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Yamaha P2200 hum

H

Hifibythekg

Super Member
My P2200 was recapped by me and has been performing beautifully but has just developed a hum. Diagnostics listed below. Please can anyone suggest the most likely cause and likely location?
  • All input sources disconnected, the hum is present.
  • Hum can be made louder or even disappear, by rotating the P2200’s volume pots for each channel.
  • Hum has equal strength through each channel.
  • When the P2200 is shut off with its inbuilt power switch audio will play through speakers for 20 seconds or so as the charge in the big caps runs down. With no inputs connected, switching off the power switch immediately ceases the hum.
  • At normal listening levels during silent passages the hum is clearly audible but not really loud.
Please can anyone provide a check list of the areas and components to first examine?

Many thanks.
 
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Thanks Dave, appreciate the reply.
Please could you tell me the title of the board(s) I should be looking at on the P2200?
Sounds silly but I can’t tell which one is the power supply area... presume that it’s neither of the two Drive pc boards.
Also, could the meter board cause any hum?
 
Check the ground connections where the two largest e-caps are joined together.
 
Hifibythekg said:
Terrific, will check these out.
Thanks again.
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Did you ever resolve the humming issue on your amp? I have the same problem with p2201 and p2200. When I connected P2201 to high sensitivity speakers (99dB) I realized that the left channel hum is noticeably louder. The hum disappears if I set the volume pots to highest (pass-through) setting. I had all electrolytic replaced in P2201 with exception of main power caps.
 
tpaxadpom said:
The hum disappears if I set the volume pots to highest (pass-through) setting
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Are you referring to the input attenuators? If so, it sounds like and amplifier input grounding issue. Between the amplifier input and the input attenuators.
 
avionic said:
Are you referring to the input attenuators? If so, it sounds like and amplifier input grounding issue. Between the amplifier input and the input attenuators.
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Yes I am. The amplifier inputs have ground connected to the chassis. I did install new RCA terminals that are isolated but the 1/4" plug is grounded and all connectors there (including 2 XLRs) all have GND point. Also I can see that both attenuators are grounded to the chassis. The grounding point is not common but they are within a few inches of each other. Perhaps I should jump input gnd to attenuators gnds to see if that makes a difference. Thank you for the pointer. When I was studying schematic I figured that is what I should try first.
 
Here are the symptoms I am dealing with.
With input floating I am hearing hum in the left channel only with attenuator set to bypass mode. Shorting the input pins on the driver board gets rid of the hum. Enabling attenuation reduces amount of hum.
1) Checked the GND from inputs to chassis. All good.
2) Checked the attenuator GND connection and measured 4.9Ohms on the left attenuator. Removed the knob loosened the nut and cleaned the GND connection. The shaft had some kind of grease on on the threaded part. Measured ok afterwards.
Nothing changed, the hum is still there in bypass mode.
If I touch the attenuator plastic casing the hum goes away. Similarly I can try to rotate knob CW passed the hard stop the hum goes away. So there is something inside the attenuator that is making a poor contact.
Can the attenuator be cleaned with cleaner spray or do I need to take it apart?
 
Nashou66 said:
Why not try the spray first , then if no go open her up and do a good cleaning.

Nashou
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That is exactly what I did. Sprayed it first and also reheat solder joints on the ground wire connected to ALPS. No difference. Opened up the attenuator and cleaned. Actually cleaned both of them since I was there. Now the hum is even louder and is also audible on the right channel. If I press on the volume knob the hum disappears. Similarly if I touch the plastic casing of the attenuator it goes away. Seems like some kind of contact issue.
 
tpaxadpom said:
That is exactly what I did. Sprayed it first and also reheat solder joints on the ground wire connected to ALPS. No difference. Opened up the attenuator and cleaned. Actually cleaned both of them since I was there. Now the hum is even louder and is also audible on the right channel. If I press on the volume knob the hum disappears. Similarly if I touch the plastic casing of the attenuator it goes away. Seems like some kind of contact issue.
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Here you say Volume knob and also Attenuator. Do you mean Volume knob on your preamp or is the volume knob the same Attenuator on the Amplifier?

Athanasios
 
Nashou66 said:
Here you say Volume knob and also Attenuator. Do you mean Volume knob on your preamp or is the volume knob the same Attenuator on the Amplifier?

Athanasios
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sorry for confusion. In all cases I have meant ALPS attenuator on the amplifier. The inputs on the amplifier are not connected to anything (floating). I have cleaned the GNDs on the left channel with sand paper. Look nice and shiny, though it made no difference what so ever...
 
reinstalled everything back and connected to my DAC. Low level humming noise is present now mostly in the right channel but the amp behaves differently now. I don't hear the hum being increased now when I activate attenuation. Still the hum is there but the level is quite low.
Cleaned the gnd connections on inputs and attenuator on the right channel. Reassembled back, heard hum on the left channel (louder than what is was before). Noticed that I had wires for thermistor on the left channel improperly routed when I was touching up some of the caps I had replaced in the past. Rerouted back, reassembled and now the hum is lower. Unlikely related to the routing issue, but definitely the issue is not fully addressed.
To summarize, if leaving the amp inputs floated (disconnected) there is a hum in the left channel. When connected to DAC the hum goes away. I no longer have hum increasing when using attenuators as I had last time. I have a second amp I should try clearing GND points on next.
PS: one horrible side effect of me wiggling the attenuator is that I have pushed it beyond hard stop a few times and now it rotates a little more (basically has one additional step). It happens in both directions (CW or CCW) even though I was trying to push it only in CW direction. Did anyone ever try to fully disassemble this attenuator. It would be great to figure out if I could fix it, otherwise I maybe looking for replacement if one shows up at the right price. :(
 
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Sparkplug said:
It’s a long shot but make sure the volume, attenuators, etc. are tightly fastened to the frame behind the front panel. I’m talking about the M7 nuts holding the pots to the frame. If not tightened, they can cause havoc.
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thank you. I ill look into that.
 
tpaxadpom said:
With input floating I am hearing hum in the left channel only with attenuator set to bypass mode. Shorting the input pins on the driver board gets rid of the hum.
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I'd clean all the external input jacks in back if ya haven't already. While back there tighten the nuts on the input phono jacks. Hum is often an ungrounded/poorly grounded/or dirty input.
 
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checked the M7 nuts once again and didn't find any issue with not being tight. Took the attenuator apart once again, reassembled the same issue. When connected to DAC, the hum goes away (there is a quiet hum that is mostly heard from the midrange driver). The input signal is routed away from the AC lines that are going to the power switch. I guess I will need to find a replacement attenuator or just give up.
 
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