RMI-FC100, a single stage audio power amplifier

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#1,442
zdr said:
Voltage drop across all Re must be between 18 and 20mV, regardless of resistor value.
Click to expand...
No, it's not. With 20mV drop over 0.1R emitter resistor bias current will be 200mA. 20mV drop over 0.22Re bias current will be 91mA. Voltage drop over 0.22Re must be twice higher.
This is Class AB amplifier. Recomended bias current for OP devices 150-200mA if I'm not wrong. However it could be raised much higher for the best distortion value, but heatsink has to be huge enough.
 
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#1,443
AndriyOL said:
No, it's not. With 20mV drop over 0.1R emitter resistor bias current will be 200mA. 20mV drop over 0.22Re bias current will be 91mA. Voltage drop over 0.22Re must be twice higher.
This is Class AB amplifier. Recomended bias current for OP devices 150-200mA if I'm not wrong. However it could be raised much higher for the best distortion value, but heatsink has to be huge enough.
Click to expand...

No one (that I could find in the thread) ever recommended modifications of voltage drop across Vre outside range 18-20mV, so I would avoid recommending it. Yes, that would obviously lead to change in Re current and therefore class A power, but I never claimed it wouldn't. My recommendations are based on proven statements in this thread, not my own opinion:

https://www.diyaudio.com/forums/sol...age-audio-power-amplifier-53.html#post1697928

RMI-FC100, a single stage audio power amplifier
 
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#1,448
Here's the THD at 1W/8Ohm, 1Khz.
 

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#1,451
This FFT seems strange. It looks like your noise under 1KHz is quite high which the 50Hz and it’s harmonics would be hearable since it shows 72-18= 54db (1W) at 150Hz...unless your measurement setup is picking noise not present in the amp itself....😕

Fab
 
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#1,452
fab said:
This FFT seems strange. It looks like your noise under 1KHz is quite high which the 50Hz and it’s harmonics would be hearable since it shows 72-18= 54db (1W) at 150Hz...unless your measurement setup is picking noise not present in the amp itself....😕

Fab
Click to expand...

That's correct, I was not able to competely get rid of it. See separate thread here:

Transformer HUM.

I guess the only remaining idea is to move to dual transformers as opposed to single toroid. My other amp which is built the same way has two transformers and no audible hum.
 
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#1,456
zdr said:
That's correct, I was not able to competely get rid of it. See separate thread here:

Transformer HUM.

I guess the only remaining idea is to move to dual transformers as opposed to single toroid. My other amp which is built the same way has two transformers and no audible hum.
Click to expand...

Hi ZDR,

That result looks like it could be your computer causing a noise floor issue, I have been using ARTA with a laptop running from batteries.
I also noted that the measurement cabling, internal amp layout and environment can have a significant effect.

Even so, the THD number and harmonic distribution looks pretty good...

- Dan
 
#1,457
danieljw said:
Hi ZDR,

That result looks like it could be your computer causing a noise floor issue, I have been using ARTA with a laptop running from batteries.
I also noted that the measurement cabling, internal amp layout and environment can have a significant effect.

Even so, the THD number and harmonic distribution looks pretty good...

- Dan
Click to expand...

I measured FocusRite alone, and it seems noise floor is quite low.
 

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