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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?
.
/ optimally proportioned triangles are our friends
Edits: 09/10/24 09/10/24Follow Ups:
if not, then take a look inside. You can slide the case partially off to take a look inside where the input opamps are.
It's possible the opamp on the offending channel has lost proper connection in the sockets when originally shipped and ended up loosing or loosening contacts with one of the pins. It only takes one to screw it up, so if you are able to carefully remove it out of the socket and put it back in, it may return it to working condition.
BUT!! - do not attempt this if you don't think you are able to handle something like this in the first place - have someone else do it who does or send it back to Fosi
Yeah I will just send it back or send it back and negotiate for 2 monos discount.
The inmate who posted their "revision" of a Phase Linear amp yesterday is not me. I'll see if anything is clearly loose but that's it.
Plus, that microphonic sound was not coming from the preamp is the funny thing. The Fosi was making microphonic sounds when I tapped it before that channel failed. I was tapping it with a tiny wooden dowel.
/ optimally proportioned triangles are our friends
Did the tiny wooden dowel look anything like this? It is rather odd that a solid-state amp would go microphonic like that.
Edits: 09/11/24
I swear I thought I did this very basic task right but apparently not. It's a tiny little wooden brush, like a camera lens or even better, telescope lens brush.
Getting to telescope season. Northern Hemisphere rules!
Sadly every neighbor within a 10 mile radius lights up their house as if any moment they expect a security breach. You can still see the basics, but jeez. You don't even need visible light anymore for a home security system.
But here we are. Lights R Us.
/ optimally proportioned triangles are our friends
Try checking the interconnect cables and jacks. They are the common denominator when you physically tap either component. A short, loose, or dirty connection can introduce the symptoms you are experiencing.Jonesy
Edit: Also try reversing interconnect channels to ensure it's not the preamp. Reversing speakers cables as you did only tells you the speakers are fine.
"I know just enough to get into trouble. But not enough to get out of it."
Edits: 09/11/24
Just wondering.
.
/ optimally proportioned triangles are our friends
... see if you can take the top or bottom of the case off and take a peak at the interior. Who knows, maybe it is just a loose connection that can be unplugged/replugged to fix the problem. You won't know unless you try, and it costs nothing.
Contact Fosi and explain the situation, and instead of wasting money on shipping fees back and forth, ask for a discount credit toward new Fosi V3 Monoblocks.
I know that some of the now popular Chinese brands (e.g., Topping, via ASR) are fairly "outward-facing" in their customer communities.
It also seems to be the case that other brand names are just.. names.
I don't know where Fosi falls on that spectrum.
All in all, and FWIW (which I realize is very little! ), given the price, logistical complexity, and commercial murkiness of products like these amps -- my default assumption is that they're disposables. :(
That said, I am glad the OP's going to look into options with Fosi, and I will certainly be interested to read the follow up(s)!
all the best,
mrh
It's refreshing.
They have clearly built a business model that includes ez customer relations. It's on purpose. Maybe only the English-speaking users get this, but Fosi and Aniyima (sp?) both are providing an invaluable piece of the puzzle.
I bought this cute little unit, because I knew I could return it or get it replaced easily.
If one only has one power amp, for example, the Fosi V3 is the painless choice for a back-up. However, I run 4 Ohm magnepans. The Fosi likes 4 ohms. Has rising distortion into 8 ohms.Might be fixed by now.
I view the Fosi V3 as my go-to "Texas Instruments based" amplifier. I find it hilarious that computer chip manufacturers are in the hi end space.
/ optimally proportioned triangles are our friends
the TI's were socketed, I waited a month for the amp to break in then I put the B-B's in. Much better, mostly in the depth department.
And I'm running Quad 57's, a difficult load to deal with.
Just saying
...but, I bought an Aiyima A70 amp (similar to the stereo Fosi) a month and a half ago and was surprised as to how responsive the company has been to my questions. My first question had to do with the 12 volt trigger and I got a helpful response within 24 hours. Next, I did a positive buyer's review but did comment, that as with many Chinese products, they might want to consider having a native English speaker review their ad wording to make them clearer and grammatically better, though nothing in the present ad was inaccurate when it came to the A70's performance. Again I heard back within a day asking a question or two about my comments.
Have to say I'm very pleased with the way this amp sounds and the responsiveness of the company. A great buy for the money.
Just for fun (or, as I like to say, shoots and googles ), I did a search at ASR for "Fosi support". Obviously, that brings up some off-axis hits (i.e., support of certain formats) but it does pull up a smattering of customer support comments. Most relate to sales support, but some are after-sales support comments. A quick scan of results shows that it's not a horror story -- which is encouraging! :) Here's a link to the search, FWIW.
'Fosi support' thread search at ASR
I also note that Fosi does indeed have a outward-facing (so to speak) account at ASR:
Fosi account at ASR
Hope that this is helpful, or at least interesting! :)
all the best,
mrh
If you do decide to ship it back to Fosi, I'd be interested in knowing the shipping charge.
I have a pair I'm using for an active digital speaker setup. I paid $176 for 2 amps and 2 48V/5A power supplies. So far they've made it through the 100+F heat of August and September OK.
The V3 is what caused me to pull the trigger and build this active system. Otherwise I was looking at a 4-channel Hypex amp for $925. Quite happy with the sound of the little Fosis so far.
Alright I'll test it once more to make sure and do the return thing. I know how to be a good customer, if they want to be a good manufacturer, fine. I'll mail back for repair a 60 dollar amp ;)
I'll update after I get the deets.
.
/ optimally proportioned triangles are our friends
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