Magicbox,
Mike is right. Whatever works for you.
I don't like cascodes. They are indeed useful where you are limited in voltage ratings and can divide voltages with a cascoding transistor.
My prejudice is born of building and listening, and has little to do with ppm, which has specious correlation with listening anyway.
However, as Mike said, you don't have to like or dislike what anyone else likes, particularly if you only build for yourself. But if you build for others, you are forced to consider what 'sounds good', even though it cannot strictly be measured.
Mike is right. Whatever works for you.
I don't like cascodes. They are indeed useful where you are limited in voltage ratings and can divide voltages with a cascoding transistor.
My prejudice is born of building and listening, and has little to do with ppm, which has specious correlation with listening anyway.
However, as Mike said, you don't have to like or dislike what anyone else likes, particularly if you only build for yourself. But if you build for others, you are forced to consider what 'sounds good', even though it cannot strictly be measured.
I'm not a strict PPM guy. I listen to music with my ears, not with a THD meter if you know what I'm saying *persuading look*. But at the same time, I try to correlate THD and other measured behaviours to what makes an amp sound good and the only way to correlate is to build them, which is what I do with my designs.
On topic of cascodes, I believe those that serve as a cascode to a current source do not alter sonics when properly implemented. Those that serve to cascode a VAS device are more likely to impact sonics as it impacts VAS output linearity. Which is a measurable aspect. That's the exact reason why I made the IPS and VAS cascode a tracking cascode.
Originally Posted by juliovideo
".......but what's the point of wasting 20 years to end up right where we started ? "
Harmonic Distortion over the Decades
Where do I come from?
Where am I going?
Who am I?
A Tiny History of High Fidelity, Part 1
A Tiny History of High Fidelity, Part 2
---------------
Cascode can work fine I have a input voltage amp with tubes in cascode, it sounds very good and have low distortion.
listen here cascoded 6H8C, cascode is not bad at all, but tubes are not transistors or mosfets
6H8C-cascode-sound - YouTube
listen here cascoded 6H8C, cascode is not bad at all, but tubes are not transistors or mosfets
6H8C-cascode-sound - YouTube
The Borbely simulation uses not exactly the same devices as Erno did.
The input cascode devices are 2 sk982 and 2sj148 with an LM 329 voltage reference. The jfet - jfet - mosfet input cascode only appears when he did a high power version to handle the higher rail voltage.
The VAS cascode devices should be 2SK2013 and 2SJ313.
Output drivers are 2SK216 and 2SJ79.
The reason for the double jfets in the VAS is to get the current up to the value he wanted - too hard to find enough V grade devices with a high enough IDSS so he parralleled and matched 2 BL devices.
The input cascode devices are 2 sk982 and 2sj148 with an LM 329 voltage reference. The jfet - jfet - mosfet input cascode only appears when he did a high power version to handle the higher rail voltage.
The VAS cascode devices should be 2SK2013 and 2SJ313.
Output drivers are 2SK216 and 2SJ79.
The reason for the double jfets in the VAS is to get the current up to the value he wanted - too hard to find enough V grade devices with a high enough IDSS so he parralleled and matched 2 BL devices.
Last edited:
Hi Ian,
Can you give some idea of the kind of spec to look for these ferrites.
I'm grappling with a 50meg oscillation and want to cure it with the least performance degrading method
thanks
mike
Hi Mike
Apologies for the late reply, I have been preoccupied for some time with vision issues but I am fairly confident that the ferrite grades used are very high frequency types to kill that range of VHF without even imaginary audio effects.
Neosid F14 (long out of production) is the reference material I use and one of the Nickel-Zinc types but Fair-Rite (successors to Amidon in the USA) manufactures all kinds of beads and Mouser markets them inexpensively. Have a look at their small bead ref. 2643000301. Incidentally, this was the grade used in those big 2-hole baluns once ubiquitous on VHF matching baluns for TV aerial connections.
