My little Amplifier

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Hi guys.

i designed this audio amplifier based on what i learned from the internet and my books.

my question is simple "what do you think about it".

any suggestions, improvements and corrections are appreciated.

 

thanks.

 

Last Edited: Wed. Mar 18, 2020 - 09:15 AM
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well it look like standard but why? you will not get a lot of power, sound will be a AB class bof bof... 

a lot of finish IC will give you less distortion and better sound... 

Thierry Pottier

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well it look like standard but why? you will not get a lot of power, sound will be a AB class bof bof... 

a lot of finish IC will give you less distortion and better sound... 

you probably right. but i wanted to build something with discrete components and maybe learn something along the way. beside this is only the power amplifier stage. the complete design includes an active tone controller and an audio mixer. not to mention this is going to be a stereo system.

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If you wanted discrete components, then use a long tail pair instead of the opamp. Douglas Self has some books on the subject.

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Kartman wrote:
Douglas Self

now that name rings a bell!

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ok, if it is for this reason, it is a very good way. good luke. 

Thierry Pottier

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So about 15W if you are lucky? Limited by the supply rails to the op-amp.

 

If you want to use an op-amp there are more interesting ways to do it which free you from that limitation (if it is one).

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Cute trick with the Szikai (sp?) driving, where you have opposite types instead of a (more) common Darlington arrangement.

Suggestions:

 

1) Specify Vcc and Vee.

2) Stick Q8 and Q10 on a big heatsink.  AB amplifiers are not efficient - expect to have to throw away as much power in heat as you put into the speaker(s).

3) Replace D1 and D2 with a thermally-coupled Vbe multiplier - i.e. physically and thermally (if not electrically) attached to the same heatsink as Q8 and Q10.

4) Don't use four-way intersections with connection on a schematic.  angel

 

S.

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Scroungre wrote:
on a big heatsink. 

else it really will be an ampli-fire !

 

surprise laugh

 

EDIT

 

Too bad that typo in the title has now been fixed !

 

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Last Edited: Wed. Mar 18, 2020 - 10:46 AM
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I always prefered amps that glow in the dark!

 

 

 

 

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K-AVR wrote:
"what do you think about it".

I like it.  Too many times the 'easy' solution of an amplifier module is used...and I personally think the sound is not as good as discrete components. 

 

TPE wrote:
sound will be a AB class bof bof... 

And that has been the common standard as the sound is excellent for about 95% of the world.  I prefer Class A myself, but hey.  Give teh OP a break and a pat on teh back.

 

TPE wrote:
a lot of finish IC will give you less distortion and better sound...

I don't know about IC amplifiers made in Finland, but the ones I have used leave a lot to be desired.   Personally I think they suck, but again, thats a personal opinion, YOMD.

 

Scroungre wrote:
Don't use four-way intersections with connection on a schematic. 

I myself use them, nor do I mind them.  As long as you put a connection 'DOT' on teh intersection to indicate that it is in fact a connection for all four components then you're good.  Again YOMD,

 

ki0bk wrote:
I always prefered amps that glow in the dark!

AS DO I!!!

 

Have you powered this amplifier up and checked its frequency response yet?

 

JIm

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

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Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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jgmdesign wrote:

And that has been the common standard as the sound is excellent for about 95% of the world.  I prefer Class A myself, but hey.  Give teh OP a break and a pat on teh back.

Scroungre wrote:
Don't use four-way intersections with connection on a schematic. 

I myself use them, nor do I mind them.  As long as you put a connection 'DOT' on teh intersection to indicate that it is in fact a connection for all four components then you're good.  Again YOMD,

 

ki0bk wrote:
I always prefered amps that glow in the dark!

AS DO I!!!

 

Have you powered this amplifier up and checked its frequency response yet?

 

JIm

 

Class A amps are going to be even less efficient, because they blow off power even while quiescent.

 

That crack was in response to another thread - so do I, occasionally.

Observe how many 4-way intersections there are in ki0bk's tube schematic... 

 

S.

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thank you all.

about the "glowing amplifiers" i have to say that unfortunately i do not have access to vacuum tubes.

and of course we need a big heat sink for the transistors Q8 and Q10 otherwise... well bad things will happen to your amplifier and even maybe your power supply.

but i can not argue about the efficiency, i mean it is not an efficient amplifier. from what i learned the efficiency must be around 78.5%(good enough, i guess!).

 

two more questions:

A)if i use a Vbe multiplier instead of the diodes D1 and D2 where i should connect the op amp output. to the base of Q7 or Q9 or somewhere else in the circuit?

B)is the bias current of the diodes affect the output signal in anyway? i know that a bigger bias current means a bigger collector current in the Q8 and Q10. and very small current means that the diodes will not conduct and they do not act as a voltage source.

 

and about the power rails, i am going to use a +12/-12 volt  linear power supply.

 

PS

if i use a Vbe multiplier can i remove the Wilson current sink down there?

 

 

 

 

Last Edited: Wed. Mar 18, 2020 - 02:55 PM
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Scroungre wrote:
Class A amps are going to be even less efficient, because they blow off power even while quiescent.

