Do you think i am rigth or wrong?
But explain your point of view.... it is open to you to open your mind and explain your thoughts...do you like to help?... do you have knowledge to use to help people?
Then come on!.... say what you think.
The hidden gênius..the shy ones..have now a subject to talk about.
I found that Techno, by Bora, is one of the best ones into focus and resolution...you can listen instruments other amplifiers just erase, delete them...just disappear....but Techno can reproduce... using a single speaker and comparing we see that Techno is better than several others.
You see.... the attached AD chip is also considered very good..observe the topologie is almost the same you have into Techno.... you have just to install CCS to the Techno Drivers.
Watch and search for similarities....for things alike.
regards,
Carlos
But explain your point of view.... it is open to you to open your mind and explain your thoughts...do you like to help?... do you have knowledge to use to help people?
Then come on!.... say what you think.
The hidden gênius..the shy ones..have now a subject to talk about.
I found that Techno, by Bora, is one of the best ones into focus and resolution...you can listen instruments other amplifiers just erase, delete them...just disappear....but Techno can reproduce... using a single speaker and comparing we see that Techno is better than several others.
You see.... the attached AD chip is also considered very good..observe the topologie is almost the same you have into Techno.... you have just to install CCS to the Techno Drivers.
Watch and search for similarities....for things alike.
regards,
Carlos
Attachments
What is my assumption...what i am thinking about
If that chip sounds the best!...and the topologie is the same as Techno, this explains why it sounds so good..and may be the best ...because this simple direct logics.
Observe with care...take a good look.... see, despite some auxiliary parts..the basic schematic, the frame, the basic extructure, the topologie..is almost the same.
regards,
Carlos
...........................................................................
Of course is not my intention to say Bora has copied the chip internal schematic....for sure he do not need to do those things...but WE CAN DO... WE CAN!... we can search for good sounding chips and copy the internal schematic and produce it discrete... if we do not know what makes good sound we can search for good sound ones and use the same frame, the same extruture, the topologie.
If that chip sounds the best!...and the topologie is the same as Techno, this explains why it sounds so good..and may be the best ...because this simple direct logics.
Observe with care...take a good look.... see, despite some auxiliary parts..the basic schematic, the frame, the basic extructure, the topologie..is almost the same.
regards,
Carlos
...........................................................................
Of course is not my intention to say Bora has copied the chip internal schematic....for sure he do not need to do those things...but WE CAN DO... WE CAN!... we can search for good sounding chips and copy the internal schematic and produce it discrete... if we do not know what makes good sound we can search for good sound ones and use the same frame, the same extruture, the topologie.
Yes... i could see that..thanks folks!
The second stage is not differential...i have watched with carefull and i could see i was wrong.
But we can explore that AD chip topologie...may sound good too doing it discrete.
thank you folks.
regards,
Carlos
........................................................................................................
LET THE THREAD DIE...it is non sense..i could see that.
thank you all.
The second stage is not differential...i have watched with carefull and i could see i was wrong.
But we can explore that AD chip topologie...may sound good too doing it discrete.
thank you folks.
regards,
Carlos
........................................................................................................
LET THE THREAD DIE...it is non sense..i could see that.
thank you all.
Watch this folks...listen and think about
very interesting:
http://www.youtube.com/watch?v=s3PyVeUCIBk
very interesting:
http://www.youtube.com/watch?v=s3PyVeUCIBk
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Joined 2009
Paid Member
I always understood that the chip designers have different constraints than 'us' DIYers because of this they may end up with a topology that is different than would be the case if you started with the idea to make a discrete amp. Perhaps if we know what these different constraints are we would understand the chip design better when looking for inspiration for new discrete options ?
Watch this bigun.
Darlington style, two stages differential.... current sink and CCS to feed.... VAS using two stages.... driver having low current and output in quasi complementary
Observe the regulator to the VAS.
This seems to be the topologie..so...if we build something like that may sound so nice as the TDA2050 chip.
Maybe a little better, as we have not the protections, that use to disturb a little... compresses... reduces dinamics...limits power, and sometimes distort clipping when the AGC cannot hold extremelly high transients.
It is alike the HRII...but uses a CCS to the differential and a composed diferential (4 transistors)...also uses quasi complementary..and have the advantage the internal transistors are matched when we cannot have them preciselly matched that way.
HRII has more treble because the lag compensation..smaller capacitors..also the phase advance system developed by Sansui..that capacitor in parallel with the driver stop resistance.
