John Curl's Blowtorch preamplifier part II

[Variac]

Thread is open..

[john curl]

I would like to ask PMA, in particular, from his circuit analysis of the j-fet Comp-diff 4 quadrant folded cascode preamp model, what he thinks the effective open loop bandwidth is with 1K loads.

[john curl]

Just to remind those new to this thread, the 4 quadrant complementary differential j-fet, mosfet topology is what the CTC Blowtorch used to buffer the line pot and to amplify the audio signal.
Perhaps someone from the past can put up a simplified schematic, so we know where to start.
This design is at the heart of the CTC Blowtorch and most of Charles Hansen's Ayre designs. It is particularly useful for open loop designs,
We could also talk about and compare 4 quadrant all j-fet, non-folded cascode designs as well. such as is in the Parasound JC-2 preamp, just released this year. The 4 quadrant differential is not a new topology, as I first used it 40 years ago with bipolar transistors. However, with cascode, it gets even better, especially with j-fets.

[Wavebourn]

Originally Posted by john curl

Would somebody put up the Telefunken schematic, so we can 'discuss' it?

Originally Posted by Zen Mod

I will ;
you want RtR , or mic ?



so - let's make old geezers tumbling in their graves

Originally Posted by john curl

I don't know, either one, I guess, or both.

Since Zen Mod meant Gu-50 tube, should we put a schematic of a Telefunken microphone that used it?

[john curl]

I still think that a Telefunken schematic would be interesting to discuss.
My only Telefunken schematics are from quality portable radios from the 1960's, including one that Dick Sequerra worked on. However, even though they are very good sounding units, they are made with germanium transistors that are difficult to get today.
In my opinion, we should start somewhere, not changing from A to D, or amps to mikes. It makes it more useful, that way.

[Wavebourn]

Originally Posted by syn08

I would also open a "Solid state design principles" sticky thread which would hopefully allow some productive discussions, without endorsing or being endorsed by anybody in particular.

It would be nice to have such a thread, but are you ready for the role?
First of all, you need a plan of the course. No doubt, you have some already, you may start from physics and technology of semiconductors. Then, 24/7 duty, voluntary.
Are you ready?

[anatech]

Hi John,

Again, a request to close the most popular thread on this website, because it is not 'politically correct'. The real reason is to get rid of the open controversy related to newer ideas in how to make good audio circuit designs. Then the status quo designers would not be pricked by annoying critics of high feedback, the existence of PIM, etc.
Can everyone see this? This is not about circuitry or circuit ideas, but an attack on my person, background knowledge, and ideas.
If 'they' can provoke me, or anyone else to go over the top, then they can and do demand the thread be closed, rather than 'them' just going away and addressing another thread, and leaving 'us' alone.
You see, there is more to this, than just bad manners.

I'm sorry, I can't agree with this post at all.
It was closed for reasons different than what you attempted to pass as a true reason.

Can we call a halt to "putting down" other members, this forum and it's moderators from now on? The same would apply the other way. No personal attacks allowed towards you. In other words, let's keep everything professional. There is no room for egos here.

However, even though they are very good sounding units,

Yes, they really are compared to what you normally get these days. I am pretty sure it comes down to much better speakers and a more linear part than silicon transistors.

they are made with germanium transistors that are difficult to get today.

Yes, and expensive! I have some stored in a box, including many JIS numbers. I may be able to help if you need a couple one day. They can get pretty leaky though.

In my opinion, we should start somewhere, not changing from A to D, or amps to mikes.

John, I couldn't agree more with you on that. Do you want to start with the BT diagram and go from there? Of course, any other design that illustrates the point you want to make would make an excellent addition as a diagram for discussion.

-Chris

[anatech]

Hi Anatoliy,

It would be nice to have such a thread, but are you ready for the role?

To be honest with you, that's a great idea. There are pleanty of topics that do not fit in this thread. I'm sure John would agree, just as I'm sure you would as well.

I don't think it's up to MJL21193 to plan the course of the thread. That's a bit much to ask. How about simply letting the thread find it's own way, and stay away from directly commenting on John's design in this one.

I know you were joking a bit here Anatoliy, but it is a great idea. Would you like to start it? MJL21193? Anyone? I can, but we should give someone else a chance at the mechanics of it.

-Chris

[john curl]

One of the best examples of the 4 quadrant folded cascode topology was put up on this website, by Justcallmedad, on 5-30-2006. This is a fairly easy to read schematic, and only has a few 'extra' resistors that could be removed without changing the circuit, fundamentally. I do have a copy of it here. However, it should be in the website files as well.

[ostripper]

A new thread ? With a more professional atmosphere ?

Amps to mikes ? .. power amps , headphone amps , preamps .. they are all amps. One amp design can be applied to another amp.

To discuss germaniums , the "sound of tubes" , would not be too "offtopic" if it helped others to understand the history and theories behind the designs.
State of the art ? Surely, BJT amps could be "new" , maybe even embracing SMD's (aussieamps) , microprocessor control (syn08) , but SOTA ?... this would be in the realm of mean, green Class D. (I personally do not believe this)

"Design principles" would be good for us "greenies" , we could hear the opinions of those "hardened ones" and ask questions (without being put down). Sounds good in concept !

OS