Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

AGC preamp for audio of a TV set

Status
Not open for further replies.

mhtplsh

Full Member level 3
Joined
Feb 21, 2007
Messages
153
Helped
7
Reputation
14
Reaction score
4
Trophy points
1,298
Activity points
2,197
I want to make agc preamp for audio.
Input will be from satelliete receiver & outputwill go to audio in of TV.
The different channels in satelliete receiver hv different audio levels.
so everytime u hv to set the audio level after changing the channel.
I am thinking that using such preamp will solve the problem.
 

A.Anand Srinivasan

Advanced Member level 5
Joined
Oct 15, 2005
Messages
1,804
Helped
257
Reputation
514
Reaction score
39
Trophy points
1,328
Location
India
Activity points
10,680
Re: agc preamp

such a circuit would be needing variable feedback or controlling which would need a variable resistor or some other component.... since it is in the preamp you have to take care that the noise contribution by this extra component must be very low...
 

mhtplsh

Full Member level 3
Joined
Feb 21, 2007
Messages
153
Helped
7
Reputation
14
Reaction score
4
Trophy points
1,298
Activity points
2,197
Re: agc preamp

I found this circuit on the net. I assembled it but it is noisy. I used 2N5109 as fet.
 

IanP

Advanced Member level 5
Joined
Oct 5, 2004
Messages
7,942
Helped
2,309
Reputation
4,620
Reaction score
531
Trophy points
1,393
Location
West Coast
Activity points
66,459
Re: agc preamp

To switch from channel-to-channel you don't need 50dB gain ..
Most likely a gain of 6db (x 2, max 4 ) will be enough ..
Try to reduce the gain of the opamp stage by decreasing 33kΩ to, say, 1kΩ and, if you can, replace LM358 with a "low noise" amplifier ..
After all, the LM358 is just a general purpose opamp and as a such is rarely used in audio applications ..

Regards,
IanP
 

mhtplsh

Full Member level 3
Joined
Feb 21, 2007
Messages
153
Helped
7
Reputation
14
Reaction score
4
Trophy points
1,298
Activity points
2,197
Re: agc preamp

Yes. I will reduce the gain & change the opamp.
Any other suggestion welcome.
 

A.Anand Srinivasan

Advanced Member level 5
Joined
Oct 15, 2005
Messages
1,804
Helped
257
Reputation
514
Reaction score
39
Trophy points
1,328
Location
India
Activity points
10,680
Re: agc preamp

i think J176 is a low noise FET... so try finding an equivalent one and use.... i think reducing gain will have a lesser curative effect on the noise [that is what i remem learning]:D
 

Status
Not open for further replies.
Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top