If we want TDA2050 sonics..and it is very good...we have just to build this way.
regards,
Carlos
Darlington style, two stages differential.... current sink and CCS to feed.... VAS using two stages.... driver having low current and output in quasi complementary
Observe the regulator to the VAS.
This seems to be the topologie..so...if we build something like that may sound so nice as the TDA2050 chip.
Maybe a little better, as we have not the protections, that use to disturb a little... compresses... reduces dinamics...limits power, and sometimes distort clipping when the AGC cannot hold extremelly high transients.
It is alike the HRII...but uses a CCS to the differential and a composed diferential (4 transistors)...also uses quasi complementary..and have the advantage the internal transistors are matched when we cannot have them preciselly matched that way.
HRII has more treble because the lag compensation..smaller capacitors..also the phase advance system developed by Sansui..that capacitor in parallel with the driver stop resistance.
If we want TDA2050 sonics..and it is very good...we have just to build this way.
regards,
Carlos
Attachments
I have not listened the Stee amplifier...looks good..but those things..only building
and listening...there's no other way...can be excelent.... or the opposite...seems good...but no one can be sure just watching..or sniffing.
DHR Turbo was my last amplifier made..... also the Trust...but trust was something very old...just to be playing with..nothing really serious.
This one you told the name i do not know..maybe other guy have made something with name turbo.
regards,
Carlos
and listening...there's no other way...can be excelent.... or the opposite...seems good...but no one can be sure just watching..or sniffing.
DHR Turbo was my last amplifier made..... also the Trust...but trust was something very old...just to be playing with..nothing really serious.
This one you told the name i do not know..maybe other guy have made something with name turbo.
regards,
Carlos
Carlos,
The Techno - and you realise this now I'm sure - is a conventional Hitachi AN topology from the early seventies, publicised to sell their new fangled mosfets of the day. Real straightforward, and the basis of many pro-audio and PA amps. It's extremely rugged, reliable, and delivers very good sound with clean clipping characteristics, low phase shift and excellent stability.
I think after all the exposure on this forum of the folded cascode many understand it sounds very, very good. The diamond buffer is another good one. What is less easy to figure out - and I don't pretend to understand this either - is the connection between the simulations, the spectral distribution of the distortion and the subjective listening experience. If someone could nail that relationship, I would be most grateful.
Cheers,
Hugh
The Techno - and you realise this now I'm sure - is a conventional Hitachi AN topology from the early seventies, publicised to sell their new fangled mosfets of the day. Real straightforward, and the basis of many pro-audio and PA amps. It's extremely rugged, reliable, and delivers very good sound with clean clipping characteristics, low phase shift and excellent stability.
I think after all the exposure on this forum of the folded cascode many understand it sounds very, very good. The diamond buffer is another good one. What is less easy to figure out - and I don't pretend to understand this either - is the connection between the simulations, the spectral distribution of the distortion and the subjective listening experience. If someone could nail that relationship, I would be most grateful.
Cheers,
Hugh
Member
Joined 2009
Paid Member
Carlos,
looks interesting - not so sure I like those Darlington input pairs. How does TDA2050 compare with the sound from HRII ?
Probably a dumb question, but looking at the AD797 in the first post, what does Q12 do ?
Hugh/Carlos,
I think we should put all of the goodies from these different topologies together...
Front end = either CFP LTP or BJT-JFET Cascode LTP
aim: maximize linearity of the error amplifier
VAS = folded cascode + mirror
aim: symmetrical fast slew rate
Drivers = Diamond Buffer
aim: isolate VAS from OS, non-switching output
Output = BJT/MOSFET CFP
aim: maximum linearity and SOA, operates in semi-ClassA due to non-switching Diamond driver stage
We get to use JFETs, BJTs and MOSFETs.
It must be good then. TPA. The Perfect Amplifier ...
It can be the DIY reference topology
looks interesting - not so sure I like those Darlington input pairs. How does TDA2050 compare with the sound from HRII ?
Probably a dumb question, but looking at the AD797 in the first post, what does Q12 do ?
Hugh/Carlos,
I think we should put all of the goodies from these different topologies together...
Front end = either CFP LTP or BJT-JFET Cascode LTP
aim: maximize linearity of the error amplifier
VAS = folded cascode + mirror
aim: symmetrical fast slew rate
Drivers = Diamond Buffer
aim: isolate VAS from OS, non-switching output
Output = BJT/MOSFET CFP
aim: maximum linearity and SOA, operates in semi-ClassA due to non-switching Diamond driver stage
We get to use JFETs, BJTs and MOSFETs.
