I think I might have asked this before in here, but I've recently changed over to high efficiency drivers, and as a byproduct, noisy hash has crept in.
There are 4 computers in the area, as well as networking gear.
I have 3x 20A circuits in the room where all the gear is. Do you all think it would be wise to make sure that the audio gear is plugged into a different branch so that the audio gear doesn't share a hot with all the smps devices?
Also, a friend gave me an old Viz Isotap II, maybe if I insert that before the smps devices, that might help any stray garbage coming back into the supply? Does anyone think there's any benefit to be had placing it before things like MiniDSP or a receiver? It's rated for 4A, so obviously I can't put big amplifiers on it, but I could probably at least get the PC that's an audio source and the MiniDSP on it.
Or maybe building a linear supply for the MiniDSP might help, as it came with a laptop style inline brick.
I dunno, I'm open to any and all suggestions, I have enough wiring to do pretty much anything I need to do, up to drilling through the concrete floor and driving in a new earth pole.
There are 4 computers in the area, as well as networking gear.
I have 3x 20A circuits in the room where all the gear is. Do you all think it would be wise to make sure that the audio gear is plugged into a different branch so that the audio gear doesn't share a hot with all the smps devices?
Also, a friend gave me an old Viz Isotap II, maybe if I insert that before the smps devices, that might help any stray garbage coming back into the supply? Does anyone think there's any benefit to be had placing it before things like MiniDSP or a receiver? It's rated for 4A, so obviously I can't put big amplifiers on it, but I could probably at least get the PC that's an audio source and the MiniDSP on it.
Or maybe building a linear supply for the MiniDSP might help, as it came with a laptop style inline brick.
I dunno, I'm open to any and all suggestions, I have enough wiring to do pretty much anything I need to do, up to drilling through the concrete floor and driving in a new earth pole.
Hi Guys
You have to determine the entry path first as the hash might be picked up in other ways.
The first thing to check might be the speaker cables, since you say the noise appeared with the new speakers. Excess cable should not be coiled. Regular zip cord is the best for speakers - NRC proved it in the '70s.
Anything that might block mains-borne noise is good. Easiest to block it from the source since those are likely lower powered items than your stereo. An easy filter is simply an isolation transformer. The frequency response of most PTs is poor, so high-f noise won't get through. Corcom filters are good, as well - bulky and expensive.
The isolation PT works very well to provide clean power to PAs. Obviously such a device has to handle the power input to your amp but being just an isoaltor they are not that expensive.
You have to remember that in North America the 240V comes in from a CTed transformer. The two ends provide 120V power with respect to the CT BUT only the difference current goes through the CT. If there is 20A of load on one side and 4A on the other side, the CT conducts the 16A difference but the other 4A goes through dives on one side then through devices on the other side. It makes no difference that each room or circuit has its home-run to the breaker panel. This should also make it pretty clear that wasting money on a fancy power cord is exactly that.
Most electronic equipment is supposed to have at least a minimal amount of noise reduction filtering on its mains input, to block or reduce noise in both directions - in and out. Much of this circuitry is more aesthetic than functional.
Have fun
You have to determine the entry path first as the hash might be picked up in other ways.
The first thing to check might be the speaker cables, since you say the noise appeared with the new speakers. Excess cable should not be coiled. Regular zip cord is the best for speakers - NRC proved it in the '70s.
Anything that might block mains-borne noise is good. Easiest to block it from the source since those are likely lower powered items than your stereo. An easy filter is simply an isolation transformer. The frequency response of most PTs is poor, so high-f noise won't get through. Corcom filters are good, as well - bulky and expensive.
The isolation PT works very well to provide clean power to PAs. Obviously such a device has to handle the power input to your amp but being just an isoaltor they are not that expensive.
You have to remember that in North America the 240V comes in from a CTed transformer. The two ends provide 120V power with respect to the CT BUT only the difference current goes through the CT. If there is 20A of load on one side and 4A on the other side, the CT conducts the 16A difference but the other 4A goes through dives on one side then through devices on the other side. It makes no difference that each room or circuit has its home-run to the breaker panel. This should also make it pretty clear that wasting money on a fancy power cord is exactly that.
Most electronic equipment is supposed to have at least a minimal amount of noise reduction filtering on its mains input, to block or reduce noise in both directions - in and out. Much of this circuitry is more aesthetic than functional.
Have fun
Hi Guys!
I made a lot of mods in the past days on my amp and among other things adding some
extra main PS caps on the "second floor" extreme near to the input pot as you can see.
A little hum appeared (typical cap charge noise...) so I started to investigate...
First I removed the extra caps but the hum decreased just a tiny bit...
Then I tried my trafo material metal "tape" around my trafo and it helped a bit.
But fortunately I didnt stop at this point but made some other experiments.
BTW: I tried to apply this post factum belly band as tight as possible but it
made some mechanical noises even if I put a sponge layer/foil between the parts
and it turned out the metal tape in itself produces some noise so I had to look
for some other solution... So if the magnetic shielding helped maybe it's better
to shield the sensitive point instead of the trafo so I started to look for the
sensitive part... Then after an hour accidentaly I found the part: the output coil...
Its not extreme near to the trafo but about a 10cm and when I put this Si tape around
it the hum disappeared completely... Then if I put back all of the extra caps the amp
remain completely silent... This coil is also some new "improvement" it wasn't there
when I started the chase before so it wass another good lesson to learn... 🙂
I made a lot of mods in the past days on my amp and among other things adding some
extra main PS caps on the "second floor" extreme near to the input pot as you can see.
A little hum appeared (typical cap charge noise...) so I started to investigate...
