Clipping/distortion from receiver...definitely internal EQ related

[neiman]

So I have this aging receiver (TEAC AG-V8060) that has stood the test of time up until recently. I noticed that the left channel sounded like it was clipping. At first I thought I blew a woofer cone, since it was mostly occurring with the kick drum. I freaked out and took the cloth grille off of my speakers to assess the damage. Turns out the speaker was just fine. I hooked up a different pair of speakers and sure enough, the left one was clipping too. I started fiddling with the control knobs, and I discovered that the "loudness switch" (low volume eq preset thing) caused lots of distortion and clipping in both channels when I jiggled it/depressed it partially. I tried the onboard preamp, and sure enough, the headphones were distorted too. It seems to clip primarily with low frequencies. Playing with the EQ knobs does not affect distortion. When the loudness switch is turned on, there is no clipping or distortion. This leads me to believe that there is something wrong with the internal EQ.

Side note: receiver has a "line straight" mode which supposedly bypasses the EQ processing. I normally leave this setting on. The loudness switch still changes the sound even when the receiver is in direct/straight mode.

My instincts say that the switch contacts are worn. Has anyone experienced this before?? I am going to open it up and check it out with a multimeter. I have access to an electronics lab, so I can investigate with an oscilloscope if needed.

Thanks.

 

[DaveVoorhis]

My instincts say that the switch contacts are worn. Has anyone experienced this before?? I am going to open it up and check it out with a multimeter. I have access to an electronics lab, so I can investigate with an oscilloscope if needed.

Experienced this before?

Many, many times.

It's likely that the switch contacts aren't worn but are simply dirty or oxidised. Judiciously spray them with Deoxit or similar electrical contact cleaner, then operate the switch repeatedly. That should fix it.

While you're in there, you might want to do the same with other switches, and the volume/tone/etc pots too.

 

[swechsler]

Agreed. I wasn't even halfway through your first paragraph when I figured that it was mostly likely due to dirty or oxidized contacts.

While you can usually spray through the front (after removing the knobs), I recommend removing the top cover to make sure that any excess doesn't drip inside (maybe put a rag underneath the controls while spraying).

 

[blhagstrom]

Since direct tone bypass doesn’t change the effect, the tone control appears to be innocent.

Cleaning the controls is a good move and usually the first “first aid” effort to clear up issues in old gear.

If that fails to “fix” things, I suspect old electrolytic capacitors acting poorly or perhaps a transistor in the amp has gone south.
The issue you describe is very typical of those failures.

 

[neiman]

Thanks for the help everybody. I popped the metal cover off and hit all of the buttons and pots on the front panel with contact cleaner. The receiver sounds great.

Judiciously spray them with Deoxit or similar electrical contact cleaner, then operate the switch repeatedly.

Cleaning the controls is a good move and usually the first “first aid” effort to clear uexcp issues in old gear.