erictoucan-
But, 0.1% crossover distortion could be very audible while 0.1% distortion in magnitude is definately inaudible.
------------------------------------------------------------
lets keep things in perspective above a certain level each kind of
distortion becomes audible, if you gona say otherwise show the
evidence and the scientific data to prove it
"0.1% crossover distortion could be very audible "
please show us what you mean
Reagards
But, 0.1% crossover distortion could be very audible while 0.1% distortion in magnitude is definately inaudible.
------------------------------------------------------------
lets keep things in perspective above a certain level each kind of
distortion becomes audible, if you gona say otherwise show the
evidence and the scientific data to prove it
"0.1% crossover distortion could be very audible "
please show us what you mean
Reagards
Hi Lineup,
There is a lot of non-linearities in the whole audio chain - especially in the ear where the mechanisms of hearing are complex and active.
With the relative recent resurgence of tube amplifiers (on a large(ish) scale) vanishingly small THD figures are now more accepted as not being the be all and end all of hifi performance.
The follower configuration I use in my amplifiers drives the transformer from a lower than normal impedance source which is the key to reducing transformer distortion/non-linearities.
I started with a clean sheet with my amplifier development and asked myself the initial question "what is a loudspeaker, how does it work"? Really thinking about the basics and trying not to let any assumptions that I might have (which may be correct or erroneous) cloud my thoughts.
Most tube builders have to use transformers of necessity! I have based my amplifier design around the premise that the transformer is the primary component from which everything else evolves.
No pressure. It took me several years to develop my amplifier.
Um, one of the things that I was looking for in making the transformer based amplifiers was a design that could be made by "normal people" such as myself.
Maths is not my strong point, and I still have not got a satisfactory transformer model for Spice simulation...
... and winding multi filar transformer bobbins is more a matter of patience than any innate skill (honest).
Best wishes,
Susan.
lineup said:
There is a lot of non-linearities in the whole audio chain - especially in the ear where the mechanisms of hearing are complex and active.
With the relative recent resurgence of tube amplifiers (on a large(ish) scale) vanishingly small THD figures are now more accepted as not being the be all and end all of hifi performance.
The follower configuration I use in my amplifiers drives the transformer from a lower than normal impedance source which is the key to reducing transformer distortion/non-linearities.
I started with a clean sheet with my amplifier development and asked myself the initial question "what is a loudspeaker, how does it work"? Really thinking about the basics and trying not to let any assumptions that I might have (which may be correct or erroneous) cloud my thoughts.
Most tube builders have to use transformers of necessity! I have based my amplifier design around the premise that the transformer is the primary component from which everything else evolves.
No pressure. It took me several years to develop my amplifier.
Um, one of the things that I was looking for in making the transformer based amplifiers was a design that could be made by "normal people" such as myself.
Maths is not my strong point, and I still have not got a satisfactory transformer model for Spice simulation...
... and winding multi filar transformer bobbins is more a matter of patience than any innate skill (honest).
Best wishes,
Susan.
Hi Rozak,
As per the schematics and pictures on your thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=56808
I assume?
Of note is that we both have four transformers and a PP mosfet follower 2:1 output stage referenced to ground.
I would imagine that the sound is similar although I perhaps have a higher second harmonic in relation to the third with the SE input stage (so only one TX-102 is needed per channel, rather than two) particularly in the tube version?
You have had some time to "live" with the sound of the system and from your comment I take it that you are pleased with what you have.
Best wishes,
Susan.
rozak said:
As per the schematics and pictures on your thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=56808
I assume?
Of note is that we both have four transformers and a PP mosfet follower 2:1 output stage referenced to ground.
I would imagine that the sound is similar although I perhaps have a higher second harmonic in relation to the third with the SE input stage (so only one TX-102 is needed per channel, rather than two) particularly in the tube version?
You have had some time to "live" with the sound of the system and from your comment I take it that you are pleased with what you have.
Best wishes,
Susan.
Yes, Susan,
sound of my system is very good, distortionless for ears at least,
big and powerful. 25W sounds like 250W.
