The Adcom GDA 600 modification thread

aloutah

It seems that the current market price is above what I was asking.

george daniel

Hmm,, I paid 100 bucks for mine,,IEC,cord,box,manual,digital interconnect,,single owner.Mine is tricked out now,,so if I sold it,I'd ask 285.00,,but it's not stock either,, enough of the derail here,,,caps are on the way to those that I promised.

heiney9

aloutah wrote: »

If anyone is interested, I have this DAC and im not currently using it. If anyone is interested, I would take 200 for it.

You might want to read the rules of the PF and selling. It's pretty much frowned upon for someone to join just to hock their goods.

Good luck with that. Why not stick around and be a regular contributing member?

H9

FWIW. I paid $140 for mine 5 years ago.

aloutah

I joined to get some info/help with speakers I was purchasing. I have since bought a pair of ls50's and a pair of rta11t's. So I didnt join to hock stuff. This is the first item I have offered for sale. Thought it may be of use to someone here, so I thought I would mention it here before I tried ebay. I also am asking much less than I have seen them sell for recently on ebay. Check the links above. Also, this one is in perfect condition.

george daniel

Welcome to club polk-- if ya'll don't mind,,lets keep this thread on track,as others are and will be modding their units,,so let's keep it on subject--thanks all

heiney9

You need to make a proper for sale thread in the appropriate forum. It's improper form to go around to random threads (especially more than one as you have) and offer things for sale.

We have a section called the Flea Market, that's the only place one is allowed to sell their items.

Please, as I suggested earlier, read the Flea Market rules and follow them.

Good luck

H9

aloutah

Thanks for the info. As I said, im new here and really am not familiar with the rules and protocol. Everyone here has been very helpful. I just thought someone I could help someone out here before I tried other places. Thanks again.

george daniel

Analog stage with Sonicaps
# 1 Ferrite inductors removed and replaced with jumpers
# 2 Caps removed (nothing is replaced
# 3 .1uf Bypass Caps (4)
# 4 Browndog OPA adapters (2)

The sonicaps slipped in just fine,,I have tried to point out everything that I have removed,jumped or replaced.Note,, on the underside of the board is where the 120uf 25 volt (2 per opamp) are connected to the + and - pins of the op-amps and then the remaining +and- leads are connected to the chassis ground,,work permitting,I'll post a diagram. Later tonight I'll post the pics of the power supply board upgrades.
Thanks,,I hope this helps in some small way,:)

Note; the pin corresponding to the "B" on the browndog adapter is pin #1,,proper orientation when removing/replacing opamps is very important.

backsigns

So how do you like the sonicaps?

heiney9

Thanks George,

Now if you could show how you did the caps on the bottom of the board supplying the op-amps and how the ground is routed.

How are the Sonic caps?

H9

george daniel

heiney9 wrote: »

Thanks George,

Now if you could show how you did the caps on the bottom of the board supplying the op-amps and how the ground is routed.

How are the Sonic caps?

H9

LOL,, dunno,, just got them installed,, I wanted to post the pic .

george daniel

Power supply

This one is pretty straightforward
The two green caps on the right are 22uF 25 volt Panasonic bi-polar electrilytics (C122 C 123)
Moving to the left @ C 100 & C104 470uF 35 volt Panasonic FC series
The smaller caps at C101,102,103,105 and 106 are 120uF 25 volt Panasonic FC Electrolytic( I have 100+ of these,,don't buy any as I have plenty)

Careful to maintain polarity when replacing the electrolytic's,, the two green caps are bi-polar as they replaced smaller non-electrolytic caps.
That does it for the power supply

george daniel

Well,, I exceeded the edit time,,, refer to the opamp pinout,,, two electrolytics per opa,, negative soldered to pin 4,,positive to pin 8,, twist the remaining two leads together,, and connect to ground. I soldered some chasis wire to the leads,, ran it to the power supply ground(green wire on the ps pic),,repeat this with the other opamp,,and connect to ground.
Whew--re assemble and sit back a get ready for some extremely good detail.
There may be a better/easier way to connect the 120uf 25 volt caps to the opa's,,if so I'll report back. Hope this helps==all for now
George--over and out.

george daniel

A Better Way to install the 120uf's ,,Instead of the way pictured,, install with the .1uF bypass caps adajacant to the opa's,, I'll do this and post pics when I get home--this is gonna be so much easier--Remember--maintain proper polarity-- Fred just updated me with this suggestion--thanks Fred.:)

backsigns

I wrapped the wire around the leg of the sockets I put in then attached the ground wire to the free legs and it ran on top of the board. I liked the neatness of yours better, why do you want to change it?

george daniel

backsigns wrote: »

I wrapped the wire around the leg of the sockets I put in then attached the ground wire to the free legs and it ran on top of the board. I liked the neatness of yours better, why do you want to change it?

