destroyer X said:
Carlos,
you walk around half naked in the sun between nice bikini bottom girls all day, you are living my dirty fantasy, what do you care ?
Resistor - CCS - that is the question!
Unless a current mirror has adjustable degeneration, it is by definition unbalanced when the output is single ended.
This seriously skews the distortion spectrum.
I do enjoy a chat.......!
Cheers,
Hugh
Unless a current mirror has adjustable degeneration, it is by definition unbalanced when the output is single ended.
This seriously skews the distortion spectrum.
I do enjoy a chat.......!
Cheers,
Hugh
Hi HUGH DEAN
I just would have liked more substantiated critical analysis of the CFP and technically discuss about it rather than refering to fact that Self used it.
I am very interesting for the pros and cons of CFP in a general manner and not only in power output stages. It is used in the input stage of the Halcro amp. I have done some simulations of this input stage, I would have think it would be a near perfect input stage, I was disappointed, it is not. The general behaviour is not good, I think, because the input and output transistors are of opposite polarity, more current in the first means more current in the second. So I studied a variant, a pseudo-CFP with same polarities (it can't be called a CFP anymore) which requires additional components : the "new" circuit is quite similar to a solid state version of the White Cathode Follower or the forgotten Taylor power circuit. Distorsion is a bit worse than CFP but thermal behaviour should be better.
Hi LINEUP
"This is clearly a difference between using a resistor to feed the input pair. The sum of current in input pair is changing, because of input voltage."
If we want to absolutly retain a resistor in place of a CCS, there is a solution to mimine this problem : make the amp inverting with a virtual earth input. The first John Curl's amp wasn't it inverting ? Same for Quad 303, Electrocompaniet, Curtis's Mission. Why do designers use so rarely inverting configurations ?
Hi CHRISTER
"Yes, cascodes are known to oscillate sometimes. Did you try a base stopper?"
Yes, I tried it. I retained the 1 kOhm solution instead of a LED + base stopper for the biasing of the upper common base (NPN transistors) because it was more simple and as efficient, as far as I remember.
About Rush
I consider the Rush configuration as a series differential stage, it is not a cascode (there was a thread mentionning Christopher Rush last year, with some analysis of the circuit), and the common long tail pair as a parallel differential stage.
"Sorry, but that is not a good analogy. The photographer is an artist, just like the musician. Just like a violinist can prefer to use a Stradivarius of a Guernari, or a pianist can put chains or other strange objects on the strings to alter the sound, the photographer chan choose to blur pictures, play with depth of field, etc. Those are artistic decisions by the performer.
If you look at a slide photo using a projector, you are reproducing the artwork of the photographer, and then you typically don't want to blur or otherwise distort the picture. You want to see it as the photographer intended it. In the same way a sound reproduction system should (at least in my opinion) achieve an objective acccount and not add to the artistic decisions of the musician. You can, of course, choose to deliberatly modify the reproduction of the photo, or the music, but then you are infringing on a work of art. It would be like buying a painting and then start to repaint parts of it, or to buy a novel an rewrite the parts you don't like."
"
Most of subjectivists won't agree. Your thinking is quite near from mine. If we go more profoundly, it would mean that a good audio system should respect not the original sound but what was the sound recorder's intention, just like a photo is not the visible truth but the work of the photographer. This is a philosophic debate. I have another comparison with the photographic rendition (in
relation with contrasts) and I may start a new thread just for that.
Hi DESTROYER
"The extraordinary designer, Mr. Michael Bittner"
This thread is full of nice subjective comments.
QUOTED
"I've never met anyone smart enough to tell me how something will sound by merely looking at the schematic."
Have you ever met somebody who can objectively tell how is the subjective rendition of an amp ? And would somebody number 2 tell the same ?
~~~~~ Forr
§§§
I just would have liked more substantiated critical analysis of the CFP and technically discuss about it rather than refering to fact that Self used it.