It must be good then. TPA. The Perfect Amplifier ...
It can be the DIY reference topology
The techno - closest thing to ampslab's HX-350 (with mosfets) or my supersym (better CCS +higher rails/more op's), same thing as the hitachi. carlos is right about hearing more (subtle instruments/breathing/fret noises) with this topology when used with fast , low Cob devices.
I would not profess to know this relationship for all the topologies, but for this one (techno/supersym/HX) ,there is a very predictable correlation between the 2nd/3rd - 5-7 at both 1k and 20k and how "livable" or "mystical" the subjective listening experience is afterwards. The initial current I run the VAS at, (3-6ma) and how much I cripple the open loop gain afterwards changes H2,3,5,7 and the sound... beyond subjective (you can hear it). I did go all the way and used the cascoded variant of the hitachi (roenderRMI/abomination) , it did sound better , but this could be psychological.
OS
The HRII distorts in a more ugly way when you overdrive it
the HRII has better and louder treble..... TDA2030 seems more mufled and has not very clean treble.... reason why i am thinking to give a try using discrete, as we can arrange things to reproduce better treble... we can listen the TDA2030 for hours long... this is not possible while listening some other amplifiers.... you became tired and you have to shut off the damn thing.
What make us tired while listening?... i do not know.
I do think, Ostripper, the Symassym has a lot of things that remembers the Techno....but they sound different.... sometimes we have harsh treble into Symassym (the basic version, the first one..the original)... techno has better high end.... Symassym has more dinamics..sounds more powerfull and bass is a little bit more present.
I remember i used to show a music to Michael Bittner, a fortissimo moment where the amplifier use to harsh (the first model)... was the music theme, the movie theme from Wallace, the heroe you had into Scotland....... Brave heart the movie or other name..here in Brazil the title translations are very crazy and have not the same meaning... sorry because of that..i cannot tell you the movie tittle..seems to be Brave heart.... Wallace was the leader against English i think...the music theme has a very strong fortíssimo with violine together other instruments...in that peak the Symassym used to turn unstable and harshes...the first one only.... the second one i have not built.
I do think, all those ones are very good amplifiers... in the reality, the differences are not that enormous...what was very impressive to me was to listen more details, more instruments and more clear voices when listening Elton John recording.
What i mean with that..... not easy to explain....but is focus, precision into the reproduction..... two voices are not fused, melted together producing a third voice that is the resultant..you can listen both voices.... something alike Orange, banana and milk into the electrical mixer.... you can have a resultant..something that may taste alike a new fruit... a new thing, or you can taste orange.... and trying you can taste banana....and trying (making some effort, concentrating yourself) you can taste the milk flavour.
I am a cappuccino Coffee lover...and you can make it taste only chocolate...that flavour can dominate..or the milk flavor (cream), or the cynamon can dominate too...or the coffee taste... when very well ballanced...having a good proportion (ratio) you may be able to feel the milk, the chocolate, the coffee and the cynamon... that's the difference.... taste can be a resultant.... or to keep the original components.... they can be mixed loosing character or not..this is what i am calling focus and precision.
That performance was something that made me very surprised...i could listen things never listened before in that recording..and using the same CD player that was an old sony those days...i have assembled the Techno years ago... and i had to tweak.... i could not make it work with the standard resistance values.
The Techno amplifier has room to modificatins...seems to me the input should have another supply voltage... a more stable supply to the input circuit.... maybe stop resistance to the output.... another type of condenser into the gain line and several other things may turn it even better.... was made to be simple and very good...and it really is simple and very good.
I do not know how it will behave reproducing other kind of musics..when i have built (and i keep it playing for 2 days long)... and this happened in 2005 i think, i have perceived super controled bass.... the unit sounded alike studio monitor amplifiers...very good, very precise.... different...but the bass was not that strong...i felt is a little bit weak.... sounded flat...when i like the bass more present (this is personal)
Some amplifiers give you a little bit more than others.... Krill is one of those ones.... Techno too.... i think HRII surprise us about the power..it seems to be much more powerfull than it really is...Dx Standard reproduces a very warm sound.... each one of them with their good points.
If i could arrange the TDA2030, buiding it discrete, and fixing that treble problem.... without disturb presence, bass and clear sound...it would be a superior amplifier....one of the best ones...but will loose to the Techno into the "focus" department.
