Got some catching up to do . . .
NOISE vs. DISTORTION:
Do some cascode topologies generate increased noise to get reduced non-linear distortion?
Transistors generate noise. I've been very selective of low noise JFETs and Bipolars, and very careful to use topologies like the JFET-Bipolar folded cascode to achieve the most gain and linearity with the fewest transistors in the signal path.
I have studied more complex constant power cascode topologies, but I have been reluctant to build these designs for fear of creating increased noise on my 100db/watt system.
Should I worry about the "transistor memory" Hawksford researched more than transistor noise and build more extensively cascoded topologies?
Do some cascode topologies generate increased noise to get reduced non-linear distortion?
Transistors generate noise. I've been very selective of low noise JFETs and Bipolars, and very careful to use topologies like the JFET-Bipolar folded cascode to achieve the most gain and linearity with the fewest transistors in the signal path.
I have studied more complex constant power cascode topologies, but I have been reluctant to build these designs for fear of creating increased noise on my 100db/watt system.
Should I worry about the "transistor memory" Hawksford researched more than transistor noise and build more extensively cascoded topologies?
Hi all
Thank you for your asnswers and opinions.
Yes Jonathan, cascode is risky circuit, that's exactly what I wanted to say.
A not-so-low impedance at base, achieved by base stopper or simply getting ref. Voltage from resistor voltage divider, is a common and often succesful cure for oscilations.
Mikeks
Thanks for refs.
cheers
Thank you for your asnswers and opinions.
jcarr said:
Yes Jonathan, cascode is risky circuit, that's exactly what I wanted to say.
A not-so-low impedance at base, achieved by base stopper or simply getting ref. Voltage from resistor voltage divider, is a common and often succesful cure for oscilations.
Mikeks
Thanks for refs.
cheers
Hi Jocko
This seems sensible, mosfets have bigger capacitances, so they suffer more from Cg-d Miller effect, being a frequency compensation of a cascode.
For mosfet-mosfet cascode it is also vital to have the reference voltage high enough to keep sommon source stage far from 'triode range', where capacitances are higher.
regards
Jocko Homo said:
This seems sensible, mosfets have bigger capacitances, so they suffer more from Cg-d Miller effect, being a frequency compensation of a cascode.
For mosfet-mosfet cascode it is also vital to have the reference voltage high enough to keep sommon source stage far from 'triode range', where capacitances are higher.
regards
Hi Jonathon,
I appreciate your comments regarding adjusting the degree of modulation of cascode bias to optimise distortion. My recent design achieves 0.002% while maintaining absolute simplicity but there's another effect which makes it a trade off as it can degrade PSRR so the two need to be balanced.
Some comments made regarding effect on square waves of cascode biassing are only reasonable considering the effect a low Z bias will affect amplifier bandwidth. It can be easily seen with a before and after bypass by running bode magnitude plots on a sim.
Cheers,
Greg
I appreciate your comments regarding adjusting the degree of modulation of cascode bias to optimise distortion. My recent design achieves 0.002% while maintaining absolute simplicity but there's another effect which makes it a trade off as it can degrade PSRR so the two need to be balanced.
Some comments made regarding effect on square waves of cascode biassing are only reasonable considering the effect a low Z bias will affect amplifier bandwidth. It can be easily seen with a before and after bypass by running bode magnitude plots on a sim.
Cheers,
Greg
You are assuming that guys as old as I am either know how to use a simulator or trust them. Besides, back when I built amps and preamps for a living, they were too expensive to buy.
Jocko
Jocko
Sorry Jocko, but you could download a freebie simulator and have a go. Have a look at my posts on "Purpose of this capacitor..." thread for thumbnail pic. Beats blowing expensive parts up on an oversight.
It's not age discriminatory...
Cheers,
Greg
It's not age discriminatory...
Cheers,
Greg
Yes, now I can. But 20 years ago, you couldn't. Don't build amps now..........don't see the need to use a sim. Why change now when I should be enjoying not working.
Go ahead..........say it.........."Because you aren't enjoying it. That is why."
Jocko
Go ahead..........say it.........."Because you aren't enjoying it. That is why."
Jocko
Forr:
Some 😉. But realistically, I have too much data on cascodes to fit into any single post, and the relevance of each number to a particular situation needs to be qualified. In fact, I probably shouldn't have wrote what I did earlier, because I didn't qualify my statements properly (not that I intend to do so now - there is simply too much ground to cover).
