Simple audio amp design

I remember all the heat precautions from years ago. A while back I started the SMD soldering and using a heat gun. Really had me worried that playing all that hot air on the devices, but sofar in the few I have replaced they seem to survived. Most of the SMD are smaller than the tip of the soldering iron.

Yebbut, tin whiskers are the spawn of communism dressed up as environmentalism, and Crusty Oldloon must rail against them.

Cursitor Doom wrote: =================

1. The BC108 can stay

1. Change T2 to a BC178 or similar TO18
2. Change T3 to 2N2904 or similar TO5
3. Change R3 to 820 ohms.
4. Change T4 to TIP31
5. Change T5 to TIP32

Step 2 ( Vbe multiplier) solves the bias issue for the new, Si outputs.

...... Phil

This is sci.electronics.design. It's about designing electronics, not a place where you ask for advice about trivially simple class A/B audio amplifiers which have been around since transistors were first invented.

Douglas Self and other audio guru's have spelled it out

-- Bill Sloman, Sydney

IEEE Bill the FAKE snipped-for-privacy@ieee.org wrote: ===================================

Been correctly argued already that the NG name is ambiguous. So it MUST include examination, analysis and all questions about existing designs..

..... Phil

Or Phil thinks it must. Cursitor Doom's aim to stick with just five transistors is a constraint on design - but it isn't a rational one.

I wonder what Phil meant by that? He probably means he finds the design of class A/B amplifiers complicated, which it isn't.

According to Phil, who aspires to the same kind of following, but isn't good enough at being "impressively expert" to make money out of it.

Mostly because what Phil thinks are "mistakes" are what other people count as differences of opinion.

I do make mistakes from time to time - rather fewer than Phil likes to think - and there are posts (mostly including the word "oops") where I admit it.

There's even one where I eventually agreed that Phil was probably right - Cursitor Doom and Eeyore are almost certainly different people.

Phil will have forgotten that, in the same way that he seems to forget his own pratfalls. Phil snipped the link to what Douglas Self had had to say on the subject - and skipped the opportunity to tell us what was wrong with it. I wasn't all that impressed with output stage of that amplifier - I don't find npn and pnp Darlington as nice as complementary Darlngtons - Sziklai pairs - which are what I used in my home built version (back around 1978).

It's mainly a biology-lab problem, that. The interaction of formalin preservative with the laser-printed labels in the bottle next to the specimen... was to float the letters off the paper, making a little stack of vowels and consonants.

well if youre hard-core restorer & remain faithful, and if you cant get original parts, then you take the old part, carve out its insides and sneak a new modern part inside. May have to include a resistor or two, to emulate the old part.

True, CD's post is not about "new design", its really about restoration or rehabilitation of an old one. (And he put "Simple" in the title, even though "simple" is subjective, as Phil implied). I do find this area interesting, and suggest it be one of our allowed topics for discussion. Practically speaking, we need more good topics. We all want this usenet group to live, & well, I assume. There just doesn't seem to be enough "new design" posts to keep this group that narrowly defined. So we must evolve.

Rich S wrote: ===========

I also pointed out the merely changing the bias setting device to Silicon solves that issue. Is a Vbe multiplier a strange thing to others here?

...... Phil

The circuit isn't that simple anyway, check out that compensation network. How the whole amp operates in principle is easy but figuring out the values so it's stable and doesn't suck is harder, just dominant-pole compensating and calling it a day isn't an option I don't think, its low-frequency open-loop gain isn't huge to begin with.

well not to me, but to many, it could.

My point to everyone is, you don't really know how much our audience knows or doesn't know. There's no "entrance exam" to joining this group ;-) I assume for every 1 (semi-)regular poster there are 100 (semi-)lurkers. And many may

So I dont my mind, being a little kind, and welcome unsophisticated questions & responses. When Man meets The Internet, all sorts of the sublime & the crazy will ensue. We do pretty well, here, considering.

Rich S wrote: ==================

How come just swapping the Ge part to Si do the trick ?

..... Phil

(Uh oh, a Phil challenge, do I risk it?) I assume, doing the Ge > Si swap, on BOTH the output stage and the "rubber diode"* the proportions setup by the resistors can remain as is.

cheers, RS

roughly 2*Vbe biasing two Vbe, as long as they are all the same type it adds up

snipped-for-privacy@fonz.dk wrote: ==============

..... Phil

I couldn't agree more. Too many 'designs' nowadays are just people modifying existing designs or interconnecting ICs to do the heavy lifting. Both approaches are cop-outs in my view. Sure they get the job done quick, but where's the satisfaction in that? This was a chance for folk here to come up with something original using discrete components. I'd have thought the modest challenge of that; hardly insurmountable by any standard, would have appealed at some back-to-basics level. But maybe experienced designers here are lost without recourse to their usual go-to ICs. :-/

And your opinion couldn't be less relevant. Your "contributions" are entirely negative - mostly links to "Russia Today" and "Zero Hedge" disguised as tinyurls.

If that solves the problem that needs to be solved, where's the problem?

How can they be "cop-outs"? Design is all about putting something together to solve a problem - sometimes you want the cheapest possible solution, sometimes the one that takes up the least space, and often the one that can be completed as quickly as possible. These are all perfectly legitimate constraints on the design process.

Design isn't about leaving the designer feeling satisified. It's about leaving the end user feeling satisfied.

Why on earth would anybody bother?

But who would put in the effort to make Cursitor Doom - of all people - happier.

And maybe Cursitor Doom doesn't know what he is talking about.

On a sunny day (Wed, 22 Dec 2021 00:33:33 +0000) it happened Cursitor Doom snipped-for-privacy@notformail.com wrote in <sptrou$nrt$ snipped-for-privacy@dont-email.me:

There is some truth in that, but in today's world you could say build an AM FM radio with some old transistors, or new ones, but if you go HD TV the codecs and other stuff need highly integrated chips. You could code that in an FPGA (for example a mpeg2 decoder) to show YOU can do it too, but then you are already using existing chips.

But to have some transistors to be ably to send an SOS in case you ran out of solder, why not:-) Point is I have done all that transistors design for all sort of things, and tubes too before that, And fixed thousands of circuits, some simple, some very complicated, in broadcasting and in my repair shop. I can tell you that (having to look) looking at so many different circuits from so many designers is a great learning experience. In my opinion coming out of some EE school and just connecting IC_type1 to I_type2 is a different art perhaps. It is what it does and how it works that counts, It would take many years and hands on experience to get to know that,

All electronics designs, be it a simple audio amp or switcher etc. are interesting, there is a lot you can learn or should have learned ;-)

At least it is on topic, unlike what the slow man just started,