You can Google F14 or Fair-Rite easily - there is some interesting Blurb and even some technical raves and archives out there. I hope you have success but I would caution against the modern SMPS and computer suppression grades which certainly have higher impedance but well down into the MF spectrum too. Of course, where attenuation is insufficient, I beleive it is better to cram as many beads of HF type rather than a single LF type. Perhaps F8 or equivalents may work without much audio impact but I have steered away from MF types. There are many grades of course, but finding them with certainty is not simple.
Come back if you have further queries.
Apologies for the late reply, I have been preoccupied for some time with vision issues but I am fairly confident that the ferrite grades used are very high frequency types to kill that range of VHF without even imaginary audio effects.
Neosid F14 (long out of production) is the reference material I use and one of the Nickel-Zinc types but Fair-Rite (successors to Amidon in the USA) manufactures all kinds of beads and Mouser markets them inexpensively. Have a look at their small bead ref. 2643000301. Incidentally, this was the grade used in those big 2-hole baluns once ubiquitous on VHF matching baluns for TV aerial connections.
You can Google F14 or Fair-Rite easily - there is some interesting Blurb and even some technical raves and archives out there. I hope you have success but I would caution against the modern SMPS and computer suppression grades which certainly have higher impedance but well down into the MF spectrum too. Of course, where attenuation is insufficient, I beleive it is better to cram as many beads of HF type rather than a single LF type. Perhaps F8 or equivalents may work without much audio impact but I have steered away from MF types. There are many grades of course, but finding them with certainty is not simple.
Come back if you have further queries.
Last edited:
Thanks Ian,
My parasitic is in region of 16meg hz and square wave ringing due to a difficult load ( 100nF ) is around 1 meg.
100 ohm gate stoppers cure the parasitic but exacerbate the square wave ringing so I'm hoping to steer between them with ferrites.
I ordered some leaded beads with very similar spec to those you recommend which hopefully is a good sign.
My parasitic is in region of 16meg hz and square wave ringing due to a difficult load ( 100nF ) is around 1 meg.
100 ohm gate stoppers cure the parasitic but exacerbate the square wave ringing so I'm hoping to steer between them with ferrites.
I ordered some leaded beads with very similar spec to those you recommend which hopefully is a good sign.
The best way to get a good amp is to use ring emitters like the 2SC3264 and 2SA1295 these are very liniair, I am testing a amp without feedback who has low distortion, mosfets are still very non liniair and need feedback or better a distortion correction.
Because of no feedback I use multiply emittor followers for best bass.
Because of no feedback I use multiply emittor followers for best bass.
I think you are on the right track with this approach, depending on the design of the leaded ( I assume a pre-wound slug or bead) ferrite.
Usually, above 10MHz, single pass beads are adequate for low level damping. I can't imagine core saturation being an issue at gate charging currents but others may care to comment on that.
As an alternative, I've also used 47R/100 pF Zobels on each device (gate to drain), and these work OK too - at least with mild cases of just a few volts P-P which is what I usually find with a 100MHz analogue 'scope. Mosfets seem to go much higher with oscillation than BJTs - perhaps as high as 100 MHz though the laterals I use seem to range 10 - 60 MHz, as you find.
This is pretty cheap and easy to try out so why not give it a bash whilst waiting? Perhaps too, say, 47R stoppers in combination may be less of a problem there with ringing. I haven't measured this myself and neither tried out dual die Mosfets which could be more problematic, so it could be interesting.
I'm back from the dead and keen to start experimenting again...now to go read the last few months worth of progress
Hi Greg,
Good timing from my point of view. After a longish break doing other things I just did a rebuild of my DC linked version - sounds even better than before
Actually it sounds very valve like.
I'm planning to post about my progress soon.
I wonder where you are with ur research ?
mike
Greg,
I'm so glad you are back, I've been trying to phone you for weeks....
I have now sold 172 pcbs for the FetZilla, it has been very successful. IN fact, Group Buy #3 is now complete and mailout is this week.
Yesterday the amp was tested using Clio 5, the latest THD software, using a battery powered laptop. Very quiet. Brilliant results, too, very low THD, around 0.008%, all H2, at 1W output. Max output is only 40W, however, rather less than we expected, but still goes damn loud.
I will email you now, in fact.