I am very interesting for the pros and cons of CFP in a general manner and not only in power output stages. It is used in the input stage of the Halcro amp. I have done some simulations of this input stage, I would have think it would be a near perfect input stage, I was disappointed, it is not. The general behaviour is not good, I think, because the input and output transistors are of opposite polarity, more current in the first means more current in the second. So I studied a variant, a pseudo-CFP with same polarities (it can't be called a CFP anymore) which requires additional components : the "new" circuit is quite similar to a solid state version of the White Cathode Follower or the forgotten Taylor power circuit. Distorsion is a bit worse than CFP but thermal behaviour should be better.
Hi LINEUP
"This is clearly a difference between using a resistor to feed the input pair. The sum of current in input pair is changing, because of input voltage."
If we want to absolutly retain a resistor in place of a CCS, there is a solution to mimine this problem : make the amp inverting with a virtual earth input. The first John Curl's amp wasn't it inverting ? Same for Quad 303, Electrocompaniet, Curtis's Mission. Why do designers use so rarely inverting configurations ?
Hi CHRISTER
"Yes, cascodes are known to oscillate sometimes. Did you try a base stopper?"
Yes, I tried it. I retained the 1 kOhm solution instead of a LED + base stopper for the biasing of the upper common base (NPN transistors) because it was more simple and as efficient, as far as I remember.
About Rush
I consider the Rush configuration as a series differential stage, it is not a cascode (there was a thread mentionning Christopher Rush last year, with some analysis of the circuit), and the common long tail pair as a parallel differential stage.
"Sorry, but that is not a good analogy. The photographer is an artist, just like the musician. Just like a violinist can prefer to use a Stradivarius of a Guernari, or a pianist can put chains or other strange objects on the strings to alter the sound, the photographer chan choose to blur pictures, play with depth of field, etc. Those are artistic decisions by the performer.
If you look at a slide photo using a projector, you are reproducing the artwork of the photographer, and then you typically don't want to blur or otherwise distort the picture. You want to see it as the photographer intended it. In the same way a sound reproduction system should (at least in my opinion) achieve an objective acccount and not add to the artistic decisions of the musician. You can, of course, choose to deliberatly modify the reproduction of the photo, or the music, but then you are infringing on a work of art. It would be like buying a painting and then start to repaint parts of it, or to buy a novel an rewrite the parts you don't like."
"
Most of subjectivists won't agree. Your thinking is quite near from mine. If we go more profoundly, it would mean that a good audio system should respect not the original sound but what was the sound recorder's intention, just like a photo is not the visible truth but the work of the photographer. This is a philosophic debate. I have another comparison with the photographic rendition (in
relation with contrasts) and I may start a new thread just for that.
Hi DESTROYER
"The extraordinary designer, Mr. Michael Bittner"
This thread is full of nice subjective comments.
QUOTED
"I've never met anyone smart enough to tell me how something will sound by merely looking at the schematic."
Have you ever met somebody who can objectively tell how is the subjective rendition of an amp ? And would somebody number 2 tell the same ?
~~~~~ Forr
§§§
Subjectivism
Forr
>
Have you ever met somebody who can objectively tell how is the subjective rendition of an amp ? And would somebody number 2 tell the same ?
>
It is easy to objectively describe the subjective but it remains subjective.
By definition all subjective impressions differ as subject and enviroment differ. So what. We all hear differently and like different things. We should choose what we like, not with an FFT!
The whole point of subjectivism is that we need to know what we are looking for and what we are trying to fix. This can only be done "outside the box " with our ears!!
Looking inside the box alone you never know what you are looking at sonically or whether it has any relation to any real listening issue!
You just play with numbers and make yourself feel happy. How do you ever tell if you have done good other than subjectively??
The answer is to do both in a never ending cycle but subjective always comes first and last !
cheers
Forr
>
Have you ever met somebody who can objectively tell how is the subjective rendition of an amp ? And would somebody number 2 tell the same ?
>
It is easy to objectively describe the subjective but it remains subjective.
By definition all subjective impressions differ as subject and enviroment differ. So what. We all hear differently and like different things. We should choose what we like, not with an FFT!
The whole point of subjectivism is that we need to know what we are looking for and what we are trying to fix. This can only be done "outside the box " with our ears!!
Looking inside the box alone you never know what you are looking at sonically or whether it has any relation to any real listening issue!
You just play with numbers and make yourself feel happy. How do you ever tell if you have done good other than subjectively??
