This is a very common and often returning issue and I guess it would be useful at last to have an "ultimate"
topic having all the basic concepts and practical solutions helping to get rid completely of the hum in an
amplifier and saving the time of our good old members to write again these things for the millionth time.
First of all I would like to clarify the main target of this thread to focus on:
Get rid of the hum INSIDE an amplifier. There are already a lot of excellent articles about eliminating "external" ground
loops at component level when connecting different devices together so I hope it is quite enough just to reference these:
http://www.diyaudio.com/forums/diya...udio-component-grounding-interconnection.html
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
http://www.bennettprescott.com/downloads/grounding_tutorial.pdf
The concept would be to start this thread together and to build up the knowledge in a conventional forum like way
but meanwhile I would create and maintain a "final" and "ultimate" clarified diyaudio article (maybe like the
one at the first link above if possible or a simple PDF) where all of the info would be present in a structured
way but just the essentials without any forum "noise". Untill then I'll maintain this extract here at the first post.
Already existing great materials:
1) Bonsai's great PDF which is practically perfect and a complete material in this topic:
http://www.diyaudio.com/forums/soli...ing-arrangements-star-ground.html#post3971339
Newest version: http://hifisonix.com/wordpress/wp-c.../How-to-wire-up-a-Power-Amplifier_Updated.pdf
2) ostriper's posts based on building his SlewMaster Amplifier up (down) to -115dB
starts here: http://www.diyaudio.com/forums/solid-state/248105-slewmaster-cfa-vs-vfa-rumble-132.html#post4248395
3) D. Joffe article: http://www.updatemydynaco.com/documents/GroundingProblemsRev1p4.pdf
4) Rod Elliots article: Power Supply Wiring Guidelines)
As a starter I just structured and merged these materials hoping we could enrich it even more based on our
real life experiences (and not with just theoratical thoughts... 🙂)
Usefull images will be created bit later...
Here is the extract to achieve a 100% hum free amp:
Grounding
Create and separate 2 main ground meeting point inside your amp and connect
them via a SLB (Safety Loop Breaker) = 35A rectifier bridge || (10R 1W + 10nF).
Wiring
Thumb rules:
Trafo
Other
topic having all the basic concepts and practical solutions helping to get rid completely of the hum in an
amplifier and saving the time of our good old members to write again these things for the millionth time.
First of all I would like to clarify the main target of this thread to focus on:
Get rid of the hum INSIDE an amplifier. There are already a lot of excellent articles about eliminating "external" ground
loops at component level when connecting different devices together so I hope it is quite enough just to reference these:
http://www.diyaudio.com/forums/diya...udio-component-grounding-interconnection.html
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
http://www.bennettprescott.com/downloads/grounding_tutorial.pdf
The concept would be to start this thread together and to build up the knowledge in a conventional forum like way
but meanwhile I would create and maintain a "final" and "ultimate" clarified diyaudio article (maybe like the
one at the first link above if possible or a simple PDF) where all of the info would be present in a structured
way but just the essentials without any forum "noise". Untill then I'll maintain this extract here at the first post.
Already existing great materials:
1) Bonsai's great PDF which is practically perfect and a complete material in this topic:
http://www.diyaudio.com/forums/soli...ing-arrangements-star-ground.html#post3971339
Newest version: http://hifisonix.com/wordpress/wp-c.../How-to-wire-up-a-Power-Amplifier_Updated.pdf
2) ostriper's posts based on building his SlewMaster Amplifier up (down) to -115dB
starts here: http://www.diyaudio.com/forums/solid-state/248105-slewmaster-cfa-vs-vfa-rumble-132.html#post4248395
3) D. Joffe article: http://www.updatemydynaco.com/documents/GroundingProblemsRev1p4.pdf
4) Rod Elliots article: Power Supply Wiring Guidelines)
As a starter I just structured and merged these materials hoping we could enrich it even more based on our
real life experiences (and not with just theoratical thoughts... 🙂)
Usefull images will be created bit later...
Here is the extract to achieve a 100% hum free amp:
Grounding
Create and separate 2 main ground meeting point inside your amp and connect
them via a SLB (Safety Loop Breaker) = 35A rectifier bridge || (10R 1W + 10nF).
- One for the metal case (chassis + heatsinks + pot metal case): connected to AC Earth at only one point
- Note: input RCAs should be isolated from the chassis and the GNDs should be connected right to the chassis via 1nF
- And one for the main PS GND. Main PS GND layout should be developed following these rules:
- Create a "T" at the main PS filter between the +- caps common part to separate the cap charging currents from other GND currents.
