The Adcom GDA 600 modification thread

annihilatorg

hey guys, i decided to use the turkey weekend to install the Burson Regulators. That's all done, but I'm having issues getting any readings on my volt meter (and this is not my first time to the rodeo).

First, concerning resistor and capacitor removal...
U100: removed R110, bridged R111, bridged C122
U104: removed R112, bridged r113, bridged C123

U100 was replaced with the 78XX. This needed to be re-pinned so that ground went to pin 1 (black cable) white +out to pin 2, and red +in to pin 3.

U104 was replaced with the 79XX and the pinout was the same from stock 1-red-ground 2-in-black, 3-out-white

For testing, I've got the two circuit boards in a plastic tray so they don't short to each other or to the case. I didn't see any reasons in the documentation why they might need to be directly tied to ground. I figure I'll employ some velcro or something similar for the final mounting, there's plenty of room for them between the PSU board and the DAC board.

I've plugged it into the wall and powered it on (btw, the series 2 regs have those annoying blue LEDs that everything 'techy' seems to require these days).

Using my trusty radioshack digital meter, I'm not getting anything for voltages on J101 pin 7 or 8 when connected to ground. I'm using the green cable screw point as my ground (ground from power plug). pins 7 and 8 on J101 are the + and - 15v pins that connect to the main DAC board. I've played a bit with the pots (turned each one a half-turn) but I've not gotten any difference in voltages.

Is there a better place to try and use for ground or a better place to find the correct output voltages? Seems like diode cr101 and cr109 might give me correct voltages on one side or the other, but I'm only getting miniscule microvolt differences on testing those.

perplexed. :frown:

FTGV

Try using the jumper at R111 or R113 as your ground probe point.

annihilatorg

FTGV wrote: »

Try using the jumper at R111 or R113 as your ground probe point.

ah ha! yes r111 is giving me magical volts! looking at the schematic i see why. going to play with the pots and report back.

Thanks again FTGV!

edit: I'm reading +15.00v on pin7 and -15.00v on pin 8 using R111 and R113 as my ground. Those pots required a large number of turns from 11-ish volts to 15v. Case Re-Assembly commencing.

FTGV

Your welcome.

heiney9

george daniel wrote: »

Okay-- components removed and jumpers in place.Since the regulators will not fit side by side unless I bend the pins,,I'll need some help here

Is this the correct position for the lm 337 in the U 104 slot?(the one on the right.)?

Yes, back to this. FYI I reloaded all my pics so they show up again in this thread. I had inadvertently moved them to another folder in my Photobucket account. I restored them to the original location so the links are working again.

A local Polkie Agfrost (Jay) is getting ready to mod his, and I need to get the regulators installed so I bumped this thread ttt.

George I have a question about photo number 4 aboove. Are the regulators mounted in this photo? Because it looks like they are in the resistor positions. Probably an optical illusion but they look out of place.

H9

SCompRacer

Way kewl! I love the DIY challenge of will it work better, or at all, when I am done.:twisted::cheesygrin:

I got my second shunt PS done for my next project so there is more space available on the bench.

george daniel

heiney9 wrote: »

Yes, back to this. FYI I reloaded all my pics so they show up again in this thread. I had inadvertently moved them to another folder in my Photobucket account. I restored them to the original location so the links are working again.

A local Polkie Agfrost (Jay) is getting ready to mod his, and I need to get the regulators installed so I bumped this thread ttt.

George I have a question about photo number 4 aboove. Are the regulators mounted in this photo? Because it looks like they are in the resistor positions. Probably an optical illusion but they look out of place.

H9

Brock,, if we are talking about the same pic,,they are not mounted,,IIRC one went in U-104(right side) and the other in U-100,,,it's been playing for for about 20 months now.I hope this helps.

agfrost

Thanks for fixing up your pix, Brock. I was rereading this thread last night and was wondering if you'd yet gotten around to installing the regulators. One of the two needed is now sold out at Parts Connexion, so if I wanted to replace those, I'd have to "get out of the boat" (sorry, George!). Perhaps the newer models might work, but that can wait.

