Distortion Issue On Old Yamaha Receiver

[Lone Stranger]

I have an unusual (I think) problem that I would like some input on. I have a Yamaha RX-485 stereo receiver that is nearly 20 years old and has been a great receiver. Recently I picked up an old Technics SL-P550 CD player from a thrift store. When I play demanding music such as choir with organ and brass I get clipping which really sucks. I also have the rec-out of the Yamaha connected to another audio system in my basement and I do not hear any distortion on that system with the same CD player playing through the Yamaha. At this point I have not tried FM or another line source but have listened to LPs through the Yamaha but there is no distortion.
Does this sound like a pre-amp issue? I am keep the volume low so as not to kill my tweeters but the volume setting has no effect on the amount of distortion. I will do some more tests this week with headphones as well as other line sources and a spare stereo receiver I have lying around.

 

[Deleted member 133]

If I correctly understand and follow all of the troubleshooting permutations and combinations that you describe below I conclude that:

1. Neither of the two sources is to blame since they pass through ok. (That one of those is a phono section eliminates the possibility that you misconnected CD to phono.) Ditto for the inputs for those two sources.

2. You say the distortion is independent of level - therefore I don't see this as an amplifier clipping issue.

3. Since you say the distortion happens on demanding music, I'll go out on a limb and guess that the signal's peaks are to blame and that the culprit is the volume control on the receiver. Try disconnecting your speaker leads and and rotating the volume knob quickly from one extreme to the other very quickly for ten seconds or so. Turn it all the way down, reconnect the speakers, and turn it up slowly. Any improvement? If so the volume control should be thoroughly cleaned and or replaced. (I have a 34year old Yamaha that has a very similar problem.) If the volume control's contacts (assuming it's old enough to have them) are dirty / worn, it can lead to a "clipping-like" sound that's independent of volume setting. You could take the case off and, depending on the volume control, give it a good shot of contact cleaner.

That's my best guess - for now. And the easiest to check / deal with.

Jeff

 

[Lone Stranger]

It is actual audio clipping. I am guessing it is before the volume control circuitry. I did try the internal FM and it is clipping as well. Not the phono which with the particular LP I played was sounding louder than the CD I tried. I don't hear any static in the actual adjusting of the volume control.
One thing I may try is to disconnect the connection from the Yamaha's rec-out to the other (Pioneer) receiver. This clipping started pretty much after I connected the Technics CD player as well as connecting the audio between the Yamaha and the Pioneer.
I will keep troubleshooting over the next few days. I would hate to ditch that Yamaha since it has been an excellent performing machine for nearly 20 years.

 

[Botch]

I was going to suggest the same thing Jeff did, as my 34-year-old (wow!) Yamaha does the same, but it only crackled while moving the volume or balance knobs. Yours sounds more like clipping, as you mention. Good luck!

 

[Lone Stranger]

OK, I think I have it figured out. When I disconnected the RCA patch cords going from the Yamaha's rec-out to the Pioneer's line-in the clipping disappeared. When I reconnected the cord the clipping came back. I suspect there is some weird electrical interference messing with the Yamaha's preamp when the Pioneer receiver is powered off. Since any listening of music on the basement system (Pioneer) is not critical would it make sense to put an isolation transformer in-line with the patch cord? I don't have ground loop noise but wonder if the transformer will make a difference. I don't want to fry the Yamaha. The Pioneer I won't cry as much about if it were to fry. In the meantime I will keep it disconnected.