I'm just offering an easier way,as has ben suggested,, I don't know that I will go back and change mine,,as the board has been out at least 12 times,,LOL,, hey,,how is yours sounding? I still have not got my ear on those sonicaps yet,, maybe tonight.

NJPOLKER

George,
Nice work and seems like your having a lot of fun too. This is above me and my patience.

george daniel

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.

backsigns

Of course we want a list.:D Soon Fred will have replaced the whole board! LOL
Thanks for sharing the step by step!

george daniel

Well it's still burning in,, my wife, who has better ears than me,, said she thought it was "mind boggling",, lol,, I don't know if that means it sounds that good,, or I was able to complete this one without any sparks flying,,breakers tripping.I did notice the pretty red fire extinguisher in the pantry though,and her CPR card is current.I think the biggest bang was the op amps,,and then the ps caps,followed by the sonicaps.I say that because this mod was performed in stages,,and listened to after each tweak,, mainly due to my less than basic understanding of electronics(Attaboy Fred),and some of the parts were lost/backordered.Crazy hobby this is. ;)

backsigns

I didn't realize that the PS caps had made that much difference. I was all about the sonicaps, of course I don't have the power supply upgrades yet. Good to know!

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.

Thanks for being the guinea pig George. A list and corresponding board numbers would help a lot.

No, your source is actually the Adcom

H9

george daniel

Glad it turned out well,, it's going on 24 hours of continous play now, sounding very good,,still detailed,but sounding a little more organic now,very smooth,not bright in my system,,a tad more towards the organic side and it will be perfect for me.Did I say that I've learned alot performing this mod? Fred must have the patience of Job,,to have put up with me.;)

george daniel

After 96 hours of continious play,the Adcom seems to have just the right mix of detail with that "organic analog" sound. I attribute that to the burning in of the Sonicap Gen I's, as that was my last tweak. At this point I'm ready to put the top back on and call this one DONE.

ben62670

Congrats George!

engtaz

Congrats Great work George.

heiney9

George, I received the package................THANKS so much!!!

Do you have a specific link to the socketed version of the Op-amps? Still from Brown Dog? I want to use the sockets, but I also want to make sure I get *exactly* the right stuff.

For those thinking about doing this mod, you might be able to get all the parts (not the Op-amp) from Parts Connexion w/o having to buy a minimum. I am using Multi-caps instead of Sonicaps for the yellow mylars around the Op-amps. I am also using Nichicon FG's for the (6) 2200uF 35v power supply caps and replacing the (2) 75R 5W sandcast resistors in the ps section (R151 and R152) with Mills of the same value.

In addition to what George has already mentioned. George still a little shakey on the caps which attach directly to the op-amps. It will probably be a week or two until I get all the rest of the parts and get started on this.

H9

george daniel

dogs

http://cimarrontechnology.com/twopre-mountedopa627auop-ampson020302adapterpnopa627au-020302s.aspx

and this one,,although I soldered mine to the board,,next time I'll use these,,and YES,,I will be modding another,as soon as I pick one up


http://cimarrontechnology.com/othercomponents.aspx

heiney9

Ha, I was thinking the same thing George. Let me know if you are bidding on one, etc. so we don't bid against each other.

I was alos looking at these. If you could maybe you could send Fred a quick e-mail and he could give some advice which ones to get. A dual matched pair is only $179

http://www.partsconnexion.com/opamp_burson.html

The cost isn't quite double, but a discrete Op-amp has me intrigued.

H9

george daniel

I'm not bidding on any,, so proceed sir,,I'm shopping elsewhere,, actually,, I was thinking about the bursons too,,then A-B those little jobbies and see which one wins out.But I'll tell you what,I can easily live with mine for a long time--please keep us posted as to your progress.