Congratulations Susan. All the excitement in this thread has reminded me of a small sign I saw once. It was on a wall behind a secretary's desk and it said something like this.
"When it came to dancing Ginger Rogers was just the same as Fred Astair............except she did it backwards in high heels."
"When it came to dancing Ginger Rogers was just the same as Fred Astair............except she did it backwards in high heels."
I am somewhat confused about contradictory information about life expectancy of Bass Loudspeaker (Life expectancy: 100 years plus for the cabinet (the drive units may need refurbishing before this) and Spheroidal Marble Speakers (Life expectancy: 100 years plus for the cabinet (the drive units may need refurbishing before this).
About electrolytical capacitors in power supply nobody has no any doubts...
About electrolytical capacitors in power supply nobody has no any doubts...
Hi Susan,
I guess the question ' What's inside your 'speaker ?' would also have been as relevent, because the amplifier-loudspeaker combination is more important than either the amp' or 'speaker when viewed alone in isolation.
You quote 2.78 ohms output impedance. That would not satisfy me for use with 'conventional' loudspeakers.
However your Marble enclosures appear to house what looks like a Jordan JX92S, which can be 'bright' when driven by a low output impedance amplifier, this to the extent that many users prefer to use them with a series L//R 'baffle step' corrector. Now wouldn't that make for a super A-B comparison; your system, versus a good conventional amp plus baffle step, using the same source and loudspeakers!!
You suggest small drivers like the Jordan are 'bright', but when you get 9 or 16 of them in a line, the brightness disappears due to physical spacing, which is why a tweeter becomes necessary at hf for non-'far-field' listening. But then who could afford 9 or 16 Jordans per channel ? I'm not so sure that parallel connection down to 0.5 ohms is going to sound any better than evenly or 'field' distributed series/parallel chains; as you say, even the Quad has distributive response tapering.
Your amplifier does have its own internal voltage NFB - at the sources wrt input. Indeed, when there would be any transformer/driver resonance leading to momentarily high impedances at the sources there would be a potential for waveform rectification, though your amplifier controls this via its push-pull arrangement. Did you ever try any resistor damping at each source wrt ground, say 22 ohms ? I don't think your circuit would work so cleanly if it were single ended.
You mention
1 pre-amp cables............ not a problem if the pre-amp designer knows to buffer properly with resistor feed and loading.
2 NFB .............. not a problem if the amp designer examines for amplifier response to predictable crossover/loudspeaker induced back EMF.
3 cables .............. not a problem if the crossover is before the amplifiers or driven at genuinely low impedance then with inexpensive cables going to the loudspeaker drivers.
You have covered these aspects with your own design in a way that most commercially available systems have yet to do.
It is not signal path capacitors or NFB that are the problem, indeed there are those of us who could equally complain that transformers are a problem, but then you know your own design in a way that we cannot.
I thank you for your offer for remote listening, but alas I have my own as well as family health probs to cope with. You would not believe the difficulties I had just completing the text for my article; my own hands on work has become almost non-existant. Hows about comparing your amp at home with a class-A like the JLH, for Jordan loudspeakers can be well driven by any of the JLH class-A's ?
Never let us wear you down,
Cheers ............ Graham.
I guess the question ' What's inside your 'speaker ?' would also have been as relevent, because the amplifier-loudspeaker combination is more important than either the amp' or 'speaker when viewed alone in isolation.
You quote 2.78 ohms output impedance. That would not satisfy me for use with 'conventional' loudspeakers.
However your Marble enclosures appear to house what looks like a Jordan JX92S, which can be 'bright' when driven by a low output impedance amplifier, this to the extent that many users prefer to use them with a series L//R 'baffle step' corrector. Now wouldn't that make for a super A-B comparison; your system, versus a good conventional amp plus baffle step, using the same source and loudspeakers!!
You suggest small drivers like the Jordan are 'bright', but when you get 9 or 16 of them in a line, the brightness disappears due to physical spacing, which is why a tweeter becomes necessary at hf for non-'far-field' listening. But then who could afford 9 or 16 Jordans per channel ? I'm not so sure that parallel connection down to 0.5 ohms is going to sound any better than evenly or 'field' distributed series/parallel chains; as you say, even the Quad has distributive response tapering.