- From that "T" section create a rather "bus" GND layout instead of star ground with this order (starting from the cap side):
- Chassis connection via the SLB circuit.
- Other auxiliary circuits GND connection like protection, digital signal boards etc.
- Speaker GND
- Small signal PS GND (decoupling caps)
- Small signal reference GND (Input signal GND, Preamp GND, etc.)
- Note: Signal GND and PS GND can be connected via 10R if needed to prevent forming a ground loop
Wiring
Thumb rules:
- keep wires as short as possible (and thick as reasonable)
- input RCA to amp PCB
- AC lines to trafo primary
- trafo sec to filter caps
- DC rails to amp OPS
- keep loops as small as possible -> twist the pair of wires tightly as possible
- add round shielding for the following cables as an extra protection beyond twisting:
- input wire: connect shield to signal GND
- AC line input and trafo primary: connect shield to AC earth
- trafo secondaries: connect shield to PS GND
- DC rails: connect shield to PS GND
- speaker wires: connect shield to PS GND
- keep sensitive sections (input, feedback wires) away from strong current parts (trafo sec, DC rails, speaker output wires)
- shield the output coil with a piece of metal around it can pick up a lot from trafo EMI!
Trafo
- ask for a shielding screen (between the primary/secondary windings)
- and for a "belly band" (thin film) around the trafo at the outside
- connect them to the "chassis meeting point"
- be carefull with the takeoffs not point to sensitive circuit areas (input section)
- check the best phase of the secondaries with a headphone:
- can be done only when using 2 separate rectifier for the 2 secs
- just the trafo, rectifiers and caps are needed for this test
- wrap a few (~5) turns on your trafo with an insulated wire
- put the ends this piece of wire directly to your headphone and listen to the noise
- now try the other combinations with the 2 secondary "polarities"
- and choose the one with the least noise produced
- if you have a bigger trafo (>300VA) and has a DC level on the AC main line use a circuit like this:
http://www.diyaudio.com/forums/attachment.php?s=&postid=16083&stamp=1012084233
Other
- auxiliary circuits should either have a floating GND or referenced through a lift resistor
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Cortez,
Thank you for putting this all in one place and making it easy to read and understand. You have a follower.
Steven
Thank you for putting this all in one place and making it easy to read and understand. You have a follower.
Steven
I collected some suspected basic phenomenas behind the hum please check them out and comment if there is anything wrong.
I also have prepared some questions as well to analyze the background behind the hum issues.
Root source of all hum noise (except device level ground loops of course)
Type of hum spreading
Questions
I also have prepared some questions as well to analyze the background behind the hum issues.
Root source of all hum noise (except device level ground loops of course)
- basically the large cap charging transient currents (from AC main line -> primary -> trafo -> secondary -> rectifier -> last filter cap terminal)
Type of hum spreading
- galvanic (via wire connection)
- cause: poor wiring/PCB trace when PS cap charging current creates voltage on a shared (and R>0) grounding path with a sensitive section
- solution: wires/traces for different GNDs connecting to a star/bus kind of meeting point
(right order from the trafo side: higher, dirty currents first, sensitive ground paths last)
- inductive (via magnetic field)
- cause: inductive coupling: via magnetic field radiation and other wires (or loops) acting like antennas connected to sensitive (low impedance & amplified) point
- the longer the loop/antenna (piece of wire/PCB trace) the greater the induced noise will be
- in a lot of cases such loops are undiscovered for the first glance
- capacitive (via electric field)
- between wires in a twisted pair
- between long/large surface PCB traces
- trafo primary || secondaries
- heatsink || transistors
Questions
ostriper posted that round shielding the main wires, primary, secs and even the DC rails helped a lot to get a minimum level of noise.
As I know it correctly such a shielding only protects against electric fields and not against magnetic fields is this true?
If yes how is this shielding still working?
On top of that can a 50/60Hz signal spread out via electric field in a capacitive way inside an amp?
Or just HF/RF noise is distributed in such a way?
If we would like to test the effect of the trafo radiating field is it possible to place it ~1m away using long wires temporary?
In this case the sec wiring should be long or a rectifing part with caps should be put right to the trafo and a DC rail should
be long and then at amp side another bank of caps can be placed to decouple any noise induced on these extreme long PS lines?
Normal ripple voltage can produce any hum in an amp with feedback or just in case of improper grounding?
I am just asking because I found some posts earlier where the solution was to increase filter caps or use C multiplier..?!
Feedback wire: where it is returning so where the loop is created and how sensitive this loop is in your experiences?
I saw at a lot of SlewMaster amps that this wire just goes alone far from the PCB without any tightly twisted GND pair.
