AU-317 replace broken microphone jack chassis problem

Rovalo

New Member
Dear all,

On my Sansui AU-317 (mk I) the mic input is not working properly. I hope you experts can help me to understand the wiring in order replace the jack chassis part. I my attempts so far I got an oscillation sound, so I probably misinterpret the schematic diagram of mic amp circuit board F-2756 and its connection to control amp board F-2752.

Initial problem: very thin sound (with lack of earthing noise) on the mic input, but when I extremely move the mic cable plug in a certain position I get better sound. I removed the jack chassis and tried to clean it, but it fails. I think there is a mechanical cause, so I want to replace the chassis, preferably with XLR.
I'm testing with a balanced mic (stereo jack), I'm not sure if the +/-/GND pin-out matches the AU-317.

I'm refering to the schematic diagram, can you pls help me to understand or advice
1. which of the chassis jack plug contacts is the ring and which the tip, the drawn position of the contacts is confusing, I would assume the tip is the plug contact without the switch;
2. the electrical meaning of connections M (ground?), P (+V?), g (signal ground?) and f (signal?);
3. the function of the switch, does it connect f to ground without jack plug inserted?
4. which of the contacts would correspond to the balanced mic pins +/-/GND?
5. a way to replace the jack chassis with a XLR plug which has no switch function?

Your help is much appreciated!
 
Maybe I need to change the thread title to something like "AU 317 mic circuit board F-2756" but I don't see how, any tips?
 
In the past I have tested the AU-317's mic input with a Mono Mic terminated to a Mono 6.3mm jack plug

1. From the schematic of F-2756 - I would assume the tip of a Mono jack would connect to R01 & 02
2. The +Ve supply to this board is via pin 4 (aka "P"), -Ve supply is via pin 5 (aka "M") - Signal ground is Pin 2/3 (aka "g") & Output is Pin 1 (aka "f")
3. Correct - from the schematic it looks like that with no jack plugged in the output at pin 1 (aka "f") is grounded
4. Not familiar
5. Have never seen this done on any AU-317 (so far)
 
The TRS (stereo) plug you are using is incompatible with the mono input jack on the 317, which is more likely the cause of the problem than there being a mechanical fault with the mic input jack.

4. Mono jack tip contact to XLR Pin 2 (+). Mono jack sleeve contact (GND) to XLR Pin 3 (-). XLR Pin 1 (GND) not connected.
5. XLR Pin 3 would also need to be grounded to chassis. However by replacing the jack you will lose the 'switch to ground' which could result in noise.

First, I would suggest making a small cable with an XLR connector on one end and a mono plug on the other end. The Rane Note for proper pin connections is a useful reference for doing this.

http://www.rane.com/note110.html

This way you can make sure you have everything working without making any modifications which could upset the amplifier's internal grounding system.
 
Both AUD101 and richardpp, thank you very much for your excellent answers, information and advice!

I did not realise that the pinout from the balanced mic converted to a balanced (stereo) jack is incompatible with the AU317 because that input is actually mono...

I will check again on the jack input chassis with the knowledge that it is mono. If it turns out to be OK I will put it back in the 317 and use the recommended conversion cable from mono jack to XLR unbalanced.

When I know more I will reply here to let you know. Thanks again!
 
Fortunately after some time I found back the original jack chassis part and measured it again according to your explanations (mono). It turned out to be ok :thumbsup:.

I put it back in the AU-317 the same way and made the proposed converter cable using a mono jack to XLR. It works perfect that way!! The converter cable is a good solution for me.

Thanks again for your help!
 
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