AU-D9 integrated amp with faulty phono section

[mosinagant]

I have an AU-D9 integrated amp that sounds great. The phono inputs cause the amp to go into protection mode when I use the turntable. The AU-D9 works great with the other inputs. I assume there is a problem with the preamp section that the turntable runs through. Any ideas on what the problem could be? Any ideas as to the severity of the problem, or the cost of getting it repaired?

 

[ckelly]

Hello mosinagent

I think a possibility is the TT has a preamp built into it. Have you tried the TT on the AUX?

Chris

 

[dr*audio]

Some Sansui integrateds have stability problems. The phono stage could be oscillating. Make sure you have a ground wire connected from the tt to the amp. Try different settings for the input impedance and capacitance, if there are switches for that. try disconnecting the ground on the tt. If none of that helps, the amp probably needs service. I am in cleveland, OH and I can fix it. PM me if interested.

 

[mosinagant]

Do you have a ball-park figure as to the cost of servicing the integrated amp?

 

[ProAc_Fan]

It's probably more cost effective to just buy a seperate phono stage and run that into any of the line level inputs. Odds are a decent stand alone phono stage will sound better than the one in the AU-D9 anyway and then you won't spend any dough to fix the amp.

Mike

 

[jfzea]

I have an AUD11 with the same problem : now I'm using it only with the high level inputs and no TurnTable connected to the phono input, but when I switch to the input phono the same thing : the protection circuit works, but only sometimes.

I know the protection circuit works when detects a certain value of DC for certain time, in this case the protection is for the speakers.

The DC value I think in this case could be generated by the phono preamp (may be a kind of oscillation is the origin as someone said). So it's the stage to work.

In the AUD11 I have identified two cards for this purpose, the two in vertical position - on the right side of the amp. The last one (near to the bottom) marked as the MC (moving coil) preamp. The other card near to the front is the MM amplifier and both are connected.

I think that this is the main cause of the problem because the MC needs a very high gain (the level of the MC is very low) and when you work with very high gain using only transistors and resistors it’s very probable to have inestability problems.

What I'll do this week is to disconnect the supply for this card, I have seen it's only a white connector that comes from the transformer. As I only have MM (moving magnet cartdriges) there is no problem.

Try to test this solution is very simple.

Jorge

 

[sandawa]

i have experienced the same problem on one of my Sansui amps in the past, but the solution was quite simple. i just activated the low frequency filter/subsonic button and it worked. i'm luckier with my amp i guess.

 

[jfzea]

If you want to know, finally I opened the unit and disconnected the supply connectors for the MC amp - the problem continues. So I went to the other vertical card - it is marked as the EQ and servo AMP.

This card is separated in two parts, one for L and the other for the R channels. Near to the the two white connectors coming from the power supply there are two transistors that I think are for adecuate the DC voltage (some kind of regulators).

The fact is : when the problem is present one of these transistors gets really hot and a DC voltage is sent to the amp - and to the the speakers, working in this case the protection circuit of the amp.

So this is the card to review. now I'm searching the diagram so it can be repaired. I have one but it’s not very clear.

 

[mosinagant]

Some Sansui integrateds have stability problems. The phono stage could be oscillating. Make sure you have a ground wire connected from the tt to the amp. Try different settings for the input impedance and capacitance, if there are switches for that. try disconnecting the ground on the tt. If none of that helps, the amp probably needs service. I am in cleveland, OH and I can fix it. PM me if interested.

Hi. The amp still has that issue that is unresolved. Do yu have any idea on what the problem could be, or how much it would cost to fix it/ Do you do electronic repair as career, or a hobby?

 

[mosinagant]

The trouble is that when the phono section worked, it sounded great. I am tempted just to replace everything on the phono cards and then see if it will work.