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First One - mosFET amplifier module

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pinnocchio

pinnocchio

Member
Joined 2010
quebecdiy.forumactif.com/
I have tried the V type connection for DC power and implemented the suggested diodes/resistor scheme for earthing the SMPS to chassis gnd but nothing is working.

I'm getting a hum/buzz sound from powering with a single supply. The weirdest thing is if I disconnect one of the two RCAs (does not matter which side), everything becomes absolute silence on both channels. So it's most likely a ground loop, but how to break it?? I've tried isolating the signal GND on one side by lifting it but as soon as the signal (+) makes contact with the RCA jack, it starts to hum/buzz again. I also tried isolating the signal GNDs on both RCA with 10R lift resistors but it is even worst as disconnecting one RCA now still allow the loop.

I have another member on my forum that use a single Hypex SMPS1200A400 and has the exact same issue... Same planet, different continent... :D

Can anyone tell me their success stories using a single SMPS supply for two FirstOne amp modules?

I will eventually have two SMPS but for now I'm using a single 1200W SMPS.

Thanks
Do
 
Lazy Cat

Lazy Cat

Member
Joined 2007
Hi Do
Metal chassis must be on earth potential, zero ohm.
GND from power supply to GND terminal on each First One module.
Speaker positive and negative wire directly from PCB terminals.
Input positive and negative wire directly to isolated RCA connector.
No GND loops, no hum, tested. ;)
L.C. :cheers:
 
pinnocchio

pinnocchio

Member
Joined 2010
quebecdiy.forumactif.com/
Lazy Cat said:
Hi Do
Metal chassis must be on earth potential, zero ohm.
GND from power supply to GND terminal on each First One module.
Speaker positive and negative wire directly from PCB terminals.
Input positive and negative wire directly to isolated RCA connector.
No GND loops, no hum, tested. ;)
L.C. :cheers:
Click to expand...

This is what I've done. Remember, this is using a single supply for both modules. I'll post some pictures later on so you can see, maybe something is still not right with my setup..

Someone else on my forum is using a different supply than me, the Hypex 1200W and he has the same problem.

I can tell you that when using dual Audiopower DPS-500/UR it works like a charm and it sounds beautifully.

Thanks
Do
 
F

fredlock

Member
Joined 2008
Hi Pinnocchio,

Attached is a picture of my First One with single SMPS. No hum was encountered. The chassis is not even connected to ground or to the power supply ground, means to say its floating. I'd been busy lately and didn't have time to hook up the chassis to AC gnd. I also need to upgrade to V1.3.

I was on vacation for 2 weeks and when I came back the left channel measured 15 mv DC offset. The right cahnnel was 7 mv. I need to recalibrate this DC offset. Just wondering why it change but so far its playing good music. I'm satisfied with this amp and I will be using it for a while.

I hope this helps.
 

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e_fortier

e_fortier

Member
Joined 2001
pinnocchio said:
This is what I've done. Remember, this is using a single supply for both modules. I'll post some pictures later on so you can see, maybe something is still not right with my setup..

Someone else on my forum is using a different supply than me, the Hypex 1200W and he has the same problem.

I can tell you that when using dual Audiopower DPS-500/UR it works like a charm and it sounds beautifully.

Thanks
Do
Click to expand...

Hi Do,

Sorry to hear about your hum issue, these are a PITA to find.

If the fact that using 2 power supplies works like charm why are you using only one ?

It's normal that when using the Audiopower all is great...you are using 2 of them. To verify your set-up try using a single Audiopower to feed both FO, at least you'll be comparing apple with apple and you'll find out if the supply is the issue or if your set-up is the issue.

Good luck.

BR,
Eric
 
Last edited:
Lazy Cat

Lazy Cat

Member
Joined 2007
Hi Fredlock
It amazes me every time I see your chassis, perfect simplicity and gorgeous heatsinks just as made for the First One amp module. BTW who's producer?
Only to add power inlet connector and DC sense modules to finish it.
DC offset is OK for power amp, if wished you can trimm it down by TR1, TR2. If it's negative trimm it with TR2 only or if it's positive trimm it down with TR1 only. Anything between +/-5 mV is job well done. :up:
 
F

fredlock

Member
Joined 2008
e_fortier said:
Hey Fredlock,

May I ask you where you got these heatsinks..smoking hot !!

TIA,
Eric
Click to expand...


Hi Eric, I bought it somewhere on the internet a year ago. Its 3 inches high and 12 inches long and not enough to cool down the First one amp. Heat goes up to 60 - 65 when playing music, but this time of the year (December) its just fine. If it could have been an inch higher, maybe it was okay.


Esperado, that's a good question, Maybe this heatsink was designed for other application and not for amp. I just gave it shot since it looks cool.


Andrej, thanks for the advice and sharing this nice amp with DIY community. I will definitely play with those trimmer resistors when I have time.
 
pinnocchio

pinnocchio

Member
Joined 2010
quebecdiy.forumactif.com/
e_fortier said:
Hi Do,

Sorry to hear about your hum issue, these are a PITA to find.

If the fact that using 2 power supplies works like charm why are you using only one ?

It's normal that when using the Audiopower all is great...you are using 2 of them. To verify your set-up try using a single Audiopower to feed both FO, at least you'll be comparing apple with apple and you'll find out if the supply is the issue or if your set-up is the issue.

Good luck.

BR,
Eric
Click to expand...

Hi Eric,

I'm trying a single SMPS as part of the test I'm conducting on the FO but will definitely use two SMPS in the end. I always prefer using two power supply in my builds.

I'm still trying to figure out the issue but will try other supplies in shared configuration to see the outcome.

Ciao!
Do
 
pinnocchio

pinnocchio

Member
Joined 2010
quebecdiy.forumactif.com/
Hi LC,

I have one module that has 30mV DC offset and the other 3mV offset. Also, the voltage drop on my PSU is ~0.5Vdc difference between the two modules when I supply them one at a time. I'm suspecting that one of the modules has a higher bias... Could this be a source of problem when sharing a supply?

I have tried to follow your adjustment guide in the FO manual but there's missing steps to adjust the FO. Do you have a complete adjustment procedure that you can send me by PM, email or just post? This would be truly appreciated.

Is this guide complete?
https://hifiduino.wordpress.com/2014/11/11/first-one-build-adjusting-operating-parameters/

Thanks
Do
 
analog_sa

analog_sa

Member
Joined 2002
pinnocchio said:
I have one module that has 30mV DC offset and the other 3mV offset. Also, the voltage drop on my PSU is ~0.5Vdc difference between the two modules when I supply them one at a time. I'm suspecting that one of the modules has a higher bias...
Click to expand...


The settings on my boards were all over the place. The multiturn pots are super sensitive at the chosen position, so a tiny knock is sufficient. Luckily it takes only a minimal effort to re-adjust. This has no relevance to sharing a supply of course.
 
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