I have some ground control problems, but not Space Oddity of David Bowie. That can be a nice song in the background while reading this.
This is not my first amplifier build, so I have some knowledge and have had and solved some ground problems in the past, but this one is killing me.
First picture of amplifier layout:
Normally I build dual transformer/dual psu units. This time I decided to reduce cost and used one 600VA toroid. I have tried some different layouts of wiring, but same result.
1. With nothing connected to inputs the amplifier is absolutely silent.
2. With inputs connected together with cable - each to other, the amplifier is absolutelly silent
3. With inputs connected to source there is noise - bzzzzz. Source is Marantz amplifier with preouts - no issues with other amps.
I tried to change grounds from connector to just one point, a screw in the picture on top of capacitors, same problem.
Tried ground lift with greatz, same problem.
The solving of problem was removing the connection from common ground (the green yellow) to the eart point on top near the big resistor, where the chasis is grounded. You can see now the wire on top of the screw of common ground. If I connect this to chasis earthing point there is noise. On other amplifiers, without this wire I had noise, with this one the oposite.
What is the cause of this and can I just leave it like this. The chasis is grounded to the mains jack, but the amplifier 0V -ground is NOT.
This is not my first amplifier build, so I have some knowledge and have had and solved some ground problems in the past, but this one is killing me.
First picture of amplifier layout:
Normally I build dual transformer/dual psu units. This time I decided to reduce cost and used one 600VA toroid. I have tried some different layouts of wiring, but same result.
1. With nothing connected to inputs the amplifier is absolutely silent.
2. With inputs connected together with cable - each to other, the amplifier is absolutelly silent
3. With inputs connected to source there is noise - bzzzzz. Source is Marantz amplifier with preouts - no issues with other amps.
I tried to change grounds from connector to just one point, a screw in the picture on top of capacitors, same problem.
Tried ground lift with greatz, same problem.
The solving of problem was removing the connection from common ground (the green yellow) to the eart point on top near the big resistor, where the chasis is grounded. You can see now the wire on top of the screw of common ground. If I connect this to chasis earthing point there is noise. On other amplifiers, without this wire I had noise, with this one the oposite.
What is the cause of this and can I just leave it like this. The chasis is grounded to the mains jack, but the amplifier 0V -ground is NOT.
Attachments
https://hifisonix.com/wp-content/uploads/2019/02/Ground-Loops.pdf
Starting from P36, please see details about Hum Breaking Resistor.
Starting from P36, please see details about Hum Breaking Resistor.
That should solve the ground loop issues. I have an AV receiver that breaks out multi channels into multiple amps. No hum at the listening position at least. This is the only solution that solves the ground loop for me.
Besides ground loop, another common issue is RF interference is got demodulated at PN juction of the input transistors. That will also cause noise. Putting a RC filter at the input of the amp is highly recommended.
on this forum, amp ccts have been posted with the resistor incorrectly placed.
post you amp cct and your grounding scheme.
If i take a look to the picture i can see 2 different PE connections (or is one connection hidden under the plate ?). Its better to choose only one point for PE connecting the chassis .
You have built a starpoint with PE directly connected. In my oppinion it is better to use a loop breaker. https://sound-au.com/earthing.htm post 9. You can try a 10 ohm 5 watt resistor first.
Another try is to use little wires to connect the input hbr, signalground, with the starpoint. Perhaps you get hum with a potential difference at rca (perhaps.... the rca connection is very short, fine ). Make sure that your RG 10 ohm is set right.
You have drilled the speaker output together with the power wires. I would not do so...drilling is good, but i try to seperate...
I have uploaded two pictures...
You have built a starpoint with PE directly connected. In my oppinion it is better to use a loop breaker. https://sound-au.com/earthing.htm post 9. You can try a 10 ohm 5 watt resistor first.
Another try is to use little wires to connect the input hbr, signalground, with the starpoint. Perhaps you get hum with a potential difference at rca (perhaps.... the rca connection is very short, fine ). Make sure that your RG 10 ohm is set right.
You have drilled the speaker output together with the power wires. I would not do so...drilling is good, but i try to seperate...
I have uploaded two pictures...
Attachments
Ground/earth from power jack is connected to chasis.
This is the only point of conecting of chasis to ground/earth.
The 0V of power supply is now not connected to this point and everything is perfect and silent.
I have tried other wirings, also not together speaker to power, dirrect signal gound to starpoint ecc.
I will leave it like this now. Seems to be Ok. The chasis is grounded, this is important for safety reasons.
This is the only point of conecting of chasis to ground/earth.
The 0V of power supply is now not connected to this point and everything is perfect and silent.
I have tried other wirings, also not together speaker to power, dirrect signal gound to starpoint ecc.
I will leave it like this now. Seems to be Ok. The chasis is grounded, this is important for safety reasons.
if you look a this thread post1 shows how it should be
https://www.diyaudio.com/community/threads/l20-5-finished-amp-with-hum.425750/#post-7970465
check your setup by measuring from input skt gnd to amp pcb main 0V - you should get 10 ohms.
this is also a safety connection, by making it o/c you have broken the loop, but a 10ohm (+diodes/cap) should also work
Just a screw for connecting all grounds to the 0V of power supply. Just one thing I tried because I thought that there is a problem with connecting 0V ground to each of +- connectors. I have connected to this point also the speaker return, and chasis tring to solve the problem.
I am a complete novice here, so excuse the stupid question, but does your toroid have dual secondaries? If yes, ignore my post.
I just finished a Class B amp last week. The first toroid I used had only one secondary winding which I split between two amp boards and I had a terrible hum, which I thought was a ground loop problem. A toroid with dual secondaries solved my problem.
I just finished a Class B amp last week. The first toroid I used had only one secondary winding which I split between two amp boards and I had a terrible hum, which I thought was a ground loop problem. A toroid with dual secondaries solved my problem.