appropriate use of cascodes

SteveG

Account Disabled
2002-01-07 7:20 pm
Newton Falls, Ohio
So, I was reading through the "sound of cascodes" posting, and it left me with one big question:
How do you know when to use a cascode?
I was going to use them with my balanced line stage, but now I'm not so sure. On paper, it looks excellent! Why not? Seems like a good way to clean up a little distortion on a single gainstage circuit.
One of the most important characteristics of good audio, in my opinion, is dynamic contrast. Dynamic contrast and resolution of the finest details are, to me, what seperates the good from the mediocre.
As the post was wandering away from it's original direction, I will ask the million dollar question again- Does anyone know why cascodes can steal the musical life from some circuits? I'm starting to subscribe to the simpler is better theory.
Steve
 

SteveG

Account Disabled
2002-01-07 7:20 pm
Newton Falls, Ohio
Sounds like a good idea. THe only problem is $$$ right now. I don't have enough to build a good amp to try out the preamp. I will eventually try both ways out, and see what sounds best to me and post the results.
I was thinking of building the balanced line stage driving a follower, which would be driving the Ciuffoli power follower using 6 paralleled stages to cut down on the dissipation per device. Any thoughts on how this would work out?
Steve
 
How do you know when to use a cascode?

I've used them most every place I can. Been doing it so long, I do not remember what "the sound of cascode" is, and why the "magic" is not there. Nor do I care.

But........cascodes are real handy if you use JFET inputs. They can't handle 50 V rails, so it is hard to build an amp with them without a cascode.

Inverted cascode is a neat circuit. Usually uses a current source, too.

There: 2 things some people hate in one circuit. Such a deal.

Jocko
 
Cascode

I like JFET-Mosfet casode current sources with drain resistors for capacitance isolation and RF stability . I would post a schematic but that would offend the bandwidth challenged. I would discuss its technical advantages but that would offend those who didn't understand it; those who were idealogically opposed to it for reasons that they can not quite explain; and those who were idealogically opposed to it because they didn't understand it. Harmony before inquery....

H.H. (hardly humorous)

JFET: junction field effect transistor
Mosfet: metal oxide semiconductor field effect transistor
RF: radio frequency
 

SteveG

Account Disabled
2002-01-07 7:20 pm
Newton Falls, Ohio
Jocko,
I can't really see a reason not to use them- it looks like a win-win to me. I will have to try it and see if I can hear what they're talking about.
I'm cringing as I ask this, but do you know of a schematic showing inverted cascode? I would like to see what it's all about.

Harry,
Go ahead and offend them... let's see that schematic! I'm willing to admit my lack of experience, but I try to not be closed minded about what I don't understand. All the same, I would ask you for an explanation, but you seem to be against giving out free advice. Let me know where to send the check.
Steve
 
Posted by H.H

"I would post a schematic but that would offend the bandwidth challenged. I would discuss its technical advantages but that would offend those who didn't understand it; those who were idealogically opposed to it for reasons that they can not quite explain; and those who were idealogically opposed to it because they didn't understand it."

This is typical of the supercilious attitude displayed in the majority of your posts. I made no suggestion that schematics should not be posted, merely that the superfluous and gratuitous images which add no value to a thread should be avoided.

Since joining this forum a short while ago, you have repeatedly whinged about the number of posts related to heatsinks, MOSFET matching etc. Nobody came back at you in a sarcastic manner, because you are entitled to your opinion (but not to dominate this forum by telling people what they can and cannot discuss).

You have also repeatedly made snide comments about using the search facilities so that the same topics are not raised time and time again. Had you followed your own advice, you would have found that the topic of using the search function has been covered several times previously, including a dedicated thread that I started at the beginning of January.

Your attitude of 'I know the answer but I'm not telling you' is of no help to anyone. It merely serves to waste your time and that of everyone reading the thread. If you cannot post something constructive then it would be better to not post at all.

Geoff
 

SteveG

Account Disabled
2002-01-07 7:20 pm
Newton Falls, Ohio
Jam,
THanks for the offer. I have a working circuit- it's the Zen balanced line stage using cascode MOSFETs with a bipolar current source- about 80mA bias current, 60V positive rail, I can't remember what load resistors, and using 5.1v zeners to bias the cascodes. It seems to be able to swing quite a lot of voltage (at least in simulator). I was more interested in seeing the inverted cascode that Jocko was talking about, but I do appreciate the offer.

