application.

I decided to avoid safe choices – selecting the very fast, high bandwidth LM6172. This was apparently Sony’s first choice for I/V conversion, and you can see it in the service manual schematic. But because of other things Sony did or didn’t do – the LM6172 didn’t work out and the OPA2604 was substituted in production. I felt that I had reversed enough of Sony’s questionable design and component choices to give the LM6172 another go. I hadn’t quite – but more about that later.

As you may have noticed, Sony used no local bypass caps on this op amp. Instead, Sony used a pair of laminated supply rails that act like a continuous bypass cap down the center of the board. However, the rails are rather distant form most active components – including these op amps. And these op amps need to by bypassed at the pins – they have a 3,000V/uS slew rate!

I added .1 uF NPO radial ceramic bypass caps between pins 4 and 8 on the LM6172’s. The caps are the Kemet Goldenmax brand in the C350 case size (available from Mouser). The caps have about the same lead spacing as the op amps so it’s possible to get extremely short lead lengths. Sony left plenty of space on the underside of the board – so the caps mount nicely on the underside. And yes, these caps cost more than the op amps.

The NPO ceramic caps were the second bypass caps I tried. Initially, I decided to follow the advice of Thorston Lorch on bypassing the LM6172. I used 1 uF Vishay 1826 stacked film bypass caps, similar to the Siemens capacitors used by Thorsten. These caps took awhile to break in – and the sound of the op amps changed wildly throughout the break in period. Unfortunately, they didn’t settle in a good place. So, before ditching the LM6172’s, I decided to follow National Semiconductor’s recommendation and use ceramic caps. And what a difference a cap makes!

Believe it or not – the LM6172 actually sounds lush with the NPO ceramic caps in place. The bass is ample and powerful – and far more articulate than the bass of the OPA2604. The treble is extended and smooth – no hard edges. Cymbals shimmer and every brush movement can be traced. Now I know that some of you are thinking that this can’t be a description of the LM6172 – or that I’m partially deaf. But what the LM6172 sounds like all depends on the bypassing. Without the right caps in the right configuration, the LM6172 can sound lightweight with a hard treble and diminished mid-bass. But with the right caps – the sound is glorious – at least for an op amp.

Perhaps the biggest change from the OPA2604 is the LM6172’s vastly superior resolving power – which in turn can produce some very realistic soundstaging on well recorded discs. In complex musical passages the LM 6172 is absolutely unflappable – not congestion at all. Dynamics are more lifelike – especially micro dynamics (as in you can hear them). The macro dynamics of the OPA2604 never bothered my cat’s sleep, but she is occasionally startled by the macro dynamics of the LM6172.

After listening to the LM6172, it sounds as if the OPA2604 is wearing a veil on top and a hula skirt on the bottom. The veil hides a bit of an ugly treble and the hula skirt blurs and accentuates movement down low. If properly implemented, the LM6172 is a big upgrade – and you won’t miss anything about the OPA2604.

And now for the bad news:

You also can’t do this mod in isolation of some other mods – or you’ll be ripping out the LM 6172’s just like Sony did. At minimum, I would say that you must at least replace the four AD712 op amps on the Audio Board as well. And that brings me to another digital power supply mod.

It all started when audioeyedoc and I were corresponding about replacing the AD712 op amps in the output buffer stage with OPA2132U’s. He wondered if he should replace the AD712’s in the voltage reference for the current-pulse DACs and I said no. Thankfully, he paid no attention to me and replaced them anyway with another pair of OPA2132U’s to great effect. In retrospect, I think the OPA2132U’s sound better because of their significantly superior PSRR. The SOT-89 voltage regulator feeding these op amps is a noisy little cuss.

The best thing about this mod is that it produces richer more relaxed (dare I say analog-like) sound. Plucked strings take on a less forward sound. The bass becomes deeper and more powerful. The soundstage expands and voices and instruments sound right-sized. And without these changes – the bass and especially the treble of the LM6172 just don’t sound quite right. I know -- I did the LM6172 mod first.

The AD712’s are surface mount devices and require special skills and tools replace. And while you’re at it – lose the AD712’s in the output buffer stage as well (link below). The OPA2132U (the hi-spec version) makes an excellent replacement in both locations.

And then there is the issue of synergy with passive components in the analog signal path. Thorsten reports that the LM6172 doesn’t mix well with BlackGate capacitors and recommends Elna Silmics. The good news is that Sony already gave you Elna Silmics – but if you’ve replaced them with BlackGates, you might want to stay away from this mod. I would also guess that the LM6172 would be a better match with the stock Riken resistors – or with Caddocks. If you’ve switched to Vishays – proceed with caution. I’m reporting results with a mix of Rikens and Caddocks.

And for the anxiety ridden among us – are there good choices other than the LM 6172’s?

The AD826 is another viable – and perhaps safer choice. It’s also a dual hi-speed bi-polar op amp with a high slew rate and quick settling time. Fmak has used this op amp and likes it a lot. I haven’t heard it – but it’s rumored to have a slightly sweeter treble than the LM6172 and a more powerful sounding bass. On the other hand – it doesn’t have quite the resolving power of the LM6172.

And then there are the single op amps that require add-in boards. I’ve already mention the OPA627 that’s part of the Audiocom mod. I believe that both audioeyedoc and phopson are using AD825s on add-in boards. These are relatively quick FET input op amps with better slew rates and settling times than the OPA2604 or OPA627. They are reported to sound sweet with a powerful bass – but are significantly less resolving than either the AD826 or LM6172. I stayed away from add-in boards because they add length and solder joints to the feedback loops -- and at least in theory – this isn’t a good idea.