I don't believe that I have observed much dependency on frequency (at least anything which appears unique to cascodes), but bias voltage, absolutely. And there is a relationship between bias voltage, input device choice, and drive impedance.
Depending on how these other issues are treated, it is possible for a cascoded input circuit to generate higher distortion than if no cascode were used at all.
Cascodes really deserve a full length article - even limiting the topic to same-polarity devices.
I believe that you mean a folded cascode. Although this is not used quite as frequently as a series-connected cascode (same polarity devices), it is by no means rare. A search of diyAudio for folded cascode should turn up a number of posts and possible threads.
BTW, the Baxendall cascodes are another topology which is prone to high-frequency oscillation - more so than single-device cascodes, IMHO. I have used them in some of my commercial designs (Connoisseur 5-0), but in general wouldn't recommend them unless you really enjoy troubleshooting.
hth, jonathan carr
Some 😉. But realistically, I have too much data on cascodes to fit into any single post, and the relevance of each number to a particular situation needs to be qualified. In fact, I probably shouldn't have wrote what I did earlier, because I didn't qualify my statements properly (not that I intend to do so now - there is simply too much ground to cover).
I don't believe that I have observed much dependency on frequency (at least anything which appears unique to cascodes), but bias voltage, absolutely. And there is a relationship between bias voltage, input device choice, and drive impedance.
Depending on how these other issues are treated, it is possible for a cascoded input circuit to generate higher distortion than if no cascode were used at all.
Cascodes really deserve a full length article - even limiting the topic to same-polarity devices.
I believe that you mean a folded cascode. Although this is not used quite as frequently as a series-connected cascode (same polarity devices), it is by no means rare. A search of diyAudio for folded cascode should turn up a number of posts and possible threads.
BTW, the Baxendall cascodes are another topology which is prone to high-frequency oscillation - more so than single-device cascodes, IMHO. I have used them in some of my commercial designs (Connoisseur 5-0), but in general wouldn't recommend them unless you really enjoy troubleshooting.
hth, jonathan carr
Hi, Jcarr,
I just look at your website.
You looks different than the previously website. Looks like a Japanese playing 20string guitar 😀. Is it really you? So different than the previous picture I see.
I can't (yes, I can't) believe you are a single-fighter engineer in developing Lyra products (from phono pick-ups to preamps). How many tons of books and papers have you read all this time? 😀
I think your products will have superb sound, because you are used to pay attention and caring about small vibrations and 100's MHZ behavior 😀 Giving me insight about the "proper" design process. I wish I had enough equipment.
I just look at your website.
You looks different than the previously website. Looks like a Japanese playing 20string guitar 😀. Is it really you? So different than the previous picture I see.
I can't (yes, I can't) believe you are a single-fighter engineer in developing Lyra products (from phono pick-ups to preamps). How many tons of books and papers have you read all this time? 😀
I think your products will have superb sound, because you are used to pay attention and caring about small vibrations and 100's MHZ behavior 😀 Giving me insight about the "proper" design process. I wish I had enough equipment.
jcarr said:
AKA complimentary cascode... 🙂
By the way Jonathan....the build quality of your work is mouth-watering... 🙂
Yummy SOTA
Someone who makes phono pickup needle must be taking attention to things that ordinary people wouldn't think of when making preamp/power amp.
When will Lyra power amp come up?
Wow! Thanks for the compliments, fellows, much appreciated. Believe it or not, I do think about function as well as form, so the execution of the Lyra-Connoisseurs is not only about styling and craftsmanship. At the same time, if I can come up with a number of methods that allow me to meet my engineering goals, I am not adverse to choosing the most aesthetically pleasing solution. 🙂
Also, although SOTA may have meaning in a given context, I do not necessarily think that what is SOTA in one context is applicable to other contexts, particularly if the cost vs. return equation is altered. For example, although the design and build methods of the L-Cs are suitable for the production budget allocated and the performance goals, they would be totally misplaced and inappropriate for lower-cost products.
Project managers allowing, it is undoubtedly possible to have the finished product clearly convey the designer's background, personality and aesthetics. In my own case, I am sure that designing cartridges has encouraged me to develop a much more structural and physical way of looking at things than most other electronic designers.
