• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Sansui making crackling noises

WillVT

WillVT

Super Member
The other day, I was listening to an LP through my Sansui AU-7500. When the record ended, I was on the other side of the house and didn't go shut things down. A few minutes later, I heard some kind of static crackling noise coming from the living room. It was coming from the left channel, and was not affected by any change in volume, balance, or input selection.

I checked speaker connections and disconnected the amp and tried another just to make sure it wasn't the speakers. Speakers are fine.

What could be going on here? I have not had a chance to look under the hood, but will this weekend. Anything I should be on the lookout for? I have a multimeter but not a whole lot of knowledge of amp guts.

I had been considering taking the plunge and doing my first recap of this thing before this problem struck. I love this amp, and want to see it back in action.
 
Register to hide this ad
Unaffected by volume suggests the amp driver transistors. It could be bad solder joints (which is something you can inspect) but the old drivers may be going noisy. If you do a search on AK, you'll probably find threads regarding the crackling sound.
 
Thanks. I took the cover off today, and everything looked ok. Actually the crackling is gone. Maybe it only happens after things warm up a bit? I will experiment.

Where are the driver transistors on this thing? I searched around the forum and found folks with similar problems, but answers were so technical, I just kinda glazed over. Is there a "DIY for Dummies" section on AK? I'm not totally electronically illiterate, but most of this stuff is new to me.

Here is a pic of the guts:

Thanks again.

DSCN0092.JPG
 
I suspect the drivers are the four smaller ufo-style transistors way at the bottom of the pic. The bigger ones are the outputs.
 
Alienz said:
I suspect the drivers are the four smaller ufo-style transistors way at the bottom of the pic. The bigger ones are the outputs.
Click to expand...

Thanks, that's what I thought. Are they easy to find/replace? Should I just go ahead and replace them, or is there a way to test them?

Sorry for all the questions. This is my first repair of something like this. I really appreciate all the knowledge folks have around here!

-Will
 
WillVT said:
Thanks, that's what I thought. Are they easy to find/replace? Should I just go ahead and replace them, or is there a way to test them?

Sorry for all the questions. This is my first repair of something like this. I really appreciate all the knowledge folks have around here!

-Will
Click to expand...

I'm still a novice too so be warned! :)
But I'm sure someone more experienced will correct me if I say something stupid.

Has the noise returned yet? The kinda noise problems can be very intermittent.
You can get replacements for those drivers, only problem is they seem to be T0-66 style cases but I'm not sure. These cases not available anymore. I replaced some on a Luxman with TO-220's which needs some creative but not too difficult soldering.
Can you read whats on those transistors?
I dont have have experience with this particular amp but in some i repaired with similar problems it was the differential pair of transistors. In your case I think those would be on the circuitboard right next to board with the drivers and outputs. Those would be easier to replace than the drivers.

Good thing is you can unscrew those drivers and test them out of circuit, no need to unsolder.
 
Well it seemed better for a while today, but about halfway through the second LP, the left channel suddenly started crackling again. Maybe temp related?

What capacitators should be checked?

I am going to get the cover off again soon and get the numbers off those driver transistors.
 
If this problem oinly occurs when using your TT and the amp's phono section, I'd suggest a little more testing before replacing components. It may be something as simple as a bad cartridge, loose TT wire or something as mundane. You could eliminate the TT and phono section by using another source played through the "Aux" input of the amp.

Also, if you are deeply in love with the AU-7500, why not clean it up a bit and Deoxit the controls as long as you have the cover off? She'll like that.
 
The Deoxit might just solve the crackling. If anyone has a picture of a "Flying Saucer" transistor. I would like to see what they look like. After looking at nothing but receivers the lack of complexity of an integrated amp looks refreshing to me. That amp looks easy to get around compared to the Model Eight Deluxe I have been poking around in recently. Good luck with the Deoxit; I hope it works for you.
 
My sui 9500 just got back from being repaired with the same exact symptoms you described. My tech replaced what appears to be 2 tiny resistors; TR704 and TR706. I've been playing it for almost a week now and the crackling is gone.
 
I cant remember off hand which ones in particular, but in the phono and pre-amp section there are a few problematic transistors, I had the same thing with my AU-9500.
I would try and isolate the pre-amp so you can eliminate the power-amp section, and narrow it down from there......
Took me all of 20 mins to track the offending transistors down and replace them, not a big job if you have the experience....
Otherwise a competent tech could do it easily enough....
 
Good points. You should always check if the problems occur on all inputs. If its indeed only on the phono that will narrow it down.
 
Thanks for all the responses. I will hopefully have some time to check things out again this weekend.

Do I need more than a simple multi-meter to test things like resistors?
 
WillVT said:
Thanks for all the responses. I will hopefully have some time to check things out again this weekend.

Do I need more than a simple multi-meter to test things like resistors?
Click to expand...

Resistors, no; transistors & capacitors, probably...

As a novice myself, one thing I would also do is visually inspect the solder joints on the other side of the circuit boards, reflow any that look cracked.
 
WillVT said:
Well it seemed better for a while today, but about halfway through the second LP, the left channel suddenly started crackling again. Maybe temp related?

What capacitators should be checked?

I am going to get the cover off again soon and get the numbers off those driver transistors.
Click to expand...


Replace orange colored capacitors on my friends. Forgot which one though. Check the caps for leakage and bulging. Better yet replace them all.
 
Sorry it's been a while, but I finally got back to looking at this problem. I listened to almost a full LP before the crackling started. I tried taking out the pre/main jumpers and plugged the pre out into my HT receiver. Crackling was still there in the left channel. So, am I right to assume the trouble is before the power amp section, and somewhere in the pre amp?
I can say this theoretically, but I don't know what I'm doing or what to look at when I take the cover off.
 
You must log in or register to reply here.
Back
Top Bottom