In my imagination, Techno may have advantage related the Harmonics... seems does not produce too much (dinamically)... sounds does not mix one each the other producing a third thing..seems more "purified"..... the fourier is perfect and the Total Harmonic distortion is very small (0.02% THD)
I would suggest you to try the Techno...it is a nice sonic experience to listen that one.... will surprise you.... i give you guarantee you will feel surprised.
Here is the schematic...have to check the current into the second differential...maybe you cannot use BC556 there...i remember i have tried using BD139/140.
regards,
Carlos
the HRII has better and louder treble..... TDA2030 seems more mufled and has not very clean treble.... reason why i am thinking to give a try using discrete, as we can arrange things to reproduce better treble... we can listen the TDA2030 for hours long... this is not possible while listening some other amplifiers.... you became tired and you have to shut off the damn thing.
What make us tired while listening?... i do not know.
I do think, Ostripper, the Symassym has a lot of things that remembers the Techno....but they sound different.... sometimes we have harsh treble into Symassym (the basic version, the first one..the original)... techno has better high end.... Symassym has more dinamics..sounds more powerfull and bass is a little bit more present.
I remember i used to show a music to Michael Bittner, a fortissimo moment where the amplifier use to harsh (the first model)... was the music theme, the movie theme from Wallace, the heroe you had into Scotland....... Brave heart the movie or other name..here in Brazil the title translations are very crazy and have not the same meaning... sorry because of that..i cannot tell you the movie tittle..seems to be Brave heart.... Wallace was the leader against English i think...the music theme has a very strong fortíssimo with violine together other instruments...in that peak the Symassym used to turn unstable and harshes...the first one only.... the second one i have not built.
I do think, all those ones are very good amplifiers... in the reality, the differences are not that enormous...what was very impressive to me was to listen more details, more instruments and more clear voices when listening Elton John recording.
What i mean with that..... not easy to explain....but is focus, precision into the reproduction..... two voices are not fused, melted together producing a third voice that is the resultant..you can listen both voices.... something alike Orange, banana and milk into the electrical mixer.... you can have a resultant..something that may taste alike a new fruit... a new thing, or you can taste orange.... and trying you can taste banana....and trying (making some effort, concentrating yourself) you can taste the milk flavour.
I am a cappuccino Coffee lover...and you can make it taste only chocolate...that flavour can dominate..or the milk flavor (cream), or the cynamon can dominate too...or the coffee taste... when very well ballanced...having a good proportion (ratio) you may be able to feel the milk, the chocolate, the coffee and the cynamon... that's the difference.... taste can be a resultant.... or to keep the original components.... they can be mixed loosing character or not..this is what i am calling focus and precision.
That performance was something that made me very surprised...i could listen things never listened before in that recording..and using the same CD player that was an old sony those days...i have assembled the Techno years ago... and i had to tweak.... i could not make it work with the standard resistance values.
The Techno amplifier has room to modificatins...seems to me the input should have another supply voltage... a more stable supply to the input circuit.... maybe stop resistance to the output.... another type of condenser into the gain line and several other things may turn it even better.... was made to be simple and very good...and it really is simple and very good.
I do not know how it will behave reproducing other kind of musics..when i have built (and i keep it playing for 2 days long)... and this happened in 2005 i think, i have perceived super controled bass.... the unit sounded alike studio monitor amplifiers...very good, very precise.... different...but the bass was not that strong...i felt is a little bit weak.... sounded flat...when i like the bass more present (this is personal)
Some amplifiers give you a little bit more than others.... Krill is one of those ones.... Techno too.... i think HRII surprise us about the power..it seems to be much more powerfull than it really is...Dx Standard reproduces a very warm sound.... each one of them with their good points.
If i could arrange the TDA2030, buiding it discrete, and fixing that treble problem.... without disturb presence, bass and clear sound...it would be a superior amplifier....one of the best ones...but will loose to the Techno into the "focus" department.
In my imagination, Techno may have advantage related the Harmonics... seems does not produce too much (dinamically)... sounds does not mix one each the other producing a third thing..seems more "purified"..... the fourier is perfect and the Total Harmonic distortion is very small (0.02% THD)
I would suggest you to try the Techno...it is a nice sonic experience to listen that one.... will surprise you.... i give you guarantee you will feel surprised.
Here is the schematic...have to check the current into the second differential...maybe you cannot use BC556 there...i remember i have tried using BD139/140.
regards,
Carlos
An externally hosted image should be here but it was not working when we last tested it.
