what could be the reasons for High freq roll off after 14khz - Page 5

rhythmsandy · 6th February 2013, 01:39 PM

can I know why hiraga super class A 30w doesnt have this RL.

http://diyaudioprojects.com/Solid/Je...-Schematic.png

Can I know how its not oscillating.

Another question is that there are no Emitter resistors which is still good for higher fidelity as there are no passive components in the path.

can we use such resistor less pushpull config? I do understand the importance of it so how come the hirga amp doesnt have it...

I know a friend of mine built hiraga and also F5 says hiraga is way too ahead of F5 even though Nelsons designs are very famous. What could be the reasons...

I have even seen Nelsons schematics no amp has got a RL they might have RC shunted but not RL...

Im a bit confused..

ill get the measurements soon..

llwhtt · 6th February 2013, 07:43 PM

Since you mentioned that some Nelson Pass's amp don't use an RL network on the output why don't cruise on over to the Pass forum and ask him. I'm sure he will fill you in on the whys and why nots.

Craig

JMFahey · 7th February 2013, 01:40 PM

It's impossible that the few uHy typical "stability inductor", normally consisting of less than 20 turns of enamelled wire around a 1W resistor, cut output above mere 14 KHz.
I think you used a "bought" inductor and misread or mis ordered its value.
Go for the simple DIY solution and remeasure.
Or your problem lies somewhere else.

rhythmsandy · 7th February 2013, 01:54 PM

like the way its said in previous thread it looks like the NFB where the upper freq is cuttoff at relatively lower freq...

But i tried cutting the Inductor to 4 turns and now its much better but im just doubtful that will that work fine in terms of stability

rhythmsandy · 02:58 PM

absolutely there is something wrong...
I have simulated the circuit with TinaTI with all the same values used in the schematic and im getting a very bad response
Imageshack - respu.jpg
please have a look..

I think somebody said in the previous posts that the prob with NFB it seems right...

what I need to do is to rework on the NFB can anybody recommend me the values?

multisync · 7th February 2013, 03:08 PM

R1C1 need to be before the output inductor

rhythmsandy · 7th February 2013, 04:09 PM

changed the position of R1 C1 still getting the same freq response...

JMFahey · 7th February 2013, 04:19 PM

There's nothing in your schematic on post#19 which can justify such response.
And with the huge peak you show !!! .

rhythmsandy · 7th February 2013, 04:44 PM

after some time in tweaking the values I finally got this..
This is the actual sch
Imageshack - sclm4702.jpg

now after changing the values Im getting this but if there is something pretty small in the previous ckt pls tell me that I can fix..

Can we go with these values?
Imageshack - respmod.jpg

rhythmsandy · 7th February 2013, 05:00 PM

aha it seems i finally got what is the wrong with this ckt its the RC network at the output..
the C1 Cap stated in the design is 100nf it has to be 100pf and everything works fine on the simulation..
Imageshack - sclm4702correction.jpg

Ill do this practically and see the results...

7th February 2013, 02:52 PM	#45
rhythmsandy diyAudio Member Join Date: Aug 2012	absolutely there is something wrong... I have simulated the circuit with TinaTI with all the same values used in the schematic and im getting a very bad response Imageshack - respu.jpg please have a look.. I think somebody said in the previous posts that the prob with NFB it seems right... what I need to do is to rework on the NFB can anybody recommend me the values? Last edited by rhythmsandy; 7th February 2013 at 02:58 PM.

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6th February 2013, 01:39 PM	#41
rhythmsandy diyAudio Member Join Date: Aug 2012	can I know why hiraga super class A 30w doesnt have this RL. http://diyaudioprojects.com/Solid/Je...-Schematic.png Can I know how its not oscillating. Another question is that there are no Emitter resistors which is still good for higher fidelity as there are no passive components in the path. can we use such resistor less pushpull config? I do understand the importance of it so how come the hirga amp doesnt have it... I know a friend of mine built hiraga and also F5 says hiraga is way too ahead of F5 even though Nelsons designs are very famous. What could be the reasons... I have even seen Nelsons schematics no amp has got a RL they might have RC shunted but not RL... Im a bit confused.. ill get the measurements soon..

6th February 2013, 07:43 PM	#42
llwhtt diyAudio Member Join Date: Jun 2008	Since you mentioned that some Nelson Pass's amp don't use an RL network on the output why don't cruise on over to the Pass forum and ask him. I'm sure he will fill you in on the whys and why nots. Craig

7th February 2013, 01:40 PM	#43
JMFahey diyAudio Member Join Date: Mar 2009 Location: Buenos Aires - Argentina	It's impossible that the few uHy typical "stability inductor", normally consisting of less than 20 turns of enamelled wire around a 1W resistor, cut output above mere 14 KHz. I think you used a "bought" inductor and misread or mis ordered its value. Go for the simple DIY solution and remeasure. Or your problem lies somewhere else.

7th February 2013, 01:54 PM	#44
rhythmsandy diyAudio Member Join Date: Aug 2012	like the way its said in previous thread it looks like the NFB where the upper freq is cuttoff at relatively lower freq... But i tried cutting the Inductor to 4 turns and now its much better but im just doubtful that will that work fine in terms of stability

7th February 2013, 03:08 PM	#46
multisync diyAudio Member Join Date: Jan 2008 Location: Carp	R1C1 need to be before the output inductor

7th February 2013, 04:09 PM	#47
rhythmsandy diyAudio Member Join Date: Aug 2012	changed the position of R1 C1 still getting the same freq response...

7th February 2013, 04:19 PM	#48
JMFahey diyAudio Member Join Date: Mar 2009 Location: Buenos Aires - Argentina	There's nothing in your schematic on post#19 which can justify such response. And with the huge peak you show !!! .

7th February 2013, 04:44 PM	#49
rhythmsandy diyAudio Member Join Date: Aug 2012	after some time in tweaking the values I finally got this.. This is the actual sch Imageshack - sclm4702.jpg now after changing the values Im getting this but if there is something pretty small in the previous ckt pls tell me that I can fix.. Can we go with these values? Imageshack - respmod.jpg

7th February 2013, 05:00 PM	#50
rhythmsandy diyAudio Member Join Date: Aug 2012	aha it seems i finally got what is the wrong with this ckt its the RC network at the output.. the C1 Cap stated in the design is 100nf it has to be 100pf and everything works fine on the simulation.. Imageshack - sclm4702correction.jpg Ill do this practically and see the results...