Ring mains has it's issues that's for sure!
What we have is two separate rings for all the wall sockets and another two for all the ceiling light fittings. Then there's the heating spur, cooker spur etc even one for the doorbell transformer FFS!
Basically everything on a ring can feed and return in both directions however it's rarely equally balanced and you quite often get a low 50hz hum in the walls of folks houses. As the wiring ages, things can get weird to say the least (sick house syndrome).
It was brought in to save on copper during WW2 and has never left us. You can get away with using 2mm wire in a ring when to feed that many appliances off one spur you would need 4mm.
Who thought 240v @ 50hz running in a number of loops around your home was a good thing?
I could wear out boots kicking their butt!
What we have is two separate rings for all the wall sockets and another two for all the ceiling light fittings. Then there's the heating spur, cooker spur etc even one for the doorbell transformer FFS!
Basically everything on a ring can feed and return in both directions however it's rarely equally balanced and you quite often get a low 50hz hum in the walls of folks houses. As the wiring ages, things can get weird to say the least (sick house syndrome).
It was brought in to save on copper during WW2 and has never left us. You can get away with using 2mm wire in a ring when to feed that many appliances off one spur you would need 4mm.
Who thought 240v @ 50hz running in a number of loops around your home was a good thing?
I could wear out boots kicking their butt!
I too have been chasing a slight hum almost cured by pgnd. I kind of resolved to live with it as it is almost inaudible....but it is still there. All this activity in the threads has renewed my interest in solving this. What struck me today while looking at the pic of the metal clad iec inlet is that the whole housing is a ground connection. So the iec is grounded to my back panel and to a central point on the base of the chassis. All of these points are all conductive. I removed all ground connections except of course the iec housing to the back panel and fired everything up. Interesting the hum was still there, but very slight and rose in volume a little as I turned up the volume pot. Before if I had the amps on with no pgnd the hum was very loud. So I am going to swap out the inlet for a plastic clad unit. I used the plastic clad type in my last build and had no problems. Keep your fingers crossed!
From what I can make out, if the hum increases when you turn the volume up, the source of the hum is either inside the unit containing the pot, or before it.
I have found that while the FE's are indeed stunningly good amps, they are quite sensitive to any external noise either in the mains or in the signal fed to them.
If you have a portable battery powered source, mp3 player/iplod etc you could try feeding the amps straight off that, if you get no noise it's not the FE's.
Mains transformers in sources can send noise to them either through the mains supply or the signal feed.
Did you use a single transformer to power both boards or are they separate?
I have found that while the FE's are indeed stunningly good amps, they are quite sensitive to any external noise either in the mains or in the signal fed to them.
If you have a portable battery powered source, mp3 player/iplod etc you could try feeding the amps straight off that, if you get no noise it's not the FE's.
Mains transformers in sources can send noise to them either through the mains supply or the signal feed.
Did you use a single transformer to power both boards or are they separate?
The DC readings are good.
The AC readings are terrible.
Even 1/10 times would be bad.
You should be measuring <0.3mVac and preferably <0.1mVac
Members that use their ears to measure hum are deceiving themselves into thinking that ears make good instruments.
The "ring main" supply system used in the UK gives no worse hum field than all the other cables that are not part of rings in and around the house.
The receiving equipment when designed properly rejects most of this to give an acceptable performance.
I have 6 power rings feeding my house. Five are fed from 32A or 20A RCBOs into 2.5mm².
One is fed from 32A MCB into 4mm² to my lounge. The lounge is farthest from the distribution board and the thicker cable was adopted to keep the volts drop within the UK wiring regulations. The MCB was adopted to avoid excess leakage shutting down the main music systems.
The receiving equipment when designed properly rejects most of this to give an acceptable performance.
I have 6 power rings feeding my house. Five are fed from 32A or 20A RCBOs into 2.5mm².
One is fed from 32A MCB into 4mm² to my lounge. The lounge is farthest from the distribution board and the thicker cable was adopted to keep the volts drop within the UK wiring regulations. The MCB was adopted to avoid excess leakage shutting down the main music systems.
Andrew, ring mains are quite well known for causing noise especially as the wiring ages. You can actually hear the hum in some houses well before a fault develops to the point of failure. I've had issues in two houses with it. My current home is only 14 years old and on some nights we get an annoying hum coming from our bedroom wall, a domestic electrician checked it out but as it's intermittent he said he could not track it down.
Richard Dunn of NVA has been quite vocal about ring mains issues with HIFI over the years.
It works fine as long as all the connections in each ring are good but it only takes one to have a higher resistance for issues to appear. I've spoken to a few domestic electricians about it over the years, some acknowledge certain issues, some don't.
You should see the effect a ring mains has on a boats compass, the field produced is an issue. I always installed a separate spur for each appliance but some owners get domestic electricians to install their mains wiring. Some of the through hull bronze fittings were totally destroyed by stray current after only a few years because some idiot connected a ring mains system's earth to the vessels anode wiring. Boats have been lost because of that error.
Sorry for the OT conversation Dario. I'll shut up now
Richard Dunn of NVA has been quite vocal about ring mains issues with HIFI over the years.
It works fine as long as all the connections in each ring are good but it only takes one to have a higher resistance for issues to appear. I've spoken to a few domestic electricians about it over the years, some acknowledge certain issues, some don't.