Hugh
I'm so glad you are back, I've been trying to phone you for weeks....
I have now sold 172 pcbs for the FetZilla, it has been very successful. IN fact, Group Buy #3 is now complete and mailout is this week.
Yesterday the amp was tested using Clio 5, the latest THD software, using a battery powered laptop. Very quiet. Brilliant results, too, very low THD, around 0.008%, all H2, at 1W output. Max output is only 40W, however, rather less than we expected, but still goes damn loud.
I will email you now, in fact.
Hugh
Last edited:
Ah, great news and great to hear from you both. To be honest I haven't done a single audio related thing in months, but that hopefully changes this weekend. Mikelm, do post your final version.
Hugh, glad you're still here after so long. Great news about the group buys. I take it people are happy with the sound?
Amazing results with the testing too! I would never have thought 4 fets could measure so well while being so pleasing sonically. Why is this thing not a cult icon yet? haha.
If I had to criticise one thing about the amplifier, after months of listening, it would have to be a slight loss of competence and control during very complicated music with high intensity transients. That said, probably no more than any other mortal amplifier.
Look forward to progressing the art over the coming months. First job this weekend is to clear out the shed and move my audio "lab" from the guest room.
Hugh, glad you're still here after so long. Great news about the group buys. I take it people are happy with the sound?
Amazing results with the testing too! I would never have thought 4 fets could measure so well while being so pleasing sonically. Why is this thing not a cult icon yet? haha.
If I had to criticise one thing about the amplifier, after months of listening, it would have to be a slight loss of competence and control during very complicated music with high intensity transients. That said, probably no more than any other mortal amplifier.
Look forward to progressing the art over the coming months. First job this weekend is to clear out the shed and move my audio "lab" from the guest room.
FetZilla Clio 5 Results
Folks,
I have the Clio measurements on the FetZilla, kindly supplied by Graeme Huon and Paul Bysouth, highly competent EE friends of mine here in Melbourne, taken Monday 27th Feb 2012. They are taken at 1KHz, into an 8R resistive load, at outputs respectively of 1W (+10dB), 13.3W (+20dB), and 26.5W (+23dB):
Fundamental 10.00dB Fundamental 20dB Fundamental 23dB
H2 -93dB 5.012E-10 H2 -78dB 1.585E-08 H2 -78dB 1.58489E-08
H3 unmeasureable H3 -93dB 5.012E-10 H3 -88dB 1.58489E-09
H4 unmeasureable H4 -105dB 3.162E-11 H4 -93dB 5.01187E-10
H5 unmeasureable H5 -102dB 6.31E-11 H5 -103dB 5.01187E-11
H6 -96dB 2.512E-10 H6 -106dB 2.512E-11 H6 -110dB 1E-11
H7 unmeasureable H7 -110dB 1E-11 H7 -101dB 7.94328E-11
H8, H9 and H10 are all unmeasureable
THD by voltage 0.00274% (1W, +10dB); 0.01284% (13.3W, +20dB), and 0.0134% (26.5W, +23dB)
Measurements below about -80 dB can be assumed to be insignificant except in ultraclean designs
These figures are surprisingly good, but with output bias set to 370ma the first 5.5 watts of output are in Class A, so perhaps not so surprising after all.
I would add that the THD does not correlate well with the sound qualilty; rather, it is the profile of the distortion artefacts that affect the perceived sound quality for the human ear.
Not bad for a jfet, two mosfets, and two lateral output fets - only five active devices in total!
My thanks to Graeme and Paul for generously giving their time to measure the FetZilla!
