Seasons greetings all.
My preamp, a Yamaha C4, works and sounds excellent.. apart from a hum!
Am having ridiculously immense difficulty locating the source of this.
Lots of reflowing of solder and switch cleaning haven’t yet resulted in discovering the cause. It can be heard on all inputs but is loudest when ‘Phono’ is selected.
Question:
Can anyone tell me if the following statement allows one to determine the area of the amp where the hum fault is most likely located?
With INPUT selecting Phono the following occurs:
When PHONO is set to Phono-3 MC the hum is equal on both channels.
When Phono 1, or Phono 2 is selected the hum is much stronger through the left speaker.
Also might anyone have a reasonable circuit board diagram of the C4, my own copy is virtually illegible.
My preamp, a Yamaha C4, works and sounds excellent.. apart from a hum!
Am having ridiculously immense difficulty locating the source of this.
Lots of reflowing of solder and switch cleaning haven’t yet resulted in discovering the cause. It can be heard on all inputs but is loudest when ‘Phono’ is selected.
Question:
Can anyone tell me if the following statement allows one to determine the area of the amp where the hum fault is most likely located?
With INPUT selecting Phono the following occurs:
When PHONO is set to Phono-3 MC the hum is equal on both channels.
When Phono 1, or Phono 2 is selected the hum is much stronger through the left speaker.
Also might anyone have a reasonable circuit board diagram of the C4, my own copy is virtually illegible.
Check the input RCA jacks solder connections. Also clean the ground shells and check for a tight fit.
Look for bad electrolytic capacitors (esp low voltage caps), or dirty switch contacts.
https://www.hifiengine.com/manual_library/yamaha/c-4.shtml
Look for bad electrolytic capacitors (esp low voltage caps), or dirty switch contacts.
https://www.hifiengine.com/manual_library/yamaha/c-4.shtml
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Thanks Rayma, much appreciated.
Can I ask, from the symptoms, does it suggest on which board the bad caps would probably be located?
Thanks also for the link, unfortunately the scan on hi fi engine is the one with the illegible pcb diagram.
Can I ask, from the symptoms, does it suggest on which board the bad caps would probably be located?
Thanks also for the link, unfortunately the scan on hi fi engine is the one with the illegible pcb diagram.
Make sure your turntable cable is not the problem first.
This seems to be on the phono board. But first I would clean and check the input jacks
for tightness and a good connection, and then their solder joints. If that is not it, then
clean all the phono stage switching contacts. If that is not it, then look at the 6V capacitors
in the phono stage. Caps like these will often go bad. Replace those with Nichicon UES series,
with the same uF values, but rated at 16V.
This seems to be on the phono board. But first I would clean and check the input jacks
for tightness and a good connection, and then their solder joints. If that is not it, then
clean all the phono stage switching contacts. If that is not it, then look at the 6V capacitors
in the phono stage. Caps like these will often go bad. Replace those with Nichicon UES series,
with the same uF values, but rated at 16V.
Thanks my friend.
And does it suggest that the issue must be on the left channel...?
And.. the dreaded wafer switches.. I just deconstructed and reassembled the Phono wafer switch.. could it be the Input wafer at fault..?
Sorry to ask, it's just that I'm desperately trying to rule out all the potentially fruitless but time consuming tasks available to me. I've spent days on it already...
And does it suggest that the issue must be on the left channel...?
And.. the dreaded wafer switches.. I just deconstructed and reassembled the Phono wafer switch.. could it be the Input wafer at fault..?
Sorry to ask, it's just that I'm desperately trying to rule out all the potentially fruitless but time consuming tasks available to me. I've spent days on it already...
The left, large board, at the lower end. It says phono 1,2, and 3 input on the lower right side.
Then follow the outputs from its lower right side, to the next board to the right.
Have you tried the turntable on another preamp to make sure its cables are ok?
Then follow the outputs from its lower right side, to the next board to the right.
Have you tried the turntable on another preamp to make sure its cables are ok?
Maybe, but the RIAA gain is much higher. More likely it's the reverse.
There could be small ground noise or supply noise that goes to the RIAA stage
and is amplified there.
There could be small ground noise or supply noise that goes to the RIAA stage
and is amplified there.
Thanks.
Could you tell me where the RIAA stage is, maybe a cap or transistor code number or two?
Could you tell me where the RIAA stage is, maybe a cap or transistor code number or two?
With the volume way down, try tapping around on the RIAA circuit with a
wooden pencil or other insulated tool. Maybe you can find a bad solder joint.
wooden pencil or other insulated tool. Maybe you can find a bad solder joint.
Thanks Rayma, yes, that’s exactly what I’ve been doing. Getting some very faint effects through the left speaker now and then and will keep trying. If I turn it over and and tap, with care, the components... is that ok too?
Yes, just don't bend or physically move any parts, since that could break a lead or connection.
Do you have any freeze spray? Sometimes that can localize a bad part or connection.
Do you have any freeze spray? Sometimes that can localize a bad part or connection.
I read post # 11. The fact that hum manifests itself strongly on the phono section does not mean that the defect is in this block. The amplification of the phono stage is much larger than that of the other sections. I am convinced that it also exists in the other sections, CD, TAPE, AUX. A simple check can be done with an oscilloscope, or professionally with a spectrum analyzer.