Hello ....
I want to build a non feedback (NFB)amplifier now... Is there some body knows the advantage and disadvantage of NFB? And who have circuit of NFB amp???Is there any theory on WEB for NFB amp??
Best regards,,
Lukio
😀 😀
I want to build a non feedback (NFB)amplifier now... Is there some body knows the advantage and disadvantage of NFB? And who have circuit of NFB amp???Is there any theory on WEB for NFB amp??
Best regards,,
Lukio
😀 😀
Why would you like to built non feedback amp? I have never seen a non-feedback power amplifier without excessive distorsion and/or excessively high output impedance 😎
zero neg feedback
This is my opinion:
By having no gobal feeback, the amp is essentially isolated form the speaker which is non linear so that no alien signal is being feedback to the input stage.
Due to low loop gain at high frequency and compensation which is mandatory in any feedback amp, the feedback loop is not very effective at high frequency to reduce distortion. In fact, the amp produces many higher order harmonics.
I have a few zero FB amp design, all have current feedback complementary feedback pair as output stage operating in Class A
I don't design any class AB amp without gobal FB.
If you are interested to see a few no FB amp design, pop me a email.
This is my opinion:
By having no gobal feeback, the amp is essentially isolated form the speaker which is non linear so that no alien signal is being feedback to the input stage.
Due to low loop gain at high frequency and compensation which is mandatory in any feedback amp, the feedback loop is not very effective at high frequency to reduce distortion. In fact, the amp produces many higher order harmonics.
I have a few zero FB amp design, all have current feedback complementary feedback pair as output stage operating in Class A
I don't design any class AB amp without gobal FB.
If you are interested to see a few no FB amp design, pop me a email.
LC Audio has done a NFB amp. I built a previous version (MKII) and it was a very nice AMP. I had to discontinue its use when the preamp gave up and i bought an integrated amp.
There is a schematic at their website for their current version, look for the manual of the amp.
There is a schematic at their website for their current version, look for the manual of the amp.
Re: zero neg feedback
Yes ...you are right...
I have talked about the some ...many times in this forum but nobody care 🙂
The first person, that i knew talk about the problem is M. Otala.. ..and he call it interface induced distortion...
But if you build a amp with a very low open loop output impedance...then you can use overall feedback and get even lower distortion...
Congratulations!!
Is very rare in this forum people come with solutions that are not the usual ..."text book engineering solutions" 😉
PS: I would like see some of yours NFB design !!!
PS(2):Your's designs also use feedback (a complementary feedback pair at the output use heavy inside feedback)...they must be called "Overall Feedback Free" 🙂
Praise! said:
Yes ...you are right...
I have talked about the some ...many times in this forum but nobody care 🙂
The first person, that i knew talk about the problem is M. Otala.. ..and he call it interface induced distortion...
But if you build a amp with a very low open loop output impedance...then you can use overall feedback and get even lower distortion...
Congratulations!!
Is very rare in this forum people come with solutions that are not the usual ..."text book engineering solutions" 😉
PS: I would like see some of yours NFB design !!!
PS(2):Your's designs also use feedback (a complementary feedback pair at the output use heavy inside feedback)...they must be called "Overall Feedback Free" 🙂
millwood said:
Older Pass designs...in times of Treshold used even written in the front panel... "Overall Feedback Free"
I still have one of this ...the S 350 ..😉
Using NFB around the voltage gain stage with the O/P stage outside the loop can also work well and avoids the tricky business of designing a stable, low distortion, low gain open-loop voltage amplifier.
Re: zero neg feedback
I can agree to the second part of the statement (the first part is not true of course, the amp is not isolated, it is fully connected to the speaker).
But having a non-fb amp connected to a non-linear speaker load means that the output signal becomes very dependent on the speaker behaviour. This is made worse by the fact that the amp output impedance is also non-linear. That in itself can be a source of large distortions. So, it is difficult to say what is best and what is worse. What you say is partly true, but only part of the picture. The other part can be much worse.
Jan Didden
Praise! said:
I can agree to the second part of the statement (the first part is not true of course, the amp is not isolated, it is fully connected to the speaker).
But having a non-fb amp connected to a non-linear speaker load means that the output signal becomes very dependent on the speaker behaviour. This is made worse by the fact that the amp output impedance is also non-linear. That in itself can be a source of large distortions. So, it is difficult to say what is best and what is worse. What you say is partly true, but only part of the picture. The other part can be much worse.
Jan Didden
Richard C said:
Yes..that is what use Densen...but they claim...a non feedback design.. 😉
At least in the DM10...
You might consider this:
http://www.altmann.haan.de/splif_page/#the feedback
(The ALTMANN "SPLIF" Amplifier Topology)
http://www.altmann.haan.de/splif_page/#the feedback
(The ALTMANN "SPLIF" Amplifier Topology)
The virtual load...
I have see that...but how can we make a simulated load, equal to the speaker load?
rbroer said:
I have see that...but how can we make a simulated load, equal to the speaker load?
Rudolf,
This is utter nonsense. Read the patent (or better, don't bother).
Either the load on the lower amp is not equal to the speaker load, and then the feedback signal has no bearing on the output signal and isn't doing anything for the oputput signal.
Or the load on the lower amp EXACTLY mimics the speaker load, and in that case you might as well take the feedback from the speaker and save yourself an output stage. Really...
Jan Didden
This is utter nonsense. Read the patent (or better, don't bother).
Either the load on the lower amp is not equal to the speaker load, and then the feedback signal has no bearing on the output signal and isn't doing anything for the oputput signal.
