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help to find amplifier section input
http://www.diyaudioprojects.com/Forum/viewtopic.php?f=12&t=6879
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Author:  pawlowski4 [ 13 Aug 2020, 09:43 ]
Post subject:  help to find amplifier section input

Hi, i want to disconnect audio (from tuner section) input and connect "my source" to amplifier section of the nordmander 170a.
where can i find an amp in.?

kind regards, Tom

Author:  NviGateSystems [ 01 Sep 2020, 00:44 ]
Post subject:  Re: help to find amplifier section input

I'm not very good at reading schematics but an easier way to get input to the amp stage is by finding out which pin of the volume potentiometer is the input. This input would be the input from the radio.

Depending on how the radio was designed, you may be able to disconnect that input and put a switch on the chassis allowing you to control where the audio source is coming from.

A typical audio pot has three terminals. The outer two are ground and input, and typically (read: not always) the middle pin is the output. To find which one is input, you typically just need to find which one is connected to ground. Once you do, the other outside connector is the input.

On vintage equipment you have to be careful as the traces for the boards can be very brittle and lift easy, I've had to repair a few where I let the iron stay too long.

Author:  Suncalc [ 01 Sep 2020, 21:20 ]
Post subject:  Re: help to find amplifier section input

The input to the audio section of the amplifier is the base pin of Q7. And, as NviGateSystems has said, this is connected to the wiper of VR1 through C43. C43 has an important DC blocking function in this circuit so follow NviGateSystems' instructions and put a selector switch between the VR1 wiper and C43. It looks like VR1 is off board according to the printed circuit diagram.
Attachment:
board.jpg

Hope this helps.

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