Your amplifier does have its own internal voltage NFB - at the sources wrt input. Indeed, when there would be any transformer/driver resonance leading to momentarily high impedances at the sources there would be a potential for waveform rectification, though your amplifier controls this via its push-pull arrangement. Did you ever try any resistor damping at each source wrt ground, say 22 ohms ? I don't think your circuit would work so cleanly if it were single ended.
You mention
1 pre-amp cables............ not a problem if the pre-amp designer knows to buffer properly with resistor feed and loading.
2 NFB .............. not a problem if the amp designer examines for amplifier response to predictable crossover/loudspeaker induced back EMF.
3 cables .............. not a problem if the crossover is before the amplifiers or driven at genuinely low impedance then with inexpensive cables going to the loudspeaker drivers.
You have covered these aspects with your own design in a way that most commercially available systems have yet to do.
It is not signal path capacitors or NFB that are the problem, indeed there are those of us who could equally complain that transformers are a problem, but then you know your own design in a way that we cannot.
I thank you for your offer for remote listening, but alas I have my own as well as family health probs to cope with. You would not believe the difficulties I had just completing the text for my article; my own hands on work has become almost non-existant. Hows about comparing your amp at home with a class-A like the JLH, for Jordan loudspeakers can be well driven by any of the JLH class-A's ?
Never let us wear you down,
Cheers ............ Graham.
As it was mentioned the amp is push-pull source follower with transformer as a load. I would like to ask what is the quiescent current of each FET? Is it class A or AB? During one half-cycle of the input signal one follower will feed not only the load but the other follower too. What will be if the FETs are slightly different? What measures are taken to avoid dc component in the output transformer due to imbalance? Having experience with high-current triodes like 6C33C, 6C18C I know that the output transformer core jumps to saturation even with small imbalance.
Hi,
Thank you for your question and interest in my amplifier
I assume you mean 400 W of full bandwidth hi quality audio rather than an FM RF amp or ultrasonic driver for side scan sonar?
No problems John, supportful comments always welcome.
===
I see the practical limit at around the 120 watts point, not just because of the rising distortion but the more pragmatic one that I simply wouldn't be able to lift an amp of any greater power due to the weight.
However I would posit that you would not need 400 watts in a normal domestic listening situation (for which my amplifier is designed) unless you were after a bass guitar amp or such like?
As previously mentioned I am of the opinion (rightly or wrongly) that one should split out the low bass where speakers are operating in piston mode (and therefore require lots of power) from the rest of the audio range - where one should use single wide range drivers (perhaps in line arrays). The discussion then becomes one of whether crossover phase distortion is more or less problematic than Doppler distortion.
Low bass - which could benefit from several hundred watts if you are really going for the sub 20 Hz stomach rattler - can be driven directly by a conventional solid state amp - perhaps with motion feedback BUT one needs a big room to be able to hear this as most domestic living rooms (here in the UK anyway) as sufficiently small that true low bass can't be reproduced because the (half?) wavelength of the sound is bigger than the room dimensions and it cancels out.
Crossover point at say 120 Hz.
The rest of the audio band with decent sensitivity speakers shouldn't need more than 30 to 50 watts max even in a large room.
Hope this helps.
Best wishes,
Susan.
Thank you for your question and interest in my amplifier
Circlomanen said:
I assume you mean 400 W of full bandwidth hi quality audio rather than an FM RF amp or ultrasonic driver for side scan sonar?
john curl said:
No problems John, supportful comments always welcome.
===
I see the practical limit at around the 120 watts point, not just because of the rising distortion but the more pragmatic one that I simply wouldn't be able to lift an amp of any greater power due to the weight.
However I would posit that you would not need 400 watts in a normal domestic listening situation (for which my amplifier is designed) unless you were after a bass guitar amp or such like?
As previously mentioned I am of the opinion (rightly or wrongly) that one should split out the low bass where speakers are operating in piston mode (and therefore require lots of power) from the rest of the audio range - where one should use single wide range drivers (perhaps in line arrays). The discussion then becomes one of whether crossover phase distortion is more or less problematic than Doppler distortion.
