Help! - noise problem on vintage Pioneer receiver

[street legal]

A couple of months ago I bought an old Pioneer SX-1010 receiver off of Ebay.
The unit is super-clean & everything was working perfectly. Over the past 2 weeks or so however, I've been getting a fairly loud, erratic, static-like sound coming out of the left speaker ONLY when I power the receiver up. It usually lasts for about 15-30 seconds, & then peters out to nothing, & everything is fine. All functions work perfectly & there is nothing wrong with the sound.

Now here's the weird part: As I said, this crackling noise only comes out of the left speaker, & if I turn the balance control all the way to the right, I still get the static sound coming out of the left speaker. Also, if I turn the volume up while it is producing this noise, it doesn't get any worse. In fact, if I turn the volume all the way down AND turn the balance control all the way to the right, I still get the crackling sound coming out of the left speaker!

I've cleaned both the volume & balance controls very thoroughly with contact cleaner, but it hasn't improved the problem at all.

Any ideas on what the problem may be?

[tommy-thewho]

Deoxit is about the only suggestion I can come up with. Sounds like a dirty volume or balance knob. Look for Caig Deoxit a lot of the other stuff isn't as good.

Can't be anything serious since it goes away.

[Doug Sclar]

A couple of months ago I bought an old Pioneer SX-1010 receiver off of Ebay.
The unit is super-clean & everything was working perfectly. Over the past 2 weeks or so however, I've been getting a fairly loud, erratic, static-like sound coming out of the left speaker ONLY when I power the receiver up. It usually lasts for about 15-30 seconds, & then peters out to nothing, & everything is fine. All functions work perfectly & there is nothing wrong with the sound.

Now here's the weird part: As I said, this crackling noise only comes out of the left speaker, & if I turn the balance control all the way to the right, I still get the static sound coming out of the left speaker. Also, if I turn the volume up while it is producing this noise, it doesn't get any worse. In fact, if I turn the volume all the way down AND turn the balance control all the way to the right, I still get the crackling sound coming out of the left speaker!

I've cleaned both the volume & balance controls very thoroughly with contact cleaner, but it hasn't improved the problem at all.

Any ideas on what the problem may be?

Well it sounds like it's in the left amplifier, which is after the volume and balance controls. As a result it's not at all weird that the volume and balance controls don't affect it.

If it only lasts for a 15 seconds, and all sounds fine after, it may be more trouble than it's worth to hunt it down. It could be a lot of things.

[Doug Sclar]

Deoxit is about the only suggestion I can come up with. Sounds like a dirty volume or balance knob. Look for Caig Deoxit a lot of the other stuff isn't as good.

Can't be anything serious since it goes away.

Doubt that will do anything since it seems to be in the amplifer section, which is after the controls. If it was a dirty control, he'd probably hear it when he adjusted the controls. If that was the case, cleaning the controls would definitely be in order.

My guess is a leaky capacitor, but it could be a lot of things.

[street legal]

Thanks, guys. Another thing that I forgot to mention is that I am fairly positive at this point that it only exhibits this problem when it is turned on "cold". In other words, if I turn off my system & then turn it on again, say within an hour or so, it doesn't make the noise. It only seems to do it when it is turned on after not having been used for at least several hours.

Honestly, it's not "that" big of a problem, & I can live with it as long as it doesn't get a whole hell of a lot worse. My only real concern is that it may damage my speakers. It is not a pleasant sound, & sometimes gets fairly loud.
Turning down the volume temporarily does not alleviate the problem either. There's no way around it.

[street legal]

If it was a dirty control, he'd probably hear it when he adjusted the controls. If that was the case, cleaning the controls would definitely be in order.



Right. That's another thing that I forgot to mention. If I turn the volume and/or balance controls while it is making the noise, the noise remains the same. It doesn't get any better or worse.

[Pickoid]

Have you measured the DC offset? See this thread at Audiokarma. (http://www.audiokarma.org/forums/showthread.php?t=5634) I'd be concerned that the amp is outputting a high DC voltage to the speaker while the noise is occurring, in which case you will soon be shopping for replacement speaker drivers on that channel. Trust me on this, I speak from experience. Melted voice coils smell really bad. Count me in the "I think it's serious and you should have the amp checked out" camp. I think those who have suggested a bad capacitor are probably on the right track.

