The Adcom GDA 600 modification thread

george daniel

BTW-- the Adcom GDA for 100 bucks is still there,, local pickup,,,anybody?

McCloud Oklahoma craigslist.

Poee7R

You interested in it George?

Ive never been to McCloud, but I could take a run out there for ya.


Dave

george daniel

thanks for the offer,,I was hoping someone here would jump on it

george daniel

FTGV wrote: »

heheChassis mount,then just use some short lengths of hook up wire.

Okay-- for my education,please explain the wiring from the board to the chassis mount rca's,,I'll post a pic soon.I think I have it,just wanna be sure.

FTGV

george daniel wrote: »

Okay-- for my education,please explain the wiring from the board to the chassis mount rca's,,I'll post a pic soon.I think I have it,just wanna be sure.

There was shall I say an interesting discussion about same last evening.:D

First I would make sure your chassis opening is big enough for the connector you plan on using.

After they are installed you would simply solder some short pieces of hookup wire from the new connectors to the same solder pads on the circuit board where the stock ones were removed from.(The center pin of the new con will be positive the outer solder tab will be ground).
Be sure to use the teflon insulating washers that come with the connectors as these isolate them from chassis ground preventing the posibility of creating a ground loop.

woodguru

I have a brand new in the box GCD-600 that has never even been opened that I saved for myself in case I ever wanted to downsize which I have been doing. I sold about 20 of these to guys I was setting up sleeper systems for where I wanted a big bang for the buck system. I always considered these to have a great sound.

I'll try the mod you are talking about as I am selling my beloved and revered Electrocompaniet EMC-1up.

These are so good I can only imagine what an improvement does.

Thanks

Here's a little tip, find an Audience AU-24 or JPS Labs SC2 interconnect to use from the CD to your preamp and prepare to be blown away. They'll go for around $300 or so if you can find one.

Don't beat me up, I just saw that you were talking about the DAC not a CD player, oops. :eek:

Face

Or pick up some Neotech OCC I/C wire before it all disappears, that's what Audience uses.

woodguru

Face wrote: »

Or pick up some Neotech OCC I/C wire before it all disappears, that's what Audience uses.

I'll have to check that out as I'm not a dealer anymore, thanks. I wasn't a fan of Audience the company, just the AU-24

FTGV

woodguru wrote: »

my beloved and revered Electrocompaniet EMC-1up.

Not well known but definately a manufacturor of some excellent products.

Don't beat me up, I just saw that you were talking about the DAC not a CD player, oops. :eek:

I assume it's of the same vintage as the DAC so may have similar if not identical digtal and analog sections .If so the mod's would equally apply to the CDP.A schemtic would be telling.

heiney9

woodguru wrote: »

Here's a little tip, find an Audience AU-24 or JPS Labs SC2 interconnect to use from the CD to your preamp and prepare to be blown away. They'll go for around $300 or so if you can find one.

I prefer MIT's, but thanks for the tip.

H9

george daniel

Face wrote: »

Or pick up some Neotech OCC I/C wire before it all disappears, that's what Audience uses.

This one?

http://www.vhaudio.com/neotech-nei-3002.html

Face

Yes, but I'd prefer to buy it from here: http://soniccraft.com/products/wire/interconnect/neotech.htm

george daniel

thank you sir

heiney9

^^good question, maybe Fred will chime in.

Congrats, it should prove to be a very nice sounding unit.

H9

bikerboy

Hi George,
I bought 12 ft of the neotech 3002 wire from soniccraft and am going with something else. PM me if you are interested. Good to see you are still doing the mods on this dac. Lots of help on teh forim makes it not so daunting of a task.

FTGV

echidna wrote: »

As I am doing this on a tight budget I started with Nationals lm6172 op amps in sockets this gave very good results.

The 6172 is on my to try list.It's a real screamer, with that high a slew rate is very well suited to I/V conversion duties(U502,503). Hopefully you used high quality machine pin sockets or you might have oscillation issues.

Now for a question does anyone know what resistors R502, R504, R540 & R541 and other channel R503, R505, R542 & R543 do?

Are R502 and R503 actually installed?The schematic shows them but no value is indicated.As for R504 and R505 I'm not certain what purpose they serve.R540,541,542,543 connected between the opamp's output and the negative voltage rail will pull a few extra milliamps of current through the output stage of the opamp effectively biasing it into Class A.The oddity is that is the same purpose of the Fet's Q502,Q503,Q504and Q505 so not sure why they are using both unless it was an option to use one or the other?Does your unit have the the Fets and resistors installed?

FTGV

echidna wrote: »

To stop oscillation the power supply pins on the opamps are by passed with Rubycon ZA 100uF/25v in parallel with the original .1uF film and 1.5uf/25v tantalum (this is beneath the board) I picked this up from an application note on high speed op amps.

