• 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 A-40 distorted right channel.

W

wschnitz

New Member
Hi guys, picked up this A-40 for fairly cheap on craigslist for a desk setup for my PC, and eventually use it for a shop amp, but I noticed some pretty bad distortion as I get over Volume setting 2 on the amp.

Im running Infinity Reference One's I also picked up off craigslist for really cheap, the reference ones seem fine, they were reconed and foamed with nice graphite coated cones or whatever and when I switch their channels the distortion flips so I am very certain its not the speakers.

Upon inspection of my amp I noticed the ceramic coffin style metal wire resistors on one side have kind of exploded out the top, and looks like it was worse at one time and a previous owner cleaned it up. I am going to pick up a multimeter tomorrow to test the output transistor wattage but would this be an obvious cause of the distortion?

Amp manual: https://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Sansui-A40-Service-Manual.pdf

Resistor pic:
Untitled by William Snitselaar, on Flickr

If this ends up being the cause, can i replace them with nicer metal film resistors like Vishay's of the same resistance and wattage?

I may end up just recapping most of the thing since It seems like the previous owner obviously lied about it being recapped sometime in its life, I'm not complaining it was cheap.

Thanks for any help or direction to help.
 
Last edited:
Register to hide this ad
Looks like cement overflow when the resistor was manufactured. Does measure OK?

Craig
 
I figured it was an expansion from overheating because of the residue on the heat sink above it, but I will find out for sure tomorrow when my friend brings his digital multimeter.

Im at school so all my tools n **** is 2400 miles away makes testing hard.
 
Last edited:
wschnitz said:
I figured it was an expansion from overheating because of the residue on the heat sink above it, but I will find out for sure tomorrow when my friend brings his digital multimeter.

Im at school so all my tools n **** is 2400 miles away makes testing hard.
Click to expand...

There is nothing inside resistors which can expand and overflow if overheated.

As @llwhtt mentioned, it's most likely a result of the manufacturing process. If it looks like it has been cleaned up previously, there's a chance that someone has inadvertantly placed some heatsink thermal compound on the resistor, although it is unlikely.
 
wschnitz said:
If this ends up being the cause, can i replace them with nicer metal film resistors like Vishay's of the same resistance and wattage?
Click to expand...
You can replace them with nicer resistors, but not metal film, they have to be high wattage 'cement type' resistors, or a suitable alternative. (such as Mills MRA05 series resistors, but these would be overkill for this modest amplifier).
 
Last edited:
Hyperion said:
You can replace them with nicer resistors, but not metal film, they have to be high wattage 'cement type' resistors, or a suitable alternative. (such as Mills MRA05 series resistors, but these would be overkill for this modest amplifier).
Click to expand...
You are talking like these right?
https://www.mouser.com/ProductDetail/Vishay-Mills/MRA-05R3300FE12?qs=IV0Ba5T5nsjruUSQFAEFjA==
otherwise i assume identical coffins like these are fine:
https://www.newark.com/vishay/cp0005r3300je14/wirewound-resistor-r33-5-axial/dp/69P4707

I have a strong feeling its the caps now after watching some videos on sansui repairs, Im not huge into electronics but I assume I would be alright to replace the 42V main caps with 50V, iirc being above is ok, but below is not.
 
If I'm lucky its just a really ugly resistor some factory worker put in but still works fine, otherwise ill grab those or the nicer vishay ones, and pop them in, may as well buy like 10 and replace all of them in the system.

Ill know for sure in a few hours, I also picked up an analog oscilloscope from a surplus sale for $20 and it works fine according to the calibration pole on front so I can use that to test the output's and make sure they are not clipped.
 
So friendo forgot his Multimeter, andI forgot to stop at a store to pick up something 8ohm as a dummy load for using osci, but I still popped it open to check for issues and noticed the bottom of the PCB had a lot of crud on it.

After cleaning it all off with some 90% iso the distortion is now inaudible till at least 4 on the amp.

It also appears as if someone has resoldered a lot of the components on the bottom near the output, most of which were covered in the crud so I suspect they maybe used some flux and didnt clean it after. Added new thermal compound to the transistors though I doubt they really needed it.

Probably still going to recap it as practice for the 'real' system I grab for living room when I get my own apartment after graduating. Maybe an AU717/919 and some nicer more living room appropriate infinitys.
 
You must log in or register to reply here.
Back
Top Bottom