Intermittent slight Hiss FET-9 Preamp

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New Electrolytics installed in
-Remote Power Supply
-(4) in Power Regulator circuits
-(2) in Phono Stage

Adjusted V+ & V- to recommended settings (within 0.01 by my Fluke DVM)
Those adjustment Pots are touchy little buggers... In the future, it might be nice to replace ‘em with something a bit less “twitchy”.

Getting a subtle background hiss that seems to occur in conjunction with certain voices and sounds in the music like brushed cymbals.

Other than THAT, the thing sounds MARVELOUS (and I don’t use that term loosely).

This unit is new to me - so I do not have any comparison or before and after sounds to go by. (I re-capped it as a preventative measure and did not attempt to hook it up before doing so.)

The Hiss doesn’t appear to be there all of the time - background is dead quiet when it’s supposed to be so.

Have not tested the phono stage yet, so I doubt if it’s anything there.

Any ideas on what to check?
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Official Court Jester
Joined 2003
Paid Member
sorry , I'm easy to be confused and distracted ... it goes with age and spirit :clown:

so , link to pics ?

yeah - if both channels , and PSU is shared , it must be common culprit for both channels

if just one , look for bad solder points ( not always possible to solve with visual inspection only) , also wiggle-wiggle of suspicious part can change amount of his

sometimes old parts are having pin -corosion inside of case , so wiggle can save you :)
Yeah - I suppose that I can pop the covers again and re-flow any questionable solder joints.

Any particular type of solder work best on these fancy-ar$e, Ag-Plated Circuit Boards.
(As I do not do this often and not worried about exposure, I'm thinking old-school stuff with Pb probably flows nicer in a fine-size rosin-core. But other than that???)

Also need to double-check the Gain Jumpers setting -
with my Power Amp (Emotiva XPA-2 Gen 3), it goes pretty loud before dial hits 12:00 position
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You can get Euthetic solder (with Pb that is) and some 2% silver if you want to go fancy.

Definitely stay away from PB-Free solder for a repair job on that type of stuff...

Kester 44 is often cited by your fellow americans, should be fine for the job. Now that's getting me wondering what you used for the recapping ob...
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Yeah - at Work, in order to minimize problems with waste disposal, etc,
EVERYTHING has gone to ROHS-compliant stuff, including the stuff that they pre-tin the leads and solder pads on Circuit Boards with.

Naturally, this means that although it is more "environmentally friendly" - it flows like a warm turd :yuck:

(Sort-of like water-based Varnish...)

Bring back the stuff marked with the Skull and Cross-Bones :skull:
When you saw it - you KNOW that you need to be careful with the stuff, but you also KNOW that the darned stuff actually WORKS!
Just buy some Kester 44 with either reference, find a small spool if it's a 1 time job.

Don't upset ZM with esoteric solder, even the 2% silver stuff moves him in some way :p

Sn62Pb36Ag02 44 0.020 0.50 66 3.3% Leaded Contains Halogen Sn62Pb36Ag02 3.3%/44 .020 1 LB SPL 2471500010 Rosin
Sn62Pb36Ag02 44 0.025 0.60 66 3.3% Leaded Contains Halogen Sn62Pb36Ag02 3.3%/44 .025 1 LB SPL 2471500018 Rosin
Sn62Pb36Ag02 44 0.031 0.80 66 3.3% Leaded Contains Halogen Sn62Pb36Ag02 3.3%/44 .031 1 LB SPL 2471500027 Rosin

I would go go with either 0.025 or 0.031 .... the last numbers starting with "2471" are the manufacturer part numbers, try your preferred seller.
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Got a chance to do a little more listening, but not enough time to touch-up any solder joints (maybe tonight - got some old-school Kester 44 core solder from one of the techs at work who had a roll stashed, and I snagged a few feet of the stuff).

The "hiss" is intermittent (it comes and goes) - when it occurs it sounds similar to a ceramic plate rattling gently on a glass shelf.

The "hiss" occurs in the Left Channel.
It also occurs via BOTH the "CD Player" and "Video" Inputs - so I suspect that it IS NOT a bad / iffy selector switch or a position on a selector switch.
This seems to point to something in the Rear portion of one of the PCBAs and/or "V+" Section of the Power Supply.
I checked the "V+ REG" & "V- REG" for DC Voltage (set to 17 VDC +/- 0.01 by my Fluke 77). Also checked for AC Volts and got NADA.
(But those readings were with NO source signal going through it.)
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Removed Cover and Poked-around with Bamboo Poker & Flashlight with CD running. Did not find anything, but one Banana Plug setscrew was loose on Left Speaker wire, so maybe that had been there for a while and didn’t notice. If the hiss is still there, it’s BARELY noticeable.

Connected Turntable (Teledyne/AR “The Turntable”, Straight Gelco Tonearm, & Shure V15-VMR. Played a side of “Mask” by Kansas & “Eye in the Sky” by Alan Parsons Project. Wifey thought that I had hauled out some Old CDs... Sounded TERRIFIC. I was hearing stuff/ instruments / sounds that I do not recall hearing on these before (in a GOOD way).

This thing certainly has THE BEST phono section that I’ve ever had connected to MY System.
-Huge step UP from late 1970s Zenith receiver
-Way better than “classic” NAD receiver that I had been using as a Pre-Amp

Makes me want to find a classic Stasis Series or PL Power Amp as an upgrade for my relatively new Emotiva XPA-2 (which is pretty decent, but probably NOT up to the standards set by Mr. Pass).

Time to think about building an Upgraded Power Supply for the FET-9.
Never got into the Dope part (although there WAS that time when I built a stick-model airplane in my college dorm room and got higher than the bejeezus when I "doped" the wings - SPLIT-TING Headache the next day...):smash:

Some "Action-Pics":


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