The answer is to do both in a never ending cycle but subjective always comes first and last !
cheers
Hey y'all........somewhere in the deep dark depths of this thread someone wanted a listening impression of an AKSA.
Well I'm your someone......I've had the pleasure and frustration of an AKSA 100 for a little while now. I acquired this amp because 1) I was a soldering novice, 2) I wanted a new amp, 3) I wanted an Oz made amp, 4) it fitted the budget and 5) there was reasonable evidence to suggest it was better than the existing 100w Yamaha integrated amp I was using. The technobabble, number chucking rubbish that was being spouted at the time by fans, foes and even the designer meant not very much to me. Still doesn't to be true. But I consider it part of the baggage that seems to come with all luxury toys....
The amp started out in Nirvana form (mainly because the option was available and still within budget) so I can't speak for the base model.
Build was easy although it was compromised somewhat by my thrift and distinct lack of case design skills. The odd bit of destructive brain fade didn't help either.....(I'm getting to the listening bit).
First thing is that this little trucker is rather susceptable to hum. Yeah I know that it's all about wiring layout but if you are a bit of a bunny (or in a hurry) it's rather easy to get a ringing in your ear.
Otherwise how's it sound. Well it royally shat over anything some mates and I tried in terms of commercially available amps worth about the same money. No question. Using the same speakers every time (Krix Lyrix floorstanders) there was way more detail and control, it had a soundstage with depth as well as width and there was the sort of emotion you get when you listen to vinyl after you've been hearing CD. None of those listening were wiring/design/audio dudes (we couldn't spell audiophile and we assumed it was a fancy name for a ******) but we knew what we liked - music. Any everybody who bought their music to the player found something in their tunes they'd never heard or experienced before. Happy people.
So how does it sound compared to the audio jewelery that has been spouted so far in this thread. Dunno. They're just names to me. But in the price point that the AKSA sits at then it soundly thumps all comers so far that I've heard.
Except in one area. Bass. If you like bass (and I mean REALLY like bass) then you may find others that can create more. My music contains a fair swathe of bass heavy electronica and it certainly reproduces that in a way I enjoy - Groove Armada's "Suntoucher" off the 'Goodbye Country, Hello Nightclub' is a personal fav test track because of deep bass frequencies and lots of little details hidden away too. But I have found a couple of commercial amps that will do bigger bass than the AKSA . Downside is that they only do this bit better and in truth the AKSA wasn't that far behind. Personal preference no doubt but I suspect that if doof is your preference then consider something bigger.
I've since upgraded to Nirvana Plus and I have to admit this is where my ears gave out. I could only get a general sense that something was 'better'. My ears aren't good enough to pin down how but it just 'felt' better. And neither could my 'impartial observers' get much more out of it - would couldn't really compare the N and N+ anyway since the N was lost in the upgrade. Possibly the only thing that got helped to my ears was improved bass control over the N.
Oh and I didn't really 'hear' the Black Gates bedding in either. There was a bit of a wobble early on but after about 10 hours all was sweet. Perhaps the high ambient temperatures at the time helped (we were in a run of 40 degree C plus days at the time).
So whatever the design.............it works.
The other big improve was the inclusion of the AKSA GK-1 Pre-amp too. Main result here was bigger and more precise 3D soundstage - previous pre was the pre in the Yamaha integrated.
The frustration? That was the wiring up (remember the HUmmmm) and the case work. We are approaching case number three at this time..........that's the frustrating part.
Well I'm your someone......I've had the pleasure and frustration of an AKSA 100 for a little while now. I acquired this amp because 1) I was a soldering novice, 2) I wanted a new amp, 3) I wanted an Oz made amp, 4) it fitted the budget and 5) there was reasonable evidence to suggest it was better than the existing 100w Yamaha integrated amp I was using. The technobabble, number chucking rubbish that was being spouted at the time by fans, foes and even the designer meant not very much to me. Still doesn't to be true. But I consider it part of the baggage that seems to come with all luxury toys....
The amp started out in Nirvana form (mainly because the option was available and still within budget) so I can't speak for the base model.
Build was easy although it was compromised somewhat by my thrift and distinct lack of case design skills. The odd bit of destructive brain fade didn't help either.....(I'm getting to the listening bit).