Or the load on the lower amp EXACTLY mimics the speaker load, and in that case you might as well take the feedback from the speaker and save yourself an output stage. Really...
Jan Didden
It's wonderful to see how people loves non-linearities
I suggest comparing the output waveforms of a global-feedback design and a no-global-feedback design both loaded with some non-linear evil load like a string of diodes resistors and capacitors in series/paralell
The results of the test are rather self-explaining and say a lot about which option has better 'load isolation'
I suggest comparing the output waveforms of a global-feedback design and a no-global-feedback design both loaded with some non-linear evil load like a string of diodes resistors and capacitors in series/paralell
The results of the test are rather self-explaining and say a lot about which option has better 'load isolation'
Eva said:
Bingo!!! That must be that Iberic sun!!!
Yes you nail it!!!
Before i used the null i usually used to hear the output from the CD...and then the output from the amp under test with the some output voltage...(This with another amp)...
Usually the output from the under test amp is allways warm...euphonic...slower...specially in low or no negatif feedback amps...
That experience make me see the "sound" of distortion...many times the distortion make the sound "nice" but not accurated...
Only clipping and crossover distortion "sound " bad...the others are like a loudness filter aded to the sound...
No wonder some people "like " the amp's with more distortion... 😉
Re: Re: zero neg feedback
Hi,
Well said, well said.
You are right. Complemenraty feedback pair uses 100% FB. But this FB is different from "loop" feedback. It is more like a "local" FB.
It's quite funny that you praise yourself but you are right: Having a low open loop output impedance by for example paralleling output transistors does reduce the problem but here is the problem: COST.
You may agrue that using CFP will lower the impedance but CFP has worse cross over distortion performance than emmiter follower. Incidentally, in a design that I just conceive today for various churches, a 100W design, I use 8 pairs of Toshiba's 2SC5200-O/2SA1943-O configure as emmiter followers. What a coincidence! ;-)
I'm sorry that I cannot show you some of my Class A no NFB design. The reason being that it takes a lot of time to draw a circuit properly. Some of them uses innovative ideas that I don't want to disclose to the public yet. Some others are conventional: Again variants of CFP configuration.
Looking after my customers is busy enough for me let alone spending half a day to draw a circuit. Sorry about that but once my website is up, you can browes as many times as you like! ;-)
Oh I forgot: If you use CFP configuration with a compound emmiter follower at the second stage of the whole CFP, the output impedance will be very low. Check out the British guy Class A amp site, H****'s amp.
Sorry, can't remember anything.
I will try to remember telling you when my website is up. Again, I apologise for not fullfilling your hope.
James Yung
Praise! Audio
Tube_Dude said:
Hi,
Well said, well said.
You are right. Complemenraty feedback pair uses 100% FB. But this FB is different from "loop" feedback. It is more like a "local" FB.
It's quite funny that you praise yourself but you are right: Having a low open loop output impedance by for example paralleling output transistors does reduce the problem but here is the problem: COST.
You may agrue that using CFP will lower the impedance but CFP has worse cross over distortion performance than emmiter follower. Incidentally, in a design that I just conceive today for various churches, a 100W design, I use 8 pairs of Toshiba's 2SC5200-O/2SA1943-O configure as emmiter followers. What a coincidence! ;-)
I'm sorry that I cannot show you some of my Class A no NFB design. The reason being that it takes a lot of time to draw a circuit properly. Some of them uses innovative ideas that I don't want to disclose to the public yet. Some others are conventional: Again variants of CFP configuration.
Looking after my customers is busy enough for me let alone spending half a day to draw a circuit. Sorry about that but once my website is up, you can browes as many times as you like! ;-)
Oh I forgot: If you use CFP configuration with a compound emmiter follower at the second stage of the whole CFP, the output impedance will be very low. Check out the British guy Class A amp site, H****'s amp.
Sorry, can't remember anything.
I will try to remember telling you when my website is up. Again, I apologise for not fullfilling your hope.
James Yung
Praise! Audio
Musical instrumens are actually nothing but distortion generators... Everything stats just as one or more fundamental frequencies [that sometimes may be even supressed in the acoustic output], and then, a huge load of harmonics is generated by the particular non-linearities found on the materials of the instrument and is equalized by the particular frequency response of those materials and structures
Some people actually likes audio gear designed in that particular 'musical instrument' fashion [and most recordings sound 'better' with some touchs here and there...]
I wonder why there isn't a dedicated market of 'adjustable audio-modifying-gear' intended to allow people to intentionally add colouration and harmonization to the recordings they listen
I think this would be much better than just relying on the pleasing but mysterious signal-alterations caused by some expensive 'vodoo' speakers, amplifiers and preamplifier
Sometimes I do the mixing and the PA stuff for small live audio performances, and although my skills on mixing are poor, one of the things I've noticed is the huge amount of compresion and colouration that some things need to sound right [although other things sound better without alterations]
Some people actually likes audio gear designed in that particular 'musical instrument' fashion [and most recordings sound 'better' with some touchs here and there...]
I wonder why there isn't a dedicated market of 'adjustable audio-modifying-gear' intended to allow people to intentionally add colouration and harmonization to the recordings they listen
I think this would be much better than just relying on the pleasing but mysterious signal-alterations caused by some expensive 'vodoo' speakers, amplifiers and preamplifier
Sometimes I do the mixing and the PA stuff for small live audio performances, and although my skills on mixing are poor, one of the things I've noticed is the huge amount of compresion and colouration that some things need to sound right [although other things sound better without alterations]
- Status
- Not open for further replies.