class A amplifier

olivier.scalbert · 2008-10-13T13:44:49+00:00

Hello,First, I must say that I have not done analog electronics since a longtime. So please be indulgent !I want to do a small class-A music amplifier + preamp. I want to findthe best trade-off between simplicity and sound quality.My approach is very incremental. I have started with one old 2N3055,polarized with voltage divider composed of 2 resistors.As the gain of the transistor is to low I finally put a (too?) smallBC546 in front of the 2N3055 (Darlington).See schema:As I need a preamp for the volume control, I have add another BC546 toamplify the input signal.See schema:The DC is provided by a lab power supply (0-30V, 0-3A). I use from 5Vto 12V as the 2N3055 heatsink is to small.When I first test it, I was expected to have a crappy and plasticsound, and even smoke, but I was very surprised. The sound is cleanand contains a lot of details (speaker: B&W DM110).What I want to do now is to improve:- the schematic (there are certainly mistakes ...)- the component choice (better capacitor ? , better transistor ?)Any remarks and suggestions are welcomed !Thanks very much,Olivier

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Eeyore 17 years ago

I wouldn't bet on that.

I've fixed 3 'runaways' including one in marine radar. I could tell you a story or two about that. I turned a turkey into a significant commercial success. There was a restructuring going on at the time. The Technical Director was being promoted to Managing Director, his Technical Manager was becoming Technical Director and quite a few of the R&D staff suggested I should apply for the open Technical Manager post (staff of about 40).

I was VERY flattered.

Graham

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John Fields 17 years ago

So prove it. If, in fact, discrete analog design is one of your strong points, you\'d know that if you\'re introducing some nuance into a previously proven design and, therefore, don\'t know about the nitty-gritty of the combo and/or you don\'t know how to simulate it properly, Then you need to build a few a of them, test them over the expected changes in supply voltage, ambient temperature, and load impedance, and report your findings. JF

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Eeyore 17 years ago

Well you beat me there by a factor of 3 or so.

Graham

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John Fields 17 years ago

concepts like using

client's copyright.

clot handed them over

The buck stops where? JF

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John Fields 17 years ago

concepts like > using

client's > copyright.

could see loads of

If frogs had wings... JF

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Jamie 17 years ago

being

Don't let that go to your head, over here, that's one method of getting rid of some one.

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"

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Eeyore 17 years ago

Yes, darling !

Graham xxxxx

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Eeyore 17 years ago

concepts like >> >

client's >> >

could see >loads of

GGF. The MD and I were discussing dismisalls today. Trouble is, I just took on another contract on Monday. His timing is poor. Poor chap, he's always had the wool pulled over his eyes by idiots who never deserved the positions they had.

Graham

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Olivier Scalbert 17 years ago

Ok so I can start from Fig 1A

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with an op amp instead of the entry stage ? And with a 2N3055 and a MJ2955 ?

Olivier

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Kevin Aylward 17 years ago

Then you

I disagree with this. If one can obtain a decent BSim3 model of the lateral fets, then an empirical test is pretty much irrelevant. The design of SOC analogue ics, with 10'000s analogue devices, entirely in simulation, that work, is routine. In fact, bench work is not even feasible. Indeed, using worst case corner tools (

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and Monte Carlo simulation allows one to far better ensure that products will work reliably in production than a few bench tests, with nominal devices, can possible hope to achieve.

Kevin Aylward

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-SuperSpice

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Olivier Scalbert 17 years ago

Other question Graham ... Suppose I work in class A with a current of 1A in the two output transistors. If the current of one transistor goes to 1.5 A the other one should go to 0.5 A and 1A goes through the load. If I forget to connect the load (and I am sure I will), what is going to happen ? Thanks

Olivier

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John Fields 17 years ago

Open wide... JF

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John Fields 17 years ago

concepts like >> >

the client's >> >

could see >loads of

another contract on

eyes by idiots who

So you think that it would be OK for you to pull the wool over his eyes because you\'re more deserving of the position? JF

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John Fields 17 years ago

I\'d agree had you not snipped a little early. Here\'s the whole thing: " If, in fact, discrete analog design is one of your strong points, you\'d know that if you\'re introducing some nuance into a previously proven design and, therefore, don\'t know about the nitty-gritty of the combo and/or you don\'t know how to simulate it properly, Then you need to build a few a of them, test them over the expected changes in supply voltage, ambient temperature, and load impedance, and report your findings." JF

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Kevin Aylward 17 years ago

Ok, I'll buy that. I didn't really notice the full "or you don't know how to simulate" bit. The sentence was just a tad too long for me to take it all in.

Kevin Aylward

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class A amplifier

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