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Old 4th November 2009, 06:55 PM   #1
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Default pre regulator problem in Adcom 565 mod

I am following the instructions for mod-ing a GFP-565 per Galo in Audio Ex. It's going pretty well but ran into an issue I'm not smart enough to figure out.

I purchased the super regulators from Per-Anders and they are superb. I have an issue w/ the voltage coming into them from the pre regs - parts LT1085CT LT1033CT.

+20.2 coming from the 1085 seems ok. -19.7 from 1033 seems low? Or is it?

These inputs give me 14.2 which is what I'd expect for + side but -13.6 from the (-) side.

I think that .6 v difference is too much for a regulated supply for the gfp-565. YEs/

Anyway, anyone have any thoughts? And thanks for any and all help.

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Old 6th November 2009, 06:10 PM   #2
eyoung is offline eyoung  United States
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Check out this link...

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Old 6th December 2009, 12:52 PM   #3
Herb S is offline Herb S  United States
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Default Adcom gfp 565

How are you coming with your pre reg problem? I've been wanting to do this upgrade for years and am finally serious. Would like to follow your progress. Please keep us up to date. Are you going by the articles or have their been any additional mods since they were written?

Regards, Herb S
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Old 7th December 2009, 01:01 PM   #4
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Talking It's done

Well, Since you asked.....I finished the entire mod last week. If you are not aware, the mod is detailed in 4 different articles from Galo in the Audio Express. He did an unbelievable job!!!!! There was only one error in all of that detail which is impressive indeed. Don't ask me what it was 'cause I don't recall and am not inclined to go back and figure it out- if you are doing the mod, just follow the instructions closely and you'll see it right away- I did and I would not call myself all that inclined towards detail.......

I did buy the super reg's from Pers-A who I found through this site. His regs appear to be outstandingly well made and his support was/is outstanding. Not to mention a BIG time saver, reasonably priced etc etc. I did add heat sinks to some of the transistors that seemed to get kinda warm but that is a bad habit I picked up from Galo....

I managed to blow up the filter in the external power supply the first time around but other than that, it has been: assemble, test good, go on to the next step.

It finally got a short listen yesterday through some very shaky speakers, Arcam CD player, rebuilt thoren td-160 and Carver 705 5 channel power amp. The preliminary results were very satisfying even on speakers that were sub par ( I am modd'ing my Maggie 12's so they are out of commission for a bit).

I will post detailed impressions when I get the chance to listen in earnest through the maggies but the noise floor is very low even at full v through the phone input w/ turntable attached.

Can't wait to hear this set up through the MAggies!!!

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Old 12th December 2009, 01:12 PM   #5
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I second the recommendation of Per Anders regulator boards -- you can look at the Super Regulator thread and see the noise measurements I made vis a vis the extant Jung Didden boards.

Did you use the big Triad transformer in the Adcom Mod?

It almost broke my heart when one of the knobs for my Adcom went missing. I was moving it and the thing was somewhat loose and it hasn't been seen since. Fortunately there's a guy selling an almost identical knob on EBay.
Why, silly hare, are you fleeing from the fierce jaws of the lion now grown tame?
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Old 21st December 2009, 02:24 PM   #6
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fwiw, the pre-regulator described by Galo was described in a 2000 follow-on to the 1995 super-regulator series by Walt Jung and Jan Didden. If you are using PA's board, take a look at the schematic and you'll see why it's unnecessary.

I still don't know why Galo used an outboard transformer, unless he blew up the one he had on hand.
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