how is it possible that AUX is clear music, but PHONO is scratchy when I adjust volume knob. Same knob for AUX. it is a 2 pot control. I cleaned both with deoxit. Still scratchy. Plays good music just scratchy when knob is adjusted. Can bad resistors cause this or is it more likely rca jacks or clean pot more? The loudness switch is also scratchy when adjusted on phono, but clear with AUX.
AUX clear, PHONO not
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Assuming the Phono is RIAA it probably has 2-3 extra tubes in that equalization circuit, so maybe clean tube contacts, re-tension pin sockets.
Imanoldee
Super Member
Seems like a dirty pot. If it is only scratchy when turning it.
Why only on the Phono and not the Aux?
Because the Phono section is a low voltage section which has to be
gained up to Aux level and then on through the system and gained up again in the output section.
Which is to say your Phono section is more sensitive to low level noise problems.
If cleaning the pot does not help.
It may mean the pot resistor material has worn away and left a bare spot.
The pot might be fixable if you (or your tech) disassemble the pot itself and change the position of the wiper.
Why only on the Phono and not the Aux?
Because the Phono section is a low voltage section which has to be
gained up to Aux level and then on through the system and gained up again in the output section.
Which is to say your Phono section is more sensitive to low level noise problems.
If cleaning the pot does not help.
It may mean the pot resistor material has worn away and left a bare spot.
The pot might be fixable if you (or your tech) disassemble the pot itself and change the position of the wiper.
What unit is this on??? So far everyone has blamed the RIAA circuit, Tube pins/sockets, Pot material on ?which? pot???, Function switch??, resistors. However this is all conjecture without knowing WHAT UNIT IS HAVING THIS ACTUAL PROBLEM??? If the unit has PEC's they could be a part of the problem, in addition to everything else. So we need to know the actual unit having problems
Your question is analogous to taking your car in to a mechanic and telling him it doesn't work, fix it. All kinds of possibilities pop into his head and $$$ signs are floating around his wallet. If you tell him exactly what it's doing, and what caused you to drop it off, he'll have a smaller troubleshooting list of things to check and could probably fix it inexpensively.
Same thing here. Telling us what the unit is narrows down the list to a specific model, so a schematic can be looked at and specific areas can be troubleshot. Which is better than blindly running from one thing to another looking for a problem that may not exist in a part.
Your question is analogous to taking your car in to a mechanic and telling him it doesn't work, fix it. All kinds of possibilities pop into his head and $$$ signs are floating around his wallet. If you tell him exactly what it's doing, and what caused you to drop it off, he'll have a smaller troubleshooting list of things to check and could probably fix it inexpensively.
Same thing here. Telling us what the unit is narrows down the list to a specific model, so a schematic can be looked at and specific areas can be troubleshot. Which is better than blindly running from one thing to another looking for a problem that may not exist in a part.
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Imanoldee
Super Member
I read it to mean he is writing about the Volume knob, it is scratchy when turning it when in the Phono mode.
Also a scratchy sound when switching the loudness knob, also only when in Phono mode.
In my experience it is dirty pots, Volume and Loudness.
A 2-3 applications of Fader lude should fix it.
Also a scratchy sound when switching the loudness knob, also only when in Phono mode.
In my experience it is dirty pots, Volume and Loudness.
A 2-3 applications of Fader lude should fix it.
Can't be the Volume pot or Loudness, as it's NOT scratchy in AUX. If it were in the pot, AUX would be noisy too. That has to be in the phono section. But the question is; What unit is it so we can narrow it down in the circuit. Aux is Actually downstream in gain stage in most amps/receivers.
Dadbar
Super Member
In most of my gear, I have to turn the volume control higher for phono. Maybe just a small section of your loudness pot is scratchy.
This may be a stretch, but maybe the coupling caps in your phono section need changing...if, in some weird way, they are throwing DC onto your volume pot
This may be a stretch, but maybe the coupling caps in your phono section need changing...if, in some weird way, they are throwing DC onto your volume pot
The phono stage on the C11 has 3 tubes in it. V1-V2-V3 for 3 sections of 12ax7 gain. Check them for mismatched sections and poor emissions and gm, clean pins on tubes, and retighten tube socket leaves. V3 especially as each 1/2 runs a channel, you'll see it in the scat. Are you hitting the same spot on the the Volume control in AUX as in Phono?? If you are using more volume in Phono than Aux, try that volume setting in Aux, tuner, etc. If it DOES NOT scratch or crackle then, the volume control is NOT at fault. If it does, the Volume control is at fault.
As I thought, Aux is injected into the circuit past the phono circuit, directly into the Balance control, then the Loudness and Volume and then V4 which is the 2nd stage. Phono is the 1st stage. So unless the Volume pot is suspect which I don't think it is, unless the settings for Phono and Aux are totally different, the phono stage is the prime suspect. Loose tube socket leaves, worn tubes, or coupling caps. As you stated that in AUX you had no problems with Loudness, or Volume (try the Balance pot also and post results), just phono, and both phono and Aux end up both going thru Balance, Loudness, and Volume, the the problem is most likely in the phono section.
As I thought, Aux is injected into the circuit past the phono circuit, directly into the Balance control, then the Loudness and Volume and then V4 which is the 2nd stage. Phono is the 1st stage. So unless the Volume pot is suspect which I don't think it is, unless the settings for Phono and Aux are totally different, the phono stage is the prime suspect. Loose tube socket leaves, worn tubes, or coupling caps. As you stated that in AUX you had no problems with Loudness, or Volume (try the Balance pot also and post results), just phono, and both phono and Aux end up both going thru Balance, Loudness, and Volume, the the problem is most likely in the phono section.
I LIKE MUSIC
Super Member
Not having looked at the schematic, I would hazard a guess that there may be a small amount of DC on the volume control. Could be from a leaky coupling capacitor.
Switching to AUX in would eliminate the small DC.
Switching to AUX in would eliminate the small DC.