Distortion in darlington amplifier

[audioguru]

Graphs in datasheets and simulation models use "typical" spec's. But you purchase transistors with a range of minimum, typical or maximum spec's. So you must either buy hundreds of transistors and test them to pick typical ones, or you can calculate a power supply voltage, and resistor and capacitor values that allow good performance with minimum to maximum transistor spec's.

The idle current of the amplifier depends on matching the forward voltage and Vbe of the transistors which is barely affected by hFE.

The antenna signal strength, the circuit of the AM radio and its amount of Auto-Gain-Control determine its audio output level.

 

[gophert]

Your point taken. You are not helping.

For future reference, when YOU post your next thread here, you should add "please only give answers that agree with my current mis-understandings and any proposed improvements should have fewer parts than my current design".

 

[Stan2020]

Your point taken. You are not helping.

 

[gophert]

Your point taken. You are not helping.

That's ok, none of the posts from other members appear to have satisfied you either.

 

[unclejed613]

Did I make it clear enough?
Now yet another simple question:
why the Ic at rest of this circuit is so huge (320 ma)?

Yep, a shortcut there was. Breadboards, we love them. Idle is 6 mA now.

yeah, breadboards can do that if you're not careful...

Next: I am planning to use this amp for AM radio, vintage style - transistors only.
Do I need a preamp or I can connect it directly to detector output? I am planning 2 transistors RF amplifier.
This is not a simulation question. This is not a theoretical question.

use at least a two stage audio preamp, assuming your detector is a simple germanium diode (1N34). most transistor radios back in the day had in addition to at least 1 RF amp, a couple of IF amp stages after a mixer stage, but using a superhet design is probably to complex for what you are trying to accomplish. the IF strip part of a superhet radio gives plenty of gain before the detector, requiring less audio gain in later stages. the problem with a superhet is you need a local oscillator (requiring an additional section on a tuning capacitor) and a mixer stage, and then 1 or 2 IF (intermediate frequency, usually 455khz) amplifiers, then the detector followed by a preamp stage, followed by the amp. from what you have written it sounds like you want 2 RF stages, then the detector, then 2 or 3 preamp stages, then the amplifier. just how many preamp stages you will need will depend on how much gain you have in the RF stages.

 

[throbscottle]

What a very educational thread! It's rare that I read the whole thing

 

[audioguru]

What a very educational thread! It's rare that I read the whole thing

There are many websites and You Tube videos showing electronic circuits that do not work.
Some Instructables admit that some of their circuits were posted by a 10 years old kid who knows nothing about electronics.

 

[throbscottle]

Yes, and it's very annoying because I am wondering how they got to be so knowledgable when I am not! I just assume they learn these things in school these days...

 

[upand_at_them]

Yes, and it's very annoying because I am wondering how they got to be so knowledgable when I am not! I just assume they learn these things in school these days...

Don't assume they're knowledgable. There's a lot of copying going on without much understanding. I saw a kid get a job as a researcher at a university with a fundamentally flawed understanding of basics...Like he claimed an improved accuracy of a fixed frequency source by dividing down the clock. WRONG!

 

[Stan2020]

True that. I read info about the author of the first , darlington, circuit schematics...well, I should have read it before committing to assemble it. My bad.
But I object you attribute this to kids. It is just regular people who are irresponsible and eager to see there names in publication.

This is a lesson I learned, too late unfortunately: a good number of all electronic circuits diagrams published since the beginning of time - are lemon, non-functional If only someone told me this truth when I was 10y.o. kid failing again and again trying to make that radio with hard to find and expensive transistors

On a side note, I was thinking yesterday - it would be great to have something like FDA that would not allow to publish any schematics unless it was thoroughly tested and approved by central radio amateurs authority.

BTW, the second circuit is totally OK, I insist. Finished assembling a receiver with even simpler version of this circuit,works as a charm:

Was a good exercise, now to final step - follow original vintage construction, with vintage Ge transistors. BTW _that_ construction I am planning to make was proven to be functional, reproduced in thousands in1960th...although even today there are hot arguments on how and why actually it works
Here is the fragment:

 

[gophert]

Don't assume they're knowledgable. There's a lot of copying going on without much understanding. I saw a kid get a job as a researcher at a university with a fundamentally flawed understanding of basics...Like he claimed an improved accuracy of a fixed frequency source by dividing down the clock. WRONG!

At least he had a chance to get mentored by a knowledgeable & patient engineer to fill the gaps in his education with on-the-jobexperiences.

 

[audioguru]

Stan, you show the schematic of a modern "crystal radio" that has two RF amplifiers. A crystal radio was used 60 years ago when there was only one AM radio station in town, so the single tuned LC circuit did not need any selectivity. Today's AM radios have about 5 LC tuned circuits so that you do not hear a bunch of AM stations at the same time. My city and surrounding cities have at least 20 AM radio stations.

The germanium circuit has DC in the speaker which offsets it causing no sound or distortion. The DC also eats batteries.

 

[Stan2020]

Please try to say something meaningful. Don't be a captain every minute.
I am fine with receiving just WGM, loud and clear

Also, FYI, today there is a big community of radio-amateurs building pure crystal radios (no amplifiers whatsoever).
You are too under-informed to be even a captain

And obviously you missed the most unusual feature of this vintage circuit as well.

You keep disappointing me.

 

[gophert]

Stan, you show the schematic of a modern "crystal radio" that has two RF amplifiers. A crystal radio was used 60 years ago when there was only one AM radio station in town, so the single tuned LC circuit did not need any selectivity. Today's AM radios have about 5 LC tuned circuits so that you do not hear a bunch of AM stations at the same time. My city and surrounding cities have at least 20 AM radio stations.

The germanium circuit has DC in the speaker which offsets it causing no sound or distortion. The DC also eats batteries.

The way AM radio is trending in the US, we may be able to go back to crystal radios. The Pittsburgh Metro area has only 6 AM stations now. Soon it will be 4. There aren't even any "rural Pittsburgh" stations. The next closest are Youngstown, OH; Uniontown, PA and Weirton, WV and Akron.

 

[upand_at_them]

FYI, today there is a big community of radio-amateurs building pure crystal radios (no amplifiers whatsoever).

On Earth? Can't be more than a few handfuls.

 

[Stan2020]

On Earth? Can't be more than a few handfuls.

Majority rules only in bad democracies, my unknown ignorant friend. Majority will always vote for free booze and against any taxes. I personally hate majority.

 

[audioguru]

I listened to muffled AM radio until 1961 when I built a kit FM radio. What a huge difference in sound quality.
I forgot to mention that radios have had Automatic-Gain-Control for years but the simple crystal radio with two RF amps posted recently does not, so it will be overloaded and sound extremely distorted if it is near an AM radio station.

 

[Stan2020]

See you next life, my blabbering friend. Ignoring.

 

[gophert]

See you next life, my blabbering friend. Ignoring.

In your short stint here, I'm not sure your pleasant personality has attracted anyone that you can call a "friend". I'm also afraid I'm going to lose my reputation as "the resident A$$hole".

 

[Mickster]

Your initial post started out like this:

I am not good at electronics;

....but then you go on to try and trash every post that tries to help you....

Q. Are you 'not good at electronics' as you initially stated, or are you simply here to troll?