Sansui 661 speaker hiss and unit buzzing

[bberkom]

I just picked up a perfect-looking Sansui 661 for a few bucks on craigslist. I cleaned it and deoxed all of the controls, but it hardly needed it because it was so clean. I also adjusted the DC offset and bias voltages.

However, there is a persistent hiss in the speakers when the unit is powered on. It is independent of source and it is present even at zero volume. Once I am listening to music, It isn't that noticeable, but it still bothers me.

The unit also buzzes when powered on. I don't mean the speakers buzz, I mean the receiver itself emits a slight buzzing sound. It doesn't always do it, but seems to buzz once it warms up. It seems to be coming from the power supply area, and a power supply issue seems like it could be consistent with the hiss I am getting in the speakers.

Any advice on what I should troubleshoot? Little thing sounds great otherwise.

 

[Hyperion]

For the buzz sound, you could check that the transformer mounting screws (and through bolts), are nipped up tight - don't over-tighten, just check they are reasonably tight. As for the hiss sound, this is either transistors in the first stages of the power amp, or in the PSU, this is assumed as you say it happens at zero volume. I have also heard of people 'recapping' and making a dramatic difference to perceived noise, but this is unusual in my experience.

 

[bberkom]

For the buzz sound, you could check that the transformer mounting screws (and through bolts), are nipped up tight - don't over-tighten, just check they are reasonably tight. As for the hiss sound, this is either transistors in the first stages of the power amp, or in the PSU, this is assumed as you say it happens at zero volume. I have also heard of people 'recapping' and making a dramatic difference to perceived noise, but this is unusual in my experience.

Thanks for the reply. I will check the transformer screws, as that is something I hadn't looked at yet. I suspected it might be transistors causing the hiss. The hiss is present at zero volume, but when I turn the volume up, the hiss increases as well. Could it be coming from multiple places? Are the transistors used in the 661 or replacements readily available? Thanks.

 

[Hyperion]

Could it be coming from multiple places?

Yes it could, obviously if you get even more hiss when you turn the volume up a bit, that probably indicates a second source.

Are the transistors used in the 661 or replacements readily available? Thanks.

Possibly not the originals, but nice low noise replacements are definitely still available.

 

[bberkom]

Yes it could, obviously if you get even more hiss when you turn the volume up a bit, that probably indicates a second source.


Possibly not the originals, but nice low noise replacements are definitely still available.

I'll poke around again tonight and see if I can find anything that looks suspicious. I'll probably end up taking it to a tech to get serviced. I paid almost nothing for it, and it looks pristine inside and out. Great sounding little receiver.

 

[N8Nagel]

If you can find the thread there is a list of known noisy transistors, definitely had some 2SC458s go hissy on me but there are other culprits as well.

 

[bberkom]

If you can find the thread there is a list of known noisy transistors, definitely had some 2SC458s go hissy on me but there are other culprits as well.

I will take a look to see if there are any commonly noisy transistors in the 661. I didn't see any 2SC458's on the schematics in the service manual, but I'll have a real look when I get home and can open it up. Thanks for the advice.

 

[bberkom]

Yes it could, obviously if you get even more hiss when you turn the volume up a bit, that probably indicates a second source.
Possibly not the originals, but nice low noise replacements are definitely still available.

If you can find the thread there is a list of known noisy transistors, definitely had some 2SC458s go hissy on me but there are other culprits as well.

So I finally got a chance to get into this unit, and here is what I am seeing. See photos. There is some corrosion on the transistors on the driver boards, and the photo shows the worst one. Definitely seem like good candidates for replacement. The other photos shows some caps on the Power Supply board that could use replacing. Should I go ahead and replace the four large output transistors as well as long as I am replacing all other transistors and the bad caps on these boards? The four output transistors are 2SC1111's in the unit, but the service manual indicates they should be 2SC1030's. Wondering which of these I should try to match. Thanks for your help.

