George send me your DAC

ben62670

I'm ready. BTW I have the TT phono pre.

jerryj12

So how do you like the pre?

george daniel

is this what I need?
http://cgi.ebay.com/1-MODULE-OF-2-Pre-Mounted-OPA627AU-Op-amps-on-Adapter_W0QQitemZ330383162877QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item4cec5efdfd

ot the browndog thingy?

ben62670

You risk getting fakes. I have the BB2134's in stck here and I like the sound. If I were to criticizing them I would say they were a little high on the tops, but a strong sound stage with slamming bass while retaining the smooth mids in my system. Other wise go with the crimson brown dogged for a bit more

disneyjoe7

george daniel wrote: »

is this what I need?
http://cgi.ebay.com/1-MODULE-OF-2-Pre-Mounted-OPA627AU-Op-amps-on-Adapter_W0QQitemZ330383162877QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item4cec5efdfd

ot the browndog thingy?

Enlighten me what do you do with that?

george daniel

Steve,,it is my understanding that the "browndog" thingys,, go in place where the original op amps were,and that will allow you to pop others in/out to determine what "flavor" you desire--IIRC the Ah! had that option,,Ben can better explain it,, all I know is my Adcom DAC should/might sound better with some newer/updateed op amps,,as I'd loke to kick it up a notch or two.So ant suggestions/experience is appreciated.:)

george daniel

ben62670 wrote: »

You risk getting fakes. I have the BB2134's in stck here and I like the sound. If I were to criticizing them I would say they were a little high on the tops, but a strong sound stage with slamming bass while retaining the smooth mids in my system. Other wise go with the crimson brown dogged for a bit more

OK,, do I need to get the browndog things--if so,LMK as I wanna do it right the first time around.Thanks--george

george daniel

Here are a few pic's,,I'm not sure which "chips are the op amps

Schematics

http://www.audiokarma.org/forums/attachment.php?attachmentid=33267&d=1165789198

george daniel

Okay,,I've identified the op-amps,, now can anyone point me to a store that sells the Burr Brown OPA 627?
Next,,, the browndog thingy goes in place of the original op-amp allowing you to simply pop the chips(op amps) in/out without having to solder the opamp on to the board.It appears that the OPA 627 is about twelve times the cost of the original ones.

megasat16

I think Mouser has the cheapest OPA627 (OPA627AP, 8 pins DIP package) for $18.37 each.

What do you mean by "Browndog thingy"?

Burr Brown was bought out by Texas Instrument so TI is now the only manufacturer of the OPA627 op-amps.

You can use OPA627AP (more offset voltage) but the more expensive OPA627BP has lower offset values and less drift (more desirable for Audio use).

Where is GV when you need him.

Edit : You should stay away from eBay for the OP-AMPs and IC purchases since there are lots of fakes there.

george daniel

Thanks for the help and advice--I'll try to post a couple of pic's,,as I'm a "show me" kinda person.

Op amps are circled in the pic,, and here is a link to what I've been told I need.

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

disneyjoe7

Yes that's them.

megasat16

george daniel wrote: »

Thanks for the help and advice--I'll try to post a couple of pic's,,as I'm a "show me" kinda person.

Op amps are circled in the pic,, and here is a link to what I've been told I need.

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

I think I know where the op-amps are from the previous pictures you posted.

But why do you need to buy the PCB mounting op-amps modified for through hole soldering? From what I see from the pictures, the original op-amps seems to be through hole type.

All you need is to buy OPA627 in 8 Pins DIP Package and that should be direct replacement for the old ones. I believe Ben will do the modding for you? If you want to roll op-amps as you would with Tubes, you just need to order DIP8 sockets and they needs to be soldered first and plug in 8DIP opamps in the socket.

george daniel

megasat16 wrote: »

I think I know where the op-amps are from the previous pictures you posted.

But why do you need to buy the PCB mounting op-amps modified for through hole soldering? From what I see from the pictures, the original op-amps seems to be through hole type.

All you need is to buy OPA627 in 8 Pins DIP Package and that should be direct replacement for the old ones. I believe Ben will do the modding for you? If you want to roll op-amps as you would with Tubes, you just need to order DIP8 sockets and they needs to be soldered first and plug in 8DIP opamps in the socket.