First thing is that this little trucker is rather susceptable to hum. Yeah I know that it's all about wiring layout but if you are a bit of a bunny (or in a hurry) it's rather easy to get a ringing in your ear.
Otherwise how's it sound. Well it royally shat over anything some mates and I tried in terms of commercially available amps worth about the same money. No question. Using the same speakers every time (Krix Lyrix floorstanders) there was way more detail and control, it had a soundstage with depth as well as width and there was the sort of emotion you get when you listen to vinyl after you've been hearing CD. None of those listening were wiring/design/audio dudes (we couldn't spell audiophile and we assumed it was a fancy name for a ******) but we knew what we liked - music. Any everybody who bought their music to the player found something in their tunes they'd never heard or experienced before. Happy people.
So how does it sound compared to the audio jewelery that has been spouted so far in this thread. Dunno. They're just names to me. But in the price point that the AKSA sits at then it soundly thumps all comers so far that I've heard.
Except in one area. Bass. If you like bass (and I mean REALLY like bass) then you may find others that can create more. My music contains a fair swathe of bass heavy electronica and it certainly reproduces that in a way I enjoy - Groove Armada's "Suntoucher" off the 'Goodbye Country, Hello Nightclub' is a personal fav test track because of deep bass frequencies and lots of little details hidden away too. But I have found a couple of commercial amps that will do bigger bass than the AKSA . Downside is that they only do this bit better and in truth the AKSA wasn't that far behind. Personal preference no doubt but I suspect that if doof is your preference then consider something bigger.
I've since upgraded to Nirvana Plus and I have to admit this is where my ears gave out. I could only get a general sense that something was 'better'. My ears aren't good enough to pin down how but it just 'felt' better. And neither could my 'impartial observers' get much more out of it - would couldn't really compare the N and N+ anyway since the N was lost in the upgrade. Possibly the only thing that got helped to my ears was improved bass control over the N.
Oh and I didn't really 'hear' the Black Gates bedding in either. There was a bit of a wobble early on but after about 10 hours all was sweet. Perhaps the high ambient temperatures at the time helped (we were in a run of 40 degree C plus days at the time).
So whatever the design.............it works.
The other big improve was the inclusion of the AKSA GK-1 Pre-amp too. Main result here was bigger and more precise 3D soundstage - previous pre was the pre in the Yamaha integrated.
The frustration? That was the wiring up (remember the HUmmmm) and the case work. We are approaching case number three at this time..........that's the frustrating part.
HIFRYER
"Looking inside the box alone you never know what you are looking at sonically or whether it has any relation to any real listening issue!"
I know recipes to make amps very linear and I know other recipes to get no such linearity. I know recipes to get wonderfull harmonic spectrum. Marketing people know recipes to precondition people. I am not a marketing man.
Some people think this thread should only contain listening comments on an amplifer named AKSA. I am very surprised that there are so few negative comments. This is a DIY forum and this allows any diyer and amp-technically involved person to try to know why this is so and where is the magic, hence the technical discussion which, I think, I have initiated.
~~~~ Forr
§§§
"Looking inside the box alone you never know what you are looking at sonically or whether it has any relation to any real listening issue!"
I know recipes to make amps very linear and I know other recipes to get no such linearity. I know recipes to get wonderfull harmonic spectrum. Marketing people know recipes to precondition people. I am not a marketing man.
Some people think this thread should only contain listening comments on an amplifer named AKSA. I am very surprised that there are so few negative comments. This is a DIY forum and this allows any diyer and amp-technically involved person to try to know why this is so and where is the magic, hence the technical discussion which, I think, I have initiated.
~~~~ Forr
§§§
Hi seano
I sympathise re casework!
I have N+ running in.
re Hum - you should have none!! - look to your layout, wiring and interconnects. Is it still there with shorted inputs? Ask Hugh.
re bass - my bass is coming and going. I suggest 10 hrs nowhere near adequate run-in time! Wait and see. I find the BG's such a pain I'm tempted to try different. I'm highly skeptical that yours really did settle down in the time you say and suggest they relate to the bass you hear or dont hear. Do you leave your amp on all the time and play it often? If off for a period, with BG's run in almost starts again!
