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First One - mosFET amplifier module

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Lazy Cat

Lazy Cat

Member
Joined 2007
asnakeon said:
The specs for the SMPS1200 indicate that the output voltage is proportional to the mains voltage. Since our mains voltage is typically 110V this means that the SMPS1200A400 will output closer to 30V rather than 63V. I assume that we should use the SMPS1200A700 instead? Independent of the full power limitations, what is the minimum supply voltage that the First One can tolerate?

thanks
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Hi

Powered with 110-115 Vac mains, SMPS1200A400 J3 jumper has to be closed and all voltage levels are correct then. ;)
 
Lazy Cat

Lazy Cat

Member
Joined 2007
quan said:
Hi LC, just my feedback re FO. I tried with SPMS PSU but the problem does not go away ie noise through speakers even without preamp. My speaker cables are spiral types. I wonder whether this cause the amp to oscilate ?.
Quan
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Observe the output with oscilloscope for any sign of oscillations.

Connect the speakers with plain electrical wires to check whether the noise disappear.
 
Lazy Cat

Lazy Cat

Member
Joined 2007
quan said:
There is no problem with plain vanila speaker cables.
Quan
Click to expand...

OK then, First One having 0,3 uH output inductor only, so try to put extra 0,5 uH parallel with 2,2 Ohm/2 W resistor (serial output RL filter) in series with positive output wire. Normally amps having serial output inductor ranging from 0,5 - 1,5 uH. Impedance in this case should change enough (higher with freq) to prevent any unwanted effects. ;)
 
Q

quan

Member
Joined 2007
Lazy Cat said:
OK then, First One having 0,3 uH output inductor only, so try to put extra 0,5 uH parallel with 2,2 Ohm/2 W resistor (serial output RL filter) in series with positive output wire. Normally amps having serial output inductor ranging from 0,5 - 1,5 uH. Impedance in this case should change enough (higher with freq) to prevent any unwanted effects. ;)
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Thanks LC. How easy is it to remove the original inductor and resolder a higher one?.
Quan
 
Lazy Cat

Lazy Cat

Member
Joined 2007
quan said:
Thanks LC. How easy is it to remove the original inductor and resolder a higher one?.
Quan
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No, no don't do that. Extra inductor should be added on inside chassis side of plus speaker's terminal, in series of plus wire which comes from the First One module. The original inductor on PCB has to be left as it is, new one will be just added in series meaning complete inductance will be sum of both inductors.
 
F

fredlock

Member
Joined 2008
Lazy Cat said:
Hi Dirk

SMPS1200A400 datasheet with connection diagram you can find here.

DC sense is connected to shutdown function pins - connector J4: pin 9 (-), pin 10 (+)

Connection sch will be published here before anyone will receive DC sense, so no worries at all.

Regards L.C. :cheers:
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Hi Andrej,

Question for the DC sense, since I only have one SMPS1200 powering both FO amp (stereo), could I connect both DC sense board in parallel to J4: pin (9) and (10)?

Or does DC sense only meant for dual mono?
 
Lazy Cat

Lazy Cat

Member
Joined 2007
fredlock said:
Hi Andrej,

Question for the DC sense, since I only have one SMPS1200 powering both FO amp (stereo), could I connect both DC sense board in parallel to J4: pin (9) and (10)?

Or does DC sense only meant for dual mono?
Click to expand...

Yes, both DC sense output SW (optocoupler output) can be connected in parallel to J4: pin 9 and pin 10, so DC error from any channel will shutdown SMPS1200. ;)
 
H

HiroPro

Member
Joined 2009
quan said:
Thanks LC, i don't have a scope . There is no problem with plain vanila speaker cables.
Quan
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That's very interesting...

Can you please share your speaker cables because I'm apprehensive now that the amp will oscillate simply due to the speaker cables used.

Are these some strange flat solid conductor spiral WHOO (snake oil) cables or what?
 
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H

HiroPro

Member
Joined 2009
Lazy Cat said:
No, no don't do that. Extra inductor should be added on inside chassis side of plus speaker's terminal, in series of plus wire which comes from the First One module. The original inductor on PCB has to be left as it is, new one will be just added in series meaning complete inductance will be sum of both inductors.
Click to expand...

Perhaps you could incorporate this into a future rev of the DC sense PCB?

Do you have a chassis available to build this amp out into a five module chassis?
 
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