The Adcom GDA 600 modification thread

george daniel

According to Fred,, the Bursons are do-able,, but it appears that there is more than just removing the old op amps and replacing with the bursons,,I'm thinking about dropping in some cursons in my CDP-just have to find out id they have a replacement for the NES 3352 in my player.

heiney9

Thanks for checking with Fred on the Burson's. For now I'll stick with the Browndogs.

george daniel

Brock,, be sure to use the "sockets" for the op amps--you should have this done--next week?

heiney9

george daniel wrote: »

Brock,, be sure to use the "sockets" for the op amps--you should have this done--next week?

Just ordered the Opamps and sockets this AM. I will order the rest of the caps for the power supply section and a couple resistors from Parts Connexion tonight.

I went with Multi-caps rather than Sonicaps simply because I could get everything I need all from one supplier. I also went with Nichicon FG's for the Power supply section.

Solder wick
Nichicon FG's
Multicaps
Mills

Hopefully sometime next week this will be done.

H9

heiney9

George, I'll answer you question from the other thread.

The OPA's along with sockets are here. I ordered the rest of the parts I needed for the PS and Rel Multicaps to replace the yellow mylars as well as some solder supplies from Parts Connexion and those shipped on Wednesday priority. Hopefully they will be here Monday and if all goes well with my soldering buddy the mod should be done by this time next weekend.

I am very excited as I've been doing some reading on the OPA627, plus your glowing endorsement. :)

H9

george daniel

Great,, can't wait to read your review.:)

[Deleted User]

Hello,
I went with two of the OPA627 in my Kenwood KT7500 with excellent results. I love the way good FM now sounds.
Cheers, Ken

george daniel

The 627's just seem to do it right,don't they?:)

[Deleted User]

Yes, I replaced a single OPA 2132 (which sounded excellent) with two of the 627 and there was a significant improvement. It's fortunate that Baltimore has a really good sounding classical radio station that cares about how things sound. WBJC at 91.5.
Cheers, Ken

heiney9

All the parts are here and I'll be starting the mod tomorrow night

heiney9

george daniel wrote: »

Well, it is done,, I went back to the "underside" of the board and mounted the 120uf directly to the op amps as Fred had first described,, along the way I swapped some additional power supply caps,,and the 680pf's as per Freds suggestion.The 680's came from Sonicap --RTE 680pF/600 volt,, since I cannot go back and edit, I'll list all of the parts,and corresponding board numbers/affilations if anyone is interested.Now for the sound,, extremely detailed,,huge soundstage with pinpoint imaging/instrument placement,,pretty darn close to having the musicans in the room with you,, a little silky but not fatiquing while listening,, sonicaps are still burning in, so more later on that,,I can say,however,that my SDA rig has never sounded this good,especially with just 40 watts of tube power,, and remember,,my source is an old Rotel 855 cd player.All for now.

George which 680pF's? Where's the list? Or did you include these with my care package? Are they the little brown ones?

I'm starting this tonight and I wish this entire thread was a little more organized ;). I'll try and document each step with part #'s etc for future reference.

Thanks again for everything.

H9

heiney9

George you have a PM.

I managed to get the power supply section done tonight. The photos are on my brothers camera so I'll post those when I can.

heiney9

Here are some photo's


(2) Nichicon Fine Gold caps on the left



(4) Nichicon Fine Gold large caps; (2) Panasonic FC's below the larger group; way left (2) Muse (green) caps; lower right (1) Panasonic FC caps


(4) Panasonic FC caps (gold/blue); (2) Nichicon Fine Gold caps (large)

george daniel

dems' some big A$$ caps you got there Leroy.;)

heiney9

george daniel wrote: »

dems' some big A$$ caps you got there Leroy.;)

Yeah, the Nichicons are a little larger than the original caps. They are taller and just a tad more circumference, but they fit very, very nicely in their appropriate spots. Oh yeah and the Panasonics are HUGE compared to the originals . I'll do a side by side photo.

I had it up and running for about 45 minutes no issues except the one I PM'd you about with the resistors I replaced (not part of the original mod) they get too hot for my liking.

H9

heiney9

One other thing to note is how well the PS pcb was designed. Most of the caps are polarized. The board is laid out in a way where the polarity is uniform as in the left side was always negative and the right side was positive so each piece is orientated the same way rather than having to always guess which is negative and which is positive. It made getting the correct polarity a breeze.

I heard thru the grapevine a Polkie blew up his power supply during this mod. That really sucks, was it a polarity issue? Some of the smaller caps had little to no gap on the pcb between the leads and it made for a challenging time. We had to make sure we didn't accidentally solder a "bridge" between the two leads. Actually used a magnifier to make sure, as the space between the leads was too small for the naked eye.

I helped but my buddy did all the soldering, this is too intricate for a novice solderer. Thing are tight and the parts, with the exception of the large PS caps are very small, lots of patience is needed.

H9

ben62670

The audio board on my Denon is very tight with soldering points. Pretty intimidating at first.

george daniel

Remember,, never get out of the boat. Stick to the plan:)

heiney9

george daniel wrote: »

Remember,, never get out of the boat. Stick to the plan:)

LOL , I know.............I know. I think I'll put the old resistors back in. I'm telling you one of the Mills I replaced them with gets really hot to the touch, no smell but if I hold my finger on it more than 10-15 seconds I feel a bit of pain

H9

george daniel

Okay,, has anyone else completed this mod yet? If so-- impressions?

heiney9

Sorry George I have been sidetracked. My soldering buddy, who has a family (tripplets in High School), just wasn't available this week. Plus the extra caps I ordered from Parts Connexion are taking forever to get here. I ordered them last Wednesday and they just shipped yesterday :mad:. The first order, which was more parts, didn't take anytime at all.