Are the other amps with more bass higher powered or tube amps? The AKSA has very fast, tight and articulate bass but goes VERY deep if source is there.
As a joke test for fatter bass try a small ( say 2R, high power > 20W ) R in your speaker leads ;-) ( ruins damping and provokes reflex speakers - can emulate tube bass )
cheers
I sympathise re casework!
I have N+ running in.
re Hum - you should have none!! - look to your layout, wiring and interconnects. Is it still there with shorted inputs? Ask Hugh.
re bass - my bass is coming and going. I suggest 10 hrs nowhere near adequate run-in time! Wait and see. I find the BG's such a pain I'm tempted to try different. I'm highly skeptical that yours really did settle down in the time you say and suggest they relate to the bass you hear or dont hear. Do you leave your amp on all the time and play it often? If off for a period, with BG's run in almost starts again!
Are the other amps with more bass higher powered or tube amps? The AKSA has very fast, tight and articulate bass but goes VERY deep if source is there.
As a joke test for fatter bass try a small ( say 2R, high power > 20W ) R in your speaker leads ;-) ( ruins damping and provokes reflex speakers - can emulate tube bass )
cheers
Forr,
It is interesting there are no negative comments here. Maybe those who own AKSA like them??
Do YOU own and listen to an AKSA??? Have you ever heard one??
Do YOU have any negative comments? There is no censorship here!
You have losts of recipes! Do you have any for good sounding amplifiers? If so, how do you know or find out?????
I, for one, am happy for technical discussion but once this goes long and detailed it perhaps better moved to its own thread.
cheers
It is interesting there are no negative comments here. Maybe those who own AKSA like them??
Do YOU own and listen to an AKSA??? Have you ever heard one??
Do YOU have any negative comments? There is no censorship here!
You have losts of recipes! Do you have any for good sounding amplifiers? If so, how do you know or find out?????
I, for one, am happy for technical discussion but once this goes long and detailed it perhaps better moved to its own thread.
cheers
There's a couple of subtle and not so subtle references in the thread questioning what Hugh has miraculously done that those same people should expect the Aksa to sound any different, or better, than amps using the topology back when it was first realised. Then there's the flipside question (subtle and not so subtle) as to what Hugh hasn't done to the topology and again, why should anyone expect the amp to sound any better than the topologies forefathers.
I'd like to answer this as best I can though why I'm attempting to is a bit of a mystery as Hugh himself has answered, within this thread, and who-knows-how-many-others. But the question continues. The topology has been tweaked to the nth degree, to an inch of its life with various board layouts, components, component placement and the possible combinations. Consider how many variations you can have with such a circuit and that topology, layout and component choice are considered the most important aspects in a design.
Sadly, try as he might he cannot seem to get anymore performance out of the amp without compromising some of the qualities that endear it to its owners. Or, that changes that do improve bump up the cost considerably. Something many who do not own an Aksa already dispute... the cost.
It's hard to imagine a great many people out there, regardless of their background in audio electronics, who have dedicated so much time, effort and of course money, into a single design. Where most move on to the latest and greatest, only a handful could be said to perservere and squeeze the last iota of performance out of the original.
I'd like to avoid analogies, however, racing car teams are a fair example. Where a privateer competes head on with the factory owned teams, often with a car a season or more out of date. They rarely win but occasionally, they do. Hugh is a privateer, driven by passion. Obviously there's some competitiveness to the man. Whether it's competing with the factory owned teams or himself, perhaps even both, who can say? I for one just hope his passion remains because he's a winner.
The crux of the matter is, with regards to those who "question" what has been done to an old topology is exactly what Hugh has written before. It boils down to dedication and perseverence which for those willing to take a blind leap, many benefits are reaped.
My neighbour recently had the Aksa 100N+ and GK-1 for several days, Hugh's personal listening equipment. Paired to a Njoe Tjoeb 4k and Legacy Signature iii speakers. The equipment just disappeared and you were presented with silky, enveloping music. There's nothing more that needs to be said about it's performance.
So feel free to shoot me down with what is mostly to me, techno-babble. I wont be phased as I've listened to an Aksa as opposed to hearing the schematic. I bet the amp sounds better every time. A parting thought... It's natural to question something you haven't experienced. It's quite rude, however, to presume your right without the amplifier in your listening room.
