SE Newbie wants to go level 2

[mahleriana]

Hello,

For a year now, I have been buiding different SE without NFB variations around 6SL7/6SN7 and 45/2A3/EL84.
I know how to build load lines and find component basic values, how to make various stages and PSU, and find the components type that suit my tastes most in order to have a quite decent sound from my speakers (what i would call level 1). There are many useful documents or pages about all this.

I did find difficult to get an easily understandable and/or explained knowledge about optimizing an amp (what i would call level 2) : impedance matching between stages or PSU beyond Zin/Zout (ex: best relation between component values regarding ra, Cin, Rg/Rp/Rl etc), driving capability and current requirements, bandwidth... I often find just plain equations or on the contrary very technical contents.

My philosophy is first to stay with good simple designs rather that learning every way to add design complexity. I also want to understand what I make rather than just copying schematics.

Could you please give me clues, documents or links to go to this level ?

Thanks in advance,
Best regards
eric

[rman]

Hello.

Congratulations on your "stage one" accomplishments. I am not that advanced either. I have found that the various sites that explain the basics give good information on the kind of questions you have. If you have not already found it, check out " The Valve Wizard" The site is geared to guitar amplifier fans, but give great insight into the kind of questions you are having. Slog through the formulas, electronics is largely applied math.

There is no need for "Impedance matching" between stages, zout just needs to be much lower than zin of the next stage, (about 10 times?) to keep from loading the previous stage too much. Review basic low pass and high pass filters. This is important for understanding how to couple stages and keeping the frequency response good. For example, the tubes cin along with it's grid resistor form a low pass filter that limits high end response.

I have found it useful to make Excell spreadsheets of frequently used formulas, but understand how they work first!

How about some pictures of your projects?

Cheers.
Rolf.

[kmtang]

Order this book and read it. This is a very book for understanding tube amps.


Johnny

[rknize]

+1 on MJ. I have his 2nd edition, but it is still very good. You won't absorb it all on the first pass and that is OK. He dives pretty deep into the math and how it applies to the project at hand. It is not always easy to apply those methods to other projects because he often leaves out the gory details in the interest of moving forward (some of his discussion about feedback comes to mind). But you will know the right questions to ask and that alone is useful. The rest of what he talks about applies well. I imagine his 3rd edition is more detailed, given that it is split into two books. Maybe ask Santa for the 3rd edition?

[Miles Prower]

Originally Posted by mahleriana

I did find difficult to get an easily understandable and/or explained knowledge about optimizing an amp (what i would call level 2) : impedance matching between stages or PSU beyond Zin/Zout (ex: best relation between component values regarding ra, Cin, Rg/Rp/Rl etc), driving capability and current requirements, bandwidth... I often find just plain equations or on the contrary very technical contents.

What you're asking here is impossible. Every design is a compromise, and it will always be that way. Gain something here, sacrifice something there.

My philosophy is first to stay with good simple designs rather that learning every way to add design complexity. I also want to understand what I make rather than just copying schematics.

Could you please give me clues, documents or links to go to this level ?

Get familiar with Pete Millet's Site: lots of technical books available for free download.

You should start here: Radiotron Designers Handbook IV. That's a good way to get up to speed on everything hollow state.

[hemgjord]

Radoitron Designers Handbook, fourth edition. Copyright has obviosluy expired and can be found at various places on the net.

It is old but explains looots of stuff really thoroughly. Can be a little hard to grasp if you don't have an engineering or mathematical background

/Olof

Edit: you beat me to it Miles :-)

[tomchr]

A lot of newer texts would cover what you are looking for, but they are obviously targeted at the current crop of college students and deals mainly with design of amplifiers on an IC. The book I used in college (early 1990'ies) was Sedra/Smith: Microelectronic Circuits. I have both the 3rd and 5th edition. Unless, you're willing to shell out $150 on a textbook, I'd suggest getting a used copy of the 2nd or 3rd edition. The difference is mainly that the newer editions favor CMOS design over BJT/J-FET. The J-FET and triode have a lot in common in terms of characteristic curves and it wouldn't surprise me if J-FET designs could be scaled to use triodes without too much trouble. The basics of how current sources work, how cascodes improve performance sometimes, how to break amplifiers into stages, etc. is a function of the topology and not the technology used to implement them. So I'd say Sedra/Smith would be useful for tube design despite it being a solid state book.

Morgan Jones' "Valve Amplifiers" book is excellent as well, though, in many cases it treats the subject a bit too superficially. It reads more like a novel than a textbook, which is great for entertainment, but not so good for a reference text... The ultimate reference is probably Radiotron Designer's Handbook 4th Ed. (RDH4).

~Tom