 

[bberkom]

So I decided to make this 661 a project and do a recap on it. I have never done a project this big, but I figured this would be a good a place as any to start. I replaced all of the electrolytic capacitors and transistors on the driver board so far, and there was a big improvement in sound quality, although the higher noise floor remained. I then replaced all of the electrolytics on the power supply board, and I plan on doing the transistors as well. I know all of this is probably not necessary, but it's good practice for me as long as I am at it.

During a sitting, I replaced a handful of caps on the Power Supply board, C3 C4 C5 C6 C7 and C8. After I fired it back up (on the dim bulb tester of course), there was a slight buzz in both channels. The buzz is independent of volume/tone/balance/source and occurs in both channels even at zero volume. I have to be pretty close to my speakers to hear it, but it's enough to bother me, and it was not something I noted before replacing caps C3-C8. I have inspected all solder connections and the surrounding, and all look good. I had also replaced C2, C16 and C17 before I replaced these, and there was no hum. I continued and replaced all the caps, and the humm remains.

I am assuming that this new humm is coming from one of the caps C3-C8 that I replaced, but they all look fine with no lifted traces, etc. I double-checked polarity on all. Is it possible this humm could be coming from another place in the receiver or that it may have been present all along and I can just now hear it since I replaced some old caps? I am planning to replace the handful of transistors on the PS as well, but not sure if this will help. I also adjusted the DC offset and Bias on both channels, but there was no difference in the hum. I moved and I think bumped a couple of wires when I was soldering, but I didn't fracture the rubber casing on any.

Any help is appreciated.

 

[Oldsansui441]

Hi, well done for taking on your project, this is a nice series of receivers, l have a little 441 l restored. In relation to your buzz/hum if it is in both channels it would normally point toward a bad cap on the power supply, a poor earth or because you may have the bottom cover off (not sure if you do?).

Since you are in there l would replace all transistors while you are at it, not including the output transistors, these will be fine, prob a good idea to remove these though and renew the thermal paste.
Don't worry about the difference between the outputs as fitted and those listed in the service manual, l recently repaired a Kenwood KR-5200 and it uses either of the exact two numbers you mentioned.

FWIW those little sky blue Sanyo caps that you will find are known to cause problems also.

Hope you find the problem and let us know how you get on.

 

[bberkom]

Hi, well done for taking on your project, this is a nice series of receivers, l have a little 441 l restored. In relation to your buzz/hum if it is in both channels it would normally point toward a bad cap on the power supply, a poor earth or because you may have the bottom cover off (not sure if you do?).

Since you are in there l would replace all transistors while you are at it, not including the output transistors, these will be fine, prob a good idea to remove these though and renew the thermal paste.
Don't worry about the difference between the outputs as fitted and those listed in the service manual, l recently repaired a Kenwood KR-5200 and it uses either of the exact two numbers you mentioned.

FWIW those little sky blue Sanyo caps that you will find are known to cause problems also.

Hope you find the problem and let us know how you get on.

Thanks for the pointers. I've replaced all of the electrolytics on the power supply and there is still a humm. I'm going to finish up the transistors on the PS and see how the humm responds. If still there I may pull some of the new caps and see if I maybe overheated one when soldering. That's a possibility I'm guessing.

 

[Hyperion]

Have a look around for 881 threads where hum was cured - there is a screw that secures a PCB in the PSU ? - it works loose, if you clean the PCB and the metalwork, and tighten the screw it fixes it, something like that - good luck.

 

[bberkom]

Have a look around for 881 threads where hum was cured - there is a screw that secures a PCB in the PSU ? - it works loose, if you clean the PCB and the metalwork, and tighten the screw it fixes it, something like that - good luck.

That is great info, and I found the thread you are referencing. I thought it might be something like this with a ground since I have been handling and flipping the unit a lot while working. I already made sure a couple of the screws were fully tightened on the PS board, but I will make sure I didn't miss any and spend some more time cleaning those connections.

