Hi all,
This might be another humming problem. But after searching the web, I did not get the solutions that I need.
I believe this is not power supply humming problem as I am using a LCRC filtering for B+ with 30H choke and 100uF caps.
The humming comes when I turn up the volume knob. To isoloate problem, I disconnect the grid connection from the volume control and have it connected directly to the ground. The amp is dead quiet!
However, when I remove the connection from the ground, the HUM Monster comes alive.
This happens to both channel.
This is a line preamp using a single 6C4WA tube for each channel.
Where do I go from here?
This might be another humming problem. But after searching the web, I did not get the solutions that I need.
I believe this is not power supply humming problem as I am using a LCRC filtering for B+ with 30H choke and 100uF caps.
The humming comes when I turn up the volume knob. To isoloate problem, I disconnect the grid connection from the volume control and have it connected directly to the ground. The amp is dead quiet!
However, when I remove the connection from the ground, the HUM Monster comes alive.
This happens to both channel.
This is a line preamp using a single 6C4WA tube for each channel.
Where do I go from here?
effindi said:
Wellllll..... yeah........
I'm going to guess you have a 60Hz line (power switch? heaters? plate supply AC leads?) in the vicinity of your grid circuits (volume control, grid, etc.).
Is this with something connected to the input or not? Obviously the hum could be coming from a unit higher up in the chain.
Tim
Usually, any hum problems can be solved by connecting the first stage of the amplifier to the volume control's ground to the signal input jack's ground, then running that mini-star to the rest however you want. Since it's the most sensitive stage, you want as little possibility of ground loop appearing on it.
But that will neither create nor solve the effect seen here. The only thing that can is something nearby which is inducing a very small current on the input jack itself, thus there is zero induced hum when the pot is at zero, and a certain maximum amount when at full volume.
If there are no wires routed by, the pot case is grounded (think I saw that somewhere in this thread) and is of a reasonable value (anything over 100k will be prone to this as the small leakage currents create higher voltages across the resistance), I'm out of ideas.
Tim
But that will neither create nor solve the effect seen here. The only thing that can is something nearby which is inducing a very small current on the input jack itself, thus there is zero induced hum when the pot is at zero, and a certain maximum amount when at full volume.
If there are no wires routed by, the pot case is grounded (think I saw that somewhere in this thread) and is of a reasonable value (anything over 100k will be prone to this as the small leakage currents create higher voltages across the resistance), I'm out of ideas.
Tim
All that contributes,
Thank you for the input.
I have rewired the grounding to make sure that the Star implementation is good. I have ensured that the body of the volume pot is grounded as well and the wire to the grid have been screened with a better wire.
I have also run a wire from the volume pot body to the star network. There are also dedicated ground wire from the casis to the star point.
The ground from the input jack is connected to the volume ground connection and it is then connected to the input gain stage ground performing a small star before having another wire connected to the main star connection.
The hum went down to about 20% only. It is still very much audible 5 ft from the speaker.
I also notice that when I tap on the signal lines, the sound is amplified and can be herd on the speaker. It's like tapping a microphone.
Could the hum comes from the noise in the surrounding that it pick up the EMI and etc or could it be due to the heater ac noise? It really sounds like a 100hz hum.
Looking for more input to improve the situation.
Regards,
Thank you for the input.
I have rewired the grounding to make sure that the Star implementation is good. I have ensured that the body of the volume pot is grounded as well and the wire to the grid have been screened with a better wire.
I have also run a wire from the volume pot body to the star network. There are also dedicated ground wire from the casis to the star point.
The ground from the input jack is connected to the volume ground connection and it is then connected to the input gain stage ground performing a small star before having another wire connected to the main star connection.
The hum went down to about 20% only. It is still very much audible 5 ft from the speaker.
I also notice that when I tap on the signal lines, the sound is amplified and can be herd on the speaker. It's like tapping a microphone.
Could the hum comes from the noise in the surrounding that it pick up the EMI and etc or could it be due to the heater ac noise? It really sounds like a 100hz hum.
Looking for more input to improve the situation.
Regards,
This stuff can be really annoying. Here is a link to a very good grounding overview. You might want to try taking all of your signal grounds directly to your input ground, and from there, to the last ground point of your PSU.
FWIW, I use a ground plane for grounding my phono stage and have never had any problems. Every node connects directly to a copper covered pcb(shortest path) that the tubes are mounted on, and from there, a single wire goes to the PSU ground.
Edit: Also, this "hum" may also be an oscillation masquarading as hum...or a bad pot.
FWIW, I use a ground plane for grounding my phono stage and have never had any problems. Every node connects directly to a copper covered pcb(shortest path) that the tubes are mounted on, and from there, a single wire goes to the PSU ground.
Edit: Also, this "hum" may also be an oscillation masquarading as hum...or a bad pot.
pedroskova said:
Hi pedroskova
DO you remember the problem I had with the 5687 ccs stage? Well, I have tried to use the same design with the 6sn7 and again I hear noise...this time I made the circuit on a board using two ground plane. The layout seems ok but I've noticed still hummm! So I started to look for the reason of this noise. The signal input is near the heaters cables but I think this is not the reason of noise because the power supply is dc and really well dimensioned. I used an c-r-c filter with two 26.000 powerlitic and then a ccs with an lm317... Looking around I noticed that when volume was turn to 0 or max no hum comes out. The pot is connect to gnd, direct to the star point. If I disconnect the pot from gnd the noise is much higher.... Well...what did I forget? To connect gnd to earth! I used a 15000pf cap between gnd and earth and noise comes down very much. Now if I touch the heatsink on the mje I hear nothing, noise doesn't go up. I've a lot to learn about the design art of the perfect layout. effindi, maybe your problem is similar...
Mark
pedroskova said:
Ah...details, details, they'll get you every time.
Yes...I've not considered this detail because, with the same power supply, I tested three different designs. The first one had a small cap on the input and pot on the output.... silence! This is the reason why I didn't investigate with the earth connection...
I think I'll buy this book...
http://www.amazon.com/exec/obidos/t...59-2411213?v=glance&me=ATVPDKIKX0DER&st=books
Mark
progress update
Thanks for all the input and help. I thought it will be good to provide the update on the progress.
I manage to kill the last bit of the noise. The last bit was to connect a 50ohm resistor to both the +ve and the -ve end and then connect the other end of the 50ohm resistor to star ground network.
Now it is dead silence....
As the saying goes.. Silence is Golden!
Thanks to all your kind input and help..
Thanks for all the input and help. I thought it will be good to provide the update on the progress.
I manage to kill the last bit of the noise. The last bit was to connect a 50ohm resistor to both the +ve and the -ve end and then connect the other end of the 50ohm resistor to star ground network.
Now it is dead silence....
As the saying goes.. Silence is Golden!
Thanks to all your kind input and help..
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