Adcom GFP-750 Back in the System

PreCd

How do we know for sure?

heiney9 wrote: »

But there wasn't, other than they changed the color of the boards when they moved final assembly out of the USA, which I'm still not convinced makes a difference in sound.

heiney9

I am very familiar with said pre-amp and it didn't have the life cycle of the two you mentioned, especially the 555 which has been around and still is for 30 years. In 30 years there is bound to be some revisions and each generation is essentially a different amp as the revisions were that many. From the original 555 with the smooth faceplate to the ribbed faceplate to the 555II to the 5500 to the current 555 SE. The 5500 being a completely different animal using MosFet's and other changes.

The 750 never changed. Just like there is a single version of the GFA-5802 and GCD-750.

But there is a very tiny window of doubt, if it is perhaps the very first run. But based on how the inputs are shorted it makes more sense, from a cost and design POV, to short them at the plug rather than at the pcb, and why change from one to the other.

I believe the buyer is just mistaken.

PreCd

Life cycle was shorter, good point.

Just to clarify my point. When I mentioned that the GFA-555 went through revisions I was not referring to the morphing of it to the GFA-555 II. You did not elude to that but I just wanted to make sure that was understood. The 3 revisions were subtle as far as functionality went but changed the layout of the PCB, the way you set bias, etc.... When I began the recapping of my GFP-565 I could not find the schematic for my board and still have not to this date. Found one for an earlier revision but not mine. I had a helluva time finding the schematic for my 555. It was nowhere to be found online anywhere. Finally had Adcom send ALL their manuals over for the 555 Generation I and lo and behold it was there.

Information you probably already know seeing that you have Adcom history but worth mentioning in this situation. Or not :biggrin:

heiney9

PreCd, it is possible but highly unlikely the 750 changed and if it did I don't see one of the changes being how the balance cd input is shorted. I have been following the unit pretty much since it's inception and have seen numerous DIY threads, nude pics, reviews, tech talks, etc.

As with all things, anything is certainly possible and changes aren't always noted or advertised, etc.

H9

PreCd

One thing I do know about the GFP-750............I wish I owned one! Priorities priorities..............they sure get in the way.

heiney9

Lol.........one of the reasons I followed it so long, is because I always wanted one too. About 4 years ago I got one. I admit now that I run the Dared tube pre, the Adcom doesn't get much serious use. My brother said I should sell it, but I can't. It's too nice to get rid of plus I still use it on occasion and I will have a back-up if the Dared ever goes down.

H9

bikerboy

I was wrong about the jumpers! They are in the inside of the Forte f44 preamp I am using also. Sorry for the mis-information. Thats what happens when I post late at night. Dumb. But I did remove the top to see why the active mode is quieter than the passive mode. It would work occasionally. I thought in shipping something had come loose but wiggling the connectors didnt make any difference. I used it in full balanced connections only. I hope that clears things up a bit.

FTGV

audiocr381ve wrote: »

If you tell me the exact parts to order, I will do it. I have no clue where the locations for the parts are on the board but I'll find em' and get those worthless cylinders out of there.

Sorry for the tardy reply,some special parts showed up yesterday and my work bench was a callin.As for the mods I would glady help as much as I can but will take zero responsibility if an error occurs,so it's at your own risk.On the other hand replacing the coupling caps is fairly straight forward and low risk .If you take a look at the first pic in the Head Fi link all the electrolytics and 8 of the blue film caps are prime candidates for upgrading.The input caps are a paralleled combo of 10uf 'lytic bypassed with a 1.0uf film.The output caps are 100uf 'lytic bypassed with a 2.2uf film.If it were mine I would remove the both the lytic and film caps at the input and install a 10uf film,in place of the lytic and small film.Real estate seems tight so it's unlikely one of the more 'exotic films' would fit the a lotted space so I would look at somthing like Panasonic ECQ series.Assuming reasonable value it's my opinion that for coupling purposes it's better to use a good film then a lytic but since the output cap is 100uf a premuim lytic is the only choice but can be bypassed with a film(as big a value as possible.)

As well due to age one might want to replace the main filter caps while they have the PC board out.

heiney9 wrote: »

If you are willing to tutor as in paint by number, I'd give it a shot. I found the DIYAUDIO post too long and complicated and not specific enough. That pre cost me a lot of money and I don't feel like taking a huge chance on ruining it. But if you can break it down where the best place to upgrade some caps would be, I'd give it a whirl.

If you need a schematic, I can probably find one on-line somewhere.

H9

Thanks I have the schem. and referenced it for info previously in the thread.

heiney9

Would this work for the 10uF + 1uF = 11uF

http://www.diycable.com/main/product_info.php?cPath=35_139&products_id=564

H9

FTGV

Yes if it will fit.

heiney9

heiney9 wrote: »

Would this work for the 10uF + 1uF = 11uF

http://www.diycable.com/main/product_info.php?cPath=35_139&products_id=564

H9

FTGV wrote: »

Yes if it will fit.

I will be testing slightly smaller values of this model Clarity cap in a speaker x-over and as a coupling cap in the Keces DAC, if I ever get some extra time. I'll have to measure, but based on the one's I have (9.2uF being the largest) I think they will. Now to find smaller 100uF film caps.

heiney9

Fred I have no info in front of me, but what the voltage of the output caps (100uF)

heiney9

At the output how about 100uF ELNA Silmic II bypassed by a 2.7uF Clarity APW? Very economical cost wise.

H9

Toolfan66

I will be following this thread with great interest. I have thought about this many times over the last year I just need to know what to order, as far as doing the work I have zero worries..

audiocr381ve

Toolfan66 wrote: »

I will be following this thread with great interest. I have thought about this many times over the last year I just need to know what to order, as far as doing the work I have zero worries..

I'm in the same boat.

heiney9

I think these Mundorf's would be perfect for the PS caps (3 larger blue) 1000uF 100v if my eyes can read what's in the photo

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

chandler9a

Looks very interesting for sure, looking forward to the results and impressions.

FTGV

heiney9 wrote: »

Fred I have no info in front of me, but what the voltage of the output caps (100uF)

The stock ones are 100v but they won't see any where near that so even 25v would suffice.There is also in each channel a pair of series connected 470uf 10v that you might want to upgrade.

SCompRacer

FTGV wrote: »

....,some special parts showed up yesterday and my work bench was a callin.

Kewl! I got parts yesterday too! Precious parts!:cheesygrin:

FTGV

SCompRacer wrote: »

Kewl! I got parts yesterday too! Precious parts!:cheesygrin:

LOL Rich,thats definately me at the mail box yesterday.

SCompRacer

Not much time here, but more fitting.....:cheesygrin:

Drenis

Did some reading on this unit and it looks like you can setup a HT bypass of sorts with the flick of a switch.

I may have to get one of these in my rig someday. I'd like a clean pure pre for music only and use the Pioneer Alive AVR to control all my sources and inputs.

heiney9

Yes, it has a processor pass thru. I run my Dared tube pre-amp through the processor loop. Works fantastic with no degradation and I can listen at the flip of a switch from the front panel or remote. So I can listen to tubes, active or passive. Best of all 3 worlds, IMO. Also it's a stellar sounding piece on top of it all.

H9