Because of my poor English I can't describe it better.
Only one coment from frends and visitors-WOW!
Transformer topology does something to sound!
It take very long burn-in period (400-500 hours) with ups and down to reach best quality.
Any burn-in story of your system?
sound of my system is very good, distortionless for ears at least,
big and powerful. 25W sounds like 250W.
Because of my poor English I can't describe it better.
Only one coment from frends and visitors-WOW!
Transformer topology does something to sound!
It take very long burn-in period (400-500 hours) with ups and down to reach best quality.
Any burn-in story of your system?
Hello, Susan.
I note that you have had time to try the Exicon VFETs, but with rather poor results. I'm assuming you used the ECF10N20 or ECF10P20.
Could you post some details about this?
I'm assuming you've checked for oscillations; these devices are nearly as twitchy in that regard as DMOS devices, if I recall correctly. In fact, you'll probably want a source resistor between the FET and the output transformer to improve stability, as well as a zobel (either on the FET side or the speaker side).
According to the public datasheet, these devices have 500pF/700pF Ciss, 300pF/300pF Coss and 10pF/25pF, with a Vds(SAT) of 12V and 0.7S<Yfs<2S.
However, blatantly missing from the datasheet are a few important stats, such as Yos, Igss and Rds(on).
I expect Yos is probably on the order of 350-700mS<Yoss<200-400mS, while Igss is probably on the order of 1-100mA and Rds(on) is presumably at least .5<RdsON<1.4 at low output currents (more at higher currents).
Hence, the output transformer probably needs to step them down a bit to get the same damping factor as for the other FETs you've tried (just do the regular quadfilar winding, but section it and try various versions of series and paralell to see what sounds best). The drain supply would also benefit from 6-12V more headroom than the other FETs. I suspect you need to use a different value gate stopper too.
I also expect you'll need a gate buffer or low-impedance source; the gate resistance of a VFET is far lower than for a MOSFET (on the order of ohms, according to the application note).
I know you resist the idea of a second semiconductor, but a complementary JFET buffer adds 1-100ppm THD+N, with nothing over 3rd order. A single-ended CCS-loaded JFET buffer adds marginally more.
For single-ended, Linear Systems LS843 (Dual N-JFET with 1mV and 5uV/C max Vgs difference; 1.5mA-15mA), Vishay 2N5911 (Dual N-JFET with 5mV and 5uV/C max Vgs difference; 7-40mA) and Fairchild J500 (Single N-JFET with minimum 500mA Idss) spring to mind.
For complementary, 2SK146V/2SJ73V (Obsolete dual N-JFET with 20mV max Vgs difference; 15-30mA - no complete datasheet) or 2SK364V/2SJ104V (Current production Toshiba single N-JFET with 10-20mA Idss; try a Vdg of 10V at 12mA - for <10pA Igss and very linear operation with zero tempco)...
I'll try to show an idea for a circuit to do this... simpler works fine, too... Just don't drive it with a GaAsFET or heterojunction
Code:
Sample driver, one half shown (done before bedtime, so don't shoot me ;)...
[list]
[*] ===
[*] |
[*] |
[*] |
[*] |--+
[*] | Q3a
[*] +--+-->|--+------O Vss
[*] | | |
[*] === C4 V +--|
[*] | | | Q1a |
[*]Q5 +--| +--+------+--|<--+--R--+ / / /
[*] | | | | --+--
[*]+--+--|<--+ +--C5--+ | |
[*]| | | | | |
[*]L1 R1 R R4a +------|--C3-----+ |
[*]| | | | | | | |
[*]+--+------+--R2--+--R2--+-----+--R6--+--+--R3--+--R3--+ |
[*]| | | | | | | | |
[*]C1 +------|--C2--+ R5a | C3 +--+--+ | +--O HOT
[*]| | | | | | | | | | |
[*]| ( | +--C5--+ | | | | )*||*(
[*]| ( | | | | | C | ) || (
[*]| ( T2 C2 +--+------+--|>--+--R--+ | | R ) || ( T1
[*]| ( | | | Q2a | | R | ) || (
[*]| ( | C4 V +--| | | | ) || (
[*]| | | | | | | | | | |
[*]| | | +--+--<|--+------O Vdd | +--+--+ +--O COLD/GND
[*]| | | | Q4a | |
[*]| | | |--+ | [VBIAS] =
[*]| | | | | ===
[*]| | | | | =====
[*]| | | | | | GND
[*]+--+------+-------------+---------------+--------------------+
[/list]R1/L1/C1: 1 ohm / 1 uH / 47nF - example zobel.