Correct.  But thats the price you pay for zero crossover distortion. And better harmonics.

 

The 'new' Class D amps that I hear teh salesman touting as "For digital music" (I want to harm these misinformed idiots so badly) are even more efficient, but at teh cost of sonic purity, but lets not drag the OP's thread off topic.

 

Scroungre wrote:

That crack was in response to another thread - so do I, occasionally.

Observe how many 4-way intersections there are in ki0bk's tube schematic... 

 

I repair/restore classic tube amplifiers as a hobby and all those schematics have four way connections....lots of them.  In school we had them all the time as well so I do not understand why some are bothered by this.  Granted it requires teh draftsperson to make sure the connections are correct.

 

@K-AVR,

Too bad your in an area I cannot send you one of these:

https://www.avrfreaks.net/forum/...

 

I am working on a serious Class A amp for one of them. wink

 

Jim

 

 

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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The point of using a thermally-coupled Vbe multiplier is to counteract the change in gain of your power transistors as they get hot.  In short, as they get hotter they get more gain, and so get hotter, and get more gain, and so get hotter, and, and, and...  The result should be painfully obvious.  The Vbe gizmo is intended to bypass the base current such that as they get hotter, they get less base bias, and so the gain drops off again.

 

I'd connect the op-amp to one base or the other, and let the bias drive the other one.

 

Another way to do it would be replace the diodes with transistors wired like diodes, and stick them on the heatsink too.  That way's generally considered a bit shonky, but mostly works.

 

Anyhow, since you're doing this for fun and for learning?  Knock yourself out!  Blowing things up is how you learn "Not to do That"!!  Wear eye protection - capacitor housings can fly a very long way! (ask me how I know...  ;-) 

 

Have fun, S.

 

PS - Yeah, you might get 78.6% efficiency out of a harmonically-pure rail-to-rail sine wave, but out of a realistic signal?  Maybe not so much.  S.

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jgmdesign wrote:

Scroungre wrote:
Class A amps are going to be even less efficient, because they blow off power even while quiescent.

Correct.  But thats the price you pay for zero crossover distortion. And better harmonics.

 

The 'new' Class D amps that I hear teh salesman touting as "For digital music" (I want to harm these misinformed idiots so badly) are even more efficient, but at teh cost of sonic purity, but lets not drag the OP's thread off topic.

 

Consider that 'digital music' might well be considered 'Dubstep', wherein the only important bit is the "THUMPA THUMPA THUMPA".  I particularly liked the bit where it went "THUMPA THUMPA THUMP".  devil

 

And for zero crossover distortion you bias your class AB for just a bit of shoot-through at quiescent.  Costs a bit of power, but a lot less than full class A, and the distortion goes away.  As far as harmonics go?  Don't drive into clipping, and you don't get harmonics.  So there.  cheeky

 

Meanwhile, back in OP's thread...   S.

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You may find this an interesting read: http://www.steampoweredradio.com...

Southwest Technical Products used to make low cost high performance audio kits back in the 70's, above is the manual for a 60w 0.01% distortion amp.

Enjoy

Jim

 

 

 

 

 

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Look at all those 4 way connections!

 

East coast jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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jgmdesign wrote:
Look at all those 4 way connections!

True, but where there could be confusion, they break one of the crossing lines!

I've never had an issue with crossed and dotted lines, copiers are much better now!

 

Jim

 

 

 

 

 

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Scroungre wrote:
The Vbe gizmo is intended to bypass the base current such that as they get hotter, they get less base bias, and so the gain drops off again.

maybe you need to take another look to my circuit i used what is known as the constant current source witch means a constant current is going to pass through the diodes.

Last Edited: Wed. Mar 18, 2020 - 04:24 PM
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Um, no, the point isn't that a constant current passes through the diodes.  The point is that MORE current passes through the diode(s) (or equivalent) as it gets hotter!  S.

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jgmdesign wrote:

Look at all those 4 way connections!

 

All three of them?  Humph.  wink  S.

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Okay.  Maybe I wasn't real clear.

 

Bipolar transistors have thermally-sensitive gain values.  The hotter they get, the more gain they have.  This is a positive feedback problem, because the more gain they have, the more current will flow from collector to emitter for the same base current.

 

The more current that flows, the hotter they will get.  And then that will make their gain increase, and so, given a constant base current, the hotter they will get again.  And over and over again, very quickly, until they make smoke and a bad smell.

 

The Vbe multiplier, thermally-coupled, instead of the diodes provides negative thermal feedback - the hotter they get, the less base current they get, thus stabilizing them at some point or other instead of runaway overheating.

 

(As an aside, if you replace one of the resistors in a Vbe multiplier with a pot, you can tweak the bias to get zero crossover distortion, at the cost of some extra heat thrown away.  Don't turn the pot too far).

 

Zat help any?  S.

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so the improvements:

1)use a Vbe multiplier witch is thermally coupled with the power transistors instead of the diodes.

2)connect the op amp output to the Q9 base.and remove C1 and connect C2 between bases of Q7 and Q9.

??

can i remove the wilson current sink in the bottom?so the bias current goes through the op amp output?

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Try it.  See what happens!  wink  S.