Adcom DAC owners.Help w/ tool I need

fbm211

Hi all.I was getting ready to open up my GDA-600 and found that I need a allen wrench or some such to remove the 3 screws on the top front of the unit.Does anyone know what size those things are and if they are allen screws??? My new opamp will be here in a few days and Id like to find out what new caps and diodes I need to order too.Thanks...

ben62670

T8 torx. Don't argue with me;) I know. I just checked it. Got it:)
Ben

fbm211

Thanks ben....What the heck was adcom thinking.I never even heard of those.But ebay seems to have em, in droves.

george daniel

sounds like you are going to hot rod that puppy,, let us know how it turns out--good luck.

heiney9

fbm211 wrote: »

Thanks ben....What the heck was adcom thinking.I never even heard of those.But ebay seems to have em, in droves.

Very common at the hardware store. Adcom was thinking they don't want every Tom Dick and Harry poking around in there :).

I bought a set of Torx in a small screw driver sized set as sometimes that sized bit isn't available in the "multi" tool where you can swap bits, etc.

H9

Systems

So are you gettting the dual AD825 module?

If your DAC happens to have output coupling caps I would recommend replacing them with a good quality film cap or better yet remove them entirely as DC offset should be low.
You might want to replace any smaller electrolytics in the power supply and on the power rails (especially in the analog section)with larger value (more capacitance, same or higher voltage) that are of the low impedance variety.

fbm211

Yep.Thats the opamp I ordered.(I was considering the burson discrete but its 155.00 and thats too much for me since this is my first mod.)..As far as the caps go I planned on replacing all the power supply caps with black gate or rubycon.And freds diodes.I havent done any reserch into the output coupling caps yet.Is that like replacing output caps in a preamp with something like V-CAPs.(Which I plan on doing someday.) Once I get the torx I ordered Ill post a pic of the inards.I just hope that opamp is easy to swap out.

ben62670

I eagerly await your impressions. I have a GDA-700 that could use a little help;)
Ben

Systems

fbm211 wrote: »

I was considering the burson discrete but its 155.00 and thats too much

Yeah the Burson looks real good but too bad for its so spendy.I used somthing similar in my DVDA/SACD player mod.http://www.polkaudio.com/forums/showthread.php?t=55733&highlight=MODDING+SACD%2FDVD+PLAYER

I havent done any reserch into the output coupling caps yet.Is that like replacing output caps in a preamp with something like V-CAPs.

Yes the same idea, but your choice of cap may depend on space available as room on the PC board may be limited.

Systems

Lasareath wrote: »

Just attach the new caps to the underside of the top cover.

If you mean attaching it to the underside of the top cover,then you wouldn't be able to take the cover on and off.

Anyway it appears to be direct coupled like Bens 700 so he won't have to change any coupling caps.

ben62670

Thanks! No caps inline with signal:) Should be nearly the same as my GDA-700
Ben

mmadden28

Lasareath wrote: »

fbm211,

Here's a set of screw drivers that if you owned you'll never have a problem opening anything again.

http://www.wihatools.com/400seri/46099_40_pc_set.htm

Sal

Except for the hex and Torx security bits, but they can be readily found as well. Such as here

Not sure if its still the case, but Apple uses those (torx-not the security torx) in their products-well at least the older macbooks.

fbm211

Thanks for the schematic kim.I couldnt fine one anywhere and I scoured the net for hours. I opened the 600 and damn me if I couldnt find anything that looked like an opamp.Is it on the side with the power supplys? In with all those big caps? And do I need to get some more opamps since you mentioned opamps.Just how many does it have?

ben62670

Kim wrote: »

I did replace the stock Adcom Dual op amps with some Burr Brown 2134's and it does sound much better. I was also thinking of trying some 2132's if they are still available.
Don't ya' just luv Digi Key???

I have a 8 2134's in front of my face right now! Woo Hoo. Time to plug in the gun!
Thanks!
Ben

ben62670

http://www.polkaudio.com/forums/showthread.php?t=71222
Mine has 6 OpAmps
Please shoot a pic of your main board. I need to compare to figure out what is the stereo, and balanced outs of mine. Did I mention Please?
Thanks
Ben

heiney9

ben62670 wrote: »

I have a 8 2134's in front of my face right now! Woo Hoo. Time to plug in the gun!
Thanks!
Ben

Post pics Ben, with close up details.

ben62670

I did. Mine is Adcom 7AA OpAmps. The 600 Schematic is 6AA OpAmps. I can do a real fast test to see if the BB2134's will work, but I wish I knew what the Adcom badged chips really were:(

Systems

fbm211 wrote: »

And do I need to get some more opamps since you mentioned opamps.Just how many does it have?

The ones you want to replace are the 7AA's labeled U502 and U503.These are duals with one half functioning as the IV converter and the other as the low pass filter/output buffer.A nice touch is that they added a Fet at the output of the op amp to bias it into class A.

fbm211

This is the best I can do ben.I dont have a dig camera yet. Attachment not found. well that didnt work. Ben go to the forum test section I got a pic to work there.This uploading thing isnt working for me.I keep getting errors.

Systems

ben62670 wrote: »

I did. Mine is Adcom 7AA OpAmps. The 600 Schematic is 6AA OpAmps. I can do a real fast test to see if the BB2134's will work, but I wish I knew what the Adcom badged chips really were:(

Ben before installing the 2134's I would be sure that the 6aa's shown in the pics of your 700 are actually dual op amps and not singles.:DI'm betting there singles so you need OPA134's .I see 3 per channel,so likely one for the IV converter,one for the low pass filter/output buffer and one for the phase inverter on the balanced out.

ben62670

GV#27 wrote: »

Ben before installing the 2134's I would be sure that the 6aa's shown in the pics of your 700 are actually dual op amps and not singles.:DI'm betting there singles so you need OPA134's .I see 3 per channel,so likely one for the IV converter,one for the low pass filter/output buffer and one for the phase inverter on the balanced out.

Will do. I know the procedure;)
Ben

Systems

fbm,can you see 2 parts on the board labeled U502 and U503?

fbm211

yes thet are very small 8 pin chips

Systems

fbm211 wrote: »

yes thet are very small 8 pin chips

Bingo,As I mentioned in post #22 those are the op amps you will want to replace.

fbm211

Im not sure those ad825s will fit.there is a diode on one side of each and a resistor on the other side.Like real close.And the jackass at reference audio mods hasnt even shipped or charged me for the 825 I ordered over a week ago.

ben62670

I don't know how the 2134 compares but the 2134's are cheap from DigiKey.com

Edit mine are 134's

fbm211

Do I need dip or soic

Systems

fbm211 wrote: »

Do I need dip or soic

DIP,other possibilies are the OPA2604,2132 and LM4562.

Systems

The adaptor board used for the AD825's might give enough clearance underneath for the resistor and diode but other things like big caps could make it hard to fit it in the alotted space.Maybe the company has the dimensions posted on their site so you can check.

fbm211

Well this is just getting over my head kinda stuff but thats how you learn.Digi key has great live chat. So GV which do you recomend.AD825s or one of those other ones you mentioned.

Systems

If it will fit the AD825 would be my first choice.but the 2134's are only $3.32 each.