Yep bypassing is very important with such fast wideband devices.

.... the Fets are not installed they are an option on my schematic.

OK I figured that must be the case thanks for clarifying.

I will post some results when I get there.

Please do as some of us like getting feedback on these types of things.

drselect

George did you have any pics of the chassis mount RCAs you installed and did you end up going with the neotech? I am thinking about adding some extra set of RCAs to my amp with a selector switch while it torn down for repairs/mod.

george daniel wrote: »

Okay-- for my education,please explain the wiring from the board to the chassis mount rca's,,I'll post a pic soon.I think I have it,just wanna be sure.

george daniel wrote: »

This one?

http://www.vhaudio.com/neotech-nei-3002.html

Zippie14

thanks, that helped me a lot!
regards,
chantal

davide256

I've been playing with PC audio for the last 4 months, a learning experience which has shown me how insidiously destructive jitter is to lifelike musical reproduction. I have reached the point now where my PC is better than my my CD transports signal to the Adcom DAC.
Is there a reasonable project one could undertake to improve the clocking and reduce jitter for the GDA-600?

george daniel

drselect wrote: »

George did you have any pics of the chassis mount RCAs you installed and did you end up going with the neotech? I am thinking about adding some extra set of RCAs to my amp with a selector switch while it torn down for repairs/mod.

thats on my short list of things to do,, hopefully this w/e--I'll update the thread with some pic's

davide256

Arrgh. Seems the Monster Cable M650i cables have quite a grip and the inexpensive RCA outer metal contacts on the GDA-600 crimped into place couldn't hold on. Looks like I'll be doing an unplanned upgrade using the RCA jacks from Musical concepts

http://www.musicaldesign.com/Connectors.html

Still wondering if there are any clock upgrades possible to improve the GDA-600...

george daniel

I did not know that it had a clock--shoot FGTV a pm if you want to know more regarding the circuit--what I tried to do was bang/buck tweaks.Mine is still doing fine,,sounding very analog and nice. Good Luck.

ben62670

davide256 wrote: »

Arrgh. Seems the Monster Cable M650i cables have quite a grip and the inexpensive RCA outer metal contacts on the GDA-600 crimped into place couldn't hold on. Looks like I'll be doing an unplanned upgrade using the RCA jacks from Musical concepts

http://www.musicaldesign.com/Connectors.html

Still wondering if there are any clock upgrades possible to improve the GDA-600...

Did you do the analog upgrades yet? The clock is the last thing you should worry about.

FTGV

davide256 wrote: »

Still wondering if there are any clock upgrades possible to improve the GDA-600...

There is no clock per se as the the digital input reciever chip(CS8412) recieves and locks to the master clock of the transport via a PLL circuit.

You could concievably improve jitter performance by adding a second tighter PLL circuit .( such as that implemented in the UltraAnalog modified CS8412 used in the GDA700).Alternatively you could improve the clock in the transport.To take full advantage of such a mod one might also want to use true 75 ohm (BNC or RCA)input /output connectors and a good 75 ohm coaxial cable.

Another less cost effective option would be to add one of the sample rate convertor units from the likes of Monarchy or GW Labs.These are inserted between the transport and DAC.They reclock and resample the data mitigating much of the jitter from a high jitter source.

george daniel

FTGV wrote: »

There is no clock per se as the the digital input reciever chip(CS8412) recieves and locks to the master clock of the transport via a PLL circuit.

You could concievably improve jitter performance by adding a second tighter PLL circuit .( such as that implemented in the UltraAnalog modified CS8412 used in the GDA700).Alternatively you could improve the clock in the transport.To take full advantage of such a mod one might also want to use true 75 ohm (BNC or RCA)input /output connectors and a good 75 ohm coaxial cable.

Another less cost effective option would be to add one of the sample rate convertor units from the likes of Monarchy or GW Labs.These are inserted between the transport and DAC.They reclock and resample the data mitigating much of the jitter from a high jitter source.

Exactly what I did,, got the Monarchy jitter reducer thingy between the Rotle 855 and the Adcom

davide256

Hmm, so basically if I'm using a Linn Genki the clocking should be good and whatever I
hear has nothing to do with jitter?

ben62670

Worry about the analog section before the clock.

FTGV

davide256 wrote: »

Hmm, so basically if I'm using a Linn Genki the clocking should be good and whatever I
hear has nothing to do with jitter?

Doudtful,what are you hearing that you don't like?

ben62670 wrote: »

Worry about the analog section before the clock.

Ummm,he has.

ben62670

I have looked and I see nowhere indicating that he has done any mods to the analog section. I may have missed it though?