[Doug Sclar]

Have you measured the DC offset? See this thread at Audiokarma. (http://www.audiokarma.org/forums/showthread.php?t=5634) I'd be concerned that the amp is outputting a high DC voltage to the speaker while the noise is occurring, in which case you will soon be shopping for replacement speaker drivers on that channel. Trust me on this, I speak from experience. Melted voice coils smell really bad. Count me in the "I think it's serious and you should have the amp checked out" camp. I think those who have suggested a bad capacitor are probably on the right track.

This is what I was alluding to when I mentioned the leaky capacitor. Could be an insterstage coupler designed to prevent dc from stage to stage or something like that. If I had a schematic I could possibly see if it uses those.

If so, it may also be obvious by visual inspection.

DC on the output would be pretty easy to tell by hooking a DC voltmeter to the output. It still could be all internal with little or no DC on the output.

[bangsezmax]

Have you measured the DC offset? See this thread at Audiokarma. (http://www.audiokarma.org/forums/showthread.php?t=5634) I'd be concerned that the amp is outputting a high DC voltage to the speaker while the noise is occurring, in which case you will soon be shopping for replacement speaker drivers on that channel. Trust me on this, I speak from experience. Melted voice coils smell really bad. Count me in the "I think it's serious and you should have the amp checked out" camp. I think those who have suggested a bad capacitor are probably on the right track.Make sure you get a copy of the service manual. Most likely you can find this over at AudioKarma.

Not sure about the 1010, but my SX-626 was giving me wildly inaccurate DC offset readings until I plugged a set of headphones in (apparently you need some kind of load -- don't ask me why, I'm a total newbie about this stuff).

The folks at AudioKarma are very knowledgeable and helpful. There's even a msg board dedicated to Pioneer gear.

[doodlebug]

What is being described, here, is most likely a noisy transistor - it will be somewhere after the volume and balance controls. This would place it close to the power amplifier board. If this was on my bench, I'd be looking at the signal coming into the power amp board for the channel in question.

I would tend to doubt the leaky cap theory - at first pass - until I'd eliminated the noisy transistor theory. The fact that the symptoms go away tends to indicate a thermal-related problem. Thermally unstable transistor junctions are well-known culprits here.

Now, here's the danger you need to conider: If the transistor is at the front end of this powerfull receiver, then as it starts to get worse - and it most likely will - you run the risk of damaging your speaker on that channel. Yes, the unit _should_ have its speaker protection relay operating but that's not going to be good enough. DC offset, when bad enough, _should_ cause the speaker protection circuit to kick out the relay. You do hear a click when the receiver comes on, right?

So, get it looked at now is my recommendation. Don't wait.

Hope that helps.

Cheers,

David

[street legal]

Well, I seem to have figured out the problem, & purely by accident. The best part is, it's not really a problem at all anymore. :)

A few days ago, my left speaker was emitting quite a bit of noise as soon as I powered up the SX-1010. Knowing that it would probably die down after half a minute or so, I just disengaged the Speaker A switch, which I had my speakers connected to. A few minutes later, I tried to engage the switch to see if the noise had died down, & the switch wouldn't stay locked into position. "Great", I thought, "another problem!".

Not so, as it turns out that this WAS the problem all along, at least so it seems, so far. The SX-1010 has provisions for 3 sets of speakers, so I simply connected my speakers to the Speaker B jacks, & now all appears to be well.
I've had no weird noise issues for a few days now (I can't believe I didn't even think to try this earlier).

At this point, I figure that even if the Speaker B switch goes at some point down the road, I still have a 3rd chance with the Speaker C switch! :)

It feels so good to be in love with my vintage Pioneer receiver all over again.

Thanks again to all who responded to this thread. Now I can quit worrying about my equipment issues & start enjoying the music again!

[bru87tr]

I was gonna suggest that, I had the same problem with my Pioneer a while back and switched to the b section.

congrats. enjoy.

you should check dc offset anyway, those pioneers drift.