The pictures are the actual stock board of the Adcom GDA 600.What I want to do is to be able to "roll" op amps ,like you said.If I understand correctly,I need to buy a couple of the OPA 627's,,then a couple of "sockets" that I can roll op amps into. Right? Thank you sincerely for taking the time to look and respond to my post.:)

megasat16

You are welcome and you are correct that you can roll op-amps easily if you ask Ben to solder the op-amp DIP8 socket on the PCB first. I think this should do it on the cheap.

http://www.mouser.com/ProductDetail/Tyco-Electronics-AMP/1825093-2/?qs=sGAEpiMZZMs%2fSh%2fkjph1tvt1%2fmEPT%2fXobbGBNF6ZVuY%3d

This one is more exotic version for a couple of bucks more.

http://www.mouser.com/ProductDetail/Tyco-Electronics-AMP/508-AG10D/?qs=sGAEpiMZZMs%2fSh%2fkjph1tvt1%2fmEPT%2fXo7XL936HYos4%3d

george daniel

That is exactly what I want to do--thank you kind sir.:cool:

fbm211

GV Had some good ideas on modding my DAC some time back.Replacing the opamps as well as some filters and adding jumpers in the output stage.Maybe he will chime in and let us know what those were.

fbm211

Hmmm, the upload didnt work.Im sure ben has one though.

megasat16

George, before you order the op-amps (OPA627AP, OPA627BP, etc.) from mouser, check the number on the op-amps on your PCB.

I read the link from the browndog website and it is the dual mounted OPA627 in single package DIP8 package. I don't know who told you that's what you need but if that's what you really need and that info is correct, the ones from mouser will not work for you. I would check the number appears on the op-amp on PCB before ordering anything in. I couldn't read the number from the pictures.

george daniel

The numbers on the chips are Adcom 7aa
9402
004630

Thanks for your input and help--george

megasat16

Holy Christ! This is not the OPA627 on the PCB as I suspected. The service manual (page 5) you provided from AK website is saying it's Adcom 7AA as well and there are 4 of them used in the schematics. I guess they are 2 op-amps in single package since you have only two op-amps on the PCB. That means you can't use OPA627 as a direct substitute. You'll need to find dual op-amps (aka 2 channels op-amps) for this mod or use the ones from Browndog website. It'll also be a bit harder to roll op-amps too since this is a dual channel op-amp in single chip.

megasat16

While searching for Adcom 7AA op-amp, I stumbled upon a very nice thread on CP. It's from fbm211 about modding his adcom. Also, there are lots of good info from one of the retired polkies. You know who he is.

http://www.polkaudio.com/forums/showthread.php?t=71185&page=2

george daniel

Very informative--thanks very much for the link.I think that I understand it "more better" now,,so Mr. Fbm,, how did your mod turn out? Please share if you would not mind.:)

fbm211

I was looking for that old thread and couldnt find it.I did not do that mod yet.Those damn tiny machine solder joints are beyond my skills with soldering.If you take apart the DAC and look under the board youll see what I mean.VERY close together, tiny joints.
I do have a couple pairs of dual op-amps .OPA-2134s and OPA-2137s I think as well as the IC chips to install to roll different opamps.
I think GV recommended the AD-825s I wanted to go with as well.Those are said to be more Zippy compared to the laid back sound of the OPAs.If you like a warm tube sound go with the OPAs.Want more ZIP go with AD.Of course the 627s are said to be the best but will cost you a-lot more.But the good news is the 627s are available in dual.
Ill have to read that thread again but I think I posted a link to a very good opamp review that gave a good account of how certain ones sounded.
I plan to do the mod some day.Actually I plan to shoot ben a pm asking if he would do it since he could handle that kind of soldering.
Link to my opamps of choice>> http://www.referenceaudiomods.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=RAM&Category_Code=OPAMPS

george daniel

Hey--thanks for posting that,, Every post you guys make,takes me one step closer to getting this done--thank you for taking the time --george

fbm211

Here is a link to the opamp notes> http://www.tangentsoft.net/audio/opamps.html

george daniel

Well,, did it last night,,I'll post pics later,,I'll say this--easy to do,,and the difference is MORE than subtle,,detail,clarity,and "sparkle" without the "digital" edgeness". I used the browndog dual opa 627's,, wow,,definately a worthwhile project,,I now have a total of 200 dollars in this DAC,,a relatively inexpensive project,,organic,, no brightness at all. Wow, just wow.

george daniel

i circled the new opamps--scroll up and you'll se a pic of the old ones

fbm211

Did you have ant trouble desoldering the stock opamps?

Didnt you solder ICs on so you could compare other opamps??

ben62670

Now for the caps, and some bypassing. How was the soldering iron?
Ben

george daniel

Okay and update,,the opamps were not too difficult to desolder,I used one of these http://www.radioshack.com/product/index.jsp?productId=2062731

I then replaced the old op amps with these
http://cimarrontechnology.com/twopre-mountedopa627auop-ampson020302adapterpnopa627au-020302s.aspx

I toyed with the idea of using sockets ,but my impatience got the better of me.This upgrade alone,takes the Adcom to a whole new level, much better detail,upper mid bass and treble,, a tad more forward than stock,but not bright..
In my case I removed two high freq filters in the output stage,as it was felt (by those more learnd') than me,that it might affect/mask the flavor of the opamp. My next and hopefully final tweak,is to replace the film caps in the output stage with Sonicap Gen II,, if anyone is interested, I'll post impressions here.The GDA 600 bone stock is a great unit,if you are looking for a laid back--analog unit--pick one up--usually find em' for about 100 dollars.Thanks--george