Low bass - which could benefit from several hundred watts if you are really going for the sub 20 Hz stomach rattler - can be driven directly by a conventional solid state amp - perhaps with motion feedback BUT one needs a big room to be able to hear this as most domestic living rooms (here in the UK anyway) as sufficiently small that true low bass can't be reproduced because the (half?) wavelength of the sound is bigger than the room dimensions and it cancels out.
Crossover point at say 120 Hz.
The rest of the audio band with decent sensitivity speakers shouldn't need more than 30 to 50 watts max even in a large room.
Hope this helps.
Best wishes,
Susan.
Re: Hey Susan!!!
Hi,
Ah! I hadn't realized that so many people were watching - now I am feeling a little self conscious. I had better try to keep my spelling in order - not one of my stronger points being dyslexic!
Thank you, and everyone else, for the encouragement.
A quick point, the US manufacture is a source for the laminations, which is the heavy part of the transformer. The transformers will still need to be assembled (not a tricky thing to do for someone who is up to bolting power devices onto heat sinks).
I can supply wound bobbins etc. although hand winding the output transformers is not difficult due to the large wire size and relatively small number of turns.
The input transformer is a different matter which is why I was suggesting to buy them from Sowter ready made.
Best wishes,
Susan.
Hi,
darkmoebius said:
Ah! I hadn't realized that so many people were watching - now I am feeling a little self conscious. I had better try to keep my spelling in order - not one of my stronger points being dyslexic!
Thank you, and everyone else, for the encouragement.
A quick point, the US manufacture is a source for the laminations, which is the heavy part of the transformer. The transformers will still need to be assembled (not a tricky thing to do for someone who is up to bolting power devices onto heat sinks).
I can supply wound bobbins etc. although hand winding the output transformers is not difficult due to the large wire size and relatively small number of turns.
The input transformer is a different matter which is why I was suggesting to buy them from Sowter ready made.
Best wishes,
Susan.
Hi Allexx,
The Bass speaker is made from hardwood (beeswax polished) with proper carpentry and therefor should last at least a hundred years if not bashed around.
The Sphere's shells and their stands are hand carved from single pieces of solid marble, and therefor should last a minimum of a thousand years - with a possible life of five thousand years plus is well looked after.
The drive units however incorporate materials like thin aluminum foil cones and rubber surrounds and these are susceptible to corrosion and deterioration in shorter timescales. Hence the likelihood of the drive units requiring refurbishment in a shorter time scale.
I hope this answers your question.
Best wishes,
Susan.
Allexx said:
The Bass speaker is made from hardwood (beeswax polished) with proper carpentry and therefor should last at least a hundred years if not bashed around.
The Sphere's shells and their stands are hand carved from single pieces of solid marble, and therefor should last a minimum of a thousand years - with a possible life of five thousand years plus is well looked after.
The drive units however incorporate materials like thin aluminum foil cones and rubber surrounds and these are susceptible to corrosion and deterioration in shorter timescales. Hence the likelihood of the drive units requiring refurbishment in a shorter time scale.
I hope this answers your question.
Best wishes,
Susan.
Hi Graham,
Thank you for your reply and comments.
Yes, I agree entirely and this is why I am less concerned with amplifier distorsion in absentia as it does not give the whole picture.
My amplifer works as a current drive, not voltage.
"Son of Zen" is quoted as being 16 ohms output impedance.
I find that conventional speakers in the main show a noticable improvement when used with my amp - the exception being ones with over bright trebble.
My LS3/5As, which whilst very flat for frequency response (with a correspondingly complex crossover tuning circuit), are to my ears somewhat muddy driven by normal amps. With my amp the whole sound clarifies and a much improved sound stage definition is achieved.
All this is my own subjective experince of course, my ears being fussy about phase coherance as perhaps I may have mentioned previously?
Basically I want to be able to sit ten feet back with the speakers spaced sixteen feet apart and hear a complete sound stage in front of me without a hole in the middle.
Our living room is a bit smaller than this so I have to compromise.
They are Jordan JX62s, unfortunantly no longer made.
I assume that you don't think a Quad 34/306 system is in the class of a "good conventional amp" being perhaps a bit long in the tooth?