Rich, I'd consider signing a lease if you throw out a "For Rent" sign on that benchspace. :cool:

FTGV

agfrost wrote: »

. One of the two needed is now sold out at Parts Connexion, so if I wanted to replace those, I'd have to "get out of the boat" (sorry, George!). Perhaps the newer models might work, but that can wait.

Yes the Burson series two will work(see post#424,425) but will need an alternative way for mounting the PC board since they don't mount like standard 3 pin regs. Another option would be from Belleson that Rich used in his MH.They will fit in the old reg's position.

SCompRacer

agfrost wrote: »

Rich, I'd consider signing a lease if you throw out a "For Rent" sign on that benchspace. :cool:

Mod Space Available! Sign up now! We got FM down there, or cassettes with a pair of Polk 7A's with Peerless. No slumming while working, at all. (Blake has the TT. It was too much of a distraction down there).

FTGV wrote: »

Another option would be from Belleson that Rich used in his MH.They will fit in the old reg's position.

Good suggestion Fred. Of course the all time good deal ain't there like with the close out Bursons. I've got some small sinks if Jay goes that route. Shouldn't be much mA draw/heat with the chip op amps. What, a few mA?

FTGV

SCompRacer wrote: »

Of course the all time good deal ain't there like with the close out Bursons.

Yeah that deal made it a much more attractive proposition.

Shouldn't be much mA draw/heat with the chip op amps. What, a few mA?

Probably only in the 50-60ma range.

george daniel

Okay-- I promised Mike that we would get his done---let the fun begin.
Yes-Mike it arrived safely--here we go,,stock pics first.

sda2mike

my sweet little dac! they grow up so fast, then we send them away! ha! thanks good dr. george! good idea with the pics! i've been looking forward to this for a long time!


mike

FTGV

sda2mike wrote: »

my sweet little dac! they grow up so fast, then we send them away!

No worries the little fella is in good hands .Uncle G will feed him a good diet of solder and have his analog stage all blinged out before sending him home.

SCompRacer

I think I'll have one here next week to send you George.:cheesygrin:

FTGV

SCompRacer wrote: »

I think I'll have one here next week to send you George.:cheesygrin:

Dipping our toes into the old school R2R DAC waters are we Rich?l

SCompRacer

FTGV wrote: »

Dipping our toes into the old school R2R DAC waters are we Rich?l

Jay has one (agfrost). He is suppose to bring it over after school and get some experience.:cheesygrin:

agfrost

Have you ever been experienced? :afro:

annihilatorg

Hello to others who have done this mod. I've been listening to my modded DAC for, I dunno, 500 hours since I did the mod with the voltage regulators. And yes, it still sounds awesome.

But, has anyone gone back and re-checked their Burson regulators for voltage changes after extended periods / burn-in? I've not had a chance to pop the case back open again, but am thinking about looking at it this weekend. Might be paranoid, but I always think something might be wrong when it has been modded. I'm not hearing anything noticeable, just wondering.

ps and only slightly unrelated - for computer audio sources, get a linear supply if you can. It makes insane differences in analog, and I'm going to wire up my PC that's hooked up to the adcom this weekend to one as well. Not sold on it making a difference in digital transmission, but it's something to check. I got two acopian VA12H1300 supplies from ebay for a steal and have one hooked to my headphone system.

sda2mike

well the good doctor george told me, my dac is on it's way back to me!!! george didn't just take a handful of parts and slap em in there..nope, he tried different combos of parts...burned them in...listened...tore some out...listened some more...until he was satisfied with the results! i can't wait to hear it this weekend! george is what this club is all about! stand up guy helping others...just for the fun of it!

thanks george
mike

heiney9

Do tell us George D, which parts did you swap in and out and what were your impressions.

Mike, If George did the work you know it's done correctly.

Details people................we need details!

