Please help me in getting rid of the buzz.

[Nordic]

also try switching off lights and all other appliances...

[keithgreenhalgh]

The other amps that are quiet have a different design than this amp so the fact they are quiet and this one hums doesn't prove anything .As to why the hum varies from one side to the other,I don't know.Anyway at this point I am grasping at straws as to the reason.Try a different location,that will prove its is or isn't coming from the power line.If it is we can then add ckts to elimate the hum and we will know for sure what the problem is.

[rdk845]

O.K. So I did some further tests.

Originally posted by SY
For the next repair step, I'd go simple and resolder/tighten every connection between the input stage and ground, then tighten every mechanical ground or voltage supply connection for the power supply

I strengthened all solder joints that didn't look super solid. Not a lot of change in buzz though.

[i]Can you take the amp to a friends place in a different part of town [/B]

The buzz did not change in my work place.

Originally posted by Nordic
also try switching off lights and all other appliances...

Some light did seem to effect buzz slightly, but most of buzz persisted when everything else in the house was off.

I did try SY's floating heater circuit Idea anyway, and this actually increased the buzz considerably, although this time the left and right side gave same level of buzz. This time I didn't try ceramic cap bypass.

Finally I also switched left and right interstage transformer and buzz did not change either.

So for the next step, I'm considering to change 210V diodes and every parts that is directly connected to input 12AX7 tube. ( Since taking out the input tube removed the buzz) But before that I would appreciate it if some one could provide info on how to test the power supply transformer and chokes....

By the way, could a bad tube socket cause a buzz?

[SY]

I did try SY's floating heater circuit Idea anyway, and this actually increased the buzz considerably, although this time the left and right side gave same level of buzz.

It seems there are ground currents in your chassis, and if it's buzzy, they're ripple currents from the transformer-diode-first filter cap loop. When I get back later, I'll take a closer look at your photos.

[Nordic]

RK, I had to chase my tail a bit when I constructed my current main amp... all the conventional routes of wisdom failed... I ended up doing the following for an amp that was buzzing for months...
Isolating all sockets from the enclosure.
Use thinner wire from RCA socket to In-
Add an intentional ground loop--- another wire from In- RCA socket to the power ground star...In my case this was the ground pin of the ICE socket (external AC supply).
It is dead quiet now...

I think getting the buzz equal on both channels is a step closer to finding your problem...

I still think if the amp worked before, some component has given up or is in the process.. I would start by suspecting capacitors... many can safely be removed while testing to see if the problem persists...

[keithgreenhalgh]

Sorry to hear my idea of trying it at a friends place made no difference in the hum but we now know that its not a dirty A/C line trouble so we made some progress.The fact that it origionally had no hum and now has hum would seem to indicate a faulty part,most likely a capacitors.Im out of ideas.

[SY]

Was the side that had the buzz the V6 side?

Troubleshooting without a scope is a challenge!

[rdk845]

Originally posted by SY


It seems there are ground currents in your chassis, and if it's buzzy, they're ripple currents from the transformer-diode-first filter cap loop.

Do you mean that one of the transformer-diode-first filter cap loop parts is leaking current to ground? Then would it be something close to left input cap and could that be reason why the left channel buzzes much larger?

[rdk845]

Originally posted by Nordic
Isolating all sockets from the enclosure.
Use thinner wire from RCA socket to In-
Add an intentional ground loop--- another wire from In- RCA socket to the power ground star...In my case this was the ground pin of the ICE socket (external AC supply).
It is dead quiet now...

Thanks for the input. How would I isolate the sockets from enclosure? They are ceramic sockets.
When i connected ICE socket earth to circuit ground, I hear a LARGER hum. In my amp, main earth is left disconnected and enclosure is connected to the circuit ground. What do you mean by external AC supply? My wire from RCA to main circuit is 24Gauge. What was yours?

Originally posted by keithgreenhalgh
Sorry to hear my idea of trying it at a friends place made no difference in the hum ...

No problem! Thanks for the suggestion. It was something that should be tested anyway..

Originally posted by SY
Was the side that had the buzz the V6 side?

Please take a look at the posted picture where I labeled most of relevant parts.

Please let me konw what you think.

If you think what I posted above is right, the only cap that is physically closer to the Left 12AX7 than right 12AX7 is 100/400V decoupling cap on the main circuit. But this should not generate ripple/ buzz. Am I right?

[keithgreenhalgh]

Didn't you already bridge this on with a good one? If its bad it will definately cause hum but in both channels.