I couldn't afford them. I am currently looking at some cheeper wideband German drivers - initally as replacments for the Jordan contraflex drivers.
My amplifier is a curent driver, therefor works best if matched to the load. Because it is a current driver it can be configured to drive very low sub-ohm loads which simply wouldn't be possible in a conventional solid state amp.
The point with the line arrarys depends on the configuration.
People have attempted to make line arrays by stacking small bookshelf speakers on their sides one atop the other. Series/Parrallel chains with internal crossovers suffer HF loss, however true parallel drive does not have this problem.
Yes, the followers do have internal NFB, but the bandwidth is very high. There is no global feedback to an input signal.
The followers have a gain of just under unity, hence rapid dampening of any "hiccups". This may be seen as a problem with compression at high power levels but I am not aware of it in my own listening (however that doesn't mean that it doesn't happen or that other people wouldn't notice).
Most of my listening is done with the first watt or two.
The resonance problem shouldn't accour as the amp is push-pull.
I haven't tried resistor dampening. The transformer is 1:1 so wouldn't the resistors still appear as 22 ohms / 2 to the loudspeaker? The output impedance is already down at 2.7 ohms.
A single ended version of my amplifier, as I have described in my notes, would have an asymetirc output impedance; the same as any single ended triode design - and as far as I understand these matters any AB amplifier once it is into it's B class operating region.
The nice thing about audio is that there arn't any absolutes right or wrong. Transformer based impedance amplification and current drive just happens to be my hobby horse.
"One should not increase, beyond what is necessary, the number of entities required to perform a given task."
(Parker after Occam)
I am sorry to hear of your health and hope that things improve quickly for you all.
I could do the comparison, however I would have to build a pair and this will take me a week or three as I am somewhat pushed for time due to my own work commitments.
Thanks, I will try to remember this.
Best wishes,
Susan.
P.S.
Have to go do some work now, back this evening.
Thank you for your reply and comments.
Graham Maynard said:
Yes, I agree entirely and this is why I am less concerned with amplifier distorsion in absentia as it does not give the whole picture.
My amplifer works as a current drive, not voltage.
"Son of Zen" is quoted as being 16 ohms output impedance.
I find that conventional speakers in the main show a noticable improvement when used with my amp - the exception being ones with over bright trebble.
My LS3/5As, which whilst very flat for frequency response (with a correspondingly complex crossover tuning circuit), are to my ears somewhat muddy driven by normal amps. With my amp the whole sound clarifies and a much improved sound stage definition is achieved.
All this is my own subjective experince of course, my ears being fussy about phase coherance as perhaps I may have mentioned previously?
Basically I want to be able to sit ten feet back with the speakers spaced sixteen feet apart and hear a complete sound stage in front of me without a hole in the middle.
Our living room is a bit smaller than this so I have to compromise.
They are Jordan JX62s, unfortunantly no longer made.
I assume that you don't think a Quad 34/306 system is in the class of a "good conventional amp" being perhaps a bit long in the tooth?
I couldn't afford them. I am currently looking at some cheeper wideband German drivers - initally as replacments for the Jordan contraflex drivers.
My amplifier is a curent driver, therefor works best if matched to the load. Because it is a current driver it can be configured to drive very low sub-ohm loads which simply wouldn't be possible in a conventional solid state amp.
The point with the line arrarys depends on the configuration.
People have attempted to make line arrays by stacking small bookshelf speakers on their sides one atop the other. Series/Parrallel chains with internal crossovers suffer HF loss, however true parallel drive does not have this problem.
Yes, the followers do have internal NFB, but the bandwidth is very high. There is no global feedback to an input signal.
The followers have a gain of just under unity, hence rapid dampening of any "hiccups". This may be seen as a problem with compression at high power levels but I am not aware of it in my own listening (however that doesn't mean that it doesn't happen or that other people wouldn't notice).
Most of my listening is done with the first watt or two.
The resonance problem shouldn't accour as the amp is push-pull.
I haven't tried resistor dampening. The transformer is 1:1 so wouldn't the resistors still appear as 22 ohms / 2 to the loudspeaker? The output impedance is already down at 2.7 ohms.