You should see the effect a ring mains has on a boats compass, the field produced is an issue. I always installed a separate spur for each appliance but some owners get domestic electricians to install their mains wiring. Some of the through hull bronze fittings were totally destroyed by stray current after only a few years because some idiot connected a ring mains system's earth to the vessels anode wiring. Boats have been lost because of that error.
Sorry for the OT conversation Dario. I'll shut up now
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I shorted the inputs and checked the AC again. The silent channel read 0mV AC and the channel with a slight hiss read 0.1mV. My previous readings did not have shorted inputs.
you NEVER listen to music with the input open.
To hear any Source the input must be connected. That connection loads the input with an impedance typically in the range 100r to 1k0.
You can test your power amp by connecting a dummy load to the input that mimics your Source impedance. Most just adopt a zero ohm (shorted) dummy plug for the hum and noise test.
I do compare a range of dummy input loads to the sero ohm readings for my builds. It generally only becomes noisy when the source impedance >10k
An open input is the equivalent of much greater than 1M ohm. Noisy is bound to be the result.
Now connect a long interconnect and short the far end.
Are the measured results just as good?
Now connect two long interconnects and short both far ends.
Are the measured results just as good?
Now electrically short the grounds of the two interconnects at the far end.
Are the measured results just as good.
This last test is the one where most multi-channel Power Amplifiers fall down. Mono blocks pass this test. Dual monos generally fail this test, except where the builder fully understands the grounding and takes steps to ensure the multi-channel can pass this last test.
To hear any Source the input must be connected. That connection loads the input with an impedance typically in the range 100r to 1k0.
You can test your power amp by connecting a dummy load to the input that mimics your Source impedance. Most just adopt a zero ohm (shorted) dummy plug for the hum and noise test.
I do compare a range of dummy input loads to the sero ohm readings for my builds. It generally only becomes noisy when the source impedance >10k
An open input is the equivalent of much greater than 1M ohm. Noisy is bound to be the result.
Now connect a long interconnect and short the far end.
Are the measured results just as good?
Now connect two long interconnects and short both far ends.
Are the measured results just as good?
Now electrically short the grounds of the two interconnects at the far end.
Are the measured results just as good.
This last test is the one where most multi-channel Power Amplifiers fall down. Mono blocks pass this test. Dual monos generally fail this test, except where the builder fully understands the grounding and takes steps to ensure the multi-channel can pass this last test.
Andrew, it's not so much deception as it is resources and knowledge. There is no doubt the scientific and the aesthetic can and should complement each other to dial in on high quality sound. I take my lead primarily from my ears mostly cause that's what I have access to and to rely on - without lab equipment. There are many simple and useful DVM measurements shared in the posts and it would be great to have a collection of the most useful and productive, as related to these amps, at a central location.
Hope on the horizon - So often the advice and techniques provided by knowledgeable people who rely on and promote the scientific approach include the dreaded word "Scope" in their comments. I say dreaded cause up till now, it quickly becomes apparent that the cost of anything accurate enough to rely on comes in at a price of high multiples of the cost of the DIY projects themselves. I'v been pointed in two directions that seem quite promising. This Unit has been highly praised by some diyAudio veterans who already have rather sophisticated fully equipped labs. It and others from the same manufacturer are considered price/performance breakthroughs never before available. Can't wait for delivery so I can attach a Fremen Edition and attempt to resolve some of my curiosities.
The second promising approach is the Visual Analyzer thread right here on the forum. Development and tweaking of the software seems to come in spurts, but the potential of using readily available PC devices for input and detection opens the door to many without big budgets and deep circuit design backgrounds. I have it loaded on it's own PC but haven't had or taken the time to go very deep. Hopefully over the winter months.
It appears most often, and certainly in my case, the majority - and possibly the only - problems reported by FE builders are hum/ground related, that are resolved via some wire or cable mod external to the amp build. Non the less, I'm looking forward to gaining some insight into "Dario's little monster" by using both options mentioned here.
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Interesting. Hopefully some more will appear over the winter season when folks can't go outside - hope so.
FWIW - Since I'm using the RC builds to size the new chassis, I did a temporary setup with the betas. Haven't been powered up for many many months but they still sound great. Had one loose input pin on one amp, but everything fell into place.
Trusty old Sonicaps at C13, Black Gate STD at C9 and two of the three year old original 125VA transformers from ApexJr.
FWIW - Since I'm using the RC builds to size the new chassis, I did a temporary setup with the betas. Haven't been powered up for many many months but they still sound great. Had one loose input pin on one amp, but everything fell into place.
Trusty old Sonicaps at C13, Black Gate STD at C9 and two of the three year old original 125VA transformers from ApexJr.
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Another interesting (or not) hum story. With the setup in the photo I got horrible hum with no input. That was expected. For the first time I can remember, I got some hum from the Walkman and those interconnects/"Y" with nothing playing. Pushed the play button and the amps became silent - just music.
In the big system all that can be heard is the slight hiss that comes from the direct connected DAC when it isn't receiving digital data to lock to. No pot or pre this time - using PC for volume control.
Nothing really significant here except more confirmation of the influences of various connections/devices along the signal path.
In the big system all that can be heard is the slight hiss that comes from the direct connected DAC when it isn't receiving digital data to lock to. No pot or pre this time - using PC for volume control.
Nothing really significant here except more confirmation of the influences of various connections/devices along the signal path.