Attachments
Despite i love that Techno, i think i may be searching into the wrong spot
Because the National Semiconductors Engineers have the tools to test and to LISTEN variations.
You see.... the style into the differential.... 4 transistors...high gain differential..... watch they are using simple transistor..single transistor VAS (seems to me this way..maybe not..i have to watch with more carefull).... observe they are using quasi complementary.
WHY?
For sure they can use complementary and full complementary....why they did that way?...for sure they have typped into the keyboard and ordered the waffer production to produce a full complementary set...and for sure they have measured and for sure they have listened..because if i can think about that..for sure they can think too.... no human is idiot..for sure they are not.
They are using because worked fine..because sounded fine and measured fine or result something interesting having all those characteristics all together in a nice ballanced result.
So.... seems to me that's the clue to us..the ones wants to search and research and to assemble and to tweak and to make variations around the same theme....now we can develop something different.
regards,
Carlos
........................................................................................................
And we have to read, to listen, to understand, to believe and give a chance to the ones are more experienced, skilled and older than we are.... read John Curl..... Prejudice text...observe he said that simple is the best option...that he avoid complications...the guy had millions of miles into the electronic road..we must be humble and listen the man.
A pitty that i have no complementary Fet..i would be happy to try the John Curl design..for sure may be excelent..the guy is excelent!
..........................................................................................................
Because the National Semiconductors Engineers have the tools to test and to LISTEN variations.
You see.... the style into the differential.... 4 transistors...high gain differential..... watch they are using simple transistor..single transistor VAS (seems to me this way..maybe not..i have to watch with more carefull).... observe they are using quasi complementary.
WHY?
For sure they can use complementary and full complementary....why they did that way?...for sure they have typped into the keyboard and ordered the waffer production to produce a full complementary set...and for sure they have measured and for sure they have listened..because if i can think about that..for sure they can think too.... no human is idiot..for sure they are not.
They are using because worked fine..because sounded fine and measured fine or result something interesting having all those characteristics all together in a nice ballanced result.
So.... seems to me that's the clue to us..the ones wants to search and research and to assemble and to tweak and to make variations around the same theme....now we can develop something different.
regards,
Carlos
........................................................................................................
And we have to read, to listen, to understand, to believe and give a chance to the ones are more experienced, skilled and older than we are.... read John Curl..... Prejudice text...observe he said that simple is the best option...that he avoid complications...the guy had millions of miles into the electronic road..we must be humble and listen the man.
A pitty that i have no complementary Fet..i would be happy to try the John Curl design..for sure may be excelent..the guy is excelent!
..........................................................................................................
An externally hosted image should be here but it was not working when we last tested it.
Attachments
John Curl... the "Prejudice" text
Stefano site (STEE) have a link to the text...too much big to attach here.
http://www.esafono.it/ddd.pdf
regards,
Carlos
.......................................................................................................
Man!...believe me...i am less distant from John Curl mouth than his own toothbrush can be..the guy open the mouth and there i am listening and thinking about!... i know even the contradictions he said.....he is great..but human.... makes mistakes too.... and one of his main mistake is to think normal humans can understand him deeply...we need time to digest all that stuff... he does not knows he is speaking about computers to a lot of aborigines...better to give, to some of them (ME) a banana!
.......................................................................................................
Stefano site (STEE) have a link to the text...too much big to attach here.
http://www.esafono.it/ddd.pdf
regards,
Carlos
.......................................................................................................
Man!...believe me...i am less distant from John Curl mouth than his own toothbrush can be..the guy open the mouth and there i am listening and thinking about!... i know even the contradictions he said.....he is great..but human.... makes mistakes too.... and one of his main mistake is to think normal humans can understand him deeply...we need time to digest all that stuff... he does not knows he is speaking about computers to a lot of aborigines...better to give, to some of them (ME) a banana!
.......................................................................................................
An externally hosted image should be here but it was not working when we last tested it.
Member
Joined 2009
Paid Member
In terms of sound, I didn't listen to many amplifiers so I can only contribute but a few things I noticed so far
High levels of H2/H3 with reducing levels of higher orders: TGM1 - this topology sounds very good. I think this produces a very easy listenable sound. At high input signal levels it degrades with some muddiness in the sound becauase the distortions increase and generate IM products. The topology is similar as AKSA/DX but level of distortion is not necessarily the same and I know for example that I used more distortion than AKSA.
