Class (A)B output stage: why 2 emitter resistors, why not 1? - Page 2 - diyAudio
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Old 12th December 2006, 06:27 PM   #11
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Quote:
Originally posted by deleveld
Yes I agree that symmetrical clipping is a good idea!
Do you mean 0.06% of power loss in one rail must be compensated by equal 0.06% of power loss on another rail for some good idea?

What is the reason behind this idea?
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Old 12th December 2006, 08:47 PM   #12
K-amps is offline K-amps  United States
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Quote:
Originally posted by Wavebourn


Do you mean 0.06% of power loss in one rail must be compensated by equal 0.06% of power loss on another rail for some good idea?

What is the reason behind this idea?
To be a narrow mind.


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Old 12th December 2006, 09:01 PM   #13
Nordic is offline Nordic  South Africa
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Isn't odd harmonics one of the downsides to perfect symetry?
No wonder so many things in nature including ourselfes are not perfectly symetrical.
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Old 12th December 2006, 09:09 PM   #14
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Wavebourn, you make an interesting point.

I think one should try to maximise output swing before clipping occurs. I agree thats not a very objective statement. If fact it sounds like an ethical statement and I am not sure why it seems natural to describe it in those terms.

From an objective viewpoint you could consider that symmetrical clipping increases the probability that a random signal wont be clipped. Because you never know whether the signal peak will be +ve or -ve. An amp can only relaibly process signals smaller than its lowest clipping level.

I think that with a single emitter resistor then the clipping difference could very well be on the order of a few volts. If the difference in clipping levels is on the order of fractions of a volt, then the point of diminished returns has been reached. But when the clipping difference can be a few volts I think that some attention should, if possible, be paid to fixing the problem.

Doug
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Old 12th December 2006, 09:10 PM   #15
K-amps is offline K-amps  United States
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Quote:
Originally posted by Nordic
Isn't odd harmonics one of the downsides to perfect symetry?
No wonder so many things in nature including ourselfes are not perfectly symetrical.
Isn't it odd, that harmonics are one of the downsides to perfect symmetry?

OR

Aren't odd harmonics on of the downsides to perfect symmetry?

Which statement is the one you wanted to make...

As far as we go, I agree, assymmetry is built into our genome.... is that why we prefer some forms of distortion?
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Old 12th December 2006, 09:12 PM   #16
K-amps is offline K-amps  United States
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Doug,

Would it be better opimized if you used a single emitter in a quasi-complementry OP stage?
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Old 12th December 2006, 10:01 PM   #17
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Quote:
Originally posted by deleveld
Wavebourn, you make an interesting point.

I think that with a single emitter resistor then the clipping difference could very well be on the order of a few volts.
Doug
In the order of a few volts? One tenth ohm against 4 ohm load?

Let's check... Suppose, output voltage is 10V, it means 2.5A current, and 0.25V drop on 0.1 Ohm resistor, it means 0.625 W of power.
Now, you add 0.25V more of voltage drop claiming that output power before clipping will be higher? No, it will be less. Unaudible less, but anyway less.

So, what is the reason?
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Old 13th December 2006, 03:25 AM   #18
CBS240 is offline CBS240  United States
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No emitter resistors in a BJT EF could make biasing a bit touchy. Hope you have a good stock of outputs.
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Old 13th December 2006, 04:10 AM   #19
GK is offline GK  Australia
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Quote:
Originally posted by deleveld
Did you only use emitter for top or for the bottom output transistor?

I assume you had no particular problems with only one emitter resistor?

thanks,

Doug Eleveld


I put it in the top, but either way would have done. The resistor was 1 ohm, the output transistors were TIP31/TIP32 (that's what I had in my junk box). Driver transistor connections weren't an issue because there weren't any and the output devices were biased and temperature compensated with two 1N4001 diodes connected in series.
Pout was a massive 1.5 watts rms into 8 ohms.

Probably not what you were expecting!
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Old 13th December 2006, 04:56 AM   #20
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Quote:
Originally posted by CBS240
No emitter resistors in a BJT EF could make biasing a bit touchy. Hope you have a good stock of outputs.
Why?
The same idle current flows through both transistors and their common resistor. The same biasing voltage is applied between their bases.

Where's the difference?
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