I'd like to answer this as best I can though why I'm attempting to is a bit of a mystery as Hugh himself has answered, within this thread, and who-knows-how-many-others. But the question continues. The topology has been tweaked to the nth degree, to an inch of its life with various board layouts, components, component placement and the possible combinations. Consider how many variations you can have with such a circuit and that topology, layout and component choice are considered the most important aspects in a design.
Sadly, try as he might he cannot seem to get anymore performance out of the amp without compromising some of the qualities that endear it to its owners. Or, that changes that do improve bump up the cost considerably. Something many who do not own an Aksa already dispute... the cost.
It's hard to imagine a great many people out there, regardless of their background in audio electronics, who have dedicated so much time, effort and of course money, into a single design. Where most move on to the latest and greatest, only a handful could be said to perservere and squeeze the last iota of performance out of the original.
I'd like to avoid analogies, however, racing car teams are a fair example. Where a privateer competes head on with the factory owned teams, often with a car a season or more out of date. They rarely win but occasionally, they do. Hugh is a privateer, driven by passion. Obviously there's some competitiveness to the man. Whether it's competing with the factory owned teams or himself, perhaps even both, who can say? I for one just hope his passion remains because he's a winner.
The crux of the matter is, with regards to those who "question" what has been done to an old topology is exactly what Hugh has written before. It boils down to dedication and perseverence which for those willing to take a blind leap, many benefits are reaped.
My neighbour recently had the Aksa 100N+ and GK-1 for several days, Hugh's personal listening equipment. Paired to a Njoe Tjoeb 4k and Legacy Signature iii speakers. The equipment just disappeared and you were presented with silky, enveloping music. There's nothing more that needs to be said about it's performance.
So feel free to shoot me down with what is mostly to me, techno-babble. I wont be phased as I've listened to an Aksa as opposed to hearing the schematic. I bet the amp sounds better every time. A parting thought... It's natural to question something you haven't experienced. It's quite rude, however, to presume your right without the amplifier in your listening room.
forr said:
Hi forr,
When I was looking around for my first DIY amp the sceptic in me was very concerned about all the postive, glowing reports about the AKSA. Too good to be true? Anyway over the last 4 or 5 years I have only been able to find 2 people with negative responses about AKSAs. I think Hugh has a hit squad to goes around eliminating these people. 😀
Do we have any mathematicians here? I'm not.
I still believe the success of the ASKA is in the selection of the right components for the job. The chances of getting the right components is significantly easier with a simple topology. As the complexity of the topology increases the job gets far more difficult. If you double the number of components, statisically, the number of combinations is millions of times greater.
regards
HIfryer........the amp is almost certainly run in. It has been in N+ form for over twelve months and has many many hours on it.
My perception of the form during N+ run-in is my perception. Personal impression of feedback from other owners about N+ run-in is that either I'm deaf.....or others are deluding themselves over nothing very important. Since one of those 'others' is the amp designer himself then perhaps the former is more likely. Either way it matters nought as long as I'm happy. And I am.
Hum comes down to me - I know that. Just haven't got to the bottom of it quite yet. Tis only a smidge in one channel so really not a major concern to me. Original comment came from the fact that hum is easy to generate when building this amp. So if you are considering this amp then you have to bear that in mind.
My bass comment stands too. I'm happy but others may not be. Depends on your needs and musical preferences. Agree that you do get substantial bass but some commercial SS amps of similar cost and claimed output seem to generate more BUT with less control and other nice things. Can't comment about other DIY designs as I never heard them nor built them.
Ultimately, I'm satisfied that what has cost me roughly AU$1500 thus far can not be matched in terms of audio quality until such time as I happen to have at least four times that much money available to me to spend on an amp. At that ain't EVER going to happen..........in those terms alone it's a bargain. Regardless of the innovation (or lack thereof) of the design.
My perception of the form during N+ run-in is my perception. Personal impression of feedback from other owners about N+ run-in is that either I'm deaf.....or others are deluding themselves over nothing very important. Since one of those 'others' is the amp designer himself then perhaps the former is more likely. Either way it matters nought as long as I'm happy. And I am.
