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First One - mosFET amplifier module

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pinnocchio

pinnocchio

Member
Joined 2010
quebecdiy.forumactif.com/
ClaudeG said:
Hi Pinnocchio,
By the sound of it, it appears you aren't using LC's DC protection device but an other, more complete solution perhaps? If so, which one?

On an other note, on all the nice builds I don't see any DC protection cap at the FO's input. As of me, I try to have as few DC caps as possible in my system, so I have none of them in my components bare only at my amp's entry, as you never know who might want to plug into (I have a passive pre).

How did you guys deal with that DC input problem, as I understand that the FO doesn't reject DC at the input...

Many thanks, interesting thread!

Claude
PS: to Pinnocchio, clever vertical SMPS implementation of yours, congrats
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There's a few speaker protections I've used through the years, two of them are on Jim's Audio eBay site and the other one is Mirand's Audio speaker protection which uses Mosfets instead of relays, uses the amplifier PSU as supply and has over current detection as well as DC protection. I installed the last one on a six channels amplifier and really like it. If you need any links, please send me a PM as I don't want to pollute LC's thread.

As for adding caps to block DC on the input I just don't. I make sure my equipment (source) is setup to output as little DC offset as possible. The amplifier is DC coupled and will amplify any DC times its gain so just make sure you have the lowest DC offset on the amplifier's output as well as source. You won't hurt your speakers with 90mV DC offset but it's better to keep it as low as possible.

Thanks for the comment on the SMPS setup!

Do
 
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pinnocchio

pinnocchio

Member
Joined 2010
quebecdiy.forumactif.com/
maxlorenz said:
The beauty of LC's speaker protection is that it is in parallel with the signal, so no detriment to the sound that I could detect. :)
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Good quality relays have less than 50mOhm impedance and if paralleled you divide it by two so no real issue and to be honest with you, I've tried with and without and could never tell the difference.

LC's protection is ok for sure but I don't know if I want to risk 60Vdc in my speakers even if for a fraction of a second. That would mean a mega "ploc" sound and hopefully wouldn't destroy the speaker. The tweeter should be protected anyways since there is almost always a capacitor in the way unless doing active setup. Maybe I'm just going crazy for nothing! LOL

Ciao!
Do
 
Lazy Cat

Lazy Cat

Member
Joined 2007
First One M sold out

Hello guys :wave2:

Just an info for you all that FO M modules are sold out.

New FO M series in progress, estimated lead time 6 weeks. Hopefully series produced until last week of February, latest.

All interested please send inquiries to my email, I will take care that you'll get an offer in time.

FO L modules and CapBank modules still available. ;)

L.C. :cheers:
 
Lazy Cat

Lazy Cat

Member
Joined 2007
pinnocchio said:
Here's my new build coming along!

I will post more pictures when completed. So far it sounds quite good!
The SMPS are mounted on the front panel as you can see and the chassis kinda looks empty but it will eventually be filled with the FO L modules so it will leave room for the cap banks.

LC, just a quick question for you.. I biased the output stage idle current to 380mA instead of the 280mA but I wanted to know if I should keep the VAS current to 18mA or crank it up a little?

Thanks
Do
Click to expand...
Do :wiz:

Keep VAS current steady at 180 mA regardless to output bias level. Intermediate driver bjts take care of drive current (mainly AC) so there's very little change to VAS current. :)
L.C. :cheers:
 
pinnocchio

pinnocchio

Member
Joined 2010
quebecdiy.forumactif.com/
Lazy Cat said:
Do :wiz:

Keep VAS current steady at 180 mA regardless to output bias level. Intermediate driver bjts take care of drive current (mainly AC) so there's very little change to VAS current. :)
L.C. :cheers:
Click to expand...

Yeah I realized I was missing a 0 at the end of the 18mA... LOL! Ok nice, I set the VAS initially at 180mA and pump up the output stage bias to 380. I'll keep everything as is and test.

Thanks
Do
 
pinnocchio

pinnocchio

Member
Joined 2010
quebecdiy.forumactif.com/
back said:
we want feedback is 380ma sound better than 280ma
Click to expand...

Hi Back,

I won't be able to tell since I set it at 280mA many months ago and won't be able to remember exactly how it sounded like if it was A/B test.

I'll tell you about the 380mA setup for sure. With my chassis I could potentially even go to 600mA but I don't know if the SMPS would like that. Won't try that anyways!

Ciao!
Do
 
Lazy Cat

Lazy Cat

Member
Joined 2007
Mark Verhoeven said:
Perhaps L.C. can comment on this. I am curious too, as my cooling capacity is sufficient.

Am I right to assume a higher output bias causes the amp to work into class A up to higher output power?

Mark
Click to expand...
That's true, at 280 mA amp delivers 1,25 Wrms/8 Ohm in class A. The heatsink temperature set to 45 °C when amp is in idle, is your only limitation to max bias.

In FO L chassis we made, the channel supply current is set to 400 mA meaning 2,56 Wrms/8 Ohm in class A.
 
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