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Old 21st April 2005, 04:20 PM   #1
aht is offline aht  Thailand
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Question How to make constant gain amplifier circuit

I want to design constant gain amplifier circuit from standard transistor amplifier and not use negative feedback.

This amplifier must be run in class-ab is it posible ?

Constant gain amplifier can explain so easy such as ... 20log Vo/Vi = 30dB at every input voltage & every frequency & every speaker.

Can it's use electronic circuit or digital circuit for control gain ?

notice : this constant gain amplifier circuit will be insert between output of amplifier & feedback input stage

Regard
AHT
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Old 21st April 2005, 06:41 PM   #2
ilimzn is offline ilimzn  Croatia
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It is practically impossible to build an amplifier of almost any kind without some sort of feedback - at the very least, local feedback. If you are asking for an amplifier run in class AB without global feedback, this is actually quite simple. There are several mentioned on this site.
Electonic gain control should be possible though it may get complicated.
Now why would you want to insert an amplifier between an output of another amplifier and it's feedback node is something I don't understand - the net result will be an amp with attenuation and not amplification (-30dB attenuation)?
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Old 21st April 2005, 11:37 PM   #3
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Another disadvantage is the distortion of the amplifying stage between output and feedback input also shows at the output of the amp.
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Old 22nd April 2005, 02:50 AM   #4
aht is offline aht  Thailand
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This circuit no need to insert between an output of another amplifier and it's feedback node. (that is my little idea )

After I serched data about "Constant Gain" I found "Linear Amplifier" for radio tranceiver. Do I use this circuit topolohy?

http://www.hindawi.com/journals/mpe/...X04402038.html

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AHT
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Old 22nd April 2005, 10:58 AM   #5
ilimzn is offline ilimzn  Croatia
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If you could describe what you are actually trying to do (and not how - we will get to that later) we may be able to help you better...
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Old 22nd April 2005, 11:37 AM   #6
Mr Evil is offline Mr Evil  United Kingdom
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Default Re: How to make constant gain amplifier circuit

Quote:
Originally posted by aht
...at every input voltage...
By this I take it you mean high linearity, i.e. low distortion?


Quote:
Originally posted by aht
...& every frequency...
You can't have constant gain at every frequency. Frequency response can extend down to DC, but it can't extend up to infinity; there must be a limit somewhere. If you need extremely wide bandwidth then it will mean compromises in other areas, such as reduced linearity or gain.

Quote:
Originally posted by aht
...& every speaker.
Insensitivity to load, I take it this means. That's not too hard. Just keep the output impedance as low as possible and pay careful attention to stability.


You should note that all of these characteristics will be improved by using negative feedback.
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Old 23rd April 2005, 03:30 AM   #7
aht is offline aht  Thailand
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Talking Excute me

1.Every frequency = 20 - 20000Hz
2.Every input voltage = not more than 2.2V (will be satulated)
3.Every speaker = 4 & 8 Ohms impedance from really work

Sory for my bad English

Regard
AHT
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Old 23rd April 2005, 02:59 PM   #8
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Ummm...

Are you trying to build a volume control, an amplifier or address a real world implementation of something you are studying like this:

"the stabilization problem of the class of continuous-time linear stochastic hybrid systems with Wiener process. The "H-inf"state feedback stabilization problem is treated."



(from the paper you mentioned).

This is the question you need to address before anyone has any idea what you are asking about. Ok?

FYI, if it pertains to the quote above, I have no clue at this point what the heck they are yammering about!

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PS. "Linear Amplifier" for "transciever" usually means an RF device and not suitable for audio frequencies regardless.
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