What happens when we put close our hands to the amp/heatsink/insulated cables and the hum increases?
What kind of coupling is this? We are not from metal... 🙂 Where this noise then comes from..?!
Nice thread Cortez. Very good idea to put all the knowledge on this subject together in one place. Maybe the mods will make it a sticky ��
A diagram would really help as it could easily be misread. I for one am not sure exactly what you mean by a "T-section".
Ref the belly band is that really needed for a toroid? My investigations suggest that it's more use for an EI core.
And of course it helps if people can spot between unrectified and rectified hum. My poweramp is well overdue an investigation of its low level Hum so now seems a good time to try the tips as a practical feedback of the guide.
Ref the belly band is that really needed for a toroid? My investigations suggest that it's more use for an EI core.
And of course it helps if people can spot between unrectified and rectified hum. My poweramp is well overdue an investigation of its low level Hum so now seems a good time to try the tips as a practical feedback of the guide.
If you want a real good (audible) detector to probe the inside of an
amp , use a small audio isolation trafo hooked to an amp.
You can pass it over the cap banks and hear the sawtooth rectified
50/60hz , pass it over and around a toroid or any EI.
The EI's probed hum is 10X louder than a toroid , the pri/sec "split"
on the toroid is much louder than anywhere else on the trafo.
You can even hear the rectified hum on the rail wires , this actually
gets louder where the wires leave a twisted triple configuration.
It's real cool 😎 , and works very well for identifying internal fields.
OS
amp , use a small audio isolation trafo hooked to an amp.
You can pass it over the cap banks and hear the sawtooth rectified
50/60hz , pass it over and around a toroid or any EI.
The EI's probed hum is 10X louder than a toroid , the pri/sec "split"
on the toroid is much louder than anywhere else on the trafo.
You can even hear the rectified hum on the rail wires , this actually
gets louder where the wires leave a twisted triple configuration.
It's real cool 😎 , and works very well for identifying internal fields.
OS
I was thinking of winding a small coil like Thimos uses for the scope and doing the same.
Bill, a belly band does help reduce the radiated field on a torrid. Agree, EI is much much worse, but in high end gear torroid radiated field should be taken card of as well.
By the way, running a solid cable from the input connector to the earth pin on the mains inlet receptacle can also lower hum if you have a ground loop. I will update my PDFs to show this. The input connectors must still be isolated from the chassis.
I think for clarity it's very important to split the discussion into 'internal wiring' related him and into 'earth loop' issues. A powered up amp with inputs disconnected should have zero hum on the outputs. That's the first step.
I think for clarity it's very important to split the discussion into 'internal wiring' related him and into 'earth loop' issues. A powered up amp with inputs disconnected should have zero hum on the outputs. That's the first step.
Someone mind telling me what a belly band is? I think I can imagine it just from the description but where can I see a pic or something talking about this?
Opto isolation
Hi
The benefit of isolation created by breaking potential ground loops using opto coupled devices, such as LDR's, particularly for audio signals is in my opinion hard to ignore,
and should be added to the basket of solutions.
Opto-isolator - Wikipedia, the free encyclopedia
Cheers / Chris
Hi
The benefit of isolation created by breaking potential ground loops using opto coupled devices, such as LDR's, particularly for audio signals is in my opinion hard to ignore,
and should be added to the basket of solutions.
Opto-isolator - Wikipedia, the free encyclopedia
Cheers / Chris
Diagram: there will be later untill then check out Bonsai's PDF it has a great image on the desired layout.
Belly band: Nuvotem Talema :: Custom Design :: GOSS Band
Toroid field: http://music-electronics-forum.com/attachments/25591d1381278081-stray_field.gif
EMF detector: great idea.. It is always good to make the invisible visible/audible... 🙂
Bonsai / earth loop: yes, this is what I exactly declared/asked because device/component level earth loop is
a bit other story and there are already a lot of great summaries about it as linked above.
This thread is about ensuring the 100% "internal silence" when there is no/shorted input at all at the the amp.
Belly band: Nuvotem Talema :: Custom Design :: GOSS Band
Toroid field: http://music-electronics-forum.com/attachments/25591d1381278081-stray_field.gif
EMF detector: great idea.. It is always good to make the invisible visible/audible... 🙂
Bonsai / earth loop: yes, this is what I exactly declared/asked because device/component level earth loop is
a bit other story and there are already a lot of great summaries about it as linked above.
This thread is about ensuring the 100% "internal silence" when there is no/shorted input at all at the the amp.
