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.
O.K. So I did some further tests.
I strengthened all solder joints that didn't look super solid. Not a lot of change in buzz though.
The buzz did not change in my work place.
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 said:
I strengthened all solder joints that didn't look super solid. Not a lot of change in buzz though.
The buzz did not change in my work place.
Some light did seem to effect buzz slightly, but most of buzz persisted when everything else in the house was off.Nordic said:
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?
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...
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...
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.
Thanks for the input. How would I isolate the sockets from enclosure? They are ceramic sockets.Nordic said:
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?
No problem! Thanks for the suggestion. It was something that should be tested anyway..keithgreenhalgh said:
Please take a look at the posted picture where I labeled most of relevant parts.SY said:
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?
SY said:
O.K. I have tried bunch of stuff which I thought, may verify whether there is any leakage current to ground.
First I disconnected 210V and 100V secondary from board and made sure they are open from ground. Then I replaced diodes on 210V and 100V. The replcement on 210V may have reduced the buzz slightly. Then I replaced the first filter cap of 210V and 100V subsequently. No change in the buzz.
Then I removed the shielded cables connecting input RCA to 100K pot and pot to the board as well as the pot itself.
The buzz was ALMOST gone!
In order to make sure it is not a bad pot or RCA, I connected resistor networks to simulate the resistances pot gives on my typical volume level setting. As soon as I connected wire long enough from board to the input RCA (wire not soldered to RCA yet), large buzz returns. (Larger than orignial buzz) But this time left and right are equal in level. At this point, I connected the input + and ground wire to RCA and RCA ground to the Main AC earth, as Nordic did. ( at this point this is the only point in the amp that AC earth is connected inside of amp, since the chassis is connected to circuit ground.) This significantly reduced the buzz, but it still is not low enough to listen music.
If the input wire is picking up RF or something, why isn't the shielding getting rid of? IT seems that there is ground current that SY spoke of, but I¡¯m not sure how to find the cause. All solder joint seem to be solid.
Please let me know what you think.
SY. Did you have a chance to look at the labeled picture?
I tried it and it didn't have effect on my amp. But thanks for the suggestion.kstagger said:
Ground Point on Chassis
If I'm trying to connect the chassis to AC common (Main Earth) or Circuit ground at one point, how do I find the best location?
I have previously found that my chassis is some how connected to circuit ground but I'm not entirely sure whether is right, since I can't find exactly where the manufacturer inteded to ground on the chassis.
Thanks!
If I'm trying to connect the chassis to AC common (Main Earth) or Circuit ground at one point, how do I find the best location?
I have previously found that my chassis is some how connected to circuit ground but I'm not entirely sure whether is right, since I can't find exactly where the manufacturer inteded to ground on the chassis.
Thanks!
O.K. If one is to connect the circuit ground ( not AC common) to chassis, sholuld the optimal ground position be seeked in same way?keithgreenhalgh said:
The input volume controll is mounted in the front. But it is taken off for the time bieng. Instead I connected resistor network temporarily on the board. The amp is current standing on the side with bottom plate removed. The input wire is hanging in the air and not touching anything. When I put my hand closer input wire ( carefully), it buzzes more... How would I find the cause of input loop?...SY said:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.