R2/C2/R3/C3: 4th order Sallen-Key lowpass filter (e.g. 250KHz? Should complement trafo)
R4/R5/R: Self bias resistors (1-1000R typ) and gate stoppers (10R, 221R, 1000R?).
R6: Z_IN bootstrap/feedback resistor.
C4/V: Sub-nanoampere voltage source (e.g. DPAD diodes), where If(V) = Igsx(Q3|Q4).
C5: Ciss at lowest Vdg swing.
T1/T2: Input/output trafos, single leg.
Vbias: Measure Igsx(Q1)-Igsx(Q2) through the secondary, and get a suitable diode with Vref=Vgs(Q5,Iq)
Vdd/Vss: Used to cross decouple cascodes between balanced halves of the circuit.
Q1: N-channel JFET follower, low Vgs(off), high Gm, low r_ds, high current, low noise.
Q2: P-channel JFET follower, low Vgs(off), high Gm, low r_ds, high current, low noise.
Q3: N-channel JFET cascode, high Vgs(off), high Gos, high current (2Idss(Q1)<Idss(Q3)<20Idss(Q1)), high (BR)Vgss (>30V).
Q4: P-channel JFET cascode, high Vgs(off), high Gos, high current (2Idss(Q2)<Idss(Q4)<20Idss(Q2)), high (BR)Vgss (>30V).
Q5: Exicon EC-10N16 N-channel VFET follower.
You could also try to test a compound follower between about 100pcs BF246A (or similar cheap N-JFET) in paralell and a single P-channel Exicon VFET..
I wish there was a vBcode for line spacing.. I've just spent hours (literally) getting this post to render before discovering the list hack...
dual voice coil woofers
Hello all!
I know this is the totally wrong thread, but I hoped to find some transformer experts here.
There is a Japanese Fullrange speaker with two voice coils and a transformer between, at least for low frequencies.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=35625&pagenumber=3
I ask myself whether a simple 1:1 transformer between the voice coils of a dual voice coil woofer would improve the performance in combination with a low dampening factor amplifier.
Regards, Oliver
Hello all!
I know this is the totally wrong thread, but I hoped to find some transformer experts here.
There is a Japanese Fullrange speaker with two voice coils and a transformer between, at least for low frequencies.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=35625&pagenumber=3
I ask myself whether a simple 1:1 transformer between the voice coils of a dual voice coil woofer would improve the performance in combination with a low dampening factor amplifier.
Regards, Oliver
Magnetic Balanced Topology
Hi Susan,
I find a thread www.bonavolta.ch/hobby/en/audio/2sk135se.htm
They call it SE Super Nemesis Compensated.
It has equivalent idea to my previously proposed magnetic balanced topology. But, I do not see the point of connecting the gate of balancing Mosfet to the collector output by 12K. What is the exact purpose in doing that? Do you see it?
Eric
27 Dec 2006
Hi Susan,
I find a thread www.bonavolta.ch/hobby/en/audio/2sk135se.htm
They call it SE Super Nemesis Compensated.
It has equivalent idea to my previously proposed magnetic balanced topology. But, I do not see the point of connecting the gate of balancing Mosfet to the collector output by 12K. What is the exact purpose in doing that? Do you see it?
Eric
27 Dec 2006
Re: Magnetic Balanced Topology
It pays to know some history this approach has been used for a loooong time (back when tubes were the only amplification capable component in electronics).