Also, the question of how to fully utilize the resources at hand is something that I give much consideration to. Due to the cartridges, I have craftsmen that are capable of doing extremely delicate, precise work. With the L-Cs, I wanted to design something that would be a worthy match for their talents. Without them, I would have been much less aggressive about the construction and build quality aspects of the L-Cs. Conversely, if I feel that their capabilities as craftsmen are increasing, I may choose to design a more difficult challenge for them.
I am working on it, but build quality-wise, it won't be anything as extreme as the L-C 3, 4 or 5. OTOH, it will have at least one novel feature - a power supply that operates at 120kHz and is therefore highly efficient, but has a sine-wave output, and is therefore very quiet, too.
best, jonathan carr
Also, although SOTA may have meaning in a given context, I do not necessarily think that what is SOTA in one context is applicable to other contexts, particularly if the cost vs. return equation is altered. For example, although the design and build methods of the L-Cs are suitable for the production budget allocated and the performance goals, they would be totally misplaced and inappropriate for lower-cost products.
Project managers allowing, it is undoubtedly possible to have the finished product clearly convey the designer's background, personality and aesthetics. In my own case, I am sure that designing cartridges has encouraged me to develop a much more structural and physical way of looking at things than most other electronic designers.
Also, the question of how to fully utilize the resources at hand is something that I give much consideration to. Due to the cartridges, I have craftsmen that are capable of doing extremely delicate, precise work. With the L-Cs, I wanted to design something that would be a worthy match for their talents. Without them, I would have been much less aggressive about the construction and build quality aspects of the L-Cs. Conversely, if I feel that their capabilities as craftsmen are increasing, I may choose to design a more difficult challenge for them.
I am working on it, but build quality-wise, it won't be anything as extreme as the L-C 3, 4 or 5. OTOH, it will have at least one novel feature - a power supply that operates at 120kHz and is therefore highly efficient, but has a sine-wave output, and is therefore very quiet, too.
best, jonathan carr
How many other profesionals on the forum?
Jonathan
I agree with the comments on you work.
All
Just wondering how many other "professionals" we have on the forum?
Here are some pictures to my main work:-
http://www.directv.com/DTVAPP/imagine/HDDVR.dsp
Jonathan
I agree with the comments on you work.
All
Just wondering how many other "professionals" we have on the forum?
Here are some pictures to my main work:-
http://www.directv.com/DTVAPP/imagine/HDDVR.dsp
Sorry for resurrecting this old thread. I came here because I suspect I might be having an oscillating cascode and was looking for help.
This topic never gets old, right?
DIY Audio member Bonsai wrote some very useful advice on his webpage:
http://hifisonix.com/cascode-amplifier-oscillation/
This topic never gets old, right?
DIY Audio member Bonsai wrote some very useful advice on his webpage:
http://hifisonix.com/cascode-amplifier-oscillation/
I routinely use bipolars for cascodes as they tend to be more stable with regard to oscillation. Also you can occasionally stabilize an oscillating cascode with some resistance between the cascode and gain transistor.
Here is a snip from my amplifier schematic that seems to work well:
I was cautious adding base stoppers to the cascodes and also emitter resistors to the cascode.
Better safe than sorry.
It is easy to change any to zero Ohm if not needed.
This circuit apparently does not cause any trouble.
I was cautious adding base stoppers to the cascodes and also emitter resistors to the cascode.
Better safe than sorry.
It is easy to change any to zero Ohm if not needed.
This circuit apparently does not cause any trouble.
And here is a snip of an amplifier where I have some low level oscillation at roughly 4MHz that is present most of the time:
I have the same precautions here.
I don't know whether the cascode arrangement is causing issues because I also have an output offset of -20V.
Maybe there is something else wrong.
I'm still trying to figure out whether I made mistakes during assembly or I might have a damaged component somewhere.
Apart from the cascode arrangement, both amplifiers are same - one works and one doesn't.
I have the same precautions here.
I don't know whether the cascode arrangement is causing issues because I also have an output offset of -20V.
Maybe there is something else wrong.
I'm still trying to figure out whether I made mistakes during assembly or I might have a damaged component somewhere.
Apart from the cascode arrangement, both amplifiers are same - one works and one doesn't.