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First One - mosFET amplifier module

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#3,601
followup on FO VAS BIAS vs Supply

Hi guys, the topic regain some momentum , good!

LC thanks for your quick feedback about resistor change. but could you please elaborate a bit especially the value vs the Vrail, because unmounting the whole amp and changing a resistor is gona be boring!.

I ve put the "45 volt" stereo FO of my friend aside and then I decided to see how things going on with my quadFO setup, using 52V smps (which shows 2 volts drop at 100watt into 6ohms).
And then this became a bad sunday as I realized that 18ma gives me only 5Vrms of clean output. I ve raised the vas bias to 21ma and after full temperature stabilization to 45°C then I m able to get 16Vrms into 6 ohms. not more.
please see the 2 FFT below at 16V and then 20V.
An externally hosted image should be here but it was not working when we last tested it.

The second FFT shows some sort of clipping in the driver stage, right? or the cascode is set too low?
An externally hosted image should be here but it was not working when we last tested it.


After the test period, the temp decreased to 43°C and then this lowered the vas bias and then I couldn't get more than 10Vrms clean. gosh. seems the vas bias is very sensitive to the heatsink.

so long story short, with 52V smps shall I replace the 220 by 100 too ? and then what would be the recommended vas bias to get a maximum output (within the spec) ?

many thanks!
 
#3,603
Lazy Cat said:
.....According to the latest news First One won the OEM competition amongst others very competent amp modules, which is great.
Click to expand...

Lazy Cat said:
Could not reveal OEM customer at the moment. If they'll ever note the modules inside their active speakers then the link will be of course presented, but I can assure my statement is truthful.
Click to expand...

:radar:.....😉

CIA ? New SM 15 monitors | Custom Install Audio

(lookup attached pdf) http://www.diyaudio.com/forums/full...mr-balanced-mode-radiator-49.html#post4952748
 
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#3,604
It does say prototype....!

Hi Brytt,

Please don't assume too much or jump to any conclusions!

It does say "prototype" and Andrej and I have not agreed a deal yet....Just like you guys I only found out the prices last week!
As need fully balanced and dual mono that = Two FO L plus two FO medium per loudspeaker cabinet....Plus two separate Power supplies per cabinet....even two separate mains cables....Overkill by name and nature!

Then you have to add in cap banks....So that's a lot of ££££ for a pair active power amplifiers.

As I have explained to Andrej, I am getting these amazing responses from the top studio guys because of my Loudspeakers NOT because of the power amps...All demos have been done using my Belles class A/ B Pro grade active power amp modules....Not FO!

The magic is in my loudspeakers....They sound amazing with any good power amps....
Now I would love to use FO amplifiers....But it may not happen.... I have to keep my options open...I am running a business not a DIY project to build my home system!

Hope you understand and sorry to disappoint, but I don't want anyone to get the wrong idea.
My production assembly starts in approx. 8 weeks and the heat sinks can accommodate my top 3 amp modules, no final decisions have been made yet.
All the very best
Derek.
Custom Install Audio | Advanced audio equipment
 
#3,605
zas said:
This is clearly an issue. Imho extra capacitors defeat the whole purpose of this DC protection.

I'm currently looking for a good solution, I added 2x10000µF M-Lytic per channel, and it leads to:
- an even better sound, more warmth, more stability on complex music, definitively a must
- LC DC protection is prolly totally ineffective
- on power off, with no relay to cut outputs, sound can be listened for at least 20 seconds (while without caps it's something like 2-3 seconds, it depends on load), slowly degrading, and prolly not very good for speakers (symmetry, DC?)

So, i'm looking for a good, simple and compact solution to ensure protection and smooth on/off behavior
..............
Click to expand...

Why not put 3 or 4 relays, at the output, powered from the auxiliary 12V PS of the Hypex SMPS ?

Will this degrade the sound quality ?
 
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#3,609
There are only First One M and First One L amplifier modules present currently. 😎

Supporting modules are:
- CapBank Positive
- CapBank Negative
- DC Sense
- VU meter
- stereo line gain stage with attenuator
 

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#3,610
Hi Lc could you please clarify the respective value of R3/R4 for 45 and 52volts smps please? Also the max power at 0.1% thd would be appreciated as the module is said to be compatible. I will modify 6 modules so i do not want to make a mistake regardîg the big amount of effort needed. Thanks
Remarks, smps behave like having a 0.5 ohm in series and drop 2volts at 4amp rms
 
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#3,611
Hmm... Following this thread closely from page 1 but I must confess I totally missed on the "stereo line gain stage with attenuator"

Guess this is some kind of preamplifier module to go with the FO (volume, source selector, gain if needed?)... but where is that detailled?

Sorry, me getting old I presume

Claude
 
#3,617
Hello:

I´m building a FO M V1.4, and I did all the previous test:
- Power supply without load (+-58 v) (diyaudio store dual power supply)
- Power supply + FO boards (with and without current limiter)
- Bias check (both channels ok)

I did several tests, connecting a source and loudspeakers and everything was fine. An awesome sound!!.

However, when I connected today the system, I heard a noise coming from one channel followed by some smoke. I disconnected the amplifier and I checked the board. I didn´t found any burned element, but one of the big mosfets is broken (cero resistance between two legs). I used the Diyaudio store keratherm insulators for the mosfets and I didn´t found any problem.

Is it any (easy) way to repare the board?. What can I check to insure that everything is fine, and it was only a punctual problem?.

Regards
 
#3,618
Hi kike01
Well the amplifier acts similar like tamed beast, its reactions are fearsome and ultra fast, so everything has to be in order, like gnd connections, correct source signals, loudspeaker impedance, cables, etc. I can assure you that FO M works fluently if all is correct.
Output mosfets got broken so far only if short circuit was performed or power supply polarity was reversed. What else is broken, could not tell, maybe just mosfets, in worst case everything to the input.
 
#3,619
There was not a polarity mistake ( I didn´t change anything into the amplifier), and also ground was checked. It was dead silent before

I checked the power supply before and after and it looks fine.

Is it possible to replace the broken mosfet?. Anything else seems fine.

Regards
 
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