A single ended version of my amplifier, as I have described in my notes, would have an asymetirc output impedance; the same as any single ended triode design - and as far as I understand these matters any AB amplifier once it is into it's B class operating region.
The nice thing about audio is that there arn't any absolutes right or wrong. Transformer based impedance amplification and current drive just happens to be my hobby horse.
"One should not increase, beyond what is necessary, the number of entities required to perform a given task."
(Parker after Occam)
I am sorry to hear of your health and hope that things improve quickly for you all.
I could do the comparison, however I would have to build a pair and this will take me a week or three as I am somewhat pushed for time due to my own work commitments.
Thanks, I will try to remember this.
Best wishes,
Susan.
P.S.
Have to go do some work now, back this evening.
Is this something similar??? If so it is a very nice review.
www.hifichoice.co.uk/archive/perl/551_printreview.htm
www.hifichoice.co.uk/archive/perl/551_printreview.htm
Hi Susan,
You write - "My amplifier works as current drive"
But I don't view it that way ........... the Mosfet sources that are driving the output transformer are following input transformer secondary voltage.
The Mosfets are like behaving like perfect 'current' amplifiers followed by a 2.78 ohm resistor (as measured).
The 'Son of Zen' amplifier you mention is much more a current driving amplifier.
Also maybe the LS3/5As would sound better with a conventional amp plus 2.7 ohms ? I don't know.
And this is what concerns me with your design, because audio trafos (saves writing it in full all the time) tend to have a self capacitance/inductance peak at some hopefully supersonic high frequency, though with a phase change that comes in at about one third to half of that frequency. I'm not sure whether that phase change has ever been investigated/documented in audio papers, but your input trafo is susceptible to generating this effect then passing it on through to the output devices plus output trafo and load.
I suggested the 22 ohm resistors as a 'try' because they will ensure that Mosfet current will always retain a degree of resistive current flow, even when dynamically induced resultant driver/output tranfo/load currents become phase shifted wrt input voltage.
Now Circlomanen's link is interesting, for it implies a similar mode of operation to your amplifier, and it mentions a hint of 'metallic' sound on highs. Could this be trafo resonance ?... the very reason why I have mentioned split primary and secondary resistor damping at input, and say 22 ohms to ground per source. Jordan drivers tend to cut off more sharply around 20kHz than do normal tweeters.
I am discussing possible probs and possible improvements, rather that being a downer on your technological concept.
Cheers for now ........ Graham.
You write - "My amplifier works as current drive"
But I don't view it that way ........... the Mosfet sources that are driving the output transformer are following input transformer secondary voltage.
The Mosfets are like behaving like perfect 'current' amplifiers followed by a 2.78 ohm resistor (as measured).
The 'Son of Zen' amplifier you mention is much more a current driving amplifier.
Also maybe the LS3/5As would sound better with a conventional amp plus 2.7 ohms ? I don't know.
And this is what concerns me with your design, because audio trafos (saves writing it in full all the time) tend to have a self capacitance/inductance peak at some hopefully supersonic high frequency, though with a phase change that comes in at about one third to half of that frequency. I'm not sure whether that phase change has ever been investigated/documented in audio papers, but your input trafo is susceptible to generating this effect then passing it on through to the output devices plus output trafo and load.
I suggested the 22 ohm resistors as a 'try' because they will ensure that Mosfet current will always retain a degree of resistive current flow, even when dynamically induced resultant driver/output tranfo/load currents become phase shifted wrt input voltage.
Now Circlomanen's link is interesting, for it implies a similar mode of operation to your amplifier, and it mentions a hint of 'metallic' sound on highs. Could this be trafo resonance ?... the very reason why I have mentioned split primary and secondary resistor damping at input, and say 22 ohms to ground per source. Jordan drivers tend to cut off more sharply around 20kHz than do normal tweeters.
I am discussing possible probs and possible improvements, rather that being a downer on your technological concept.
Cheers for now ........ Graham.
Hi,
For those that might be interested...
http://www.susan-parker.co.uk/susan-cd-player.htm
Best wishes,
Susan.
For those that might be interested...
http://www.susan-parker.co.uk/susan-cd-player.htm
Best wishes,
Susan.