Regarding the 12k, it forms a low pass filter with the 4700uF cap which acts as a 'DC servo' of sorts keeping the balance correct. There is actually a simpler way of doing this, I am surprised they did not think of it.
erictoucan said:
It pays to know some history
this approach has been used for a loooong time (back when tubes were the only amplification capable component in electronics).Regarding the 12k, it forms a low pass filter with the 4700uF cap which acts as a 'DC servo' of sorts keeping the balance correct. There is actually a simpler way of doing this, I am surprised they did not think of it.
Magnetic balanced topology
Thank you for your remind, I think you are correct, take the same bais as the amplifing Mosfet to have exact balance. But, do we need that exact? Would 20% deviation significant? I think not and we can just use resistor or lamp of suitable resistance(no need for heatsink) to balance it without the mosfet.
Thank you for your remind, I think you are correct, take the same bais as the amplifing Mosfet to have exact balance. But, do we need that exact? Would 20% deviation significant? I think not and we can just use resistor or lamp of suitable resistance(no need for heatsink) to balance it without the mosfet.
Re: Magnetic balanced topology
Hi Eric,
Please excuse the brevity of this reply, I have been quite busy of late.
The 12K connects the DC bias level to the capacitively coupled input giving the two mosfets the same bias levels.
BTW my understanding is that Jean Hiraga's original Nemesis had a transformer coupled input.
The circuit as shown is a quasi push-pull and the mosfet is dynamically counter-balancing the current in the active mosfet (the two mosfets should thus ideally be matched).
Replacing this with a resistor is not going to be optimum.
I have (in Spice simulation) reordered the circuit to have followers (and a transformer input) and one can see the drive and balance currents. The second mosfet is clearly working for a living.
To my mind, given the relative circuit complexities, using a single mosfet with a gapped transformer is easier to understand and prototype. Once one has the basic circuit working additional stuff can be added.
Using a follower and a suitably large ungapped transformer one can drive single ended even with core magnetization and although not ideal the low impedance of the mosfet will produce more acceptable results than with a tube circuit, as is shown in my Zeus SE page:
http://www.susan-parker.co.uk/zeus-se-amp.htm
I am always interested to hear about variations and inspirations derived from this thread and look forward to reading about your progress.
Best wishes,
Susan.
P.S. I am using B2Spice V4 Pro
Hi Eric,
Please excuse the brevity of this reply, I have been quite busy of late.
erictoucan said:
The 12K connects the DC bias level to the capacitively coupled input giving the two mosfets the same bias levels.
BTW my understanding is that Jean Hiraga's original Nemesis had a transformer coupled input.
erictoucan said:
The circuit as shown is a quasi push-pull and the mosfet is dynamically counter-balancing the current in the active mosfet (the two mosfets should thus ideally be matched).
Replacing this with a resistor is not going to be optimum.
I have (in Spice simulation) reordered the circuit to have followers (and a transformer input) and one can see the drive and balance currents. The second mosfet is clearly working for a living.
To my mind, given the relative circuit complexities, using a single mosfet with a gapped transformer is easier to understand and prototype. Once one has the basic circuit working additional stuff can be added.
Using a follower and a suitably large ungapped transformer one can drive single ended even with core magnetization and although not ideal the low impedance of the mosfet will produce more acceptable results than with a tube circuit, as is shown in my Zeus SE page:
http://www.susan-parker.co.uk/zeus-se-amp.htm
I am always interested to hear about variations and inspirations derived from this thread and look forward to reading about your progress.
Best wishes,
Susan.
P.S. I am using B2Spice V4 Pro
Re: dual voice coil woofers
Hi Oliver
The dual voice coil enables the additional components shown in the schematic to linearize the frequency response of this speaker.
I am not sure what benefit you would obtain with a conventional driver unless you were wanting to do something similar to match the driver's frequency response to a specific enclosure.
You can easily try this out with a toroid mains transformer using the dual secondaries as a 1:1 transformer - will need to be minimum of 300VA, probably higher - with a voltage that approximately matches the peak AC voltage output of the amplifier. Don't forget to insulate the primaries as they could give you a nasty shock otherwise.
