Sansui AU-505 Rebuild Questions

[Yitz]

hey guys,


I've got an old Sansui AU-505 that was my grandfather's.
Audiologically speaking, it's not sounding so hot.
One channel crackles (right), it seems to be fuzzy until I crank it and then it "connects" better but it is generally sounding a bit distorted on the top and bottom end in BOTH channels.
It does get good and loud. It's just not "clean" at any volume level.

My first thought is that maybe I need a Marantz 1060, but then I had another thought.

Maybe I can rebuild this? Especially for less than a Marantz maybe?

I found this excellent thread:
http://audiokarma.org/forums/index.php?threads/sansui-au-505-rebuild.598808/

I have a few questions:
- Should I do this rebuild myself?
- If not, how much does a rebuild run?
- Should I use parts of identical values? (thinking from DigiKey maybe?)
- Should I upgrade any parts while I'm in there? (Bigger caps, higher quality resistors? What brands should I use? I'm not against using quality.)
- WHAT exactly should I be replacing? Is there a guide I should follow?
- I will clean or replace the pots per your advice.

Qualifiers:
I can solder. I've built my own guitar pedals before, though it's been a few years--so I AM familiar with
DC circuits and such to a small degree.
I've popped the hood off on this and had a look-see before. I'm only afraid of zapping myself off the bigger caps, or of destroying it, since it was Grandpa's.

Thoughts?

 

[pete_mac]

First things first... clean every switch and potentiometer carefully with a decent lubricating contact cleaner or Deoxit. This may well rectify the issue.

 

[stereofun]

As Pete_mac says ! This will give you a much better "state of the amplifier" to then proceed from, if needed. If you decide for a rebuild, see below.

I have a few questions:
- Should I do this rebuild myself?
Why not ? - its a skill set that you might as well invest in, if you enjoy this hobby. The 505 is a very easy amp and one of the best sounding within its class.

- If not, how much does a rebuild run?
Qrxrestore.com have quite a bit of expertise in those amps - check their site / call for a quote.

- Should I use parts of identical values? (thinking from DigiKey maybe?)
Yes - Digikey and Mouser are good suppliers and identical values are the goal except for upgrades.

- Should I upgrade any parts while I'm in there? (Bigger caps, higher quality resistors? What brands should I use? I'm not against using quality.)
Yes - the supply cap and two output caps can be uprated to 3300/4700/5600...along those lines.
- WHAT exactly should I be replacing? Is there a guide I should follow?
There aren't any clear answer since you can go from a basic recap to a full restoration, which includes signal transistors, trimmer pots, and film replacements in the signal line. You can also do a recap first - get the soldering skills sharpened, then listen and if there are popping or high levels of background hiss or "white noise" then do a second act, replacing the signal transistors.

There might be "cap list" available. But because of revisions, it is always recommended to make you own list. This amp only has 4 boards. One way is to download the service manual at hifiengine.com (sign up for free account) then board by board make a list of the EC's (electrolytic caps) - first based on the service manual, then you check actual values on the boards to complete the list. From that point on you write a second column with the replacements / partnumber / vendor
- I will clean or replace the pots per your advice.
It's good practice to replace trimmer pots. I can't speak for the 505 in particular, but there are amps in which if the viper looses contact with its carbon trace (say you move it after 48 years) - then this will cause full bias aka rapid heating of the output devices and likely thermal breakdown.

Qualifiers:
I can solder. I've built my own guitar pedals before, though it's been a few years--so I AM familiar with
DC circuits and such to a small degree.
I've popped the hood off on this and had a look-see before. I'm only afraid of zapping myself off the bigger caps, or of destroying it, since it was Grandpa's.

 

[smurfer77]

Yes, you can do this amp yourself .

Give her a good switch cleaning, as others have suggested. Then I would next try to narrow down the problem to pre-amp vs main amp and go from there. Unfortunately the 505 doesn't have preout/main-in if I recall correctly, so you may have to get a bit inventive. The wires that carry signal into the main amp are easy to find so you can desolder those wires so you can, carefully, inject (volume controlled) source directly to the main amp, bypassing the preamp and see what happens to the sound. Or if you have a DVM, very carefully (it's oh so easy to short two legs of a transistor) probe voltages around the transistors on the main amp board and report back.

Take care. Safety first.

 

[Yitz]

thanks guys!
Smurfer, your thread really is the inspiration to all this--so thank you for that!
I'm not sure I have the skill to sort out a pre-vs-main kind of issue, but I can start there. I do have a voltmeter handy too.

Regarding pot and switch cleaning: I've got some electrical contact cleaner that I've used before, but it seems like the switches and pots are fairly sealed up as I recall-getting cleaner in there was tough.
Any tricks or advice there? Also what tend to be the biggest culprits--or should I just blast them all out and clean everything? I remember doing it a few years ago and I'm not sure it helped a ton--maybe a bit.
thanks for the help so far! This might be a fun project while the weather still sucks.

 

[Hipocrates]

Regarding pot and switch cleaning: I've got some electrical contact cleaner that I've used before

http://audiokarma.org/forums/index.php?threads/the-idiots-guide-to-using-deoxit-revisited.207005/

The kind of cleaner that you have matters, if you have access to DeOxit usually is adviced Faderlube for pots and D5 for switches.

 

[smurfer77]

thanks guys!
Smurfer, your thread really is the inspiration to all this--so thank you for that!
I'm not sure I have the skill to sort out a pre-vs-main kind of issue, but I can start there. I do have a voltmeter handy too.

Regarding pot and switch cleaning: I've got some electrical contact cleaner that I've used before, but it seems like the switches and pots are fairly sealed up as I recall-getting cleaner in there was tough.
Any tricks or advice there? Also what tend to be the biggest culprits--or should I just blast them all out and clean everything? I remember doing it a few years ago and I'm not sure it helped a ton--maybe a bit.
thanks for the help so far! This might be a fun project while the weather still sucks.

Based on your original comments I suspect you have a faulty transistor somewhere along the way. But dirty switches and pots can cause (some) of the symptoms you described. To determine if a particular switch/pot is the culprit, play some music and fiddle the switch/pots, paying attention to if any make changes to the sound as you flip back and forth.

 

[Yitz]

Hey Smurfer,

I will definitely try the switches/pots diagnosis tricks probably tomorrow.
In your thread I noted that you had pulled about a dozen and a half such transistors... are there any I should start with or just replace the whole smash?
Along with that question, these caps have got to be very old--I've owned this unit the longside of 10-12 years and so it's minimally been 15-20 since the caps were swapped--if they were ever swapped at all.
Should I just plan on swapping out what you swapped out? I've got the manual/schematic and I can identify the various parts I think.

 

[smurfer77]

Hey Smurfer,

I will definitely try the switches/pots diagnosis tricks probably tomorrow.
In your thread I noted that you had pulled about a dozen and a half such transistors... are there any I should start with or just replace the whole smash?
Along with that question, these caps have got to be very old--I've owned this unit the longside of 10-12 years and so it's minimally been 15-20 since the caps were swapped--if they were ever swapped at all.
Should I just plan on swapping out what you swapped out? I've got the manual/schematic and I can identify the various parts I think.

Anything that looks like an M&M/UFO... those tend to go noisy. I am assuming you don't have a scope... otherwise it would be possible to following the signal path and see where the distortion comes in.

 

[Yitz]

just wanted to update you all, since you've been so helpful!
I tracked down the culprit...the SOURCE. Turns out where my audio was coming from is very much a problem...so we'll start there and move down the chain!
I think a recap (After 40 years?) is probably in the works but I won't fix things till they break.
thank you all again!