The BULLET Amplifier 10 Watt Class A and Current FB

[caglarm]

my simulation result..8.33w clean, before clip.

 

[lineup]

@caglarm
Can you post your SPICE file?

I have tested with my SPICE.
2x24VAC Transformer 10.4 Watt at THD 0.100%
With 2x25VAC Transformer 11.4 Watt.
2x28VAC Transformer 14.8 Watt at THD 0.100%

2x24VAC 32.1VDC 900mA Out:10.4W Heatsink:2x29W
2x25VAC 33.5VDC 930mA Out:11.4W Heatsink:2x31W
2x28VAC 37.7VDC 1.050A Out:14.8W Heatsink:2x39W

 

[caglarm]

Sure..

(35v for clean 10.0W no clip) input 1.152vP

 

[mkk76]

Just tried a layout . I am learning PCB layout so there may be some errors

 

[mz543578854]

I cannot use a MultiSIM file. @lineup Did you use LTSpice? Would you mind posting your file?

Thanks, Mo

 

[lineup]

I use MultiSim.

Thanks for your files and PCB.
Unfortunately I can not use ms14 files.
I run Multisim 12.

 

[lineup]

Sure..

(35v for clean 10.0W no clip) input 1.152vP

It is a mystery.
Why do you get different results from my results.
At 32.1V I get 10.4W

 

[Freedom666]

Should C5 output cap be of bipolar type?

 

[lineup]

No.
C5 15000uF is one electrolytic with +/- poles.

 

[lineup]

The ouput voltage should be adjusted to VCC/2+0.45 Volt.
For VCC=32.1V this gives 16.50V at output node.

 

[Freedom666]

No.
C5 15000uF is one electrolytic with +/- poles.

i mean is there a sonic benefit using bipolar and maybe foil in parallel?

 

[mz543578854]

@lineup I have to agree with @caglarm . In LTSpice I see just under 8.5W RMS as OK for 32.1V VCC (so if looking more closely, likely the mentioned 8.33W).
It can also be seen very clearly in THD, which rises enormously from that level onwards.

Model attached.

 

[mz543578854]

BTW... for input frequency 20kHz I get oscillation in the simulation. I fear that might also be true in real life. I found this way to put snubbers on the FTEs in some thread I do not remember.
That prevents that oscillation.
@xrk971 has PCBs for this on which you can mount the MOSFETS closely to the snubber elements.

Mo

 

[lineup]

@lineup I have to agree with @caglarm . In LTSpice I see just under 8.5W RMS as OK for 32.1V VCC (so if looking more closely, likely the mentioned 8.33W).
It can also be seen very clearly in THD, which rises enormously from that level onwards.

Model attached.

Well, I have consider this as two other have found the same.
10 Watt seems to be optimistic.
The only way is to increase Voltage supply.
Maybe use 2x25VAC transformer which should give like 33.5VDC.
This should give at least 9 Watt output.
Remember when you test using 32.1V, that the output node should be at 16.50V. Not at 50% of the supply voltage.

About the oscillation you have found.
Maybe increase the compensation cap?

Funny I get 10.4 Watt output and have not seen any oscillation.
I have run using oscilloscope function with squarewave 20 kHz and more.

 

[mz543578854]

I do not know if this is just an LTSpice awkwardness. It happens only if I use rather small simulation steps (like 1/freq/1000) and not always.

 

[mz543578854]

I indeed had adjusted the output voltage to VCC/2. Changing to 12.5V does not do too much. The distortion starts at 0.2W more.

 

[caglarm]

@lineup , Can you give me your multisim simulation file? I want to see if there is a difference between the versions.

 

[mz543578854]

Found the snubber boards for the MOSFETs again: https://www.diyaudio.com/community/threads/alpha-nirvana-39w-8ohm-class-a-amp.344540/post-5966619

 

[Brijac]

Test board is ready, it's good enough for testing the design, and by request it's not crowded.



I'm sure there will be more modifications on the schematic, so final one will be of better layout and standardised to some common heatsink/case. Will be rechecking schematic and pcb tomorrow before posting gerber, i'm tired like a dog atm, don't want a mistake to creep on.

 

[gary s]

Your 3D render looks good so far, keep up the good work.