Threshold FET two - noise in RIAA/turntable input

Hi Guys (and Nelson if your're reading this)
I recently bought a couple of vintage Thresold amps - an S200 and FET two (series 1) - I must admit I'm impressed - even though I've only listened for an hour or so.

The S200 seems like it might be a bit out on bias, but I think I found the document that illustrates how to correct this.

More seriously, the FET two has a loud "hushing" noise in the right RIAA channel - the line channels are OK, it's only using the "turntable" input (and by the way, the turntable input sounds really capable (despite the noise) judged by the limited listening I've done so far.

Anything I might be able to do my self? I know how to use my Fluke multimeter, and can build stuff - but am a novice in troubleshooting - and I have no schematic...

Best regards
Hans
 

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
Unfortunately I don't have the schematic - anyone with a copy is welcome to post
it here. I would look for bad connections in the noisy channel first, especially at the
connectors. Play with any internal switches, and maybe you want to flip the channels
feeding the inputs and see what happens. If that doesn't get you any results then
try re-soldering the parts on that channel. If none of that works, then you take
down the numbers of the transistors involved, especially the input fets.
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
.
 

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Last edited:
Thank you all for your replies. The noise is present on the MM input (when the rear switch is on one of the two "xxx pF" settings - I have not tried the 1K setting yet, which I assume will be MC?

Judging from the description, my unit seems to be an earlier model - I think the one shown in Analog_SA's thread is a Series II? Mine has different layout on the front (no power rotary switch) and also on the back (only one switct for RIAA settings).

Don't know if there's difference in the schematics between the two series..

I'll try your suggestions, Nelson - thank you very much! :)

Best regards
Hans