Hum comes down to me - I know that. Just haven't got to the bottom of it quite yet. Tis only a smidge in one channel so really not a major concern to me. Original comment came from the fact that hum is easy to generate when building this amp. So if you are considering this amp then you have to bear that in mind.
My bass comment stands too. I'm happy but others may not be. Depends on your needs and musical preferences. Agree that you do get substantial bass but some commercial SS amps of similar cost and claimed output seem to generate more BUT with less control and other nice things. Can't comment about other DIY designs as I never heard them nor built them.
Ultimately, I'm satisfied that what has cost me roughly AU$1500 thus far can not be matched in terms of audio quality until such time as I happen to have at least four times that much money available to me to spend on an amp. At that ain't EVER going to happen..........in those terms alone it's a bargain. Regardless of the innovation (or lack thereof) of the design.
AKSA said:
Hugh,
I don't quite get what you mean here. Adjustable in what way? You mean not having equal degeneration for the two BJTs in the mirror? In what way is the current mirror unbalanced?
I am not tryint to say that current mirrors must be better than plain resistors, I just wonder what you mean here.
forr said:
For what its worth, I did some simulations once of using CFPs instea of the output transistors in Diamond buffers. The result was that it did lower distorsion, but the spectrum decayed more slowly, giving a higher proportion of high order harmonics. PMA said that this spectrum character correlated with his own measurements of CFPs in general. It is not entirely surprising either, since a CFP has a feedback loop.
Diamond buffers are usually run in class A, and it turned out that doubling the bias current in the standard diamond buffer gave equally low distorsion figures as the CFP version, but with high order harmonics decaying faster. So since Diamond buffers are typically used for low power applications, increasing the bias currents seems a better option than using a CFP. However, in cases where that is not an option, the CFP may be useful. Many do like them for power amp outputs, even PMA despite his measurements.
Then there is the tendency for oscillation in CFPs to consider also.
That can still have an advantage even if we use a diff stage with very high CMRR. Since we get rid of the common mode voltage and the differential voltage is usually very smal, we get a near-constan Vce of the transistors, This avoids distorsion due to the non-linear voltage dependancy of Cob. On the other hand, cascodes can avoid that problem if referenced to the common mode voltage.
Yes, if one draws the small signal schematics for both, it is obvious how identical they are. The only difference is the extra impedance due to the tail in the diff pair. There is also the difference (not directly visible in the schematic) that the transistor currents, and thus their Vbe, are in phase, instead of out of phase) in the Rush cascode since the transistors are complementary. This means we don't have the nice property of the diff paif of being very linear for small diff voltages.
What I fail to understand is why the Rush cascode is claimed to be extremely fast. As I said, it is only the tail impedance that differ, and it hardly makes the diff pair considerably slower.
Sure, but I think they would be inclined to agree in the other, non-musiscal examples I gave. However, my point was not primarly to argue for objective reproduction, but to point out that the photographer corresponds to the perormer, the musician, not to the sound reproduction equipment. I have seen similar (in my opinion) flawed analogies before. If we are talking subjectivism vs. objectivism in audio, it is more appropriate to compare with the viewing of the photo, and whether to deliberately alter its appearance or not.
AKSA said:
Hi Hugh,
do you have any picture of the harmonic spread or figures for all harmonics up to the 5th, would be very delighted to take part of that information!
Seeing the distortion going up as little as from 0.043 to 0,05 % for 1 to 20 kHz shows it's cosistent quality!
Cheers Michael
Hi, Christer,
I think the special property of Rush cascode is not in "Fast" but in "transients".
Current Feedback (feedback to emitors) should be faster than Rush cascode (where the feedback is still to base), but Rush cascode has no CCS that limits it's transients. In differential pair, the maximum current that can pass through 1 transistor is the whold value of the CCS, while in the Rush Cascode, it can pass any current it wanted without restriction.
In sonics, this is heard as "faster" sound, while actually it is a "transient-not limited" sound.
lumanauw said:
I almost thought you had a point there for a second or two, but on second thought I doubt it. Yes, you are right that the Rush cascode isn't current limited in the same sense as the diff pair, and I admit not thinking about that myself. however, that only means that you can swing far above Iq, but Iq still limits how far below you can swing. That is, Iq still sets the limit for clipping in both cases, and I see no reason why one should be able to have a higher max Iq in a Rush cascode than in a diff pair.
