modding an Adcom GDA-600 DAC?

hpsenicka

hpsenicka

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I have been enjoying my Adcom GDA-600 DAC for several months now, but I can't help wondering if it could be updated or modded to improve the sound even further. The original design of the unit appears to date back to 1993.

In my mind, the obvious place to start would be to look at the analog output circuits for easy upgrade, such as replacing capacitors.

I don't have enough of a clue about electronics in general, and especially about digital electronics to know what changes might be realistic and/or would yeild any audible improvements.

I have a schematic of the unit attached... it would be interesting to get input from some of the more electronics savvy folks about what improvements might be realized. Of the 5 pages, I suspect the power supply section on page 1, and the analog output section on page 5 would be of most interest from a hobbyist or DIY perspective. I don't imagine there would be much value in messing around in the digital sections.
 

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An oldie thread pulled from archives............

hpsenicka,

Did you ever mod your GDA-600, and if so, was it successfull. Anyone else have luck modding one of these units for improved sound? I have a chance to pick one up but w/o mods it sounds like this doesn't sound so great as stock.
 
I never proceeded with this project, as the the Entech 205.2 DACS I am using seem to perform better.
 
hpsenicka said:
I never proceeded with this project, as the the Entech 205.2 DACS I am using seem to perform better.
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Probably something to do with that nasty LPF on the output of the DAC, and the opamps used for buffering. I just got one of these, and really appreciate the schematic you posted; it will be a big help for the mods I am planning. Dont care too much for the stock sound, as it is quite undetailed and kinda dead, but I have high hopes for it. Going to swap the output stage for a discrete folded cascode I/V, 2 pole passive LPF, and JFET buffer. Quite a number of other mods planned, but that, I suspect, will make the most change.
 
Wow,, old thread,, I'll be upgrading mine this week,,eh,, having someone more knowledgable tham me, that is,, planned power supply tweaks,, and replacing the op-amp thingys,,I'll keep ya'll posted,if anyone is interested.
 
Mods done yet? There's one for sale on A'gon that has had Stan Warren mods performed,but at $235 it's a bit pricey for a 16 year old DAC, even with his mods. I've had a couple of pieces that he's done and he's no slouch, that's for sure...I'll be interested to hear what you hear.

L'wood
 
I have a GDA 600, that I'm thinking of modding(by someone).I was told that the "browndog OPA 627" is the part(s) that I need to have this upgrade performed. Anyone able to shed some light on this" Please, any help will be welcome,my goal is to have the unit tweaked towards a tad more "intimate,analog" sound.
Thanks in advance.
 
Hopefully,I'm learning,the plan is to install the browndog adapters,and then pop in some Burr Brown OPA 627's,,in case anyone is interested,I'll post pics and impressions.Sure would be nice to hear from anyone who has been there before me. :scratch2:



Couple of pics of the stock board.
A pic of the "browndogs"
 

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Well at lear I received a reply--Okay,, here we go,, I have ordered the "browndog opa627" adapters,,and I'm gonna replace the film caps(IIRC 5) and "jump " two components on the board--should be started/finished by next weekend.I'll post pictures,details,parts and listening impressions as soon as it happens.The stock unit sounds pretty good right now,,however I am hoping for a huge improvement after this mod is completed.Keeping fingers crossed. Thanks :yes:
 
The Browndog adapters with the BB OPA 627's should be here tomorrow,looking at a "go live" on Saturday--I'll post pic's and results/impressions soon.

I posted some pic's of the stock board,and one of the "browndogs" Hopefully,I'll post the finished deal here real soon.
Thanks
 
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Chatta said:
Have you consider this? Burson opamp

I have the buffer 160. I am considering the opamp for my CDP :)
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Wow,, pricey little jobbies,,thanks for the link. After I finish the GDA 600,I'm gonna' tweak the CD player,, eventually one will stay,,I did watch the video,,that guy can solder eh? Thanks for the heads up on the Burson,,looks like partsconnexion has them.
 
Well,, the "browndog" came in,, stupid me thought there were 2 per package,,eh,, only one,,so I should have the other one tomorrow,,or Monday,,kicks self :tears:
 
Okay,, finished it last night,, installed the "browndog" dual BB 627's,,pretty easy task,, I'll get pic's posted this afternoon,,my initial impressions,, more "presence",,not bright,better detail,,a very analog sounding "tone" for lack of a better word,,I'll stop just short,but not by much,of saying that a "veil" has been lifted.If anyone has one of these and is considering the upgrade,,just do it,the board is easily removed/replaced.One note,, if you use Browndog,,a call to them will tell you where pin one is located,(pin that corresponds to the "B"),then,it's an easy desolder and replace.Then,, just sit back and enjoy the music.Thanks to all who offered help,,and God Bless the guy that posted the schematics--thanks all---george
 
hare is a pic with the browndog opa 627's installed,, a bit early, but the sound is much more detailed in the upper mids and highs,, a tad forward,, but still retaind the analog type sound,definately not laid back pre mod. Next up is to use Sonicap GenII,,,so far so geod. Did I mention the detail? :banana:
 

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