Hopefully by middle of next week you'll be hearing my impressions.

H9

comfortablycurt

Great thread!!

So, is there any word on whether or not these mods can be performed on the GDA700 as well? I'd love to try this someday...but I like the fact that the GDA700 has HDCD decoding.

For that matter...The DAC section of the GCD750 CD player is basically the same as the GDA700...could the DAC section of the 750 be modded in a similar way?

Just curious.

heiney9

comfortablycurt wrote: »

Great thread!!

So, is there any word on whether or not these mods can be performed on the GDA700 as well? I'd love to try this someday...but I like the fact that the GDA700 has HDCD decoding.

For that matter...The DAC section of the GCD750 CD player is basically the same as the GDA700...could the DAC section of the 750 be modded in a similar way?

Just curious.

The power supply, yes. Not sure what op-amp the 700 uses. It uses different Burr Brown chips, but I'd say it's probably very likely.

H9

ben62670

The audio section is more important than the DAC section.

george daniel

comfortablycurt wrote: »

Great thread!!

So, is there any word on whether or not these mods can be performed on the GDA700 as well? I'd love to try this someday...but I like the fact that the GDA700 has HDCD decoding.

For that matter...The DAC section of the GCD750 CD player is basically the same as the GDA700...could the DAC section of the 750 be modded in a similar way?

Just curious.

Can you post a copy of the schematics? Most ot the tweaks are in the analog path,, thats where the bang/buck pays off-- first thing to do is determine what op amps you have.

dacboy

Hey all! I've been researching such a project for months, and narrowed my selection down to units using the 1541 or PCM63. I found this thread and decided to jump in. I picked up a used GDA-600 yesterday, and can't wait to begin the mods! IMHO the pcm63 was the last of the good R2R dacs, and dacs period. I'm tired of playing the hyper-up-sampling game, or the latest Xingdong Wang goodly-dac v2.9 Altoid-boxed whatever... (blame the DACinthe BOX people for starting this). All of the 96/192kHz stuff is detailed but suffers from far too much digital glare. Something has happened to digital over the last 10years, it's not good, and people are beginning to wake up to this digital deception. I recently modded an old jvc xl-z1010, after yanking out the ne5532s the unit sounds unbelievably good. Every time I open a component and see 5532s on the output I just want to freaking SCREAM and rip out those horrible little insects. IMHO the ne5532 is the scourge on hi-end audio over the last 20yrs. Back to the subject at hand, has anyone considered replacing the rectifiers in the power supply while you have it torn apart? Hexfreds perhaps? Just as easy as soldering in a new cap. Also, George, I see the recommendation to remove the ferrite inductors at L 500 & L501, why not just jump back to R530 & 531 are these resisters even needed? Perhaps upgrade with some mills or Kiwame resistors? I've included a pic of my stock GDA-600. I won't be able to get to mods for about 6 or 7 weeks but will be tracking this thread with great interest!

george daniel

he,he,,I just remove em' and replace with what was suggested by a former forum member,,who is infinately more adept at circuits than I will ever be.Then plan was to get the biggest "BANG" for the buck,as the caps were pretty inexpensive,,the browndogs were the only expensive component.But the sound,,oh so sweet and detailed,,jusr the right amount of analog warmth,,but nooooo brightness,, and surprisingly good with even medicore transports.:)

FTGV

dacboy wrote: »

IMHO the pcm63 was the last of the good R2R dacs, and dacs period.

The AD1862 was an equally fine D-A chip of that era but didn't find it's way into nearly as many products.Ofcourse being limited to 20bit/48k precluded their use with new higher rez formats.

I'm tired of playing the hyper-up-sampling game... All of the 96/192kHz stuff is detailed but suffers from far too much digital glare.

IMO much of the blame must go to poor analog section and power supply design than any limitation of the DAC chip.Having heard examples of the newer 24/192k hybrid dual differential chips(DSD 1791,CS43122,CS4397/98)feeding top notch analog stages,I'm of the opinion they can sound very good indeed.

IMHO the ne5532 is the scourge on hi-end audio over the last 20yrs.

While they are far from being SOTA or the most transparent of the breed ,they are better than some of the NJR dreck that regularily gets used in Asian built products.Some designers such as Musical Fidelity still hold the 5532 in high regard and still use it.

has anyone considered replacing the rectifiers in the power supply while you have it torn apart? Hexfreds perhaps? Just as easy as soldering in a new cap.

It could be done but not quite that easily,the power supply uses full wave bridges not discrete diodes.

, why not just jump back to R530 & 531 are these resisters even needed?

Yes those resistors are needed to prevent the possibility of instability from cable capacitance.

dacboy

Thanks FTGV good info! Hey guys, I'm looking at the schematic and have begun ordering parts. I'm looking at some of the resistors around the opamps, (R523,R524, R525 Right Ch), and R520,R521,R522 Left Ch) all listed as 1.21K. I'm thinking about upgrading these along with the film caps, maybe to foil or Tantalums? It looks like these would be the most critical in the analog path? yes/no? Suggestions? It looks like these are coming out of Pin 7 of Chanel B of each opamp? Ideas? Bring on the pics and updates people!:)

dacboy

See attached