Fosi v3 mystery death, one channel

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Posted by farfetched (A) on September 10, 2024 at 05:25:43

I have really enjoyed being able to use the Fosi v3 (w/ 48v ps) to drive my Magnepan LRS's periodically, via a tube preamp (BAT vk-3i).

The mystery:

About a month ago, I noticed if I tapped on the preamp *or the Fosi* (each on a separate table) a sound like a reverb/microphonics would come out of the left channel.

I assumed a bad tube in the preamp. Changed in a set which I know is fine. Same exact problem, same exact channel.

I switched the tubes around (ch1 tubes w/ ch2 tubes) to see if problem moved to other channel. It did not, and then, the channel went out. I thought maybe the tubes finally gave out for some deeper reason (coincidences are the bane of troubleshooting) and switched the tubes around again. The same channel was still out, and the perhaps suddenly gone tube, was in fact fine.

[edit: I switched the speaker leads as well, it's the channel on the amp.]

The fact the same sound came out of the speaker even if I lightly tapped the Fosi is what gets me. It likely is the Fosi, although it is not yet the right temp Fahrenheit to test it with the other power amp. (I have my customs.)

Short version: is it possible a failing Fosi V3 would develop a microphonics-like fault?

Related question: given I can get a replacement for 60 bucks, is it worth even sending to get fixed?

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Topic - Fosi v3 mystery death, one channel - farfetched 05:25:43 09/10/24 (16)

is it still under warranty? - Story 03:32:28 09/11/24 (3)

RE: is it still under warranty? - farfetched 05:13:00 09/11/24 (2)

RE: is it still under warranty? - AbeCollins 10:24:16 09/11/24 (1)

RE: is it still under warranty? - farfetched 10:42:10 09/13/24 (0)

RE: Fosi v3 mystery death, one channel - Jonesy 20:30:20 09/10/24 (0)

Why did you start tapping on the gear? - Cougar 19:49:58 09/10/24 (1)

I moved the amp to dust, no music on. Just placing a cd down was enough to cause the effect. (nt) - farfetched 05:15:37 09/11/24 (0)

Just a thought... - mlsstl 17:13:24 09/10/24 (0)

I would barter a discount for Fosi V3 Mono's - Jon L 13:56:03 09/10/24 (5)

(probably) rhetorical question - is Fosi the type of company one can actually contact? - mhardy6647 03:31:37 09/11/24 (4)

Fosi makes this a point, as well - farfetched 07:21:07 09/13/24 (1)

I replaced the 5534 opamps with Burr-Brown 2034's - Story 08:15:45 09/13/24 (0)

Can't speak about Fosi... - mlsstl 15:48:33 09/12/24 (0)

adding to my own rhetoric :-p - mhardy6647 03:43:35 09/11/24 (0)

RE: Fosi v3 mystery death, one channel - Daverz 09:46:32 09/10/24 (1)

gotcha - farfetched 10:15:23 09/10/24 (0)

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