More linearity into the LTP (input + error amplifier): TGM2 - this change reduces the distortions quite a bit, especially at higher signal levels. The sound is clean, detailed, smooth and has very good bass compared with simple LTP. What I think happens is that bass has large signal swings and suffers the most from low order distortion and IM so you get a bit improvement in bass when you reduce the low-order distortions. In simulations TGM2 is still dominated by H2/3 with reducing levels of higher orders. Distortion is lower than TGM1 and increases more slowly as signal level rises. It sounds cleaner with more authority because the transients are better.
Low levels of H2/3: my Bryston 2B sounds clean with good bass and it never gets even slightly muddy at high power output - just keeps a clean balanced sound. But I get some fatigue when playing through sensitive single driver full range speakers. This amp has low distortion, what I have seen from published data the H2/3 is about the same level as H4/5. So I conclude that fatigue is related to higher order harmonics being more noticeable when lower order harmonics are not dominating more noticeably.
What I have observed about topologies from my simulations and readings so far:
Symmetrical designs have low even harmonics, almost no H2/H4 but readily generate H3/5.
People have reported very good sound from CFP OS, even in ClassB despite concerns about poor cross-over distortion of this topology.
There is a lot of conflicting reports on the sound of JFET input, some say lifeless, some say silky smooth
High levels of H2/H3 with reducing levels of higher orders: TGM1 - this topology sounds very good. I think this produces a very easy listenable sound. At high input signal levels it degrades with some muddiness in the sound becauase the distortions increase and generate IM products. The topology is similar as AKSA/DX but level of distortion is not necessarily the same and I know for example that I used more distortion than AKSA.
More linearity into the LTP (input + error amplifier): TGM2 - this change reduces the distortions quite a bit, especially at higher signal levels. The sound is clean, detailed, smooth and has very good bass compared with simple LTP. What I think happens is that bass has large signal swings and suffers the most from low order distortion and IM so you get a bit improvement in bass when you reduce the low-order distortions. In simulations TGM2 is still dominated by H2/3 with reducing levels of higher orders. Distortion is lower than TGM1 and increases more slowly as signal level rises. It sounds cleaner with more authority because the transients are better.
Low levels of H2/3: my Bryston 2B sounds clean with good bass and it never gets even slightly muddy at high power output - just keeps a clean balanced sound. But I get some fatigue when playing through sensitive single driver full range speakers. This amp has low distortion, what I have seen from published data the H2/3 is about the same level as H4/5. So I conclude that fatigue is related to higher order harmonics being more noticeable when lower order harmonics are not dominating more noticeably.
What I have observed about topologies from my simulations and readings so far:
Symmetrical designs have low even harmonics, almost no H2/H4 but readily generate H3/5.
People have reported very good sound from CFP OS, even in ClassB despite concerns about poor cross-over distortion of this topology.
There is a lot of conflicting reports on the sound of JFET input, some say lifeless, some say silky smooth
Yeah..this is good too Bigun.
Fet turns sound mufled... and our spectations is the opposite..maybe the capacitance.
Enjoy the Dx Pizza..the only one is is guaranteed... because it is a DIY hand made stuff.
regards,
Carlos
http://www.youtube.com/watch?v=nCtj-EJjha0
Fet turns sound mufled... and our spectations is the opposite..maybe the capacitance.
Enjoy the Dx Pizza..the only one is is guaranteed... because it is a DIY hand made stuff.
regards,
Carlos
http://www.youtube.com/watch?v=nCtj-EJjha0
But under what conditions?? Normally one must cascode the input differential to properly implement the FET's. This by itself will change the sound and the gain and the open loop response. Most of the small signal fets have just a small Cob (capacitance) but have less gain than the normal BJT input pair. Emitter degeneration is the answer (degenerate the source of the FET) .... to bring the fet input stage back to "spec" as compared to the original BJT one.
As an example, on my LTP , with 2sc1845's , 100R works good and with the cascoded fet's 22R actually gives a more detailed sound while driving the EXACT same VAS/OPS. (attached pix)
Of course they sound different , the sym cripples the VAS with both a cap and a resistor (like the otala amp) to ground. Mine and the techno are nearly identical except mine does a tiny bit of VAS "crippling" (lowers the gain of the VAS) with 2 resistors to ground .
You may disagree , but the sym with its 2n5551's will sound different than a mje350/340 or my 2sa1381/sc3503's as VAS components.
OS
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