Distorted bass on vintage receivers

slateef

Active Member
I've noticed on several vintage receivers that I've bought and restored that the bass is somewhat distorted, especially at higher volumes - imagine listening through a blown speaker; that's the sound.

What causes this? Would a complete replacement of the capacitors solve this issue? Or is it more an issue with the output transistors?

Any guidance would be appreciated.
 
What causes this? Would a complete replacement of the capacitors solve this issue?
Possibly, if the receiver in question is over ~30 years old it is overdue for a refresh. I would start with a check and reset of the 'Bias' and 'DC' offset for a start - these settings should tell you a lot about the overall health of the unit in question.
Or is it more an issue with the output transistors?
Highly unlikely.
 
I’d also think main PS caps.
Hook up a volt meter to the DC power rails feeding the main amp and see how much the voltage dips during loud bass-heavy play
 
I’d also think main PS caps.
Hook up a volt meter to the DC power rails feeding the main amp and see how much the voltage dips during loud bass-heavy play

Like he said.
TIP: :angel: Use an analogue voltmeter and watch if the needle twitches downwards to the bass beat. It's easier than using a DVM.
 
I was thinking that the OP having "restored" these units would have at least checked or replaced the caps and has brought them up to spec, ... but then "restored" is somewhat subjective here.

If you can get a decent dual-trace scope you can track the rail voltage vs output, and also compare the input-output traces. Both very useful here.
 
Clipping is my first thought. Distortion at loud volumes on multiple different units? It's possible you simply don't have enough power to get the volume levels you desire with your speakers. Details on which receivers and speakers would help.
 
If its "soft/fuzzy" distortion in both channels that gets worse the louder you turn it up - I would first look at the large powersupply caps - chances are they have dried out.

There are plenty of other issues that can cause distortion however.....
 
Try moving your balance pot back and forth. I notice on Marantz receivers the same thing and moving the balance pot back and forth (work it good before you turn the unit on) and the distortion goes away. If this works for you, the balance pot needs to be cleaned
 
I've noticed on several vintage receivers that I've bought and restored that the bass is somewhat distorted,
What causes this? Would a complete replacement of the capacitors solve this issue? .
Your post is a bit confusing. Are you saying the bass is distorted after restoration or before? If it’s before restoration, then replacing those large PS caps would do the trick. They’re either dried up or leaking which is causing the bass issue. Because the receiver is old, a total recap is needed for it to shine.
 
Clipping is my first thought. Distortion at loud volumes on multiple different units? It's possible you simply don't have enough power to get the volume levels you desire with your speakers. Details on which receivers and speakers would help.

I'm with this as most likely cause. Even more so if the bass cranked up in addition to higher volume.
 
What are you using as a source? Some CD players can can have too high of output for some vintage amps.
 
And around here the local radio station that plays current garbage really boosts the bass to the point of distortion, makes it seem stronger than it is on a bluetooth speaker I guess. But I'd suppose it's a power supply issue too. But I have wondered if the old TO3 outputs can lose hFE over the many years too?
 
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