I’ve been at this off and on for the last two years – and I think I might be done now. Looking back on the experience – I’ve learned at least three things:

Sony almost built a truly great SACD and CD player. In the end, I’ve changed relatively little – only $300 in parts costs – while making a huge difference in what this player sounds like. And some of the changes I made were to replace items of equivalent cost.

CDs can actually sound pretty damn good. I started down the hirez highway because I had lost all hope that CDs would ever sound like music. There is no question that SACD is a significant improvement – but the changes I made to my SCD-777ES also produced one hell of CD player. I now enjoy my CD collection – including discs that I had previously dismissed as “unlistenable”. In fact, I find well-recorded CDs to be more enjoyable than not-so-well-recorded SACDs. There – I said it.

The internet and this website are great gifts to audio enthusiast. Without them, I would have made many fewer mods – and might not even have purchased a SCD-777ES. The insights of others and easy access to spec sheets has been invaluable. And I’ve had a chance to correspond with some interesting people with soldering irons that I probably would have never met -- like audioeyedoc, fmak, phopson tkchan, and Alan Wright.

And in case anyone wants a parts list for all of the mods described below – here it is:

Audio Board

Capacitors
C000 Kemet C350 Radial NPO 100V .1 uF Newark 7.60
C000 Kemet C350 Radial NPO 100V .1 uF Newark 7.60
C101 Sanyo Oscon 25SP10M 25V 10 uF Capacitors Plus 1.30
C201 Sanyo Oscon 25SP10M 25V 10 uF Capacitors Plus 1.30
C102 Panasonic PPS 50V .1uF Digikey 2.54
C202 Panasonic PPS 50V .1uF Digikey 2.54
C107 RELCap TFT 100V .068 uF Parts Connexion 20.25
C207 RELCap TFT 100V .068 uF Parts Connexion 20.25
C111 Sanyo Oscon 16SP100M 16V 100 uF Capacitors Plus 1.22
C211 Sanyo Oscon 16SP100M 16V 100 uF Capacitors Plus 1.22
C113 Sanyo Oscon 16SP100M 16V 100 uF Capacitors Plus 1.22
C213 Sanyo Oscon 16SP100M 16V 100 uF Capacitors Plus 1.22
C129 Sanyo Oscon 10SP100M 10V 100 uF Capacitors Plus 1.10
C229 Sanyo Oscon 10SP100M 10V 100 uF Capacitors Plus 1.10
C302 Sanyo Oscon 20SP180M 20V 180 uF Capacitors Plus 1.50
C309 Kemet C340 Radial X7R 50V 2.2 uF Mouser 3.25
C316 Kemet C340 Radial X7R 50V 2.2 uF Mouser 3.25
C326 Kemet C350 Radial X7R 50V 4.7 uF Mouser 9.16
C327 Sanyo Oscon 16SP100M 16V 100 uF Capacitors Plus 1.22
C322 Sanyo Oscon 20SP180M 20V 180 uF Capacitors Plus 1.50
C324 Sanyo Oscon 20SP180M 20V 180 uF Capacitors Plus 1.50
C330 Kemet C340 Radial X7R 50V 2.2 uF Mouser 3.25
C334 Kemet C340 Radial X7R 50V 2.2 uF Mouser 3.25
C401 Elna Silmic 63V 47uF Sony 4.80
C402 Elna Silmic 63V 47uF Sony 4.80

IC
IC102 LM6172 Digikey 3.80
IC202 LM6172 Digikey 3.80
IC104 OPA2132U Digikey 8.20
IC204 OPA2132U Digikey 8.20
IC107 OPA2132U Digikey 8.20
IC207 OPA2132U Digikey 8.20
IC304 Audiocom +5V Super Regulator Reference Audio Mods 66.00
IC308 Audiocom +5V Super Regulator Reference Audio Mods 66.00

Resistor
R107 Caddock Filp Chip 10R Engineering Sample
R108 Caddock Filp Chip 10R Engineering Sample
R109 Caddock Filp Chip 10R Engineering Sample
R110 Caddock Filp Chip 10R Engineering Sample
R207 Caddock Filp Chip 10R Engineering Sample
R208 Caddock Filp Chip 10R Engineering Sample
R209 Caddock Filp Chip 10R Engineering Sample
R210 Caddock Filp Chip 10R Engineering Sample
R112 Caddock MK-132 470R Parts Connexion 3.95
R113 Caddock MK-132 470R Parts Connexion 3.95
R212 Caddock MK-132 470R Parts Connexion 3.95
R213 Caddock MK-132 470R Parts Connexion 3.95

Revise Grounds

AC Board

Capacitor
C482 RELCap PPMF-X 400V .1uF Michael Percy 3.95
C484 RELCap PPMF-X 400V .1uF Michael Percy 3.95

Line Filter
T481 Remove and jumper

Revise Grounds

Main Board

Capacitors
New Elna Silmic 25V Recycle from Audio Board

PIN Board
J150 Vampire CMF1/OFC RCA Michael Percy 20.00
Wire Kimber AGSS, 18" 27.75
Revise Grounds

Total 324.04

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

Replaced OPA2604’s in the I/V conversion stage with LM6172’s
This post

Set filters to “custom”

Power Supplies

Revised capacitors on Audio Board digital power supplies, revised capacitors on AC Board http://www.audioasylum.com/forums/hirez/messages/155617.html

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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Parts Connexion

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