Best wishes,
Susan.
Hi Oliver
el`Ol said:
The dual voice coil enables the additional components shown in the schematic to linearize the frequency response of this speaker.
I am not sure what benefit you would obtain with a conventional driver unless you were wanting to do something similar to match the driver's frequency response to a specific enclosure.
You can easily try this out with a toroid mains transformer using the dual secondaries as a 1:1 transformer - will need to be minimum of 300VA, probably higher - with a voltage that approximately matches the peak AC voltage output of the amplifier. Don't forget to insulate the primaries as they could give you a nasty shock otherwise.
Best wishes,
Susan.
Magnetic Balanced SE
Hi Susan,
Well, I see the 2 Mosfets in Super Nemesis is basically biased by the voltage between the 2.2K pot. The 12 K resistor can be taken as a decoupling resistor between the signal and the bais. But, it we take a lamp of the same conductance of baised 2sk135 (0.65A) would do the same thing. If you can simulate it easily by program. Would you be interested to do it?
The next interesting thing I find interested to research is the forward transconductance of Mosfet. Can we design a circuit to correct the non-linear transconductance of non-feedback SE? Not by feedback of course.
Eric
28 Jan 2006
Hi Susan,
Well, I see the 2 Mosfets in Super Nemesis is basically biased by the voltage between the 2.2K pot. The 12 K resistor can be taken as a decoupling resistor between the signal and the bais. But, it we take a lamp of the same conductance of baised 2sk135 (0.65A) would do the same thing. If you can simulate it easily by program. Would you be interested to do it?
The next interesting thing I find interested to research is the forward transconductance of Mosfet. Can we design a circuit to correct the non-linear transconductance of non-feedback SE? Not by feedback of course.
Eric
28 Jan 2006
Hi erictoucan !
For linearization of output-devices you might look into the threads about "Lovoltech" J-FETs in the Pass forum. It should be possible to get some reduction of the second harmonic by using cascoded J-FETs.
As I said before: Your idea will work. Just go ahead.
Thorsten ( not that one )
For linearization of output-devices you might look into the threads about "Lovoltech" J-FETs in the Pass forum. It should be possible to get some reduction of the second harmonic by using cascoded J-FETs.
As I said before: Your idea will work. Just go ahead.
Thorsten ( not that one )
Hi thorstenlarsen,
Thank you very much for your concern. Your idea and comment really helpful. I want to go ahead with my design. But, I am lazy and doing this part time. So, as long as I got opportunity to experiment it, I will let you know right away. So, many staff in my head Career, Finance, Philosophy. Audio development for good sounding world. As one of your interest, I always try to develope audio gear within my desired philosophy. Thank you very much for your support again.
Cheers
Eric
30 Jan 2006
Thank you very much for your concern. Your idea and comment really helpful. I want to go ahead with my design. But, I am lazy and doing this part time. So, as long as I got opportunity to experiment it, I will let you know right away. So, many staff in my head Career, Finance, Philosophy. Audio development for good sounding world. As one of your interest, I always try to develope audio gear within my desired philosophy. Thank you very much for your support again.
Cheers
Eric
30 Jan 2006
Hi John,
Thanks for your posts.
Mike posted a review on this thread - Audition of the Zeus - Post #570
http://www.diyaudio.com/forums/showthread.php?postid=528135#post528135
?
I have asked a friend knowledgeable in these matters, who listened to my system this December just passed, if he could write something up for me to post to this thread. This will hopefully be in a few days time.
Best wishes,
Susan.
Thanks for your posts.
jkeny said:
Mike posted a review on this thread - Audition of the Zeus - Post #570
http://www.diyaudio.com/forums/showthread.php?postid=528135#post528135
jkeny said:
?
I have asked a friend knowledgeable in these matters, who listened to my system this December just passed, if he could write something up for me to post to this thread. This will hopefully be in a few days time.
Best wishes,
Susan.