Hello.
I've been designing amplifier board using lm1875 - after a long time of studying and designing, yesterday i finally tested the first prototype of the amplifier board.
It supplies power using "unregulated", "capacitance multiplier" circuit after -18/CT/18VAC transformer output.
But when I turn on the amplifier, it sounds pop up and start to making hum noise like eeeeeeeeeeeeeeeeeeeeeee-. I guess that noise is almost close to 120Hz.
(My living country using 230VAC/60Hz to mains power, and also sadly I can't analyze the spectrum because I don't have an oscilloscope yet.)
The popup noise seems can be solved using relay or triac, but the main problem is the humming noise.
Whatever I turn the volume up or down, connecting audio source or not, it creates same humming noise before I turn the power switch off.
One strange thing is, affter turn the power switch off while amplifier working, I can hear nice, clean amplified music without any noises for a second(because of large amount of capacitor), and it finally pops up again and completely turns off.
So I found the internet to solve the humming noise problem, but it makes me confused more.
Many of articles say that problem may be a ground loop noise, or output ripple noise.
They say it can be solved using ground loop breaker circuit or using larger amount of capacitor.
But I wonder it really is because I already using two 10000uF capacitors and more etc on psu circuit, also I applied ground loop breaker circuit from https://sound-au.com/earthing.htm.
I also see some of comments that using linear regulator may be helpful to suppress power noises... would it be really helpful?
Is there anything I've got missed? How can I solve this humming noise problem?
Any suggestion would be really appreciated.
Thank you.
I've been designing amplifier board using lm1875 - after a long time of studying and designing, yesterday i finally tested the first prototype of the amplifier board.
It supplies power using "unregulated", "capacitance multiplier" circuit after -18/CT/18VAC transformer output.
But when I turn on the amplifier, it sounds pop up and start to making hum noise like eeeeeeeeeeeeeeeeeeeeeee-. I guess that noise is almost close to 120Hz.
(My living country using 230VAC/60Hz to mains power, and also sadly I can't analyze the spectrum because I don't have an oscilloscope yet.)
The popup noise seems can be solved using relay or triac, but the main problem is the humming noise.
Whatever I turn the volume up or down, connecting audio source or not, it creates same humming noise before I turn the power switch off.
One strange thing is, affter turn the power switch off while amplifier working, I can hear nice, clean amplified music without any noises for a second(because of large amount of capacitor), and it finally pops up again and completely turns off.
So I found the internet to solve the humming noise problem, but it makes me confused more.
Many of articles say that problem may be a ground loop noise, or output ripple noise.
They say it can be solved using ground loop breaker circuit or using larger amount of capacitor.
But I wonder it really is because I already using two 10000uF capacitors and more etc on psu circuit, also I applied ground loop breaker circuit from https://sound-au.com/earthing.htm.
I also see some of comments that using linear regulator may be helpful to suppress power noises... would it be really helpful?
Is there anything I've got missed? How can I solve this humming noise problem?
Any suggestion would be really appreciated.
Thank you.
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120 Hz noise is not generally a ground loop---that would be 60 Hz. Problem must be in the power supply---scope rails to see if it is there. It IS possible that it is improper grounding technique AFTER the power supply.
Hello dotneck and Hugo. Thank you for your reply.
Here is the schematic of power supply - please kindly note that I'm using non-filtered and fused AC inlet module before primary winding of transformer.
Also all of the components are mounted to 1oz copper trace FR4 pcb as surface mount or thru-hole components.
Here is the schematic of power supply - please kindly note that I'm using non-filtered and fused AC inlet module before primary winding of transformer.
Also all of the components are mounted to 1oz copper trace FR4 pcb as surface mount or thru-hole components.
My suggestion would be to buy an oscilloscope!
Maybe a 'sound card scope' would help in this case, but I really don't want to encourage anyone to blow up their PC.
I think looking at the transistors with a scope might show that they are saturated for soem part of the mains cycle?
Then off for a short time as the base voltage
You could either reduce R5 and R6 so that the base voltage is reduced to significantly smaller than the lowest C1 and C2 drop to during a cycle, or you could put a couple of diodes in series with R1 and R2? That would stop the load current dragging down C3 and C5.
As the AC volts drop, the load starts to pull current from C1, the current through R1 reverses?
You could simulate it in SPICE.
I could be quite wrong of course!
Maybe a 'sound card scope' would help in this case, but I really don't want to encourage anyone to blow up their PC.
I think looking at the transistors with a scope might show that they are saturated for soem part of the mains cycle?
Then off for a short time as the base voltage
You could either reduce R5 and R6 so that the base voltage is reduced to significantly smaller than the lowest C1 and C2 drop to during a cycle, or you could put a couple of diodes in series with R1 and R2? That would stop the load current dragging down C3 and C5.
As the AC volts drop, the load starts to pull current from C1, the current through R1 reverses?
You could simulate it in SPICE.
I could be quite wrong of course!