optocoupling power stage - hiss with 6N137

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The triangle is huge with +/-2.5V.
So you modulator is probaly quite forgiving.
As reference: In my breadboard proto the comparator output has less than 5ns jitter with +/-340mV input triangle, nevertheless I can hear noise when I go about 15cm close to the tweeter.
I would not expect your comparator/modulator to be the noise source, but you never know...

To search the jitter you need to look the ns-range.
Witch 0.5us/grid even a heavily jittered edge will still look like a sharp edge.
But how about 50ns/grid?
Again my proposal:
Use chanel 1 to watch and trigger to the comparator output. Use chanel 2 to watch any other point in the circuit at the same time. With this you can easily watch down to several tens of ns. Furtheron this will give you
a detailed information about your propagation delays.
 
odnaizutra said:
yes Workhorse ,but since we dont know the real cause,everything in circuit has to be checked in order to catch any change in hiss pattern and maybe have some light.
Interesting that Crown ,Powersoft and other companies are not using 6n137 on power stage of pwm amplifier.

Fredos, D-amp uses 6N137!!!!
 
I use 6N137 with TC4429 for many years without probleme, even with 74A 200V APT devices...But large dead time before 6N137, done with GAL device ( some logic are done before too...).. Maybe look at your output coil, try some Sendust or -2 from micro metal...Or it's just supply contamination trought the ground. Change the orientation of output coil too...

Fredos
 

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the problem (which is known), is the inductance of the LED, this only creates problems when used with pwm (if pwm contains audio information).
for linearity (in this case becomes noise, as says Pafi), is sufficient to saturate the LED, (as Triger input is good).
 
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