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Old 3rd August 2011, 11:59 AM   #1
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Lightbulb Simple Symetrical Amplifier

Symetrical amplifier for those who likes "keep it simple" designs above all. It works without any frequency compensation.


SSA BIGBT HP final product as a result of development in this thread here.
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Old 3rd August 2011, 12:34 PM   #2
AndrewT is offline AndrewT  Scotland
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Is that schematic correct?
I can't understand the function of the 1kVR
Are those 15V Zeners?
What is 107 cap? Do any manufacturers mark 10uF caps as 107?
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Old 3rd August 2011, 12:51 PM   #3
AKSA is offline AKSA  Australia
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Very clever circuit; current driven front end with current feedback, most ingenious...

Where did you find it, or is it original?

The zeners are a voltage supply for T1/T2 which act as voltage driven CCSs. The current they create is passed via cascode transistors BF471/472 and 1K resistors to rail to control the gates of the common source output devices.

Voltage feedback from the outputs is passed via direct coupled 1K/100R gain set to modify the current drive to ensure linearity.

Circuit would be very fast but I think the 1K/107 cap is a form of compensation....

Only down side is common source outputs. They tend to complain with reactive loads, and quiescent can be erratic.

Neat!

Hugh
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Old 3rd August 2011, 01:32 PM   #4
juma is offline juma  Germany
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Hi Andrej, interesting circuit (as always)

Maybe it will be easier to comprehend when drawn this way:
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Old 3rd August 2011, 01:38 PM   #5
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Thanks Hugh, it is purely my idea.

I like to play with circuits combinations and copying others simply not pleasures my intellect.

Of course any part of the circuit can be upgraded, for instance 1k resistors from +/- 15V can be exchanged with CS, ...

Mosfets can also act like drivers, just simply add EF BJT's for an output stage but than is not that simple amp anymore.
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Old 3rd August 2011, 01:48 PM   #6
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Quote:
Originally Posted by juma View Post
Hi Andrej, interesting circuit (as always)

Maybe it will be easier to comprehend when drawn this way:
Thanks juma

Well I just barely made this amp in p2p in the air, powered it up and plays music very, very good. What I noticed compared to other amps done is that is amazingly quiet. It doesn't have any noise noticable 10 mm from tweeter cone. Maybe if someone sym this circuit, some interesting data would come out. I know it won't be the best regarding output impedance, THD, IMD, but noise floor, frequency response and phase shift would be very good.
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Old 3rd August 2011, 01:58 PM   #7
MarianB is offline MarianB  Romania
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Very interesting indeed, but most of all very simple and quick to built, good job.

I was looking for a simple low power and not very expensive schematic to built an small amp and i think i have just found it, many thanks @Lazy Cat. I presume the fets can be many tipes, nut just the ones in youre desighn, as long as they present similar specifications, all should be good wright?
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Old 3rd August 2011, 02:01 PM   #8
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Quote:
Originally Posted by AKSA View Post
Circuit would be very fast but I think the 1K/107 cap is a form of compensation....
I think not, all the caps here just filter out the ripple from DC potentials.

1k multi-turn trimmer is there for BIAS adjustment of the outputs.

All in all very simple symetrical design and I agree, it can be tuned-up to perfection.
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Old 3rd August 2011, 02:05 PM   #9
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Quote:
Originally Posted by AndrewT View Post
Is that schematic correct?
I can't understand the function of the 1kVR
Are those 15V Zeners?
What is 107 cap? Do any manufacturers mark 10uF caps as 107?
Sometimes there is not enough time to write down 100 uF/16 V and so on ...

Hand made sch does have its charm
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Old 3rd August 2011, 02:06 PM   #10
MarianB is offline MarianB  Romania
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Correct me if i'm wrong but i think we are not always looking for perfection when building an amp, sometimes we need a simple low cost low power amp and this one looks just fine i think
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