Attachments
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In my opinion this is very bad idea. Mains earth should be connected to the chassis, and input connector earth to the star ground and the star ground connected via loop breaker to the mains earth (chassis).
Yes dadod, agree. I am not saying remove the chassis earth.
1. 3 pin IEC receptacle earth (Ground for the USA folks) goes directly to the chassis bond point (I always recomend only one chassis bond point). This ensures the chassis is earthed safely.
2. From the input RCA receptacles, run a wire from the receptable 0V to the IEC 3 PIN Earth. The RCA input receptacles must not connect with the chassis.
Why/How does this work? Any loop currents are diverted away from the input circuit and straight to the earth receptacle. This can reduce hum substantially in some installations.
You can read about it in Self's power amp design handbook. I tried it and it works quite well.
The above technique is for systems that do not use a ground lifter - typically commercial designs.
1. 3 pin IEC receptacle earth (Ground for the USA folks) goes directly to the chassis bond point (I always recomend only one chassis bond point). This ensures the chassis is earthed safely.
2. From the input RCA receptacles, run a wire from the receptable 0V to the IEC 3 PIN Earth. The RCA input receptacles must not connect with the chassis.
Why/How does this work? Any loop currents are diverted away from the input circuit and straight to the earth receptacle. This can reduce hum substantially in some installations.
You can read about it in Self's power amp design handbook. I tried it and it works quite well.
The above technique is for systems that do not use a ground lifter - typically commercial designs.
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By the way I have some hum issues in the meantime as well.
I have a dual PS in 1 partly wooden case as the metal heatsinks are the sides walls. (Attchament #1)
A just made the mods based my own summary and it helped a lot!
It is still not perfect for some reason but I hope it will be hunt down as well.
Also a strange and new discovery came out:
As you can see at the attachment a had to connect the the heatsink together at 2 different points.
I just tried it because I thought in case of a conventional metal case this is the case via the chassis.
And it reduced the hum a lot... :-o
Do you have any idea why this helped? This is a loop now anyway why is it better..?
You can se at Attchament #2 the fresh mods:
Before that I just had the HS link #1 going directly to pot case and RCA GNDs (earth wast involved at all) and even
a strange cracking noise was produced because of improper grounding while playing music with kicks (drum).
Even turning on of the amp was different and strange ticking noises were present... :-o
Do you have any ideas/comments for the remaining hum based on my layout?
A question: in case of such a dual PS in one chassis where the 2 different PS GND should be united?
At last it happens at the RCAs (just like in my current layout) but is it okay/enough this way or they
should be connected somewhere else for example between the 2 main PS GND in a star/bus point?
I have a dual PS in 1 partly wooden case as the metal heatsinks are the sides walls. (Attchament #1)
A just made the mods based my own summary and it helped a lot!
It is still not perfect for some reason but I hope it will be hunt down as well.
Also a strange and new discovery came out:
As you can see at the attachment a had to connect the the heatsink together at 2 different points.
I just tried it because I thought in case of a conventional metal case this is the case via the chassis.
And it reduced the hum a lot... :-o
Do you have any idea why this helped? This is a loop now anyway why is it better..?
You can se at Attchament #2 the fresh mods:
- HS link #1 (this goes to the earth star ground)
- HS link #2 (this is just a HS link goes nowhere, tested new earth connection doesnt improve)
- pot metal case to the earth star ground + (10R+10nF) between earth and RCA GND (without the rectifier yet).
Before that I just had the HS link #1 going directly to pot case and RCA GNDs (earth wast involved at all) and even
a strange cracking noise was produced because of improper grounding while playing music with kicks (drum).
Even turning on of the amp was different and strange ticking noises were present... :-o
Do you have any ideas/comments for the remaining hum based on my layout?
A question: in case of such a dual PS in one chassis where the 2 different PS GND should be united?
At last it happens at the RCAs (just like in my current layout) but is it okay/enough this way or they
should be connected somewhere else for example between the 2 main PS GND in a star/bus point?
Attachments
Yeah, torroids are not that quiet!
On my e-amp and Ovation 250, I used a ~3mm steel brace over the torroids (one is a 1 kVA the other 2 kVA) and it cuts the radiated field remarkably.
Cortez,
we need the skills and knowledge of jneutron here - he is normally over on the John curl thread . . . . maybe you can invite him.
we need the skills and knowledge of jneutron here - he is normally over on the John curl thread . . . . maybe you can invite him.
Cortez, is the metal body of your RK27 solidly grounded? If not, you can pick up hum.
If you short the input to power amp where it goes into the PCB's do you still have a noise problem?
If you short the input to power amp where it goes into the PCB's do you still have a noise problem?
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