First I removed the extra caps but the hum decreased just a tiny bit...
Then I tried my trafo material metal "tape" around my trafo and it helped a bit.
But fortunately I didnt stop at this point but made some other experiments.
BTW: I tried to apply this post factum belly band as tight as possible but it
made some mechanical noises even if I put a sponge layer/foil between the parts
and it turned out the metal tape in itself produces some noise so I had to look
for some other solution... So if the magnetic shielding helped maybe it's better
to shield the sensitive point instead of the trafo so I started to look for the
sensitive part... Then after an hour accidentaly I found the part: the output coil...
Its not extreme near to the trafo but about a 10cm and when I put this Si tape around
it the hum disappeared completely... Then if I put back all of the extra caps the amp
remain completely silent... This coil is also some new "improvement" it wasn't there
when I started the chase before so it wass another good lesson to learn... 🙂
Attachments
You might want to pull apart and twist your input wires from the jacks to the pot and then to the board.
I forgot this one 😱 .
When I had my trafo breakout point aimed at either of my main output
inductors , I heard a low level hum ( 30mm distance).
Your caps rectified hum is of a worse variety (more harmonics). My
caps are much further away (70mm). Your right on top of them ! 😱
PS - sheet neoprene >1mm is the desired material for GOSS bands/
tape.
OS
No need for the twist that was exactly my point with the post to share that now with
the output coil shielded there is NO hum at all despite the large caps near to the pot..!
As I said the material in itself had some mechanical resonance without having a mechanical contact to anything else... 🙄
And based my experiences now it can be spared with such a layout.
Ohh what a good feeling the life without HUM.... 😀
Put the inductor (not the resistor) on the end of a 6 inch twisted pair of wire. Then you can move it around and put it anywhere you want.
You mean like put it rather to the speaker terminal end?
Shouldn't the coil be placed as near to the OPS as possible to decpuple any reactance from the output wires?
Shouldn't the coil be placed as near to the OPS as possible to decpuple any reactance from the output wires?
For start I tried the 1cm diameter 13 turns || 10R, is is too big..?
I'll try to decrease both the L and the || R (maybe 2R2 will be enough I hope...) as well.
I'll try to decrease both the L and the || R (maybe 2R2 will be enough I hope...) as well.
Sorry I think I was confused. I see the coil you are using. It's about the right size. I am still trying to work out though how this is causing hum. It's probably 2-5 uH and one end goys to the amp output and the other to the speaker. ????
I was wondering how it was causing hum too. Unless the amp is oscillating there shouldn't be any sort of signal there.
Edit. I think it's actually picking up noise and amplifying it through the feedback.
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Yeah, why not..? Simple inductive coupling. Or this effect exists only in my amp..? 🙂
Output inductor on a high Z FB network will do as you say easily.
The CFA's not as much. But both will still do it. It seems the inductor and
even the PCB tracks will send this EMF through the FB network.
Distance is your friend , even with the 1KVA ... 3-4 cm away gives no hum.
An open (unshielded) EI will wreck havoc.
OS
The CFA's not as much. But both will still do it. It seems the inductor and
even the PCB tracks will send this EMF through the FB network.
Distance is your friend , even with the 1KVA ... 3-4 cm away gives no hum.
An open (unshielded) EI will wreck havoc.
OS
Better yet, use thick heatsinks and put the transformer on the opposite side to your amp. I've seen several commercial amps that have the trafos boxed in with heatsinks.
Measure ACV across the inductor with the amp idle. If the DMM doesn't measure something significant, then it cannot be hum induced directly by the trafo. I would think the inductor is becoming an antenna and causing the amp grief, although it should be well shorted with a 10R resistor next to it (unless the resistor is magnetic perhaps). I have never measured levels across such a small inductor large enough to be audible across a speaker, let alone when that inductor was shorted by a small resistance.
It cannot be straight inductive pickup. The output where the two emitter degen resistors join is a low impeadance point. The feedback resistors go from here back to the IP stage. The other side of the inductor is going to a Lo Z speaker load. The inductor is also shunted with a low value resistor. You would need very high L currents to drive hum through the speakers in this scenario.
If the L was accidentally inside the feedback loop then it would explain everything. But if it indeed is located correctly we have to look for another mechanism I am afraid.
If the L was accidentally inside the feedback loop then it would explain everything. But if it indeed is located correctly we have to look for another mechanism I am afraid.
Never mind the technical arguments going on here. I just re-wired my solid state phono pre within my Aikido tube pre, and all hum is gone, even with my low output moving coil cartridge, based on David Davenport's article in the articles section above.
It is a very informative article and very thorough. I thought it was my arm/cartridge giving me the hum, but after reading through it I saw that there were some things I did seriously wrong, in particular passing the ground through the noisy end of the power ground. I moved my internal interconnect ground directly to the phono section and all hum is GONE. It is as quiet as all the other inputs!!!!
YAY.
You may continue with your technical discussions now. I'll admit I don't understand more than a tiny fraction of it.
It is a very informative article and very thorough. I thought it was my arm/cartridge giving me the hum, but after reading through it I saw that there were some things I did seriously wrong, in particular passing the ground through the noisy end of the power ground. I moved my internal interconnect ground directly to the phono section and all hum is GONE. It is as quiet as all the other inputs!!!!
YAY.
You may continue with your technical discussions now. I'll admit I don't understand more than a tiny fraction of it.
You say it just can not happen ??
The fact that cortez "foiled" it , throws a wrench into that conclusion.
It was the redirection of my "breakout point" that eliminated my last
10db of hum.
This effect was much more noticeable on a VFA , BTW.
OS
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