optocoupling power stage - hiss with 6N137 - Page 5

lumanauw · 11th February 2008, 12:05 PM

Hi, Ionutgaga,

Maybe its better for you to look at FFT. Scope capture in small time/div don't reveal hiss/noise (unless the scope's time/div is big)

ChocoHolic · 11th February 2008, 01:18 PM

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.

ionutgaga · 18th February 2008, 09:00 AM

So... it is not from 6N137 opto....
My old oscilloscope did not have dual ch, and minimum time div is 200ns. Thanks ChocoHolic for your advices. Status for classD project: maybe stopped...

odnaizutra · 20th February 2008, 11:51 AM

did you try hcp instead of 6n137?

Workhorse · 20th February 2008, 01:03 PM

Changing opto would certainly have no effect.

darkfenriz · 21st February 2008, 06:38 AM

Have you tried schmitt NANDs (like...132) and inverting it then in place if ...02 NOR?

odnaizutra · 21st February 2008, 12:59 PM

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.

Workhorse · 21st February 2008, 01:01 PM

Quote:

Originally posted by odnaizutra
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!!!!

odnaizutra · 21st February 2008, 01:13 PM

Yes,Fredos uses this component for a long time and he is not in problems...
Have you increased the gate resistors just to see if fast switching is not interfering any thing before the optocoupler?
If a function generator is placed instead of modulator?

fredos · 21st February 2008, 01:33 PM

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

20th February 2008, 01:03 PM	#45
Workhorse diyAudio Member Join Date: Dec 2004	Changing opto would certainly have no effect. __________________ It's a fruitless endeavor to try and educate a fool that rejoices in ignorance

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11th February 2008, 12:05 PM	#41
lumanauw diyAudio Moderator Emeritus Join Date: Oct 2002 Location: Bandung	Hi, Ionutgaga, Maybe its better for you to look at FFT. Scope capture in small time/div don't reveal hiss/noise (unless the scope's time/div is big)

11th February 2008, 01:18 PM	#42
ChocoHolic diyAudio Member Join Date: Dec 2003 Location: Munich	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.

18th February 2008, 09:00 AM	#43
ionutgaga diyAudio Member Join Date: Jul 2006	So... it is not from 6N137 opto.... My old oscilloscope did not have dual ch, and minimum time div is 200ns. Thanks ChocoHolic for your advices. Status for classD project: maybe stopped...

20th February 2008, 11:51 AM	#44
odnaizutra diyAudio Member Join Date: Jan 2007	did you try hcp instead of 6n137?

21st February 2008, 06:38 AM	#46
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	Have you tried schmitt NANDs (like...132) and inverting it then in place if ...02 NOR?

21st February 2008, 12:59 PM	#47
odnaizutra diyAudio Member Join Date: Jan 2007	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.

21st February 2008, 01:13 PM	#49
odnaizutra diyAudio Member Join Date: Jan 2007	Yes,Fredos uses this component for a long time and he is not in problems... Have you increased the gate resistors just to see if fast switching is not interfering any thing before the optocoupler? If a function generator is placed instead of modulator?

21st February 2008, 01:33 PM	#50
fredos diyAudio Member Join Date: Mar 2005 Location: Quebec	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