Cheers,
Hugh
Folks,
I have the Clio measurements on the FetZilla, kindly supplied by Graeme Huon and Paul Bysouth, highly competent EE friends of mine here in Melbourne, taken Monday 27th Feb 2012. They are taken at 1KHz, into an 8R resistive load, at outputs respectively of 1W (+10dB), 13.3W (+20dB), and 26.5W (+23dB):
Fundamental 10.00dB Fundamental 20dB Fundamental 23dB
H2 -93dB 5.012E-10 H2 -78dB 1.585E-08 H2 -78dB 1.58489E-08
H3 unmeasureable H3 -93dB 5.012E-10 H3 -88dB 1.58489E-09
H4 unmeasureable H4 -105dB 3.162E-11 H4 -93dB 5.01187E-10
H5 unmeasureable H5 -102dB 6.31E-11 H5 -103dB 5.01187E-11
H6 -96dB 2.512E-10 H6 -106dB 2.512E-11 H6 -110dB 1E-11
H7 unmeasureable H7 -110dB 1E-11 H7 -101dB 7.94328E-11
H8, H9 and H10 are all unmeasureable
THD by voltage 0.00274% (1W, +10dB); 0.01284% (13.3W, +20dB), and 0.0134% (26.5W, +23dB)
Measurements below about -80 dB can be assumed to be insignificant except in ultraclean designs
These figures are surprisingly good, but with output bias set to 370ma the first 5.5 watts of output are in Class A, so perhaps not so surprising after all.
I would add that the THD does not correlate well with the sound qualilty; rather, it is the profile of the distortion artefacts that affect the perceived sound quality for the human ear.
Not bad for a jfet, two mosfets, and two lateral output fets - only five active devices in total!
My thanks to Graeme and Paul for generously giving their time to measure the FetZilla!
Cheers,
Hugh
Last edited:
Member
Joined 2009
Paid Member
the 'trick' with cascodes is to ensure some emitter degeneration of the cascode device. The 'memory distortion' guy called it a 'magic resistor'. I just like a little 'room' for the cascode to work within and some degeneration trades off a bit of ppm for a better harmonic structure. Maybe it's all bullcrap, but I used it in my TGM5 all the same and I like the sound
My suspicion is that a monotonic harmonic structure indicates an amp with generally well-behaved characteristics such as group delay (phase linearity) and consistent behavior over a range of operating points. IE, when the harmonics are monotonic, so is the group delay. Monotonic profile indicates that each device in an amp behaves in monotonic fashion; this also indicates that the current draw of the output stage is mirrored without major distortion all the way to the input stage; in effect, linear (monotonic) open-loop gain curve. This is the ideal characteristic for a high-performance amplifier; it ensures stable and consistent operation across a range of operating points and I think it should be a starting point for any amplifier design. This is opposed to super high-gain designs where the open-loop linearity may be very bad.
In so many words, monotonicity seems to be key. It ensures that the compensation and feedback in the amp work like intended and the amp does not fight with itself. If an amp is designed without open-loop linearity, you usually discover that it can be finicky, or it may require special external compensation to be stable with certain loads (zobels and cables).
This deviates from the conventional idea of looking at an amplifier as a voltage amplifier. Really, to make a stable and consistently well-behaved amplifier it needs to be seen not as a voltage amp or a current amp, but as an impedance amplifier, and both it's voltage and current response addressed. Current response, as well as voltage gain response, needs to be properly compensated in order for an amp to be consistently well-behaved and stable. Knowing this is key to making improved, reliable designs with our current technology, rather than trying to use faster and more linear semiconductors to support flawed designs.
These are my thoughts based on my studies on amplifier stability. Maybe I have tunnel vision, but who could blame me when I have a hammer and everything looks like a nail.
In so many words, monotonicity seems to be key. It ensures that the compensation and feedback in the amp work like intended and the amp does not fight with itself. If an amp is designed without open-loop linearity, you usually discover that it can be finicky, or it may require special external compensation to be stable with certain loads (zobels and cables).
This deviates from the conventional idea of looking at an amplifier as a voltage amplifier. Really, to make a stable and consistently well-behaved amplifier it needs to be seen not as a voltage amp or a current amp, but as an impedance amplifier, and both it's voltage and current response addressed. Current response, as well as voltage gain response, needs to be properly compensated in order for an amp to be consistently well-behaved and stable. Knowing this is key to making improved, reliable designs with our current technology, rather than trying to use faster and more linear semiconductors to support flawed designs.
These are my thoughts based on my studies on amplifier stability. Maybe I have tunnel vision, but who could blame me when I have a hammer and everything looks like a nail.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.