Jocko,
I will check that out. Thanks for the info.

Geoff,
Don't waste the keystrokes man! People have said it time and again. I think there are certain people that get off on being antagonistic around here. It's just so easy to be full of yourself when you have miles between and no threat of a fist in your face to worry about.
Steve
 
SteveG said:

One of the most important characteristics of good audio, in my opinion, is dynamic contrast. Dynamic contrast and resolution of the finest details are, to me, what seperates the good from the mediocre.

I can agree with your statment which describes the subjective impression one usually has of good vs. bad equipment.
However, how do "dynamic contrast" and resolution translate into something one can simulate or watch with a scope or spectrum analyzer? In most applications that involve voltage gain, a well-implemented cascode will improve virtually all parameters that are relevant in my book.

Greetings,

Eric
 

SteveG

Account Disabled
2002-01-07 7:20 pm
Newton Falls, Ohio
I can agree with your statment which describes the subjective impression one usually has of good vs. bad

Well, I'm glad that I got that right, but what are your parameters?

However, how do "dynamic contrast" and resolution translate into something one can simulate or watch with a scope or spectrum analyzer? In most applications that involve voltage gain, a well-implemented cascode will improve virtually all parameters that are relevant in my book.

If you had read the thread I refered to in the opening post (or if I had referenced it better), you would have noticed that cascodes were being blamed for messing with dynamics. Since the topic went way off path, I started this thread with a question about when it would be appropriate to use them. Maybe I should have clarified my question by laying down the assumptions of the previous post first, which were that cascodes were messing with dynamics in certain circumstances in audio circuitry. With that idea in mind, the question would be- "if cascodes can cause flawed dynamics in certain implementations, what type of circuit is appropriate to use them in?" Sorry for the confusion.

Do you really think that everything that relates to musicality will show up on a scope or spectrun analyzer? Yes, I lean toward the subjectivist camp . At the same time, do you think that the best violin in the world is chosen by the best musician because of how it measures? This whole subjective/objective arguement is so much nonsense! We listen with our ears, not our scopes. There is a lot to be found out by test equipment, but it is not all there. We take what we know to <i>sound</i> good and use test equipment to come up with theory as to why it sounds good, right? But how many times has something measured great, and sounded flat (dynamic contrast?) and lifeless (resolution?)? How much <i>live</I> music have you heard? I know that when I play my drums, or my guitars, that there is a certain texture there that I look for in my audio equipment. Of course it could be objectively measured to a point, but I don't believe the equipment we have is capable yet. Sure, my reference is flawed- just as my preferences for certain foods leads me to think that my wife is a better cook than yours, you know what I mean? Our music comes "pre-flavored" by the producer, who references <i>his</i> subjective criteria. I highly doubt he is watching a scope while producing. What I'm getting at here is that there is a subjective element to everything, and that there is as much or more art involved in the whole process than there is measurement. To say there is no preference is to be dishonest with yourself. Do we all hear the same? I think there is a balance to be found here, and it lies somewhere in between the two extremes. John Mellencamp put it very wisely- "I know there's a balance, I see it when I swing past".
Just my $.02
Steve
 
Another satisfied customer

"Nobody came back at you in a sarcastic manner, because you are entitled to your opinion (but not to dominate this forum by telling people what they can and cannot discuss)."

Oh really......
I am not a moderator. I have no control over what anyone says.
I have even admitted to being wrong on several occasions. If people have the right to comment on my post I feel inclined to feel free to express my opinion on thiers. The only one I have truly provoked is Grey who has never responded in direct response to my tweaking. As a moderator I suppose he has the power to pull the plug on me if he feels it appropriate. We in the United States still live in a democracy. Is begging people to show some inititive or some "gratuitous humorous images" really going to bring the forum to its knees? I have received no Email from the owner of this forum with any ultimatums in that area. I guess when my usefulness is outweighed by my playfullness, the plug will be pulled. I have gotten as much abuse I have given here with begging anyone to come to the rescue.

supercilious?

For example.....
 

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