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Intermittent slight Hiss FET-9 Preamp
Intermittent slight Hiss FET-9 Preamp
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Old 2nd December 2019, 11:46 AM   #1
Geeqner is offline Geeqner  United States
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Default Intermittent slight Hiss FET-9 Preamp

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?

Last edited by Geeqner; 2nd December 2019 at 11:49 AM.
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Old 2nd December 2019, 12:29 PM   #2
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Intermittent slight Hiss FET-9 Preamp
care to post some pics?

all voltages checked?
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Old 2nd December 2019, 12:42 PM   #3
Geeqner is offline Geeqner  United States
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Posted A BUNCH at the end of my previous “FET-9 Restoration” thread.
Gotta’ double-check listening tonight to verify if it’s isolated to one channel or not.
Will report back around 8 PM site (Zulu?) time
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Old 2nd December 2019, 01:47 PM   #4
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Intermittent slight Hiss FET-9 Preamp
sorry , I'm easy to be confused and distracted ... it goes with age and spirit

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
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Old 2nd December 2019, 02:20 PM   #5
Geeqner is offline Geeqner  United States
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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

Last edited by Geeqner; 2nd December 2019 at 02:24 PM.
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Old 2nd December 2019, 02:34 PM   #6
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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...

Last edited by coolnose; 2nd December 2019 at 02:38 PM.
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Old 2nd December 2019, 02:40 PM   #7
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Intermittent slight Hiss FET-9 Preamp
I don't care for that modern fancy solders ...... except in case where there is some silver on pcbs , in which case is nice and clever using solder with some silver .....

not that I'm doing that often ......
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Old 2nd December 2019, 02:59 PM   #8
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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

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

Bring back the stuff marked with the Skull and Cross-Bones
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!
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Old 2nd December 2019, 04:42 PM   #9
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I made a french brand (MBO) Sn62Pb36Ag2 my "standard" solder, but a 500gr. spool of 0.7mm lasts a year or so... so the cost of the solder is negligable (more/less)
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Old 2nd December 2019, 05:11 PM   #10
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I've heard good things about the Cardas products - they have solder too, for use with their wire / Litz Wire and Connectors.

Cardas Solder

From what I've heard - most of their stuff seems based upon SOUND Engineering Principles with minimal "snake oil" effect...
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