H9

sda2mike

i think after several different combos of brands, george settled on sonicaps...with the recommended brown dogs...count on me posting my impressions..;)

heiney9

The only two brands I ever found that supply the exact value caps around the dac chips are Sonicap and Multi-cap the values are odd at .022uF; .0039uF and .0027uF. The PS can use a few different brands, that's why I need details. :cheesygrin:

I chose the Multi-caps because they were less expensive and seemed to get really good reviews.

H9

sda2mike

i'm sure when george signs on again, he'll update you:cheesygrin:

soundfreak1

BTW george this is a thanks from one of my gpod friends, i sent this thread to owr tech amd je did theod on his 600 and they were bpth gobsmacked by the improvement. Enough so that my teck bought a 600 to do for himself. And the parts are in fory 700, cant wait to get it in to be done. So thanks from both pf them!

Drenis

soundfreak1 wrote: »

BTW george this is a thanks from one of my gpod friends, i sent this thread to owr tech amd je did theod on his 600 and they were bpth gobsmacked by the improvement. Enough so that my teck bought a 600 to do for himself. And the parts are in fory 700, cant wait to get it in to be done. So thanks from both pf them!

Drunk post?

SCompRacer

agfrost wrote: »

Have you ever been experienced? :afro:

You're experienced now, solder-slinger! Post them pics! :cheesygrin:

SCompRacer

Wait, I have one! I hope your pics turned out better than mine.....:rolleyes::cheesygrin:

Attachment not found.

agfrost

SCompRacer wrote: »

Wait, I have one! I hope your pics turned out better than mine.....:rolleyes::cheesygrin:

That one looks quite artsy, actually.

Well, after a few(ish) months of foot-dragging I finally made it over to master tradesman SCompRacer's house to start my soldering apprenticeship. I even had most of the parts needed for the mod! I'd been thinking about it for so long I was certain that I had all my caps in hand, but found out at the last moment that I was missing a handful (The 2200uF Nichicon FGs and the 470uF Panny FCs) for the power supply. As such, the full modding will be done in two parts.

What I did bring to the modding party was a Hakko 808 desoldering device, which has a trigger-actuated pump that removes solder through a hole in the iron's tip. It's a pretty nifty tool, but there were still several holes in the PCBs that weren't easily willing to be cleaned out. Rich has a patient hand, fortunately, and the mod went smoothly if slowly.

The main difference in our approach compared to the previous documentations (especially those of George and Brock) was how we installed the two "local power supply reservoir" caps for each opamp: Both George and Brock mounted the two 120uF Panny FCs on the underside of the board. Please read and view the description/pictures of Brock's posts 115 & 116 on page 4 of this thread to see how they mounted these caps. I decided to try to do the same task in a different manner, one which Fred (FTGV) suggested would work as well in words/pictures in post 248 of page 9 of this thread. At the time the soldering iron was hot, I was actually working from a months-old recollection of the pictures from that post as the forum disappearing-photo bugaboo was still in effect. The key thing (just as with the other method) is to make sure that the polarity of the two 120uF caps is correct with respect to pin #4 (neg) and pin #8 (pos) of the opamps.

Here's two shots of the analog board: The first half-completed, the second after completion.






So how does it sound? Well, in a word it sounds great. Right off the bench it sounded really, really good and I've had it running for 80+ hours and my rig sounds better than it ever has before. I'm super happy to have done this and I'm looking forward to completing the job with the last few power-supply caps that I now have in hand. If replacing them makes additional audible improvement, well, I guess I be that much more happy!

Special thanks to all those that have made this possible: Rich for his workshop, experience and steady hand (and for razzing me at every opportunity until I committed to a date to get this done), George and Brock for documenting well both how to do this mod and for making it clear how pleased they were with the results; and finally to Fred, for sharing your knowledge and insight--your generosity is noted and appreciated!

I'll snap a couple pics of the other board when I get around to completing it--don't hold your breath, school starts this coming week!

Jay

soundfreak1

No drunk post (regretablely) using phone big thumbs small keys and sometimes to lazy to edit typo's. LOL sorry bout that chief. Will be less lazy in the future!