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First One - mosFET amplifier module

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A

androa76

Member
Joined 2007
GND cant be problem. You probabbly pluged jack into active dac and amplifier was also turned on. At jack low impedance output, often big caps are on output. If dc is present on them that dc can damage amplifier. Often jack connect first central active pin not gnd pin. And imput impedance of amp is 20kohm range not 100ohm as by phones. So dc on big caps can*t be discharged so fast. Sorry to hear... :(
 
Lazy Cat

Lazy Cat

Member
Joined 2007
hose4 said:
I have some news.

I have seen and heard new prototypes with 8 transistors per channel and 600 Watts RMS.
2 variants of the last version are in the listening room. Hopefully we will get a locked version soon.

I have heard them on Focal Grande Utopias. They sounded truly amazing.

I hardly wait to get my hands on one.

DIY option will stay.
Click to expand...

Thanks for a brief and pleasant report my friend, it's truly like you've described. I'm very exciting about new forthcoming First One modules, after all it's two years of intense R&D involved in it (last FO modules were produced in 2016). For DIY community two power sizes will be available, one with two double-die mosfets and one with four of them. More powerful variants with 6, 8, 12 mosfets will be intended for our ready made amplifiers production and for OEM purposes as well.

Now, these days last tests are taking place to determine which of two variants will go into modules production.

I can assure all of you that these modules will be total high-end fidelity audio amplifiers, best on the market. In 2018 we had a lot of supporting equipment for our R&D purposes like Grande Utopia Focal loudspeakers, Select and Reference MSB DAC, Adagio Metrum DAC, Siegfried Reference monoblock and preamplifier VTL, Reference 10 preamplifier Audio Research and many many more. The aim of having them for comparisons was to be at least on the same SQ level like the ones mentioned.
 
Lazy Cat

Lazy Cat

Member
Joined 2007
J.M.K said:
Hi !!

I just fried (half working, bad sound, 2 led lights still on) one V1.4M module of my dual-mono amplifier. :confused::confused::confused:

I don't think it's worth trying to fix it, or is it ?

What happened: I tried to change the usual feed (cinch/RCA-RCA cables from my preamplifier) to a stereo jack/cinch adaptor from my DAC-headphone output. Unfortunately that type of adaptor has a common ground on the jack plug .......... and I guess that one of the amplifier module didn't like it very much.
Completely my fault !!

I asked for new one from the FB site ............ I have no idea if they're still available.
Unless someone here has a spare one (in good shape) for selling ?
If so, please PM me !

Thanks in advance

JMK

PS: To make my case worse, I usually have an excellent ISO-Max ground loop isolator between my preamp and my amplifier (in order to electrically separate them completely), and I bypassed it for my stupid test ............
No excuse for me !
Click to expand...

Please don't worry, to all who had problems with First One M or L modules new replacement modules will be offered, for some free of charge, for others at lower rate exchange prices. I'll handle individual cases and see what's best solution for both sides.
 
J

J.M.K

Member
Joined 2009
androa76 said:
GND cant be problem. You probabbly pluged jack into active dac and amplifier was also turned on. At jack low impedance output, often big caps are on output. If dc is present on them that dc can damage amplifier. Often jack connect first central active pin not gnd pin. And imput impedance of amp is 20kohm range not 100ohm as by phones. So dc on big caps can*t be discharged so fast. Sorry to hear... :(
Click to expand...

I guess this is exactly what happened ........ Plus I bypassed my isolator.
I usually put my amplifier off before doing that sort of test, but I didn't that time for an other stupid reason.

Anyway ........... I'm glad to hear that replacement modules will be available.
May I ask when ? just to have an idea .......... 1 month, 2 months ?

This is the best power amplifier I ever had (sound quality wise).

Thanks anyway

JMK
 
Bassivus

Bassivus

Member
Joined 2004
adason said:
rca audio connector is the most idiotic connector there is...its active side is sticking out like penis making connection before the ground does. It's unbelievable they were never replaced with something normal. They are solely resposible for countless amplifiers and speakers.
Click to expand...

Actually there is one smart alternative made by Neutrik Profi Cable Connectors - Neutrik It's patented mechanism make gnd surrounding stick out before it connects...
 
J

J.M.K

Member
Joined 2009
Fried resistor on my FO 1.4M board

OK, I finally decided to examine the board with a powerful magnifier,
and dicovered that - near the input, where the problem is likely to be situated, the R6 SMD (marked 47R0) is half exploded.
Checked with my DMM : no doubt, broken resistor, when on the other side the symetrical R5 is perfectly OK.

Is it possible that R6 worked as a fuse and merely exploded because of some over current.
The close other SMDs seem to be OK (C12, T4 & T2), not sure for the tiny tracks though.

I think it's worth it trying to fix this, and see if the module is OK.
As I don't know much on this type of resistor, would you give me some reference ?

Do you think, given this brokjen R, that more damage happened further away ?

Thanks a lot for your help and patience (which I admit I lack of, most of the time) ........

JMK
 
J

J.M.K

Member
Joined 2009
OK, I finally removed the exploded R - actually broken in the middle. Unfortunately, the bases to solder the SMD R on the board are also fried and gone, but I managed to trace their ends: one is to the row of next resistors, the other end is one of the legs of the T4 transistor. I guess I'll try to replace that SMD with a discrete 47R and see what happens.

JMK
 
analog_sa

analog_sa

Member
Joined 2002
And how would that help? Not familiar with the new modules, but the 1.2 were generally intolerant of this type of user error. As the resistors in the output Zobel have insufficient power rating, the spike the insertion of a live RCA cinch causes takes the Zobel out, the amp oscillates and often fries a tweeter. Perhaps a sophisticated protection circuit would work, but not something which only monitors dc. And the transparency of the amp will be greatly reduced by the relay.

The blown 47R resistors JMK observed are part of the NFB network. Those resistors used to also be underrated. Blowing with no signal means there is dc at output, so semis blown as well.
 
J

joztom

Member
Joined 2011
I think, this 47R resistor is part of one of both feedback rail, connect on emitor on input transistor and thru 10R and MUR to + or - voltage connector. In this case is blown output transistor on oposite voltage side.
There are no circuit to prevent high oscillations, following live connections, which immediatelly grilling and blowing output transistors.
 
M

MarkB1

Member
Joined 2005
I have 4 x First One v1.4 M and 4 x DC Sense modules that I could sell. Wasn't planning to sell them, but I have plenty of projects on the go, and it looks like some of you need them more than me....

I'd like to offer them first to those who have damaged modules rendering their builds useless. PM me if you are interested.

Also, I hope this isn't out of place but sonnya is making drop-in replacements for F1M:

https://www.diyaudio.com/forums/ven...4490-usb-dac-dsd-support-160.html#post5523920

I guess if LC is back soon it would be fair to delete this post, but until then it might be useful to some of you.
 
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