 

[bberkom]

Have a look around for 881 threads where hum was cured - there is a screw that secures a PCB in the PSU ? - it works loose, if you clean the PCB and the metalwork, and tighten the screw it fixes it, something like that - good luck.

You may be able to help with this also. I am placing an order for the T01-T06 transistors on the preamp board, and I was going to use KSC1845FTA's to replace the six 2sc1313's. However Mouser is out of stock on the KSC1845FTA for a bit. Is there another suitable replacement I can use?

 

[Hyperion]

KSC1815YTA - while not absolutely ideal, will be fine.

http://www.mouser.co.uk/ProductDetail/Fairchild-Semiconductor/KSC1815YTA/?qs=sGAEpiMZZMshyDBzk1/Wi8oN7VHZ91Ok9NiSl87vuMg=

 

[bberkom]

KSC1815YTA - while not absolutely ideal, will be fine.

http://www.mouser.co.uk/ProductDetail/Fairchild-Semiconductor/KSC1815YTA/?qs=sGAEpiMZZMshyDBzk1/Wi8oN7VHZ91Ok9NiSl87vuMg=

Thanks again. Looking at the specs, is the difference just in the maximum voltages for emitter and collector of the transistor? Just wanting to learn about what makes this a suitable replacement versus the 1845.

 

[Hyperion]

The main differences are firstly the maximum gain (hfe) lower with the '1815. And secondly the maximum collector current (Ic) higher with the '1815 - the variants of '1845 or '1815 we can get now are the lower gain ranges so the first can't really be an issue, and the second doesn't matter too much in this case.

I have some '1815's that I use mainly in PSU locations where a bit more allowable collector current is ok, I think I am right in saying that the '1815's are a direct replacement for the 2SC1313 anyway.

The '1845 and '1815 are both classed as low noise amplifier transistors, and as we can get them new - this is a huge advantage over apparently 'ok' ebay purchases.

 

[bberkom]

The main differences are firstly the maximum gain (hfe) lower with the '1815. And secondly the maximum collector current (Ic) higher with the '1815 - the variants of '1845 or '1815 we can get now are the lower gain ranges so the first can't really be an issue, and the second doesn't matter too much in this case.

I have some '1815's that I use mainly in PSU locations where a bit more allowable collector current is ok, I think I am right in saying that the '1815's are a direct replacement for the 2SC1313 anyway.

Excellent. Thanks for the expertise. I'll go with the '1815's then.

 

[bberkom]

Well I have recapped and changed transistors in the preamp/tone board, and the receiver is sounding really good. So much tighter and punchier in the low end. Sounds really great with my Polk Monitor 70's and has plenty of power for them. Phono section also sounds a lot better. There were some hairy-looking caps on the preamp board.

I am still having one issue with background noise. The noise floor is almost zero when the volume is at zero. However, when I turn up the volume, there is a background hiss that increases with volume. BUT when the volume knob approaches 12-o-clock, the hiss decreases to almost nothing, but then when I go much past 12-o-clock, it increases again. I have already deoxed the pots a couple of times, and I plan to again, but what else could cause a background noise that increases, drops off at a certain volume, then comes back? I haven't yet pulled and renewed the thermal paste of the output transistors, so I will also try that. Any other advice is appreciated. This is a symptom that has been happening since before I even started working on it, and I figured it would go away when I replaced the transistors on the preamp board, but no dice.

 

[Oldsansui441]

Great to hear it is sounding really good, maybe time for some low noise transistor replacements on the main amp also. The output thermal paste won't alter your noise floor it is just a maintenance measure as the old paste dries out an doesn't transfer heat as well as it once did.
The noise floor altering with the volume knob at around 12 then dropping again l have found to be the case on many units, this is normal as long as it is a very low noise overall. Your speakers aren't highly efficient at 90db so noise floor should be fairly low.