Problem with phono stage / Yamaha C4

dirtyblues

Member
Hi,

A couple of years ago I repaired a C4 with the help of this forum, specifically Avionic, who patiently guided me through the project. Thanks again.

This is a great sounding preamp that I've been using daily. Recently, the phono stage started making noises. Not the usual hum, or constant noise, but this:

https://drive.google.com/file/d/0B4QrjBON6BBbS18tNVhtR09tZFU/view?usp=sharing

Sorry about the bad recording, this is done with my phone.

This noise is present on the 3 phono inputs, although it sounds a bit different on the MC one. It is present whether I have the turntable plugged in or not, it doesn't start straight away when I power up the preamp, but generally starts after 1min. It is also intermittent, It sometime stops for 5-10 seconds then starts again.

Any idea what could cause this?
 
Unfortunately this damn company PC won't let me open your file. What all have you replaced in the phono EQ section ? Caps , transistors - VD1212 varistors ?
 
Hi,

A couple of years ago I repaired a C4 with the help of this forum, specifically Avionic, who patiently guided me through the project. Thanks again.

This is a great sounding preamp that I've been using daily. Recently, the phono stage started making noises. Not the usual hum, or constant noise, but this:

https://drive.google.com/file/d/0B4QrjBON6BBbS18tNVhtR09tZFU/view?usp=sharing

Sorry about the bad recording, this is done with my phone.

This noise is present on the 3 phono inputs, although it sounds a bit different on the MC one. It is present whether I have the turntable plugged in or not, it doesn't start straight away when I power up the preamp, but generally starts after 1min. It is also intermittent, It sometime stops for 5-10 seconds then starts again.

Any idea what could cause this?

Both channels ? Or just one channel ? AUX,TAPE and TUNER play OK ?
 
Let's see, sounds like family too close to the stereo and a Geiger counter. So move all your radioactive materials away from the phono inputs.

Sorry, I'm sure we'll get back on topic with the next post.
 
Hi,

A couple of years ago I repaired a C4 with the help of this forum, specifically Avionic, who patiently guided me through the project. Thanks again.

This is a great sounding preamp that I've been using daily. Recently, the phono stage started making noises. Not the usual hum, or constant noise, but this:

https://drive.google.com/file/d/0B4QrjBON6BBbS18tNVhtR09tZFU/view?usp=sharing

Sorry about the bad recording, this is done with my phone.

This noise is present on the 3 phono inputs, although it sounds a bit different on the MC one. It is present whether I have the turntable plugged in or not, it doesn't start straight away when I power up the preamp, but generally starts after 1min. It is also intermittent, It sometime stops for 5-10 seconds then starts again.

Any idea what could cause this?

Odds are that's some kind of intermittent component failure, or possibly a bad solder joint.
 
Hi,

A couple of years ago I repaired a C4 with the help of this forum, specifically Avionic, who patiently guided me through the project. Thanks again.

This is a great sounding preamp that I've been using daily. Recently, the phono stage started making noises. Not the usual hum, or constant noise, but this:

https://drive.google.com/file/d/0B4QrjBON6BBbS18tNVhtR09tZFU/view?usp=sharing

Sorry about the bad recording, this is done with my phone.

This noise is present on the 3 phono inputs, although it sounds a bit different on the MC one. It is present whether I have the turntable plugged in or not, it doesn't start straight away when I power up the preamp, but generally starts after 1min. It is also intermittent, It sometime stops for 5-10 seconds then starts again.

Any idea what could cause this?

If its a single channel left or right. I would be look'n for a noisy transistor/component in the phono EQ circuit. If its in both channels I'd be looking for a noisy component in the +/- 30vdc PS.
 
as for replacing stuff, I did replace all the electrolytic caps in the preamp. vd1212 I'm not sure, I didn't keep a log, I will look up the conversations aI had at the time.
 
here is the recording again:

https://soundcloud.com/decca-2/audio-recording-2014-12-20-20-09-17-1-1

the noise is present on both channels, only on the 3 phono inputs, aux, tuner and tape are ok.

You have a weird problem there. Scrounge up some shorting plugs and try shorting the phono inputs. Do you have any CFL´s , fluorescent tube lamps or dimmer switches in close proximity to your pre-amp ?

Did you replace D311 ? Its a VD1212 in the +/- 30 volt regulated supply.
 
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Well, you don't hear that sound every day, in fact I've never heard anything quite like it. Noises common to both channels are often power supply, so I'd start there. Is there a special regulated supply that only feeds the phono sections?
 
Noises common to both channels are often power supply, so I'd start there. Is there a special regulated supply that only feeds the phono sections?
No special supply :no:.... Just +/- 30 vdc which pretty much supplys the entire unit.
I have worked on one with a similar issue. But I'm thinking it was present at any input selected. The fix was a couple 1N4148's to replace D311. (VD1212)
 
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