So I understand this is probably a pretty well-discussed topic, but I would like to ask if you all suspect this is poor design or a hardware malfunction.
The amp is a Leslie LS-2215. I'm still figuring out the best way to take it apart, then I'll share some pics. I'll also try to post some audio samples too.
The volume of the hum is the same no matter what, which leads me to believe that there's some issue between the power supply and the power amp/output.
What is the first thing I should look for when I open the thing up?
The amp is a Leslie LS-2215. I'm still figuring out the best way to take it apart, then I'll share some pics. I'll also try to post some audio samples too.
The volume of the hum is the same no matter what, which leads me to believe that there's some issue between the power supply and the power amp/output.
What is the first thing I should look for when I open the thing up?
Yeah I just had to cut some zip-ties. The wires going down to the cabinet needed some extra slack.
I looked at the power supply board and nothing looked loose. The big electrolytics were secured in place. I cleaned up some of the solder joints but that didn't make the problem go away.
Would that cause a problem even if the inputs are all disconnected and all the volumes are down?
Right now the noise is the same even if no input is plugged in and the volumes are all the way down. It doesn't get louder or quieter.
It could, depending on the contruction. Is the noise a low pitched hum, or more of a buzzing?
It's very clearly at 60/120 Hz (Played a Bb on my bass and it was slightly above that). Not sure if 120 is just a loud harmonic or if that's the fundamental.
I unfortunately don't have a scope, but I might be able to borrow one from a friend.
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That's likely from power supply rectification ripple. If this is new, it could be a factory defect,
or shipping damage.
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Sure, but if it's in warranty I'd have a local shop do the work.
A schematic seems hard to locate.
If it's used, you could negotiate a price adjustment or return.
The shipper may not honor a damage claim if there's no visible damage.
I'm looking at it for a friend and I'd really prefer to figure it out myself since I would like the troubleshooting practice. He looked into sending it back and they were going to make him pay shipping (the thing is close to 100 lbs).
Checked all the boards for bad solder joints and cleaned up a few. Noise is no better.
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Yes, what's the P-P ripple on the main input capacitor? You can measure that with a voltmeter set to AC.
He might be able to just send back the chassis alone.
I'm reading no AC voltage on the big electrolytics (+65 and -65 VDC). On the power amp output I'm reading about 40 mVrms with no input. Seems relatively small but I guess in terms of noise floor that's enough to be problematic.
Is it possible that this signal is somehow getting amplified in the cab? I didn't prod around in there too much but it looks like there might be a transformer and a couple other components in there.
I'll work on getting my hands on a scope so I can take a closer look at that noise voltage.
Is it possible that this signal is somehow getting amplified in the cab? I didn't prod around in there too much but it looks like there might be a transformer and a couple other components in there.
I'll work on getting my hands on a scope so I can take a closer look at that noise voltage.
Thanks. It sounded like 120, but I'm going to poke around with a scope on Monday to see what's going on.
So I took some measurements with an oscilloscope and this is what I found:
There are two power supplies from different outputs on the same transformer. I label the higher voltage one as +/-V1 and the lower voltage as +/-V2.
-V1:
This one looks great. Looks like practically no ripple. This is with a 10x probe so I suppose the resolution is too low to get a reading, but the ripple seems to be quite small.
+V1:
This one looks not too great. 4Vpp ripple.
+V2:
400mVpp ripple.
-V2:
Same 400mVpp ripple as the positive.
And finally, the power amp output waveform:
And the measurements of that waveform:
So my interpretation of this is that the biggest issue is the smoothing on the positive side of the higher voltage power supply.
The lower voltage on the +V2 (compared to -V2) is probably due to some voltage drop at the point I chose to measure. There was no good way to connect directly to the nominal +24v point.
Let me know what everyone thinks of this!
There are two power supplies from different outputs on the same transformer. I label the higher voltage one as +/-V1 and the lower voltage as +/-V2.
-V1:
This one looks great. Looks like practically no ripple. This is with a 10x probe so I suppose the resolution is too low to get a reading, but the ripple seems to be quite small.
+V1:
This one looks not too great. 4Vpp ripple.
+V2:
400mVpp ripple.
-V2:
Same 400mVpp ripple as the positive.
And finally, the power amp output waveform:
And the measurements of that waveform:
So my interpretation of this is that the biggest issue is the smoothing on the positive side of the higher voltage power supply.
The lower voltage on the +V2 (compared to -V2) is probably due to some voltage drop at the point I chose to measure. There was no good way to connect directly to the nominal +24v point.
Let me know what everyone thinks of this!
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