No properly designed amp should be transient limited anyway, at least not in the input stage. The slew rate in all stages should be sufficient wrt. to the coutoff frequency of the input LP filter, so the amp isn't slewing limited. The problem may be in the output stage, where you may have high power and current demands, but that's another issue.
Edit:
There may be something to what you say though. A Rush cascode might perhaps sound better in a poorly designed amp. Remember that a diff pair has an interesting transfer function that is very linear for small diff voltages and then turns into very nonlinear and even saturates for large diff voltages. As Leach points out, if the amp is too slow and/or the cutoff frequency of the input filter is set too high wrt. to the slew rate of the amp, the diff pair can get overloaded and saturate. That won't happen that easily in a Rush cascode, since it has the usual exponential transfer function of a BJT. So yes, transients can more easily make the input stage saturate when using a diff pair, but only if the amp is poorly designed. If correctly designed, the diff pair shouldn't overload and is more linear.
Hi Christer,
Just my 2Cents.....
Rush Cascode Offers higher PSRR..then conventional cascodes and differential pairs...
K a n w a r
Just my 2Cents.....
Rush Cascode Offers higher PSRR..then conventional cascodes and differential pairs...
K a n w a r
Hi, Christer,
You are right, if it is designed right, there should be no problem. 😀
One interesting thing is the explenation of why John Curl uses input differential (K389-J106) like he uses. Somewhere here, he has explenation why he stacked those like that (using properties of Jfet, that Source is more negative/positive than it's gate), instead of using independent CCS to lower and upper differential pair. If I'm not mistaken, the explenation is about this "Transients".
I don't know what happens that such a big transients (where calculation should be able to predict the minimum) is needed, making JC uses this configuration, and writes explenation like that.
There is also an interesting thread somewhere, where Darkfenriz proposes an idea of dual complementary differential which uses no CCS, but stacked (like John Curl/Borbely Jfet version), by level shifting the input node and feedback node by 2xdiodes drop.
There is a major drawback using Rush Cascode for front stage. It cannot automaticly maintain 0 DC offset 😀
You are right, if it is designed right, there should be no problem. 😀
One interesting thing is the explenation of why John Curl uses input differential (K389-J106) like he uses. Somewhere here, he has explenation why he stacked those like that (using properties of Jfet, that Source is more negative/positive than it's gate), instead of using independent CCS to lower and upper differential pair. If I'm not mistaken, the explenation is about this "Transients".
I don't know what happens that such a big transients (where calculation should be able to predict the minimum) is needed, making JC uses this configuration, and writes explenation like that.
There is also an interesting thread somewhere, where Darkfenriz proposes an idea of dual complementary differential which uses no CCS, but stacked (like John Curl/Borbely Jfet version), by level shifting the input node and feedback node by 2xdiodes drop.
There is a major drawback using Rush Cascode for front stage. It cannot automaticly maintain 0 DC offset 😀
lumanauw said:
That Dual Differential without CCS is known as DIAMOND DIFFERENTIAL....
Rush Cascode is best used for VAS, not the input stage...😀 😉
K a n w a r
lumanauw said:
I have never read any explanation of it and have never given much thought to it before. I have just considered it a simple solution which is an opportunity you have only with JFETs. However, you now made me think about it and I think there simply is no need for CCSs. Since it is a complementary differential, any common mode voltage will appear equally at both ends of the resistor, so if each diff pair is well matched, which it should be anyway, there will always be an almost perfectly constant voltage over the resistor. It looks so simple, but is so clever, but John is a smart guy (although I don't know if he was the first to this idea).
You mean using BJTs then, I presume? Yes, I guess that would work in the same way as the JFET solution above.
Yes, and you have to either AC couple and level shift the input, or the feedback signal. One funny approach was used in the Sentec SCA-1, of which I once posted a schematic. It uses a Rush cascode consisting of an NJFET and a PNP!!! That could solve the problem if the JFET had exactly the right Vgs at the Q point, but that is more like wishful thinking, and this particular amp had a DC servo.
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