Would Like to Discuss a Sansui AU-D9

Since I still have issues with my SA-9500II to address, I thought I would get a head start on my newly acquired AU-D9. I did a lot of searches and reading on AK about the D9 and it seems to be highly regarded. I found a lot more about the D11 and wondered what the fuss was about. Having opened up the D9 I see that it is about half of what a D11 is even though the D9 is only rated at 35 watts less in output. Here is a nudie or two of the D9:



The D11 has a total of 8 cans instead of the 4 in the D9 and looks like it would be heavy enough to sink a battleship. Now on to some issues for discussion.

This D9 worked well except that the volume pot was horribly dirty and the selector switch was slightly dirty. I was inside applying the Deoxit treatment when I noticed a few troubling spots on the power amp board. This board is easily accessible and well laid out with the DC offset and bias trim pots labeled and easy to get get at. While peering at this board an area around two resistors and two zener diodes caught my eye. The area around these seemed a bit dark, although not cooked like I have seen other boards. They are symmetrical sides of the left and right amp and the left side seems to have gotten hotter over time than the right. View the photos and see if this looks like normal aging or is it maybe time to replace these diodes. The shot of the bottom also has a box around another spot that looks bad but I think it is just rosin from the soldering that was not cleaned up. Take a look and tell me what you think.





This amp also has a diode bridge like I have never seen before and thought it unique enough to show some photos. Take a look:



I don't want to mess with the zeners if I don't have to but I was worried they might be a harbinger of trouble to come. BTW does anyone have the adjustments page for the D9? I have the SM for the D11 but I think we are dealing with a whole different animal there and doubt that the procedures and bias TPs are the same. I was also curious if anyone knows if the rosewood looking case on these amps is veneered or vinyl; I can't tell for sure. As usual, I am completely open to all and any discussion and comments about this amp. Thanks.

Gary

I doubt the diode is generating the heat. The resistor next to it is probably the culprit. Looks normal to me. Power one up and feel the resistor. Bet it gets warm.

rob

Rob, you are quite correct that the resistors are both warm enough that I can not keep my finger on them for long. Might this be a normal situation or would it be possible that the resistors are aging and need replacing? No other resistor on the board are even slightly warm during modest operation. They are both about the same temperature. I have finished Deoxit procedures and the unit is on right now and sounds very good. I want to retest DC offset again and adjust it and the bias but will not attempt this without the manual. Are there any opinions about this amp out there? Who has one, who has had problems with this amp, who likes it, who hates it? I really know nothing about these and am just trying to get a feeling for what others think and know about them. I guess they are not too common.

My manual arrived from obsinc today and I have done the DC offset and the bias adjust today without blowing anything up this time. This amp has an adjustment that I have never seen mentioned before: an equalizer circuit adjustment. There is an adjustment for 0 volt on VR1 and a 0 volt adjustment on a VR Servo??? What is the purpose of these adjustments?

Also, in keeping with the lack of clarity of Sansui manuals, there is a reference under "remarks" for the original DC volts adjust: "connect point C to point A (gnd) and connect point F to point D (gnd)". I'm unsure if what this is indicating for me is to jumper the two points together while I do my reading; or is it indicating a correction in which test points are supposed to be used. The following attachments have all the info, including a photo of the equalizer board. If anyone could shed some light on this I would appreciate it. Also my question regarding the two hot resistors near the zener diodes remains unclarified. Is this a heat condition that is normal or is it something I should deal with while I have this amp opened up? Thanks.

Sansui's service manual is very clear IMHO.

It clearly states to connect/short point C/F to A/D, measure at B/E & A/D, do the 0V adjustment then remove the temporary short. Steps 1 & 2 are DC offset adjustment with the DC servo disabled. The next 2 steps (3 & 4) are with the DC servo engaged. This procedure makes a lot of sense for any DC servo circuit.

If you are uncomfortable with the heat being generated by the 2 power resistors near the zener diodes, measure the voltage across the resistor. Calculate the power ( Power = [Voltage ^2]/Resistance) and check if it is reasonably lower than the rating of what is installed on the board. You can buy aluminum clad power resistors and mount it on the chassis if you like to cool the board and increase the lifespan of the electrolytic capacitor near it. The amount of heat the zener diode can handle is inversely proportional to the power it is drawing. If the zener is not dissipating that much power then it can be operated at higher temperatures. I don't have the service manual for your amp so I can't comment on how much power/current is going through the zener.

Regards,

Joe

I own one that I bought a few months back which I (mostly) recapped. It is mint. I think the audio quality is excellent. I turned it as loud as I could stand and the clarity of the sound was very impressive....extremely neutral and very clean-sounding....and the 95 wpc really gets your attention!

Thanks Joe, I believe you are correct about the manual. That is how I interpreted it also but with so little experience with these, and having just messed up my SA-9500II by a miscalculation of the hand, I did not want to take a chance. It is the resistors that are getting hot but I understand from another source that this may be quite normal. The circuit board has a slight discoloration but nothing alarming. I'm going to leave it be.

Echowars explained that the adjustments are in the phono section and since I will never us a TT with this amp, I left it alone also.

Zekeman, I have to agree, very clean and uncolored sounding with gobs of power. Thanks to all for the posts.

COuld you tell me how it compares to your AU-7900, AU-717, AU-D11II ?

Im looking for a d9 right now.

Thanks !!

Zekeman said:

I own one that I bought a few months back which I (mostly) recapped. It is mint. I think the audio quality is excellent. I turned it as loud as I could stand and the clarity of the sound was very impressive....extremely neutral and very clean-sounding....and the 95 wpc really gets your attention!

Click to expand...

The D9 is more pure sounding to my ears. The older amps have a bit of coloration, if you will.

After hearing most amps from the 1000A receiver and AU-999 all the way to the AU-D11II I have come to prefer the AU-7900 series (the AU-7700 as well). Tons of connections and a bit more fat-sounding vs the amps from the early '80's. The AU-717 is somewhere in between.

I sold that D9 years ago.